A–Z
A READING ROOM OF IDEAS REASONED ALOUD
Every explanation, alphabetically.
The whole shelf in one list, by title.
A
79- CDA·01A calibrated roleWhy does telling a system who to be change what it knows how to say?
- MIN·01A fine that became a priceWhy did charging parents for collecting a child late make more of them arrive late?
- CDA·02A notification you did not ask forWhen something arrives unrequested claiming to come from a service you trust, how can you tell?
- PHI·01A relic proved falseWhy does a venerated object lose its power the moment it is shown to be a forgery, though nothing about the object itself has changed?
- CDA·03A schema read by two audiencesHow can one declaration serve as a machine's validator and a reader's instructions at the same time?
- CDA·04A secret you never sendHow do you prove you know something without ever transmitting it?
- PHY·01A spinning coin's last rattleWhy does a spinning coin rattle faster and faster just before it abruptly falls silent?
- CDA·05A tree in a table of rowsHow do you store something with branches in a structure that only knows about rows?
- CDA·06A tree that rearranges itselfWhy must a structure that keeps things in order keep rebuilding its own shape?
- CDA·07A valid token in the wrong placeWhy is a token that passes every check still the wrong one to accept?
- EDU·01Ability groupingWhy can sorting students by ability raise one group's results while lowering another's?
- LAN·01Accent and perceived competenceWhy does an unfamiliar accent make a speaker sound less competent when it says nothing about competence?
- ENG·01Acceptance samplingHow can testing twenty parts ever justify shipping ten thousand of them?
- MAT·01Adaptive step sizeWhy does a solver that keeps changing its own step size beat one with a well-chosen fixed step?
- CDA·08Adding a machine without moving the dataHow do you add one more server to a cluster without having to relocate almost everything?
- CHM·01AdhesionWhy do two smooth surfaces need a liquid between them in order to stick?
- FAM·01Adolescent riskWhy do teenagers take risks they can clearly explain are dangerous?
- FAM·02Adolescent-parent conflictWhy does friction with parents peak just as a teenager becomes most capable of reasoning well?
- FAM·03Adoption searchWhy do adoptees raised in warm and stable homes so often set out to find a birth parent anyway?
- MIN·02Adult attachment patternsWhy do people so often reproduce the same relationship pattern with very different partners?
- MED·01Advance directivesWhy should a document written years ago outrank what a patient seems to want today?
- ECO·01Adverse selectionWhy does a market where buyers cannot judge quality fill up with poor goods?
- EDU·02Advice from top studentsWhy does the study routine of the highest scorer so often fail everyone who copies it?
- ECO·02Aftermarket pricingWhy does a company sell the printer cheaply and charge dearly for the ink?
- HIS·01Age heapingWhy do old census returns report far more people aged exactly thirty, forty and fifty than the years either side?
- CDA·09Agreeing the shape before the substanceWhy settle the form of a conversation before either side is able to hold it?
- ENV·01Agroforestry overyieldingWhy can a field that gives a tenth of its ground to trees produce more food than the same field cleared?
- WRK·01Air balancingWhy must a newly installed ventilation system be deliberately choked back at the dampers when every duct was sized correctly?
- MIL·01Airborne drop dispersionWhy did badly scattered parachute drops sometimes confuse the defender more than tidy ones?
- TRV·01Aircraft separation minimaWhy must aircraft stay miles apart when controllers can see exactly where each one is?
- ENG·02Airplane cabin pressureHow is breathable pressure maintained inside an aircraft flying through thin air?
- TRV·02Airport access road wideningWhy does a wider road to the airport stop saving anyone time within a year?
- TRV·03Airport layoutWhy does an airport make you walk past shops to reach your gate?
- TRV·04Airport slot grandfatheringWhy did airlines fly nearly empty aircraft between busy airports rather than cancel flights nobody wanted?
- WRK·02Alert fatigueWhy does adding more alerts to catch more problems make outages last longer?
- ENG·03AliasingWhy can a filmed wagon wheel appear to turn backwards, and why does the same trap corrupt digital measurements?
- MED·02AllergyWhy does the body mount a violent defence against something as harmless as pollen?
- MIL·02Alliance free-ridingWhy does every member of an alliance underspend on a defence all of them want?
- CHM·02Alloy strengthWhy is an alloy usually stronger than either of the pure metals inside it?
- SPT·01Altitude trainingWhy do athletes go and train where there is less oxygen to breathe?
- CHM·03Ammonia synthesisWhy does squeezing a gas mixture harder produce more ammonia, when the reaction had already come to rest?
- MIL·03Amphibious buildupWhy is an amphibious landing decided less by the size of the fleet than by the width of the beach?
- EAR·01Amphidromic pointsWhy does the tide barely rise at one spot in a sea while swinging metres a short distance away?
- HIS·02Ancient population estimatesWhy can excavating an ancient city more thoroughly still leave its population uncertain?
- MIN·03Anger as a commitment deviceWhy can visibly losing your temper win a better deal than staying calm and reasonable?
- PHI·02Anonymous givingWhy do so many traditions insist that the best giving is the giving nobody sees?
- AST·01Anonymous telescope-time proposalsWhy did hiding the applicants' names change which astronomers were awarded telescope time?
- AST·02Antarctic meteorite concentrationWhy are most of the world's recovered meteorites picked up from a few patches of ice on one continent?
- EAR·02Antarctic ozone holeWhy does ozone loss peak over Antarctica each spring when the chemicals responsible were released elsewhere?
- ENG·04Antenna ground planeWhy does a car aerial hear almost nothing until it is bolted through the metal roof it is standing on?
- PHY·02Anti-reflective coatingWhy does adding another transparent layer to a lens make it reflect less light rather than more, and why is the leftover reflection purple?
- MED·03Antibiotic course lengthWhy might finishing every last tablet, long taught as the way to stop resistance, help resistance along instead?
- BIO·01Antibody affinity maturationWhy does the body deliberately scramble the genes of its own immune cells at a rate that would be lethal anywhere else in the tissue?
- MED·04Antiviral difficultyWhy are drugs that kill bacteria so much easier to find than drugs that kill viruses?
- PHI·03Apology and repairWhy should an apology change anything when the harm it addresses has already happened?
- ART·01Apparent motionWhy does a rapid series of still pictures look like continuous movement?
- GOV·01Appellate deferenceWhy does an appeal court uphold a finding its own judges suspect is wrong?
- HOM·01Appliance signatures in meter dataHow can a single electricity meter reveal the moment you boiled the kettle?
- HIS·03Apprenticeship indenturesWhy would a master craftsman spend years training the apprentice who will one day compete with him?
- CDA·10Approximate nearest neighbour searchWhy does a search that deliberately settles for approximate answers beat one that checks every record?
- EAR·03Aquifer depletionWhy does an aquifer keep falling when every farmer drawing on it wants it to last?
- ART·02Architectural atmosphereWhy can one room feel welcoming and another of identical size feel cold?
- FAM·04Arranged and chosen marriagesWhy do marriages arranged by families often report satisfaction climbing over the years while chosen ones drift down?
- TRV·05Asymmetric flight timesWhy does the same flight take noticeably longer in one direction than the other?
- MIL·04Asymmetric warfareHow can a far weaker force defeat a far stronger one?
- SPT·02Athlete biological passportWhy do drug testers now watch an athlete's own blood values over years instead of looking for the drug itself?
- EAR·04Atmospheric scale heightWhy does air pressure halve every few kilometres instead of running out at a fixed height?
- AST·03Atmospheric seeing limitWhy does a ground telescope twice as wide show no finer detail than a small one on most nights?
- FAM·05AttachmentWhy does a young child explore more boldly when a trusted adult is nearby?
- CDA·11Attention as a budgetHow does a model work out which earlier word a pronoun refers to?
- MIN·04Attribution asymmetryWhy do people explain their own failure differently from an identical failure by someone else?
- ECO·03Auction pricesHow can the rules of an auction change the price a thing finally sells for?
- AST·04AuroraWhy do curtains of light appear in polar skies but almost never near the equator?
- TRV·06AuthenticityWhy does a place feel less authentic the easier it becomes to visit?
- ENG·05Autofrettage of pressure vesselsWhy does deliberately overloading a thick tube once make it safer at every load afterwards?
- MED·05AutoimmunityWhy does a defence system built to tell self from foreign ever turn on the body it protects?
- CDA·12Autonomy as a dialWhy is 'how much may it decide for itself' a setting rather than a yes-or-no question?
- MAT·02Averaging times of dayWhy does the ordinary average give a nonsense answer when the numbers are clock times or compass bearings?
- CHM·04AzeotropesWhy can no amount of careful distilling push ethanol past about ninety-six percent purity?
B
73- CDA·13Backfilling a pipelineWhy is re-running yesterday's job harder than running today's?
- WRK·03BacklashWhy does a machinist wind a handwheel past the mark and creep back to it rather than stopping on it?
- CDA·14BackpressureWhy does a system that never asks a fast producer to slow down end up slower than one that does?
- CDA·15Backward compatibilityWhy is the hardest part of changing a widely used interface the promise you made about the old one?
- BIO·02Bacterial dormancyWhy does a bacterium that could keep dividing stop growing and seal itself inside a spore instead?
- TRV·07Baggage reconciliationWhy must a checked bag be hunted down and pulled off the aircraft when its owner simply fails to board?
- ECO·04Balance of payments identityWhy must a country that buys more than it sells be selling something it barely notices?
- BIO·03Balanced sex ratiosWhy do species keep producing equal numbers of males and females when few males suffice?
- WRK·04Balanced veneerWhy does a cabinetmaker glue an expensive sheet of veneer onto the hidden back of a panel nobody will ever see?
- PHY·03Ballast in a gas dischargeWhy does a lit neon tube draw ever more current as its voltage falls, so it destroys itself unless something limits it?
- PHY·04Ballast shakedown under repeated loadingWhy does a new railway track become more stable after the first heavy trains have pounded it?
- ENV·02Banded vegetation in drylandsWhy does dryland scrub arrange itself into even stripes that nobody planted?
- ECO·05Bank capital buffersWhy must a profitable bank hold capital that it is not allowed to put to work?
- ECO·06Bank money creationHow can commercial banks create spendable money when they make loans?
- ECO·07Bank runsWhy can everyone rushing to take their money out of a sound bank bring it down?
- HOM·02Bass through wallsWhy can you hear a neighbour's bass through the wall but not their conversation?
- CDA·16Batching and the throughput tradeWhy does serving more users at once make each individual one wait longer?
- ENG·06Bathtub failure curveWhy is a brand-new machine more likely to break this week than a six-month-old one?
- HOM·03Battery ageingWhy does keeping a phone charged to full shorten the life of its battery?
- MAT·03Bayesian updatingHow should new evidence change the probability we assign to a belief?
- MED·06Bed rest harmWhy does resting a sick patient in bed, once prescribed for almost everything, now make recovery worse?
- PHI·04Believing at willWhy can you decide to raise your arm but not decide to believe it is raining?
- CDA·17Benchmark saturationWhy does the model that tops the public leaderboard so often lose on your own task?
- WRK·05Bend allowanceWhy is the flat blank cut shorter than the sum of the sides it will be folded into?
- MAT·04Benford's lawWhy do the leading digits of real-world numbers favour 1 far more often than 9?
- ENV·03Best-before versus use-byWhy does a date printed to promise quality make people bin food that is perfectly safe?
- ART·03Bias-cut clothWhy does a woven fabric stretch generously on the diagonal while barely giving along its own threads?
- PHY·05Bicycle stabilityWhy does a moving bicycle stay upright when the same bicycle standing still falls over?
- MIN·05Binocular rivalryWhy do two different images shown to the two eyes alternate instead of blending into one?
- MAT·05Birthday problemWhy does a room of only twenty-three people probably contain a shared birthday?
- WRK·06Blameless reviewWhy does holding someone accountable for an outage make the next one more likely?
- CDA·18Blast radiusWhy is the important question about a compromised credential not what it unlocks but how far it reaches?
- PHY·06Blind analysisWhy do physicists deliberately hide their own data from themselves until the analysis is frozen?
- MAT·06Block design existenceWhy can a schedule pairing every team exactly once exist for some team counts and for no others?
- MIL·05Blockade and resolveWhy can squeezing a country's economy strengthen the very government it was meant to weaken?
- MED·07Blood compatibilityWhy can blood from one healthy person be lethal to another healthy person?
- MED·08Blood donation supplyWhy does the blood supply run short when almost everyone says donating is worth doing?
- CDA·19Bloom filtersWhy is a lookup structure that sometimes says yes when it means no more useful than one that is always right?
- MIN·06BlushingWhy would a body build a signal that broadcasts your embarrassment exactly when you least want it seen?
- ECO·08Board independenceWhy does a board appointed to keep watch over the managers so often end up agreeing with them?
- TRV·08Boarding orderWhy does boarding an aircraft neatly from the back forward end up slower than letting people on at random?
- ENG·07Bolt preloadWhy does a bolt stretched hard on assembly outlive a gently tightened one carrying exactly the same working load?
- MED·09Bone remodellingWhy does bone thicken exactly where it is worked and melt away where it is not?
- GEO·01Border prosperity discontinuityWhy can crossing a single line on the ground change incomes sharply when the land on both sides is identical?
- TRV·09Border queue surgesWhy does a passport desk that handles the day's arrivals easily on average still produce hour-long queues?
- GEO·02BordersWhy do some borders follow rivers and mountains while others run in straight lines?
- ECO·09Boundaries of the firmWhy does a company hire employees instead of buying every task on the open market?
- CDA·20Bounded contextsWhy should the same word be allowed to mean different things in different parts of one system?
- SPT·03Box score representationWhy can a player's statistics look excellent while his team plays worse whenever he is on the floor?
- MAT·07Braess's paradoxWhy can adding a new road to a city make every driver's journey longer?
- MIN·07Brain lateralizationWhy does the brain hand language mostly to one side instead of sharing it evenly?
- CDA·21Branch predictionWhy can a processor finish work faster by guessing the outcome of a test before it knows the answer?
- ECO·10Brand advertisingWhy does a firm spend fortunes on advertising that says nothing about the product?
- PHY·07Brazil-nut effectWhy does the largest and heaviest nut end up on top when a can of mixed nuts is shaken?
- ENV·04Bread stalingWhy does bread go stale faster in the fridge than on the counter?
- SPT·04Breathing urgeWhy does the urge to breathe come from carbon dioxide building up rather than from oxygen running out?
- PHY·08Brewster angle glareWhy does glare off water disappear through polarized glasses at one viewing angle but not at others?
- HIS·04Bridewealth and dowryWhy does wealth flow toward the bride's family in some societies and toward the groom's in others?
- GOV·02Bright-line rulesWhy does the law fix a speed limit at an exact number instead of asking people to drive reasonably?
- LAN·02Broadcast loudnessWhy did adverts sound louder than the programmes around them while meeting the same peak limit?
- GOV·03Budget scoring windowsWhy does a tax cut everyone expects to be permanent get priced as though it will expire?
- TRV·10Buffet holding timeWhy can a hotel buffet dish that still feels comfortably warm be far more dangerous than one that has gone cold?
- CDA·22Build cache geometryWhy does swapping two lines in a build file change how long every future build takes?
- CDA·23Building somewhere you do not ship fromWhy assemble software in one environment and then throw that environment away?
- ENG·08Building swayWhy do engineers let a tall building sway rather than making it rigid?
- CDA·24Built never to be rebuiltWhy design a warehouse so that a new source never forces you to restructure the old ones?
- CDA·25BulkheadsWhy does deliberately wasting capacity keep one failing feature from taking down all the others?
- SPT·05Bullpen specializationWhy does a team use three pitchers to finish an inning that one could have thrown?
- ECO·11Bullwhip effectWhy does a small wobble in shop sales turn into wild swings at the factory that supplies it?
- PHY·09BuoyancyWhy does a helium balloon rise through the very air that pulls everything else down?
- PHI·05Burden of proofWhy must the person making a claim prove it, rather than the doubter disprove it?
- CHM·05Butter from creamWhy does beaten cream first stiffen into foam and then, if you keep going, break into butter and water?
- MIN·08Bystander effectWhy is a person in trouble less likely to be helped when more people are watching?
C
195- CDA·26CachingWhy does a computer keep a second copy of data it already has?
- CDA·27Caching an answer nobody asked for exactlyHow do you reuse a stored answer for a question that has never been asked in those words?
- GEO·03Cadastral survey patternsWhy can you name the century a countryside was surveyed in from the shape of its fields alone?
- HIS·05Calendar driftWhy do human calendars need leap days and extra months at all?
- ART·04Cancelled printing platesWhy does a printmaker deliberately destroy the plate that could still make more money?
- CHM·06Candle wickWhy does a candle need a wick when the wax itself is the fuel?
- ART·05Canon formationWhy do a handful of works get taught for centuries while equally admired contemporaries disappear entirely?
- ART·06Canvas tension and humidityWhy does a painting's canvas sag in damp weather and pull drum-tight in dry?
- CDA·28Capability negotiationWhy do two programs that have never met agree on what they can do instead of checking a version number?
- ENG·09Capacitive sensingHow does a sheet of glass know where your finger is?
- CHM·07Carbon allotropesWhy do diamond and pencil lead behave so differently when both are nothing but carbon?
- EAR·05Carbon offset additionalityWhy can paying to protect a forest that was never threatened still earn carbon credits?
- MED·10Cardiac fibrillationHow can a heart beat chaotically when every cell in it still follows the same simple rule?
- FAM·06Caregiver of last resortWhy does the care of an ageing parent collapse onto one sibling while the others remain willing but uninvolved?
- FAM·07Caregiving loadWhy does caring for an aging parent fall so unevenly within one family?
- ECO·12Carry tradeWhy does money rush toward whichever country pays more interest, and why does that stop?
- MED·11Cartilage healingWhy does a broken bone knit itself back together while damaged knee cartilage never does?
- SPT·06Carving ski sidecutWhy does a ski cut a clean arc when the skier only tips it on edge and never steers it sideways?
- ENV·05Cassava processingWhy would a community put its staple root through days of soaking and drying before anyone eats it?
- CHM·08Cast-iron seasoningWhy does a cast-iron pan become non-stick only after years of cooking, and lose it in a single wash?
- MIL·06Casualty evacuationWhy does a medical system that treats fewer casualties near the front save more of them?
- CHM·09CatalysisHow can a substance speed up a reaction without being used up by it?
- ECO·13Catastrophe reinsuranceWhy does an insurer holding a million policies across a whole country still need to buy insurance for itself?
- MAT·08Catastrophic cancellationWhy can subtracting two highly accurate numbers leave an answer with no correct digits at all?
- LAN·03Categorical perception of speech soundsWhy does a smoothly changing sound flip abruptly from one consonant to another?
- PHI·06Causal closure of the physicalIf every physical event already has a physical cause, what work is left for a mind to do?
- EAR·06Cave formationHow does ordinary water hollow a cave out of solid limestone?
- EDU·03Ceiling on admissions predictionWhy can no admissions test tell which applicant will actually flourish once admitted?
- ART·07Cello wolf toneWhy does one note on a fine cello howl and stutter while the notes either side of it behave?
- BIO·04Cells that defect on the bodyWhy does a body of cooperating cells keep producing cells that destroy it for all of them?
- MAT·09Cellular automataWhy can a grid of cells obeying three trivial rules build structures nobody wrote into them?
- CHM·10Cement hardeningWhy does concrete set perfectly well underwater, when you would expect it to need to dry out?
- MAT·10Censored follow-upHow can a study report five-year survival when most of its patients were watched for two?
- GOV·04Census undercountWhat changes when a government miscounts its own population?
- MED·12Central sensitizationWhy does pain sometimes persist for years after the injury that caused it has fully healed?
- HIS·06Ceramic seriationHow can a pile of undated potsherds be put in chronological order without a single absolute date?
- WRK·07Ceremony as a smellWhen does a practice adopted to help a team become the thing slowing it down?
- CHM·11Chain-branching explosion limitsWhy can a hydrogen and oxygen mixture sit quietly at one pressure and blow itself apart at a pressure only slightly higher?
- CDA·29Chain-of-thoughtWhy does asking a model to work step by step improve arithmetic it could already do?
- ART·08Chance in the wood-fired kilnWhy do potters surrender a pot's final surface to a fire they cannot control?
- LAN·04Chance word resemblancesWhy do linguists distrust a striking word match between two unrelated languages?
- CDA·30Change data captureHow do you copy every change a database makes without asking the database for anything?
- CDA·31Chaos engineeringWhy deliberately break a working system that is already surviving?
- HOM·04Charging connector standardsWhy did every phone need its own charger for years when nobody actually wanted that?
- HOM·05Charm pricingWhy does a price ending in 99 sell better than the round number just above it?
- ENV·06Cheese ripeningWhy does deliberately letting microbes grow in milk make it keep for years when fresh milk sours in days?
- CHM·12Chelate effectWhy does one molecule that grips a metal ion with several arms hold it far more tightly than several separate molecules with one arm each?
- MIL·07Chemical protective postureWhy does the mere threat of a chemical attack blunt an army that is never actually attacked?
- MED·13Chemotherapy selectivityWhy does a drug aimed at a tumour also attack hair, gut lining, and blood?
- FAM·08Child fosteringWhy do households with food to spare still send their own children away to be raised by relatives?
- FAM·09Child word learningHow can a child infer the meaning of a new word from only a few encounters?
- FAM·10Children's playWhy do children spend so much of their time on activities with no obvious purpose?
- ENV·07Chilling injury in fruitWhy does a banana kept in the fridge turn black outside while staying stubbornly hard inside?
- ENG·10Chip yield and die sizeWhy does making a chip slightly larger cut the share of working ones by far more than a little?
- MIN·09Choice overloadWhy can more options make a decision harder and the chooser less satisfied?
- SPT·07Choking under attentionWhy does a practised movement fall apart as soon as the athlete thinks about how they do it?
- CDA·32Choosing an indicatorOf everything a service could measure, how do you pick the number that stands for the user's experience?
- CDA·33Choosing the first piece to replaceOf everything that needs rebuilding, how do you decide what goes first?
- CDA·34Choosing what to forgetWhen memory runs out, how do you decide what to discard without knowing what you will need next?
- CDA·35Choreography versus orchestrationShould each step know what comes next, or should one place know the whole plan?
- MED·14ChronotherapyWhy can the same dose of the same drug help more at one hour of the day than another?
- CDA·36ChunkingWhy does how you cut a document into pieces matter more than which search engine you use on them?
- CDA·37Circuit breakersWhy does refusing to even attempt a request help a struggling system recover?
- ENG·11Circuit schematics versus layoutWhy does a diagram that looks nothing like the machine make its fault easier to find?
- CDA·38Citation without verificationWhy does an answer that cites its source still need checking?
- GEO·04City locationWhy do cities often grow around river crossings, harbors, or crossroads?
- LAN·05City-to-city spread of speech formsWhy does a new pronunciation reach a distant city before the village next door?
- GOV·05Civil service tenureWhy does making officials nearly impossible to dismiss produce more honest advice than making them removable?
- MIL·08Civilian controlWhy does an armed force take orders from an unarmed government?
- EDU·04Class-size cutoff rulesWhy can enrolling one extra pupil suddenly cut a class almost in half?
- EDU·05Classroom misconceptionsWhy can a student give the correct answer yet still hold a mistaken underlying model?
- ECO·14Cleansing effect of recessionsHow can an industry grow more productive when no firm inside it improved?
- LAN·06Clickbait headlinesWhy do headlines grow more tempting and less informative as publishers learn what readers click?
- EAR·07Climate model parameterizationWhy must a climate model invent clouds that it is far too coarse to see?
- SPT·08Climbing grade driftWhy does a climbing route rated hard in one decade quietly become a moderate one later without a single hold changing?
- SPT·09Climbing versus descending weightWhy does the rider who is dropped on every climb come past everyone else on the descent?
- CDA·39Clock synchronizationWhy can two computers never fully agree on the order in which two events happened?
- FAM·11Closeness-distance balanceWhy do couples settle at a closeness neither partner says they chose?
- HOM·06Clothing size labelsWhy can two garments labelled the same size fit two completely different people?
- HOM·07Cloudy ice cubesWhy does a home ice cube turn white in its middle when the water it froze from was perfectly clear?
- WRK·08Clustered breakdownsWhy do three machines fail in one week after months of quiet?
- HOM·08ClutterWhy do possessions accumulate in a home faster than they leave it?
- GOV·06Coalition formationWhy can the party that won the most votes end up outside the government it expected to lead?
- MIL·09Coalition frictionWhy can two allied armies fighting together achieve less than either would achieve alone?
- EAR·08Coastal dead zonesWhy does fertiliser spread on inland fields end up suffocating fish far out at sea?
- GEO·05Coastal fog beltsWhy does a tropical coastline stay cold and fog-bound while the open sea just offshore looks inviting?
- MAT·11Coastline paradoxWhy does a coastline get longer every time you measure it with a shorter ruler?
- MIN·10Cocktail party effectWhy can your own name cut through a conversation you were paying no attention to at all?
- CDA·40Code that never runs, and code that runs once a yearHow do you tell the difference between a program that is dead and one that is merely rare?
- MIN·11Cognitive dissonanceWhy does being paid too little to argue a case you disbelieve change your mind more than being paid well?
- MIN·12Cognitive reserveWhy can two brains with the same visible damage produce very different degrees of impairment?
- BIO·05Cohesion-tension sap ascentWhy can a tree draw water a hundred feet up a narrow pipe when the best pump on the ground cannot lift it past thirty?
- HOM·09Coiled extension leadWhy can an extension lead overheat while coiled on its reel yet run cool once the same cable is unwound?
- HOM·10Cold floorsWhy does a tiled floor feel colder than a carpet in the same room at the same temperature?
- CDA·41Cold startsWhy is the first request to an idle service slow in a way the next thousand are not?
- HOM·11Cold-spot condensationWhy does mould appear on one cold corner of a room that is heated throughout?
- MED·15Collateral circulationWhy can one person survive a blocked artery that kills another with the same blockage?
- CDA·42Collecting changes before committing themWhy gather up every edit and write them all at the end rather than as they happen?
- BIO·06Collective ant behaviorHow can an ant colony solve complex problems without a leader directing it?
- PHI·07Collective responsibilityWhy can a crowd be blamed for a harm that no single person in it did enough to be blamed for?
- CHM·13Colloid flocculationWhy does a clay suspension that has stayed milky for weeks curdle and drop clear within minutes of a pinch of salt?
- ART·09Color mixingWhy does mixing paints darken a colour while mixing lights brightens it?
- MIL·10Combat overclaimingWhy do honest pilots report far more kills than the enemy actually lost?
- MIL·11Combatant identificationWhy do armies dress their soldiers to be seen when staying hidden would save lives?
- MIL·12Combined armsWhy does mixing tanks, infantry and guns beat a force built from the single best arm?
- AST·05Comet tailsWhy does a comet's tail point away from the Sun even while the comet is racing away from it?
- FAM·12Comfort objectsWhy does a filthy worn blanket soothe a toddler when an identical clean one will not?
- CDA·43Commands and eventsWhy does naming a message in the past tense change the shape of the whole system?
- EAR·09Committed warmingWhy would seas keep rising for centuries even if emissions stopped tomorrow?
- GOV·07Committee gatekeepingWhy does a bill most legislators would vote for never reach a vote?
- GEO·06Common high pastureWhy is the high pasture above a village so often held in common while the fields below it are owned outright?
- EAR·10Common vertical datumWhy do two countries struggle to agree how high above the sea a mountain stands?
- ECO·15Comparative advantageHow can two countries both gain from trade when one of them produces everything more cheaply?
- CDA·44Compatibility has a directionWhy is 'compatible' meaningless until you say which side upgrades first?
- MED·16Compensated shockWhy can a patient losing blood dangerously fast still show an entirely normal blood pressure?
- LAN·07Compensatory lengtheningWhy does a word that loses a consonant so often keep its old length?
- MAT·12Completing a collectionWhy does collecting the last few stickers in a set take longer than collecting all the rest?
- MAT·13Compositeness without factorsHow can a number be proved not prime by someone who cannot name a single factor of it?
- CDA·45Composition over inheritanceWhy did the feature invented to let programs reuse code become the one to avoid?
- ENV·08Compost heatWhy does a heap of kitchen scraps get hot in the middle?
- ECO·16Compound interestWhat is compound interest?
- GOV·08Compounding debt serviceWhy can a government's borrowing costs rise in a year when it borrows nothing new?
- GEO·07Compromise capitalsWhy is the seat of government so often a modest town rather than the country's greatest city?
- GOV·09Compulsory taxationWhy must a service everyone wants be funded by a payment nobody is allowed to refuse?
- ART·10Concert hall reverberationWhy does the same orchestra sound thin outdoors and rich indoors when the playing has not changed?
- ART·11Concert pitch standardWhy did orchestras have to agree on a tuning pitch that no physical law fixes?
- GOV·10Conditional spending grantsWhy does a national government buy a policy with grant money when it could simply have legislated it?
- CDA·46Confident model errorsWhy does a language model deliver an invented fact in exactly the tone it uses for a true one?
- CDA·47Configuration driftWhy does a machine nobody has touched slowly stop matching its own blueprint?
- MIN·13ConformityWhy will a person state an answer they can see is wrong once everyone else has given it?
- MAT·14Confounded factorial effectsWhy does testing eight factors in eight runs hide some of the answers inside each other?
- CDA·48Congestion collapseWhy can a network carry less traffic in total the harder everyone tries to push data through it?
- CDA·49Connection exhaustion before CPUWhy does a service designed to scale infinitely take down the database before it works up a sweat?
- ENV·09Conservation easementsWhy would a farmer sign away forever the right to sell the land for houses?
- HIS·07Conspicuous displayWhy do people spend the most on the possessions that do them the least practical good?
- BIO·07Conspicuous signalsWhy would an animal advertise its own location with bright colour or loud calls?
- GOV·11Constitutional entrenchmentWhy would a society deliberately make its own most important rules hard to change?
- ECO·17Consumer price index constructionHow can a single number stand for the price of everything a household buys?
- MIN·14Contagious yawningWhy does watching a stranger yawn set you yawning when the yawn does nothing for you?
- CDA·50Content delivery networksWhy does a copy of a file stored near you make a distant website feel local?
- CDA·51Context windowWhy does a model with no memory between messages appear to remember the whole conversation?
- TRV·11Contingency fuelWhy does a pilot who loads extra fuel for safety guarantee that the flight burns more of it?
- ART·12Continuity editingWhy does an audience read two different camera angles as one continuous space?
- CDA·52Continuity over a protocol with no memoryHow does a protocol that forgets you between every request keep you logged in?
- GEO·08Contour linesHow can flat closed curves on paper warn you that a hillside is too steep to climb?
- CDA·53Control as a classificationWhy sort what a server offers by who is allowed to invoke it rather than by what it does?
- CDA·54Control plane and data planeWhy can a platform keep serving traffic perfectly while being completely unable to change anything?
- PHY·10Convection cellsWhy does a uniformly heated layer of oil organize itself into a pattern of hexagonal cells?
- BIO·08Convergent evolutionWhy do unrelated animals living in similar places end up looking so alike?
- PHI·08Convergent moral prohibitionsWhy do societies that never met converge on forbidding the same short list of acts?
- LAN·08Conversation turn-takingHow do people coordinate who speaks next without usually agreeing on rules aloud?
- MIL·13Convoy protectionWhy does gathering merchant ships into one large cluster make fewer of them sink?
- HOM·12Cooling a room with a fridgeWhy does leaving the fridge door open in a closed room make the room warmer rather than cooler?
- GEO·09Cooling with altitudeWhy does the air get colder as you climb a mountain toward the sun?
- WRK·09Coordination costWhy does adding people to a project that is already late often make it later?
- CDA·55Copying something you can only questionHow do you reconstruct a system you are never allowed to look inside?
- EAR·11Coral bleachingWhy does a rise of barely a degree make a coral expel the very algae that feed it?
- MAT·15Corner solutionsWhy does the best way to allocate limited resources always sit at a corner of the possibilities?
- CHM·14CorrosionWhy does iron rust while gold left in the same damp air does not?
- CDA·56CORS in the webWhat is CORS?
- ENV·10Cosmetic produce standardsWhy do sound, edible vegetables get discarded before they ever reach a shop shelf?
- AST·06Cosmic distance ladderHow can anyone know how far away a galaxy is?
- ECO·18Cost diseaseWhy does a haircut cost more in real terms than a century ago when barbers are no faster?
- BIO·09Cost of sexual reproductionWhy do most species pay to find a mate when a lineage that simply cloned itself would spread twice as fast?
- PHI·09Costly religious demandsWhy do religious groups that demand the most useless-looking sacrifices tend to last longest?
- BIO·10Countercurrent heat exchangeHow can a duck stand on ice all day without draining its body heat?
- CDA·57Counting steps instead of timingWhy do computer scientists count imaginary steps rather than simply timing the program?
- MAT·16Coupled oscillator synchronizationHow do metronomes on a shared board fall into step with nothing setting the beat?
- CDA·58CouplingWhy can code with no repetition anywhere still be impossible to modify safely?
- PHY·11Cracked bell toneWhy can a hairline crack too fine to see rob a large bell of its ring?
- WRK·10Crane signallingWhy does a crane crew let only one person give signals, yet allow anyone at all to call a stop?
- EDU·06Credential inflationWhy do employers start demanding degrees for jobs that were done well for decades without one?
- ECO·19CreditWhy will a stranger hand over goods today in exchange for nothing but a promise?
- ECO·20Credit ratings cliffWhy does one notch of downgrade cost a borrower far more than the notch before it?
- EDU·07Credit transfer between institutionsHow can a student carry credits between universities that never agreed on a curriculum?
- LAN·09Creole genesisWhy do the children of speakers with no shared grammar end up with a fully regular one?
- CHM·15Crevice corrosionWhy does stainless steel rot fastest in the one crack where oxygen cannot reach, when oxygen is what rusts ordinary iron?
- PHY·12Critical massWhy does a lump of uranium do nothing at all until it reaches a certain size, then everything at once?
- ENV·11Crop gene banksWhy store thousands of seed varieties that no farmer alive will ever plant?
- ENV·12Crop rotationWhy does changing the crop each year restore a field in ways fertilizer alone cannot?
- TRV·12Cross-border shopping tripsWhy does a small price gap across a border move whole busloads of shoppers?
- HIS·08Cross-cousin marriageWhy do many societies forbid marriage to one kind of cousin while urging it with another?
- ECO·21Cross-dockingWhy can a depot that stores nothing at all cut delivery costs more than a bigger warehouse would?
- MIN·15Crowd crushWhy does a crowd in which everyone pushes to leave faster end up leaving more slowly?
- TRV·13Cruise call clusteringWhy do four cruise ships crowd one small port on a Tuesday morning and none of them appear on Wednesday?
- ENG·12Crumple zonesWhy is a car built to destroy itself in a crash instead of holding firm?
- MIL·14Culminating point of an offensiveWhy must an army that keeps winning stop advancing before anyone has defeated it?
- MIN·16Cumulative advantage in popularityWhy can one song become a runaway hit while an equally good one is never heard?
- MIN·17Curiosity as an information gapWhy does knowing a little about a subject make you far hungrier to learn than knowing nothing?
- ECO·22Currency peg collapseWhy can a currency peg hold steady for years and then break in a single week?
- MAT·17Curse of dimensionalityWhy does measuring more features of each item make the items harder rather than easier to tell apart?
- EDU·08Curse of knowledge in teachingWhy can someone who learned a skill last year explain it better than the person who has taught it for thirty years?
- GOV·12Customary international lawHow can a rule bind every nation when no legislature ever enacted it?
- EDU·09Cut scores on licensing examsWhy must the pass mark that separates a competent practitioner from an incompetent one be argued for rather than measured?
- MAT·18Cyclic majoritiesHow can a group prefer A to B, B to C, and C to A when no member of it does?
D
84- ENV·13Dairy cow energy balanceWhy does a freshly calved high-yielding cow lose body condition no matter how generously she is fed?
- MIN·18Dark adaptationWhy does seeing in the dark take twenty minutes to acquire and one second of light to lose?
- AST·07Dark night skyIf the universe is full of stars, why is the night sky dark?
- CDA·59Data contractsWhy does a producer promising not to change a field make a whole platform faster to build on?
- CDA·60Data leakage pathsHow does private information escape a system that nobody attacked?
- CDA·61Data you keep is data you can loseWhy is holding on to information a liability rather than an asset?
- CDA·62Database transactionsHow can a database keep records consistent when many users change them at once?
- WRK·11Datum lines on siteWhy do builders measure everything from one line instead of from the piece just fitted?
- MIN·19Dawn light and the body clockWhy does the same bright light advance the body clock at dawn and delay it at dusk?
- CDA·63Dead or just slow?Why can no machine ever tell a crashed neighbour apart from a slow one?
- ART·13Death and art pricesWhy does an artist's work often become far more valuable once the artist has died?
- HIS·09Debt jubileesWhy did ancient kings repeatedly cancel all debts instead of enforcing contracts they had themselves blessed?
- CDA·64Deciding apart from enforcingWhy separate the thing that decides whether you may from the thing that stops you?
- MIN·20Decision fatigueWhy does a person who chose carefully all morning start taking whatever is put in front of them by evening?
- MIL·15Decision-cycle tempoWhy can deciding faster than an opponent matter more than deciding better?
- CDA·65Declaring the destination, not the routeWhy is writing down what a system should look like more reliable than the commands to get it there?
- AST·08Deconditioning in weightlessnessWhy does a body that adapts beautifully to orbit struggle to stand up on return?
- ENG·13Dedicated machine toolsWhy does a factory making one part forever buy a machine that can make nothing else?
- EAR·12Deep sound channelWhy does a whale call fade within kilometres near the surface yet cross an ocean at a certain depth?
- MIL·16Defender's advantageWhy can a defender hold a position against an attacking force several times its size?
- MAT·19Degrees of freedomWhy does estimating a mean from your data cost you one observation's worth of information?
- MIN·21Deja vuWhy can a place you are certain you have never visited feel overwhelmingly familiar anyway?
- MIN·22Delay discountingWhy would someone take ten pounds today over eleven tomorrow, yet wait a year and a day for the eleven?
- LAN·10Delayed auditory feedbackWhy does hearing your own voice a fraction of a second late stop you speaking?
- SPT·10Delayed muscle sorenessWhy do muscles often become sore a day after unfamiliar exercise rather than immediately?
- ENG·14Delayed weld crackingWhy can a weld that passes every inspection on the day it is made split open two nights later with nobody touching it?
- MIL·17Delegated launch authorityWhy would a state make itself safer by giving away its own power to decide on retaliation?
- CDA·66Delegation without the passwordHow do you let one service act for you somewhere else without ever giving it your credentials?
- WRK·12Deliberate practiceWhy do some people keep improving at a craft for decades while others stop improving after a year?
- CDA·67Deliberately slow password checksWhy would a system be designed to check your password slowly, when speed is what everything else is tuned for?
- CDA·68Delimiters as a boundaryWhy does wrapping someone else's text in markers change how a system treats it?
- CDA·69Delivered versus retainedWhy does keeping a message after someone has read it change what the system can do?
- GEO·10Delta subsidenceWhy do river deltas start sinking once dams upstream stop the mud from reaching them?
- CDA·70DenormalizationWhy deliberately put back the duplication you spent so much effort removing?
- CDA·71Dependency conflictsWhy can upgrading one library break a program that never used it in the first place?
- CDA·72Dependency directionWhy should the part of a program that stores data depend on the part that makes decisions, and not the reverse?
- CDA·73Deploying more to break lessWhy do the teams that release most often have the fewest failed releases?
- EAR·13Depth hoar in snowpackWhy does a buried snow layer grow weaker as it ages instead of settling into something stronger?
- GEO·11Desert latitudesWhy do the world's great deserts cluster along the same two bands of latitude?
- CDA·74Design by contractWhy write down what a function refuses to accept rather than making it cope with anything?
- ART·14Design restraintWhy does taking elements off a poster so often make what remains look more expensive?
- CDA·75Detecting a theft you cannot seeHow do you find out a credential was copied when the copy works exactly like the original?
- CHM·16Detection limitsWhy does a laboratory report a contaminant as \"below the limit of detection\" rather than simply saying none was there?
- MIL·18DeterrenceHow can a weapon prevent a war precisely by never being used?
- GOV·13Devolved authorityWhy do large states hand decisions to local bodies they could just as easily make centrally?
- MED·17Diabetic complicationsWhy does mildly high blood sugar damage nerves and kidneys only decades later?
- EDU·10Diagnostic distractorsWhy can a wrong answer option on a test tell a teacher more than the right one does?
- LAN·11Dialect continuumWhy can every neighbouring pair of villages understand each other when the chain's two ends cannot?
- TRV·14Different prices, same roomWhy do two guests in identical hotel rooms pay very different prices?
- LAN·12Digital preservation churnWhy does a digital archive need constant work to stay readable when a clay tablet needs none?
- LAN·13DiglossiaWhy do some communities keep two forms of one language and use each only in its own setting?
- ENV·14Diminishing fertiliser returnsWhy does doubling the fertiliser on a field add almost nothing to the harvest it yields?
- CHM·17Directed evolution of enzymesHow can a chemist obtain an enzyme for a reaction no organism ever needed?
- CHM·18Disappearing polymorphsWhy can a compound made the same way for years suddenly refuse to crystallize into the form the factory depends on?
- GOV·14Disaster-driven building codesWhy do safety rules improve most only after the disaster they were meant to prevent?
- PHI·10Disgust as a moral guideWhy does something feeling repugnant so readily pass for that thing being wrong?
- HOM·13Dishwasher dryingWhy do plastic containers come out of a dishwasher wet when the glasses beside them are dry?
- ECO·23Dispersed knowledge in productionHow does an ordinary pencil get made when no single person knows how to make one?
- GEO·12Distorted mental geographyWhy do people confidently place one city east of another when the map says otherwise?
- CDA·76Distributed consensusWhy can a group of perfectly healthy machines fail to agree on which of them is in charge?
- CDA·77Distributed tracingHow do you follow one user's request through forty services that each know only their own part?
- GOV·15District boundariesWhy can the drawing of district lines settle an election before any vote is cast?
- FAM·13Divorce contagionWhy does a close friend's separation raise the chance that a stable-looking marriage ends too?
- MIL·19Doctrine lagWhy does a victorious army so often enter the next war with exactly the wrong doctrine?
- CDA·78Documentation that points at its evidenceWhy must generated documentation carry a pointer back to the line it came from?
- PHI·11Doing versus allowingWhy does causing a harm feel worse than allowing the very same harm?
- HIS·10DomesticationHow did wild plants and animals become the crops and livestock we now depend on?
- MIN·23Doorway effectWhy does walking into the next room so often erase the reason you went there?
- SPT·11Doping arms raceWhy do athletes who would rather compete clean still feel pushed to dope even where testing is real and penalties are severe?
- PHY·13Doppler effectWhy does a siren change pitch as it passes you, when the siren itself never changes?
- MED·18Dose-responseWhy can the same substance be a medicine at one dose and a poison at another?
- CDA·79Double descentWhy does adding still more parameters to an already overfitted model make its predictions better again?
- GEO·13Doubling citiesWhy does a city growing a few percent a year outrun plans drawn only a decade ago?
- GEO·14Downdrift beach lossWhy does a groyne built to hold one beach in place strip the beach two miles along the coast?
- SPT·12Drafting in the pelotonWhy does a group of riders who all refuse to lead travel slower than any one of them alone?
- WRK·13Drain fallWhy does a waste pipe laid steeply downhill block more often than one laid almost level?
- CDA·80Drawing the same model three timesWhy describe the same information over again at three different levels of detail?
- PHY·14Drift in accepted values of constantsWhy do successive measurements of a constant drift toward the previous answer instead of scattering around the truth?
- MAT·20Dropping incomplete recordsWhy can discarding the rows with blanks distort an answer more than filling the blanks in would?
- MED·19Drug toleranceWhy does a drug that worked well at first need a bigger dose later to do the same job?
- HOM·14Dry drain trapWhy does a bathroom nobody uses start to smell of drains?
- ART·15Drypoint burrWhy is the tenth impression from a drypoint plate worth a fraction of the first when nobody altered the plate?
- CDA·81Durable executionHow does a process survive the machine it was running on disappearing mid-step?
- EAR·14Dust-fed rainforestsWhy does a rainforest on deep soil depend on dust blown from a desert an ocean away?
E
58- LAN·14Ear-voice spanWhy does an interpreter who lags further behind the speaker often deliver a more faithful rendering?
- SPT·13Early sport specializationWhy do children who commit to one sport early often stall or quit before those who kept playing several?
- SPT·14Early strength gainsWhy does a beginner get much stronger in the first month without their muscles growing at all?
- ART·16EarwormsWhy does a fragment of a song repeat in your head for hours when you never chose to play it?
- HIS·11East-west diffusionWhy did crops and inventions spread further along a continent's width than along its length?
- AST·09Eclipse seasonsWhy is there not a solar eclipse at every new moon, when the Moon passes between us and the Sun each month?
- BIO·11Ecological successionWhy does a burnt hillside come back through plants that cannot survive in the forest they end up creating?
- MIL·20Economy of forceWhy does making every point on a frontier strong leave the whole frontier weak?
- PHI·12Effortless virtueWhy do we admire the person who does right without feeling tempted more than the one who fights temptation and wins?
- EAR·15El Nino oscillationWhy does the Pacific keep swinging between warm and cool states instead of settling into one of them?
- GOV·16Election-timed spendingWhy do public projects break ground in the year before an election rather than after?
- GOV·17Electoral thresholdsWhy can a party winning one voter in twenty end up with no seats at all?
- CDA·82Embedding spaceHow can a search find the passage about getting money back when the document only ever says refund?
- PHY·15Emergence of temperatureWhy does a single atom have no temperature at all when a jar of them plainly does?
- GOV·18Emergency powers ratchetWhy do powers granted for a passing emergency so rarely go back once the emergency has passed?
- MED·20Emergency triageWhy can treating patients in the order they arrive cost more lives than treating them out of order?
- EDU·11Emergent classroom sign languageHow can a schoolyard of deaf children invent a grammar that no adult ever taught them?
- ART·17Emerging pentimentiWhy do a painter's abandoned first attempts creep back into view centuries after being covered over?
- GOV·19Eminent domain compensationWhy must a state pay for land it already has the power to take outright?
- MIL·21Emissions controlWhy does a warship with the finest radar afloat often choose to keep it switched off?
- ECO·24Empty container repositioningWhy do shipping lines sail thousands of empty steel boxes back across an ocean instead of selling them where they pile up?
- GEO·15EnclavesWhy does a village belonging to one country sit wholly inside another, and why does nobody simply trade it away?
- GEO·16Endorheic basinsWhy do some of the world's largest rivers never reach any sea, ending instead in a basin with no outlet?
- GOV·20Enforcement discretionWhy does one written rule produce very different treatment depending on which official applies it?
- ENG·15Engine run-inWhy does a new engine run more smoothly after its first thousand miles than it did leaving the factory?
- ENG·16Engineered redundancyWhy do engineers deliberately add parts that a perfectly working machine does not need?
- MAT·21Envy-free divisionWhy does letting one child cut the cake and the other choose first end the argument?
- CHM·19Enzyme specificityHow can an enzyme distinguish its target molecule from many similar molecules?
- MAT·22Equilibrium selectionWhen a game offers several equally good solutions, what makes everyone pick the same one?
- SPT·15Equipment bans in sportWhy would a governing body outlaw a suit or a racket that would have made every competitor faster?
- CDA·83Error budgetsWhy does deciding in advance how much failure is acceptable make a team ship faster and break less?
- MAT·23Error cancellation in averagesWhy can the average of many rough guesses beat nearly every guess that went into it?
- CDA·84Error-correcting codesHow can a receiver reconstruct a message even when some transmitted bits are corrupted?
- MIL·22EscalationWhy do disputes so often grow far past the point either side originally wanted?
- PHY·16Escape of light gases from an atmosphereWhy has Earth held on to its nitrogen while losing almost all of its hydrogen?
- HIS·12Ethnic boundary formationWhy does a group's sense of who counts as one of us sharpen at its edges rather than at its centre?
- LAN·15EuphemismWhy does renaming a thing change how people feel about the thing itself?
- CDA·85Evaluating retrieval separatelyWhen an answer built from sources is wrong, how do you tell whether the finding or the writing failed?
- CDA·86Evaluation suitesWhy can you not tell whether a change improved an AI system by simply trying it?
- HOM·15Evaporative dryingWhy do clothes dry faster on a windy day than on a merely warm one?
- SPT·16Even pacingWhy does an even pace beat a fast start over a long race?
- CDA·87Event sourcingWhy store every change that ever happened instead of just what is true now?
- CDA·88Event time versus arrival timeHow does a system that never stops receiving data decide it has seen enough to answer?
- CDA·89Eventual consistencyWhy is a system that is briefly wrong everywhere sometimes better than one that is always right in one place?
- GOV·21Everyday legal complianceWhy do most people obey laws when the chance of ever being caught is tiny?
- CDA·90Exactly once is a property of the pipelineWhy can no single component promise that a message is handled exactly once?
- EDU·12Exam equatingWhy can this year's candidates sit an easier paper than last year's and still be judged on the same scale?
- GOV·22Exclusionary ruleWhy would a court throw out evidence it knows to be true and decisive?
- SPT·17Exercise-associated hyponatremiaWhy can a marathon runner who drinks steadily at every station collapse from having too much water rather than too little?
- LAN·16ExonymsWhy does almost every country have a name in other languages that its own people never use?
- AST·10Exoplanet detectionHow can we detect a planet we cannot see, orbiting a star we can barely resolve?
- ECO·25Experience ratingWhy does an insurer whose whole business is pooling risk turn around and charge each customer by their own claims history?
- ECO·26Experience-curve pricingWhy would a manufacturer deliberately sell its first units at a price below what they cost to make?
- WRK·14Experienced-worker injuriesWhy do the most experienced workers get hurt doing things a beginner would never risk?
- EDU·13Expertise reversalWhy does the teaching method that helps a beginner hold an expert back?
- ART·18Explained jokesWhy does a joke stop being funny the moment it is explained?
- ECO·27Exposure problem in package biddingWhy can a bidder who wins one of the two licences it needs end up worse off than one who wins nothing?
- EAR·16Extreme event attributionHow can anyone say whether a warming climate caused one particular flood?
F
72- HOM·16Fabric softener and absorbencyWhy do towels dry you less well after the wash that made them feel softest?
- MIN·24Face recognitionHow does the brain recognize a familiar face despite changes in angle, lighting, and age?
- MAT·24Factorial explosionWhy is a shuffled deck of cards almost certainly in an order no deck has ever held before?
- MIL·23Fading advantage of a new weaponWhy does a weapon that wins decisively on its first use rarely win that way twice?
- FAM·14Fading attractionWhy do the very traits that first attracted someone to a partner stop being noticed?
- ENG·17Fail-safe brakingWhy is a train's brake held off by pressure rather than applied by it?
- CDA·91Failing fastWhy should a program that notices something wrong stop immediately rather than carry on carefully?
- WRK·15Failure after repairWhy is a machine often most likely to break just after it has been serviced?
- MAT·25Fair lottery over the integersWhy can no lottery give every whole number an equal chance of being drawn?
- PHI·13Faith and evidenceHow can a believer and a sceptic reach opposite conclusions from the same world?
- GEO·17Fall-line citiesWhy do so many old cities sit exactly at the point where a river stops being navigable?
- SPT·18Falling recordsWhy do athletic records keep improving when the human body has not changed?
- CDA·92False sharingWhy do two processor cores slow each other down when neither one ever touches the other's variable?
- AST·11False-color astronomical imagesWhy is a picture of a nebula in colors no eye could ever see still honest?
- FAM·15Family estrangementWhy do family cutoffs last for decades when far uglier quarrels between friends are patched up within a year?
- HIS·13Famine amid plentyWhy can people starve in a year when their region harvested enough food to feed everyone?
- PHY·17Faraday cageWhy does a metal mesh you can see straight through block a radio signal almost completely?
- ENV·15Farm nitrogen balanceWhy must the nitrogen that does not leave in the crop turn up somewhere unwelcome?
- ART·19Fashion churnWhy do fashions keep changing when nobody is dissatisfied with what they already own?
- CHM·20Fast charging and battery lifeWhy can a battery be made to charge faster only at the cost of how long it lasts?
- PHI·14FastingWhy do people who deny themselves food for a month report more pleasure in eating, not less?
- CDA·93Feature flagsWhy ship code to production that you have deliberately arranged not to run?
- CDA·94Federated data ownershipWhy does a central team that owns everyone's data become the reason nobody's data is good?
- MED·21Fee-for-service paymentWhy can paying a hospital for every treatment it delivers leave its patients no healthier?
- ENG·18Feedback controlHow can a machine hold a steady temperature without ever being told the right setting in advance?
- ART·20Feedback howl in live soundWhy does a microphone that was perfectly quiet suddenly erupt into a screaming tone?
- EDU·14Feedback timingWhy can telling a student the answer too quickly weaken what they learn?
- MIL·24Feigned retreatWhy can an army that turns and runs away destroy the force chasing it?
- HIS·14Festival calendarsWhy do a society's largest festivals keep falling at the same points every year?
- MED·22Fetal programmingWhy can a person's risk of heart disease be partly settled before they are born?
- MED·23FeverWhy does the body raise its temperature during an infection?
- CDA·95Few-shot promptingWhy does showing a model three worked examples work better than describing the rule?
- CDA·96Fewer operations, slower programWhy does the structure that does less work often finish last?
- PHY·18Feynman diagramsHow can a cartoon of lines and vertices stand in for an integral nobody can picture?
- CHM·21Fibre strength and flawsWhy is a hair-thin glass fibre far stronger than a thick rod of the very same glass?
- SPT·19Figure-skating spinWhy does a figure skater rotate faster after pulling in their arms?
- CDA·97File deletionWhy is deleting a file not the same as erasing what it contained?
- LAN·17Filler wordsWhy does a speaker who pauses to say \"um\" get understood better than one who never hesitates?
- CDA·98Finding without searchingHow can a computer find one record among millions without examining any of the others?
- CDA·99Fine-tuning versus retrievalWhy does teaching a model your facts leave them stale, while teaching it your style does not?
- BIO·12Firefly synchronyHow do thousands of fireflies fall into one rhythm with no conductor among them?
- MED·24First-pass metabolismWhy can a drug that works well by injection do almost nothing when the same amount is swallowed?
- ENV·16Fish spoiling fastWhy does fish go off in days when beef keeps for weeks in the very same fridge?
- ENV·17Fishery collapseWhy can a fishery that fed people for generations collapse within a single decade?
- GOV·23Fixed-size legislatureWhy must one region lose a legislative seat whenever another region gains one?
- CHM·22Flame emission coloursWhy does each metal give a firework its own colour instead of all of them simply glowing hotter?
- HOM·17Flat-pack bracingWhy does a flat-pack cabinet stay wobbly until its flimsiest panel is fixed to the back?
- MIL·25Fleet in beingWhy can a weaker fleet that never leaves harbour still pin down a stronger one?
- WRK·16Floating panelsWhy does a joiner leave the panel of a door sitting loose in its frame instead of gluing it fast?
- CDA·100Floating-point errorWhy can a computer calculate 0.1 + 0.2 without obtaining exactly 0.3?
- EAR·17Floodplain storageWhy does a river need land that it does not touch except once a decade?
- EDU·15Fluency illusionWhy does the lecture that was easiest to follow leave the least behind a week later?
- MIL·26Fog of warWhy do two commanders given the same information reach opposite conclusions?
- ART·21Folk craft regionalismWhy do handmade crafts from neighbouring valleys settle into unmistakable local styles when nobody sets the rules?
- ENV·18Food milesWhy can food grown far away sometimes cost the planet less than food grown nearby?
- ENV·19Food preservationWhy do salting, drying, and pickling keep food edible for months?
- TRV·15Footfall wear on monumentsHow can visitors who each touch a stone step once wear the step away?
- SPT·20Forearm pump in climbingWhy does a climber's grip fail long before their arms tire, then recover after a minute of hanging straight-armed?
- EAR·18Forecast horizonWhy can we forecast tomorrow's weather well and next month's not at all?
- TRV·16Forecasting tonight's coversHow does a chef decide how much to prepare for a night nobody can predict?
- BIO·13Forest height raceWhy does a tree in a crowded wood grow tall and spindly while the same species alone in a field spreads wide and low?
- HIS·15Formulaic oral compositionHow did singers hold epics of thousands of lines steady across generations with nothing written down?
- CDA·101Foundation model economicsWhy did building one model per task give way to adapting a single expensive one?
- MED·25Fragmented prescribingWhy can every prescriber be individually right and the patient still end up on a dangerous list of drugs?
- LAN·18FramingWhy can two entirely accurate headlines about the same event leave opposite impressions?
- TRV·17Free upgrade costWhy does giving away a better room for free still cost the hotel a sale?
- PHI·15Free willIf every choice has a cause behind it, in what sense is any choice yours?
- HOM·18Freezer burnWhy does food dry out inside a sealed freezer where nothing can evaporate away?
- CHM·23Freezing-point depressionWhy does scattering salt on ice melt it in cold that would otherwise keep it frozen?
- TRV·18Frequent-flyer currencyWhy can an airline earn more from giving its seats away than from selling them?
- HOM·19Full freezer efficiencyWhy does a full freezer cost less to run than a mostly empty one?
- GEO·18Functional versus administrative regionsWhy do the regions people actually live and work across so rarely match the ones on the administrative map?
G
44- AST·12Galaxy rotation curvesWhy do the outermost stars of a galaxy orbit as fast as the inner ones when the outer planets do not?
- ART·22Gamelan tuningWhy can two gamelan orchestras built in neighbouring villages never be played together?
- CDA·102Garbage collection pausesWhy does a program that frees its own memory sometimes freeze at the worst moment?
- MED·26General anaesthesiaHow can a surgeon be confident a patient is unconscious when nobody can measure consciousness directly?
- MAT·26Generating functionsWhy can turning a counting problem into an infinite polynomial make it easier rather than harder?
- ENG·19Generative design shapesWhy do computer-evolved brackets end up looking like bones rather than beams?
- BIO·14Genetic driftWhy can a variant that helps nobody spread through a small population anyway?
- GEO·19GentrificationWhy does investment that visibly improves a neighbourhood often leave its longest-standing residents worse off?
- EAR·19Geostrophic windWhy does the wind follow the lines on a weather map instead of blowing straight from high pressure to low?
- HOM·20Ghost glow in LED bulbsWhy do some LED bulbs keep glowing faintly after the switch is turned off?
- HIS·16Gift obligationWhy does a gift create a debt that a payment of the same value would not?
- FAM·16Gift-exchange escalationWhy do families keep raising gift spending when nearly everyone would prefer to spend less?
- LAN·19Given-name fashionsWhy do given names rise and collapse in popularity like fashions when nobody coordinates the choice?
- EAR·20Glacier flowHow can solid ice flow downhill like a very slow river?
- CHM·24Glass transitionWhy does window glass soften gradually over a range of temperatures instead of melting sharply at one, as its crystalline twin does?
- PHY·19Glass transparencyWhy is ordinary glass transparent to visible light but not to every kind of radiation?
- SPT·21Golf ball dimplesWhy does a roughened golf ball fly nearly twice as far as a perfectly smooth one?
- CDA·103Grade earned, not declaredWhy does calling a dataset trustworthy do nothing, while making it pass a test does?
- EDU·16Grade inflationWhy do grades drift upward decade after decade without students getting any better?
- EDU·17Grade retentionWhy does making a struggling child repeat a year so often leave them further behind than before?
- HIS·17Grain and taxationWhy did early states tax grain when tubers and livestock fed their people just as well?
- ENV·20Grain bin hot spotsWhy does one corner of a bin of dry, sound grain heat up and spoil while the rest of it keeps for a year?
- LAN·20Grammatical evidentialityWhy do some languages force a speaker to mark how they came to know what they assert?
- FAM·17Grandmother proximity and fertilityWhy do couples living near a grandmother have more children than equally well-off couples living far from one?
- FAM·18Grandparent asymmetryWhy do grandparents on the mother's side tend to help with grandchildren more than those on the father's?
- AST·13Gravity assistHow can a spacecraft leave a planet faster than it arrived, when that planet's gravity pulls back just as hard on the way out?
- ENV·21Grazing and grassland richnessWhy can a grassland support more kinds of plant when grazing animals are allowed onto it?
- ENV·22Grazing rest periodWhy does moving a flock off before it has finished the grass leave more feed at the end of the season than letting it graze down?
- ENG·20Green wave signal timingWhy can retiming a corridor's traffic lights move more cars than adding another lane to it?
- ENG·21Grid balancingWhy must an electricity grid match supply to demand from one second to the next?
- ENG·22Grid inertia lossWhy does a power grid full of modern inverters lurch at a fault that older spinning plant would have absorbed unnoticed?
- FAM·19Grief timingWhy does bereavement often hurt most many months after the funeral rather than in the first raw weeks?
- CDA·104Grokking in trainingWhy does a model that has already memorised its training data suddenly start generalising long afterwards?
- ART·23Groove and microtimingWhy does a drum machine playing perfectly on the beat feel less danceable than a drummer who is slightly late?
- TRV·19Ground delay programsWhy does air traffic control hold an aircraft at its gate for an hour when the sky ahead of it is empty?
- EDU·18Group projectsWhy does a group of capable students so often hand in work worse than its best member alone would?
- SPT·22Group-stage tiebreaksWhy can a team win two of its three group matches and go home while a team that won only one advances?
- PHI·16Guaranteed secrecyWhy does a promise that can never be broken get told the things nobody would otherwise admit?
- CDA·105GuardrailsWhy wrap a deterministic check around a model that was already trained to behave?
- TRV·20Guest-rightWhy did societies along the hardest routes make sheltering a stranger a sacred duty rather than a paid service?
- PHY·20Guided lightWhy can light be made to follow a bending glass fibre instead of leaking out of its side?
- ENG·23Guided light in fibreWhy does light stay trapped inside a bent glass thread instead of escaping at the curve?
- BIO·15Gut colonization orderWhy can the order in which microbes reach an infant gut matter more than which ones arrive?
- PHY·21Gyroscopic precessionWhy does a spinning top lean over without simply toppling?
H
53- MIN·25Habit formationWhy does a behaviour get easier to repeat and harder to stop the more often it happens?
- MIN·26Habituation versus sensitizationWhy does a repeated noise fade out of awareness while a repeated pain becomes harder to ignore?
- MAT·27Hairy ball theoremWhy must there always be at least one place on Earth where the wind is not blowing?
- CDA·106Half-sorted is enoughWhy can a structure that never fully sorts anything hand you the smallest item instantly?
- CDA·107Halting problemWhy can no program be written that reliably predicts whether another program will ever finish?
- CDA·108Halving the haystackWhy does throwing away half of what remains find one item among a billion in about thirty tries?
- MED·27Hand hygiene complianceWhy do the clinicians who best understand how infection spreads wash their hands least reliably?
- SPT·23HandicappingHow can a game stay genuinely interesting between players of very different ability?
- AST·14Hanging still versus racing aroundWhy does one satellite hover over a single city while another must circle the world hourly?
- CDA·109Hash table clusteringWhy does a hash table's lookup cost explode while most of its slots are still sitting empty?
- LAN·21HeadlineseWhy can a headline drop half of its grammar and still be read without difficulty?
- SPT·24Heat acclimatizationWhy does an athlete who has trained through two weeks of heat finish a hot race with a lower core temperature while sweating far more?
- PHY·22Heat diffusion timeWhy does doubling the thickness of a wall delay the heat's arrival by four times rather than two?
- ENG·24Heat exchanger foulingWhy does a heat exchanger scoured back to bare metal lose more of its duty in the first month than in the whole year that follows?
- ENG·25Heat pipesHow can a sealed tube with no moving parts carry heat better than a solid copper bar of the same size?
- MIN·27Hedonic adaptationWhy does a long-awaited improvement in life stop feeling good within a few months?
- CHM·25Helium depletionWhy does a gas essential to hospital scanners keep escaping into party balloons?
- PHY·23Helium voiceWhy does breathing helium change the sound of a voice when the vocal cords are still vibrating at the same rate?
- HIS·18Herd dispersal among kinWhy do herders scatter their animals among distant kin instead of keeping the herd together where they can watch it?
- MED·28Herd immunityWhy can vaccinating most of a population protect the people who were never vaccinated?
- HIS·19Hereditary successionWhy did societies keep handing power to whoever was born first rather than whoever was ablest?
- FAM·20Heritage language lossWhy do the children of immigrants stop speaking the family language even when the parents never switch?
- CHM·26Hess's lawHow can chemists know the heat of a reaction nobody has ever carried out?
- BIO·16HibernationWhy does an animal facing a freezing winter survive it by letting its own body go cold?
- ENG·26High-voltage transmissionWhy is electricity pushed to hundreds of thousands of volts only to be dropped again at the far end?
- HIS·20Historical silenceWhat can historians responsibly infer when the people most affected left few written records?
- MIL·27Holding a reserveWhy does a commander keep the freshest troops out of the fight until the battle is nearly lost?
- MIL·28Holding conquered groundWhy is beating an army so much cheaper than governing the territory it was defending?
- FAM·21Holiday time between two familiesWhy does a couple's holiday visiting plan cause conflict that goodwill cannot dissolve?
- WRK·17Hollow section stiffnessWhy does a hollow tube resist twisting better than a solid bar of equal weight?
- SPT·25Home advantageWhy do teams win more often at home, in every sport anyone has measured?
- HOM·21Home insulationWhy does insulating a house save more than simply turning the heating down?
- BIO·17Honeybee waggle danceHow can a bee tell hivemates where flowers are when it cannot lead them there?
- TRV·21Honeypot sitesWhy does a national park funnel its visitors into a handful of crowded spots instead of spreading them thinly?
- ECO·28Hostage capitalWhy does a supplier sometimes make an investment that would be worthless if the deal fell apart?
- CDA·110Hot partitionsWhy does data split evenly across a hundred machines still overwhelm exactly one of them?
- PHY·24Hourglass flow rateWhy does sand pour through an hourglass at the same steady rate whether the upper bulb is full or nearly empty, when water would not?
- HOM·22House dustWhy does a room nobody enters still need dusting every few weeks?
- FAM·22Household money potsWhy do people who share every meal keep separate pots of money and defend them against each other?
- ART·24How can music create emotion?How can music create emotion?
- BIO·18How do birds know where to migrate?How do birds know where to migrate?
- CDA·111How does a neural network learn?How does a neural network learn?
- ENG·27How does a refrigerator cool food?How does a refrigerator cool food?
- MED·29How does antibiotic resistance develop?How does antibiotic resistance develop?
- ENG·28How does GPS find your location?How does GPS find your location?
- CDA·112How encryption keeps messages secretHow does encryption keep messages secret?
- HOM·23How much charge is leftWhy can a device that measures its own battery constantly still be wrong about how long it will last?
- MED·30How vaccines workHow do vaccines work?
- GEO·20Hub-and-feeder portsWhy do most goods pass through a few distant giant ports instead of the nearest one?
- TRV·22Hub-and-spoke routingWhy does an airline fly you away from your destination in order to get you there?
- EAR·21Hurricane intensificationWhy does a hurricane strengthen for days over warm water and fall apart within hours of crossing a coastline?
- CDA·113Hybrid searchWhy does combining a search that understands meaning with one that only matches words beat either alone?
- ENV·23Hybrid seed declineWhy do seeds saved from a superb hybrid crop give a disappointing and uneven harvest the following year?
I
47- EAR·22Ice age triggersWhy can a slight wobble in Earth's orbit swing the whole planet into an ice age?
- EAR·23Ice core recordsHow can bubbles sealed inside ancient ice tell us what the air was like long before anyone measured it?
- CDA·114Idempotent operationsWhy must an action that might be retried be designed for it rather than simply repeated?
- PHI·17Identity over changeIf every part of a thing is replaced one by one, is it still the same thing?
- CDA·115ImmutabilityWhy does forbidding a value to change make code that runs in parallel correct by construction?
- PHI·18Imperceptible harmsWhy does an act that harms nobody detectably still seem wrong when everyone does it?
- ECO·29Impossible trinityWhy can no country fix its currency, open its borders to capital and set its own rates?
- MIN·28Inattentional blindnessHow can something in plain sight go completely unnoticed?
- MAT·28IncompletenessCan a system of arithmetic prove every true statement about numbers?
- ECO·30Incumbent disruptionWhy do dominant firms so often lose to a technology their own engineers saw coming first?
- CDA·116IndexingWhy does the thing that makes reading fast make writing slow?
- LAN·22Indirect requestsWhy do people ask for things in a roundabout way when a direct request would be clearer?
- MED·31Individual treatment effectWhy can a trial prove a drug works and still never tell whether it worked for you?
- GEO·21Induced trafficWhy does a new lane added to a congested road end up just as congested?
- GEO·22Industrial district persistenceWhy does a region keep making one product for a century after the resource that started it ran out?
- ECO·31Industry concentrationWhy do some industries settle into three enormous firms while others support thousands of small ones?
- FAM·23Infant night wakingWhy do human infants keep demanding night feeds long after their nutritional needs would require them?
- MAT·29Infinitude of primesWhy can the prime numbers never run out?
- TRV·23Inflight tasteWhy does food that tasted fine on the ground taste bland at cruising altitude?
- FAM·24Inherited parenting scriptsWhy do parents who vowed never to repeat their own upbringing find themselves doing exactly that under stress?
- MAT·30Inspection paradoxWhy is the bus you board almost always more crowded than the average bus on the route?
- CHM·27Instant glueWhy does a glue that sits liquid in its tube for years harden the moment it meets a fingertip?
- HOM·24InsuranceWhy is buying insurance sensible even though, on average, it loses money?
- ECO·32Insurance poolingHow can an insurer safely take on risks that would ruin any one of its customers?
- ENG·29Integrator windupWhy does a controller that held a tank at temperature for hours overshoot wildly the first time its heater is asked for more than it can give?
- EDU·19Interleaved practiceWhy does mixing problem types during practice feel worse yet leave you better prepared?
- PHY·25Intermediate axis instabilityWhy does a book tossed spinning about its middle axis keep flipping over when the other two spins stay steady?
- ECO·33Internal transfer pricingWhy do two divisions of the same company argue bitterly over a price when the money never leaves the company?
- CDA·117Internet packet routingHow can data reach the right destination when no machine controls the entire internet?
- MIN·29InteroceptionWhy do people who cannot feel their own heartbeat also tend to misread their own emotions?
- SPT·26Interval trainingWhy can running hard in short bursts with rest between them build more endurance than running the same distance steadily?
- MED·32Intracranial pressureWhy must something be pushed out of a skull before anything inside it is allowed to swell?
- BIO·19Invasion lag before explosionWhy can an introduced species sit harmless for decades and then overrun a continent?
- HIS·21Invented traditionWhy are so many customs described as immemorial in fact younger than the railways?
- ENG·30Involute gear teethWhy must gear teeth be cut to one particular curve if the driven shaft is to turn at a steady speed?
- LAN·23Irregular verb survivalWhy do the verbs a language uses most often stay irregular while rarer ones quietly become regular?
- PHY·26IrreversibilityWhy does a hot drink always cool, when nothing in the laws of motion forbids the reverse?
- CHM·28Irreversible enzyme inhibitionWhy does aspirin keep working long after the drug itself has left the bloodstream?
- ENV·24Irrigation efficiency paradoxWhy can upgrading a valley's farms to efficient drip irrigation leave less water in the river, not more?
- ENV·25Irrigation scheduling depthWhy does watering a crop lightly every day leave it worse off in a drought than soaking it once a week?
- BIO·20Island size ruleWhy do large mammals stranded on an island shrink over time while small ones grow?
- CDA·118Isolates, containers, and startup costWhy does making a sandbox weaker sometimes make the system safer to run at scale?
- CDA·119Isolation levelsHow can two transactions that are each correct combine into a result neither would produce alone?
- CDA·120Isolation without a machineHow can a program be walled off from everything else on a computer without a computer of its own?
- CHM·29Isomer blindness in mass spectrometryWhy can an instrument weigh a molecule perfectly and still not know what it is?
- EAR·24Isostatic reboundWhy is land in Scandinavia still rising thousands of years after the ice that pressed it down melted away?
- CHM·30Isotopic provenanceHow can a laboratory tell where a sample was grown or mined with no record of it?
J
12- ECO·34J-curve after devaluationWhy does a cheaper currency make a trade deficit worse before it makes it better?
- BIO·21Janzen-Connell seedling mortalityWhy does a tropical seedling fare worst on exactly the patch of ground where its own parent is thriving?
- ART·25Jazz improvisationWhy does a jazz soloist sound freer inside a fixed chord scheme than with no rules at all?
- MED·33Jet lagHow does crossing time zones disrupt the body's sense of when to sleep?
- SPT·27Judging order effectsWhy does the same gymnastics routine score higher when it is performed late in the running order than early?
- GOV·24Judicial recusalWhy must a judge withdraw from a case when nobody has shown that they are actually biased?
- GOV·25Judicial reviewWhy do democracies let unelected judges cancel laws that elected majorities passed?
- SPT·28Junior championsWhy do the children who win national age-group titles so rarely become the adults who win senior ones?
- GOV·26Jurisdictional forum shoppingWhy do companies incorporate in a state where they keep no offices and no staff?
- GOV·27Jury deliberationHow can a jury reason fairly when witnesses and evidence point in different directions?
- ECO·35Just-in-time fragilityWhy does a supply chain tuned for efficiency break so badly when a single plant stops?
- MIN·30Just-noticeable differenceWhy does one extra candle brighten a dim room yet disappear entirely in a bright one?
K
10- EAR·25Katabatic windsWhy does air on the Antarctic plateau reach gale force downhill with no storm system driving it?
- PHI·19Keeping a rule against the caseWhy should you keep a rule in the one case where breaking it would plainly do more good?
- CDA·121Keeping the history and the snapshot in one fileHow can one log hold both every change ever made and just the current state?
- BIO·22Keystone speciesHow can removing one uncommon species reshape an entire ecosystem?
- CDA·122Killed with memory to spareWhy does a program die for lack of memory on a machine that has plenty left?
- AST·15Kirkwood gapsWhy is the asteroid belt swept empty at exactly the orbits whose timing is most perfectly regular?
- TRV·24Kitchen brigade stationsWhy does a kitchen where nobody cooks a whole dish serve whole dishes faster?
- SPT·29Knockout upsetsWhy does the strongest entrant in a knockout tournament win it far less often than their record suggests?
- EDU·20Knowledge and comprehensionWhy do two children who decode words equally well understand the same passage so differently?
- PHI·20Knowledge from testimonyWhy is it reasonable to believe almost everything you know without ever checking it yourself?
L
59- CDA·123Labelling before decidingWhy sort information by how sensitive it is before working out who should see it?
- AST·16Lagrange pointsHow can a space telescope hold station relative to the Earth and Sun for years without an engine running?
- EAR·26Lake turnoverWhy does a deep lake suddenly turn over from top to bottom at certain times of year?
- MIL·29Lanchester's square lawWhy does a force twice the size win with far more than half its strength intact?
- BIO·23Land size limitsWhy does the largest animal on land fall so far short of the largest in the sea?
- ENV·26Landfill methaneWhy does one food scrap warm the world far more buried in a tip than rotting in a garden heap?
- GEO·23Landlocked disadvantageWhy does having no coastline cost a country more than its distance to a port alone would explain?
- TRV·25Landmark restaurantsWhy do the restaurants nearest a famous landmark serve the worst food and still stay full?
- LAN·24Language abandonmentWhy can a language disappear when almost every speaker wants it to survive?
- AST·17Large mirror flexureWhy must the biggest telescope mirrors be built deliberately floppy and pushed back into shape all night?
- FAM·25Large-family parenting shiftWhy does a fourth child change parenting in kind rather than merely adding more of the same?
- PHY·27Laser coherenceWhy does laser light stay a narrow beam when a bulb's light has spread out within a metre?
- PHY·28Laser coolingWhy does shining light on a cloud of atoms -- pouring energy into it -- leave the cloud colder than any refrigerator can make it?
- HIS·22Late marriage and population restraintWhy did some pre-industrial populations stop growing well before their land could no longer feed them?
- CDA·124Late-arriving dataHow do you insert something that happened before events you have already recorded and reported on?
- BIO·24Lateral inhibition in tissueWhy does a patch of cells that are all equally able to become a bristle end up producing bristles at neat, even spacings?
- HOM·25Layered electrical protectionWhy does a house need three separate devices that all do nothing until something goes wrong?
- PHY·29Layered particle detectorsWhy build a detector from several mediocre instruments instead of one excellent one?
- CDA·125Layers are diffsWhy does adding a large file and then deleting it leave the result bigger than before?
- WRK·18Lead in short lengthsWhy does a roofer cut flashing into short pieces when one continuous strip would obviously leak less?
- ENG·31Leak-before-breakWhy do engineers deliberately design a pressure vessel so that a growing crack will dribble rather than hold?
- AST·18Leap secondsWhy does the whole world have to argue about inserting a single second?
- MIN·31Learned helplessnessWhy does an animal that once could not escape stop trying long after escape has become easy?
- WRK·19Learning a trade by standing thereWhy must a trade be learned standing beside someone doing it when the manual is right there?
- EDU·21Learning by explainingWhy does preparing to teach a topic teach you more than preparing to be tested on it?
- EDU·22Learning plateausWhy does progress in a new skill stall for weeks and then jump without extra effort?
- CDA·126Least astonishmentWhy is a correct interface that surprises the person using it a defect?
- HOM·26LED dimmer incompatibilityWhy does a new LED bulb flicker or buzz on the dimmer that ran the old one smoothly?
- SPT·30Left-hander advantageWhy are left-handers so overrepresented in fencing and boxing but not in golf or rowing?
- HOM·27Leftover spoilageWhy do leftovers spoil faster than the same food did before it was cooked?
- GOV·28Legal precedentWhen is it reasonable for a court to depart from a decision it is otherwise bound to follow?
- BIO·25Leghemoglobin in root nodulesWhy does a legume build an oxygen-grabbing pigment to starve its bacterial guests of the very air they are sitting in?
- ART·26LegibilityWhy is a page set entirely in capitals harder to read than the same words in mixed case?
- TRV·26Length-of-stay controlsWhy would a hotel with rooms standing empty refuse a two-night booking it could easily accommodate?
- CDA·127Letting callers ask for exactly what they wantWhy does giving callers precisely the data they request create a problem the rigid old way never had?
- WRK·20Light-load diesel runningWhy does a ship's engineer worry more about an engine run gently for weeks than one worked hard?
- ENV·27Lime-induced nutrient lockupWhy can liming a sour field to make it more fertile leave the crop starved of a nutrient the soil still holds?
- HOM·28LimescaleWhy does boiling water leave a hard crust in the kettle when the same water leaves nothing in a glass?
- HIS·23Liminality in initiationWhy do initiation rites so often put the initiate through a spell of isolation, hunger or humiliation?
- WRK·21Limiting work in progressWhy does forbidding people to start new work make more work get finished?
- MIN·32Limits of introspectionWhy can people explain a choice fluently and confidently while having no access to its real cause?
- BIO·26Limits of regenerationWhy can a starfish regrow a whole arm when a person cannot regrow a lost finger?
- GOV·29Line of successionWhy does a government carefully name successors who will almost certainly never take office?
- CDA·128LineageWhen a number on a report is wrong, how do you find every other number that is now also wrong?
- ART·27Linear perspectiveHow can lines on a flat surface create a convincing impression of depth?
- CHM·31Liquid crystalsHow can a substance flow like a liquid and still steer light with the precision of a crystal?
- MIL·30Live-and-let-live trucesHow did quiet stretches of front appear when both high commands forbade them?
- PHI·21Living interpretation of a fixed textWhy does a scripture whose words never change still need a living court to say what it requires?
- LAN·25Loanword doubletsWhy does a language borrow a foreign word for something it already has a perfectly good word for?
- MED·34Local anaesthetic failureWhy does a dental injection that reliably numbs a healthy tooth fail on an abscessed one?
- ENV·28Locust upsurgeWhy does a scattering of harmless solitary insects become a plague crossing continents in a single season?
- CDA·129Logged into someone else's accountHow can an attacker harm you by making sure you are signed in rather than signed out?
- WRK·22Long-hours arms raceWhy does everyone stay late when nobody gains from staying later than the rest?
- MAT·31Long-run chain behaviourWhy does a process with no memory beyond its current state settle into a fixed long-run pattern?
- GOV·30Loser-pays cost rulesWhy does making the loser pay the winner's legal costs deter sound claims along with the frivolous ones?
- CDA·130Losing it or doing it twiceWhy must a system choose between occasionally dropping work and occasionally repeating it?
- CDA·131Lossless compressionHow can a file be made smaller with nothing at all thrown away?
- CDA·132Lost in the middleWhy does a model use the beginning and end of a long document more reliably than its middle?
- AST·19Low-frequency radio cutoffWhy would astronomers put a radio telescope on the far side of the Moon to hear the longest wavelengths?
M
77- PHY·30Magnetic hysteresisWhy does a magnet's state depend on where the field has been rather than where it is now?
- SPT·31Magnus effectHow can a spinning ball curve sideways through perfectly still air?
- ENV·29Maillard browningWhy does searing meat produce flavors that boiling it never does?
- ENV·30Managed hives and wild pollinatorsWhy can adding more beehives to a landscape leave its crops less well pollinated over time?
- PHI·22Mandated rest daysWhy does a rule forbidding useful work one day in seven leave a community better off rather than poorer?
- CDA·133Many agents, one taskWhy does splitting one capable worker into five specialists sometimes make the result worse?
- GEO·24Map projection distortionWhat must a flat map of a round world distort, and why can no projection escape that cost?
- GEO·25Mapping an outbreak's sourceHow can scattered dots on a street map point to a cause nobody has yet seen?
- ART·28Marble supportsWhy do ancient marble statues lean on tree stumps and drapery that the bronze originals never needed?
- EAR·27Marine reservoir ageWhy does a shell taken from a living sea creature radiocarbon-date as though it were centuries old?
- MIL·31Maritime chokepointsWhy can holding a few narrow straits matter more than commanding an entire ocean?
- BIO·27Mark-recapture estimatesHow can you count a population when you never see more than a handful of it?
- EDU·23Marker disagreementWhy do two trained examiners hand the same essay different grades even when both follow the same rubric?
- GEO·26Market day rotationWhy do neighbouring market towns hold their markets on different weekdays instead of all choosing the busiest day?
- HIS·24Marrying outside the groupWhy do so many unrelated societies forbid marriage within a person's own group?
- AST·20Martian atmosphere lossWhy did Mars lose almost all its air while Venus kept a crushing atmosphere?
- GEO·27Mass elevation effectWhy does the treeline sit far higher deep inside a mountain mass than on its outer flank at the same latitude?
- ART·29Massed string soundWhy does doubling an orchestra's violin section add so little loudness compared with doubling one player's effort?
- BIO·28Mast seedingWhy do some trees produce an enormous seed crop in one year and almost none for several after?
- WRK·23Master keyingWhy does giving a caretaker one key that opens every door make every one of those locks easier to defeat?
- MAT·32Maximum flow and minimum cutWhy does the most a network can carry equal the cheapest way to cut it in two?
- PHY·31Maxwell's demonWhy can no clever gatekeeper sort fast molecules from slow ones and get free work out of a room-temperature gas?
- ENG·32Measurement dead timeWhy can moving a thermometer one metre further along the pipe turn a rock-steady control loop into an oscillating one?
- HIS·25Measurement standardizationWhy did rulers spend so much effort fixing the exact size of a bushel or a yard?
- ENG·33Mechanical advantageWhy does a small gear driving a large one trade away speed to gain force?
- LAN·26Media samenessWhy do rival news outlets chasing the same audience end up sounding almost identical?
- CDA·134Memory fragmentationWhy can a long-running program fail to allocate memory when far more than it asked for is free?
- MIN·33Memory reconstructionWhy can a vivid, confidently held memory turn out to be wrong?
- CDA·135Memory thrashingWhy does a computer that is only slightly short of memory crawl to a halt rather than slowing a little?
- ECO·36Mental accountingWhy does separating money into mental buckets change how people spend it?
- CDA·136Merge conflictsHow can many people edit the same thing at once without silently overwriting each other?
- FAM·26Merged kinship termsWhy do many societies call a father and his brother by one word while splitting cousins into sharply different kinds?
- CDA·137Merging oftenWhy do teams that merge their work several times a day spend less time merging than teams that do it monthly?
- BIO·29Metabolic scalingWhy does a gram of elephant burn far less energy each day than a gram of mouse?
- BIO·30Metabolic water in desert rodentsHow can an animal that never drinks stay in water balance in a desert?
- LAN·27MetaphorWhy do we explain almost every abstract idea in physical terms?
- MED·35MetastasisWhy is a tumour often harmless where it began and deadly once its cells travel?
- AST·21Meteor streaksWhy does a speck of dust entering the atmosphere make a streak bright enough to see from miles away?
- CDA·138Metered costWhy is the bill for a pay-per-use system rarely dominated by the thing you thought you were paying for?
- CDA·139Metric cardinality explosionWhy can adding one harmless-looking label to a metric cost more than the service it measures?
- ART·30Metrical verseWhy did societies without writing store their most important knowledge in rhyme and metre rather than plain speech?
- ART·31Microphone proximity effectWhy does a singer's voice gain weight and bass simply by moving closer to the microphone?
- ENV·31Mid-season yield forecastingHow can anyone forecast a harvest months before the grain has finished filling?
- BIO·31Midday stomatal closureWhy do plants shut the pores they feed through during the brightest hours of the day?
- MIL·32Military logisticsWhy do campaigns fail more often from supply than from losing battles?
- ENV·32Milk spoilage after openingWhy does milk keep for weeks unopened but sour within days once the carton is opened?
- MIL·33Mine warfareWhy can a few dozen cheap sea mines close a strait that a whole fleet cannot force?
- HOM·29Minimum payment trapWhy does paying the minimum every month leave a card balance that barely moves for years?
- MIN·34Minority influenceWhy can one person who never wavers move a group that unanimously disagrees with them?
- WRK·24Misleading fault codesWhy does the fault code that names a sensor so often lead to a sensor that turns out to be working perfectly?
- TRV·27Missed connectionsWhy can a fifteen-minute delay on one flight cost some passengers an entire day?
- MIL·34Mission commandWhy does an army built on obedience train its junior officers to depart from the plan?
- TRV·28Mixed-speed rail capacityWhy does running one fast express down a busy line cost the timetable several slower trains?
- CDA·140Model collapseWhy does a model trained on the output of earlier models get steadily worse instead of compounding their skill?
- CDA·141Model driftWhy does a model that nobody changed get worse over time?
- CDA·142Model quantizationWhy does a model keep working after most of the precision in its numbers is discarded?
- CDA·143Model routingWhy send some questions to a weaker system on purpose?
- GEO·28Modifiable areal unitsWhy can redrawing the districts on a map reverse what the very same data appear to show?
- CHM·32Molecular handednessWhy can two molecules with identical atoms joined in identical order smell completely different?
- ENV·33Monoculture fragilityWhy is a field of genetically identical plants more fragile than a mixed one?
- EAR·28MonsoonWhy does a whole season of rain arrive within roughly the same weeks each year?
- MAT·33Monty Hall problemWhy does switching your choice of door improve the odds when only two doors are left?
- AST·22Moon illusionWhy does the Moon look enormous near the horizon and small overhead, when a photograph shows the same size in both?
- PHI·23Moral luckWhy do we judge two equally careless choices differently when only one causes harm?
- BIO·32Morphogen gradientsHow does a sheet of identical cells decide which of them becomes a finger and which becomes the gap beside it?
- MIN·35Motion sicknessWhy does the passenger reading a map feel sick while the driver steering the same car feels fine?
- GEO·29Mountain language diversityWhy can a single mountain valley system hold more languages than a whole plain ten times its size?
- WRK·25Movement joints in tilingWhy does a tiler stop a floor short of the wall and hide the gap rather than tiling right up to it?
- CDA·144Moving failure handling out of the programWhy take the code that copes with failure out of every application and place it alongside them instead?
- CDA·145Multimodal fusionHow can one model read a photograph and a sentence with the same machinery?
- WRK·26Multiple lock isolationWhy does every worker fit their own padlock when one lock already stops the machine?
- PHI·24Multiple realizability of mindCould something built of nothing like neurons still be having the very same thought?
- MIL·35Munitions stockpilesWhy can a country hold years of ammunition in peacetime and empty the shelves in a month of war?
- SPT·32Muscle crampWhy do cramps seize a player late in a match even when they have drunk plenty and taken salt all day?
- ART·32Museum lightingWhy are the paintings a museum values most often hung in its dimmest rooms?
- ART·33Musical consonanceWhy do some combinations of notes feel settled while others create tension?
- BIO·33Mycorrhizal carbon tradeWhy does a tree hand a fifth of the sugar it worked all summer to make over to a fungus it can neither see nor control?
N
23- MIN·36Nap lengthWhy can a twenty-minute nap leave you sharp while a forty-minute one leaves you groggier than before?
- WRK·27Natural bed in stoneWhy does a block of stone laid the wrong way up crumble within a decade while its neighbour lasts centuries?
- WRK·28Near missesWhy do serious accidents usually follow a long trail of small ones that nobody acted on?
- CDA·146Nearest firstWhy does always exploring the closest place you have not yet visited find the shortest route to everywhere?
- MAT·34Negative edge weightsWhy does taking the cheapest next step always work until one road costs less than nothing?
- ECO·37Network effectsWhy does a product become more valuable simply because more people already use it?
- PHY·32Neutrino detectionWhy must a detector built to catch particles that pass straight through the Earth be buried a mile underground?
- HIS·26New crops and population growthWhy did one new crop change a continent's population more than a century of good harvests?
- MAT·35Newton's methodWhy does the same repeated correction converge instantly from one starting guess and fly apart from another?
- CDA·147Next-token predictionWhy does a system trained only to guess the next word end up able to summarize, translate, and write code?
- PHY·33Night window reflectionsWhy does a window turn into a mirror after dark and back into clear glass by day, when the glass never changes?
- HOM·30Night-time alarm chirpWhy does a smoke alarm always start chirping for a new battery in the middle of the night?
- LAN·28Nighttime radio reachWhy can a distant broadcast station arrive clearly after dark yet vanish completely by day?
- AST·23Nobody may own the MoonWhy did spacefaring states renounce claiming celestial territory before anyone could reach it?
- ENG·34Non-bypassable safety interlocksWhy does a machine that refuses every override protect its operators better than one that trusts them?
- PHI·25Non-identity problemWhy is it so hard to name anyone wronged by a choice that decided which person would exist at all?
- EDU·24Non-negotiable deadlinesWhy does a teacher who never grants an extension end up facing fewer emergencies?
- CDA·148NormalizationWhy split one sensible-looking table into six that nobody would draw by hand?
- HOM·31Nose blindnessWhy can a visitor smell a house that the people living in it cannot?
- EDU·25Note-taking by handWhy do students who write down less by hand remember more than those who type every word?
- GOV·31Notice-and-comment rulemakingWhy must an agency answer objections it is perfectly free to reject before its rule can stand?
- PHY·34Nuclear binding energyWhere does the energy in a nuclear reaction come from if all the particles are still there afterwards?
- MED·36Number needed to treatWhy do we ask a hundred people to take a daily tablet that will help perhaps one of them?
O
37- CDA·149Objects that do not know they are storedWhy keep the code that saves a thing away from the thing itself?
- MIL·36Obsolete fortificationsWhy did walls that had protected cities for centuries stop working within a single lifetime?
- WRK·29Occupational licensingWhy does a customer accept a licence as proof of a skill they cannot judge themselves?
- EAR·29Ocean acidificationWhy does a gas dissolving invisibly into seawater dissolve the shells of animals that never meet the air?
- EAR·30Ocean circulationWhat keeps the ocean's great currents moving instead of settling into stillness?
- BIO·34Ocean productivityWhy is the clearest blue ocean water almost empty of life while murky coastal water teems with it?
- ENG·35Oil film in bearingsWhy does a fast-spinning shaft ride on a film of oil while the same shaft turning slowly grinds metal on metal?
- CDA·150One improbable wordWhy can a single unlikely word early in an answer derail everything that follows it?
- WRK·30One-task subcontractorWhy does a capable crew pay an outsider for work they could learn in an afternoon?
- CDA·151Opaque cursorsWhy must a pagination marker be meaningless to the client that carries it?
- GOV·32Open government recordsWhy does a right to inspect records change official decisions before anyone inspects them?
- MED·37Opioid-induced hyperalgesiaWhy can taking a strong painkiller for months leave a person more sensitive to pain than before?
- PHY·35Optical pyrometryHow can you read the temperature of molten steel without ever touching it?
- ART·34Optical sizes in typeWhy does a typeface that reads beautifully at footnote size look clumsy blown up on a poster?
- MAT·36Optimal stoppingWhy should you turn down the first several candidates you interview no matter how good they seem?
- HIS·27Oral traditionHow can a long story survive centuries almost intact without ever being written down?
- AST·24Orbital debris cascadeWhy can a single collision in orbit make a whole altitude band unusable for decades?
- AST·25Orbital drag speed-upWhy does air resistance leave a decaying satellite travelling faster rather than slower?
- AST·26Orbital rendezvousWhy must a spacecraft slow down in order to catch up with another craft ahead of it in the same orbit?
- CDA·152OrchestrationWhy is the model often the least important part of a working AI product?
- CDA·153Order from pairwise rulesHow do you put a thousand tasks in a workable order when all you know is which pairs must come first?
- CDA·154Order within a sliceWhy can a system promise to keep messages in order only within one part of itself?
- MED·38Organ allocation matchingWhy does the patient who has waited longest for a kidney sometimes not receive the one that becomes available?
- HIS·28Origin of moneyHow did people get from swapping goods to accepting tokens worth nothing in themselves?
- HIS·29Origin of the stateWhy did farming societies end up with rulers and taxes when foraging societies almost never did?
- BIO·35Original antigenic sinWhy does a person meeting this year's flu keep making antibodies shaped for the strain they first met as a child?
- CHM·33Oscillating chemical reactionsHow can a stirred beaker change colour back and forth instead of settling down?
- CDA·155Output as untrusted inputWhy must everything downstream treat a trusted system's own answer as though a stranger wrote it?
- TRV·29OverbookingWhy do airlines and hotels deliberately sell more seats and rooms than they have?
- FAM·27Overclaimed houseworkWhy do both partners' honest estimates of housework add up to far more than everything done?
- MAT·37Overdetermined measurementsWhy take more measurements than unknowns when the extra ones can only contradict each other?
- MED·39OverdiagnosisWhy can finding far more cancers early lengthen measured survival without saving a single life?
- CDA·156OverfittingWhy can a model that predicts its training data perfectly be useless on anything new?
- FAM·28Overheard speech and vocabularyWhy does speech aimed at a child build vocabulary when an equal amount of household talk overheard nearby does not?
- ECO·38Overnight repo lendingWhy will a lender hand a near stranger a fortune overnight without ever examining the borrower's books?
- TRV·30OvertourismWhy can a place be spoiled by the very people who came to admire it?
- SPT·33OvertrainingWhy can an athlete who trains harder every week for a month end up measurably slower than when they started?
P
103- TRV·31Package tour pricingWhy can a package holiday that includes the same flight cost less than buying that flight alone?
- MED·40Paediatric dosingWhy is a child's dose not simply an adult's dose scaled down by body weight?
- ECO·39Pallet size lock-inWhy does the size of a wooden pallet still decide the shape of trucks and warehouses?
- HOM·32Pantry moth persistenceWhy does an infestation of pantry moths return after every visible moth has been cleared out?
- CHM·34Paper chromatographyWhy do the colours in a spot of ink separate as solvent creeps past them?
- MAT·38Paper folding limitWhy can a sheet of paper not be folded in half more than about seven times, no matter how large it is?
- PHI·26Paradox of toleranceWhy must a society committed to tolerating everything refuse to tolerate at least one thing?
- ECO·40Paradox of valueWhy does water, which nobody can live without, sell for less than a stone nobody needs?
- BIO·36Parasite host manipulationWhy does an infected ant climb a grass stem each evening and clamp its jaws where a grazing sheep will swallow it?
- MIN·37PareidoliaWhy does the mind keep finding faces in clouds, rocks, and machinery?
- SPT·34Parkrun spreadWhy does a free weekly run spread faster through a region the more towns already host one?
- CDA·157Partition pruningWhy does how you arrange stored data matter more than how fast the machine reading it is?
- PHI·27Pascal's muggingWhy can a vanishingly unlikely promise of enormous reward hijack a perfectly rational calculation?
- CHM·35PassivationWhy does stainless steel stay bright when it is mostly the same iron that rusts away in a nail?
- ENV·34Pasteurised mushroom substrateWhy does a mushroom grower heat the straw just enough to wound its microbes rather than sterilise it outright?
- ENV·35Pathogen testing limitsWhy can no laboratory certify that a shipment of lettuce carries no pathogen at all?
- ART·35Patina and age valueWhy does a darkened, chipped antique often sell for more than one restored to look new?
- EAR·31Patterned groundWhy do stones on flat Arctic ground arrange themselves into circles and polygons with nobody sorting them?
- WRK·31Pay rises by leavingWhy does changing employer often pay better than doing excellent work where you already are?
- WRK·32Paying above the marketWhy would an employer pay more than the wage needed to fill the post?
- WRK·33Paying for the five-minute fixWhy does a repair that took five minutes feel overpriced when the same fee for a full day would not?
- EDU·26Paying pupils to readWhy can rewarding children for reading leave them reading less once the rewards stop?
- MIL·37Peace negotiationWhy can two sides prefer a costly conflict even when both would benefit from peace?
- MIL·38Peacekeeping mandatesWhy can a scrupulously impartial peacekeeping force make one of the sides fight harder?
- BIO·37Peat accumulationHow can a bog that gains a millimeter a year store more carbon than a forest?
- FAM·29Pedigree collapseWhy does doubling your ancestors each generation back soon demand more people than ever lived?
- SPT·35Penalty aimingWhy should a penalty taker sometimes deliberately aim at their weaker side?
- CHM·36Perceived coldness of metalsWhy does a metal spoon feel colder than a wooden one in the same drawer?
- GOV·33Perceived crime trendsWhy are people sure crime is rising in the very years it is falling?
- SPT·36Perceived exertionWhy can two sessions that feel equally hard leave the body in completely different states?
- ENG·36Perceived lift waiting timeWhy did mirrors beside the lifts silence complaints that faster motors never could?
- MIN·38Perceptual load and distractionWhy is a nearby distraction easier to ignore during a hard task than during an easy one?
- MAT·39Percolation thresholdWhy does a randomly wired network stay in fragments and then suddenly become one whole?
- CDA·158Permission-aware retrievalWhy must a search system know who is asking before it decides what exists?
- LAN·29Persistence of misinformationWhy does a correction so often fail to undo a false story?
- GEO·30Persistent poor neighbourhoodsWhy can a neighbourhood stay poor for a century although almost everyone living there has been replaced?
- GOV·34Persistent rulesWhy do organizations keep rules that nearly everyone agrees are inconvenient?
- ENV·36Pest resurgenceWhy can spraying a crop leave it with a worse pest problem than it had before?
- MED·41Phantom limb painHow can a person feel pain in a limb that is no longer present?
- GEO·31Phantom traffic jamsWhy does a jam form and then clear on an open motorway with no crash or obstacle anywhere?
- ART·36Photographic evidenceWhy does a photograph feel like evidence in a way a painting of the same scene does not?
- AST·27Photon escape timeWhy does energy made in the Sun's core take so long to reach its surface?
- BIO·38PhotosynthesisA tree gains tonnes of mass over its life -- where does that material actually come from?
- CHM·37Physical ageing of plasticsWhy does a plastic part that has sat untouched in a drawer for a year snap where the same part fresh from the mould would bend?
- MED·42Physiological reserveWhy can an older person be entirely fine day to day and yet be felled by a minor infection?
- MAT·40Pigeonhole principleWhy must two people in a large city have exactly the same number of hairs on their head?
- EDU·27Pilot-to-scale failureWhy does a teaching programme that worked wonderfully in trial fail once every school adopts it?
- GEO·32Pingo growthWhy does flat Arctic ground heave up a hill of solid ice with no mountain-building anywhere near it?
- MED·43Pins and needlesWhy does a limb you have sat on go numb first and only hurt as it comes back?
- BIO·39Pit viper infrared sensingHow can a snake with no light-sensitive pigment for heat still strike an unseen mouse accurately in total darkness?
- GEO·33Place namesWhat can the names on a map tell you about who lived there before?
- MED·44Placebo effectHow can a treatment containing no active ingredient still reduce real symptoms?
- AST·28Planetary ringsWhy do the chunks of ice orbiting close to a planet stay a ring instead of clumping into a moon?
- WRK·34Planning fallacyWhy do experienced teams still underestimate how long their work will take?
- CDA·159Planting the source it will citeHow do you make a system that only answers from documents confidently repeat a lie?
- BIO·40Plasmid addiction systemsWhy does a bacterium keep carrying genes it would plainly be better off dropping?
- WRK·35Plaster in thin coatsWhy is a wall built up in three thin coats of plaster rather than one thick pass that would fill it in a morning?
- CHM·38Plastic weatheringWhy does a plastic chair left outdoors crumble while the same plastic indoors lasts decades?
- ART·37Played-in instrumentsWhy do players insist a violin sounds better after years of playing than it did new?
- SPT·37Playoff series lengthWhy does the better team lose a seven-game series far more often than fans expect?
- GOV·35Plea bargainingWhy does a system that guarantees everyone a trial settle almost every case without holding one?
- AST·29Pluto's seasonal atmosphereWhy did Pluto's thin atmosphere keep thickening as it moved further away from the Sun?
- CDA·160Point-in-time joinsHow do you match a record to the version of the truth that was current when it happened?
- CDA·161Poison messagesWhy does one message that can never be processed stop every message behind it?
- CDA·162Poisoning the wellHow can publishing something today change how a system behaves years from now?
- EAR·32Polar amplificationWhy does the Arctic warm two or three times faster than the planet as a whole?
- SPT·38Pole vault energy transferHow can a vaulter clear a bar three times higher than he could ever jump?
- BIO·41Pollination specificityHow can a flower's shape and scent favor some pollinators over others?
- TRV·32Poolside sunbed raceWhy do guests rise at dawn to claim chairs that nobody wanted at dawn?
- HIS·30Post-plague wagesWhy did a plague that killed a third of Europe leave the survivors better paid?
- FAM·30Post-reproductive lifeWhy do humans live for decades after they can no longer have children?
- MIN·39Practice feedbackWhy does taking away the coach's feedback during practice improve performance a week later?
- MAT·41Pre-registered analysisWhy does deciding your test in advance change what the very same number means afterwards?
- CDA·163Prefill and decodeWhy does a model charge more for the words it writes than for the words it reads?
- MED·45Pregnancy immune toleranceWhy does a mother's immune system spare a fetus that is genetically half foreign to her?
- EDU·28Prerequisite chainsWhy can two missed weeks of mathematics haunt a student for years when the same absence in history costs little?
- HIS·31Preservation biasWhy does the archaeological record hold far more pottery than the clothing everyone actually wore?
- GOV·36Presumption of innocenceWhy does a legal system accept a rule it knows will let some guilty people go free?
- WRK·36Preventive replacementWhy does a skilled worker replace a tool that is still working?
- ECO·41Price signalsHow does a failed harvest on one continent change what a shopkeeper charges on another?
- PHI·28Pricing the sacredWhy does offering money for certain things make the offer worse rather than more attractive?
- GEO·34Primate citiesWhy does one country's largest city dwarf every rival while another's cities sit evenly spaced in size?
- PHI·29Problem of evilWhy would a world made by an all-powerful and wholly good being contain suffering that appears to accomplish nothing?
- PHI·30Problem of inductionWhy can no number of past observations guarantee that the next one will match?
- EDU·29Productive failureWhy do students who flounder at a problem first outlearn those shown the method straight away?
- ECO·42Profit versus cashWhy can a firm reporting its best profits ever fail to pay its suppliers next month?
- BIO·42Programmed cell deathWhy would a perfectly healthy cell destroy itself on purpose?
- CDA·164Progress-bar estimatesWhy does a progress bar race to ninety percent and then crawl for the rest?
- PHI·31Prohibition of imagesWhy do traditions that forbid any image of the divine permit elaborate description of it in words?
- PHI·32PromisingWhy can saying a few words create an obligation that did not exist a moment earlier?
- WRK·37Promotion mismatchWhy does the best worker on a team so often turn into a poor manager?
- CDA·165Prompt chainingWhy does splitting one hard instruction into four easy ones produce a better result than the single instruction?
- CDA·166Prompt injectionWhy can text a model was merely asked to read end up giving it orders?
- CDA·167Prompt sensitivityWhy does rewording a request without changing its meaning change the answer that comes back?
- MIN·40Prospective memoryWhy is it easier to remember an errand tied to a place you will pass than to a time you will reach?
- CHM·39Protein assay adulterationWhy did a milk test that measured nitrogen invite adding a plastic ingredient?
- CDA·168Protocol errors versus execution errorsWhy is an operation that correctly reports it failed not a failure of the protocol?
- CDA·169Provenance of what you deployHow do you know the thing running in production is the thing you built?
- CDA·170Proving you started the exchange you are finishingHow do you stop someone else from completing a login you began?
- FAM·31Proxy argumentsWhy does a couple end up shouting about the dishwasher when neither of them cares about dishes?
- CDA·171PseudorandomnessHow can a machine following completely fixed rules produce numbers nobody can predict?
- AST·30Pulsar spin ratesWhy does a collapsed star spin hundreds of times a second when its parent turned slowly?
- HIS·32Putting-out systemWhy did merchants scatter cloth-making across a hundred cottages instead of gathering it under one roof?
Q
6- PHY·36Quantum error correctionHow can you protect a fragile quantum state from noise when looking at it destroys it?
- HIS·33Quarantine institutionsWhy did cities that knew nothing about germs invent a waiting period that actually worked?
- CDA·172Query plan estimationWhy can a database holding accurate statistics still pick a plan thousands of times slower than the obvious one?
- BIO·43Quorum sensingHow can bacteria act together only once enough of them have gathered, when none of them can count?
- CDA·173QuorumsWhy is the agreement of a bare majority enough to call something decided?
- WRK·38Quoting a jobWhy will a tradesman name a firm price before anyone has looked behind the wall?
R
98- ENV·37Race to fish under quotaWhy can a fishery with a strictly enforced annual catch limit still ruin both its fleet and its stock?
- HOM·33Radiant chill indoorsWhy can a room held at the same temperature feel chilly in January and pleasant in June?
- EAR·33Radiation frostWhy does frost form on a clear, still night but not under cloud, when the air temperature is the same?
- AST·31Radiation-hardened spacecraft computersWhy does a probe worth a billion dollars fly a processor slower than a cheap phone's?
- ENG·37Radio diffractionWhy can a radio signal reach around a hill when light from the same direction cannot?
- AST·32Radio interferometryWhy can two small dishes placed far apart resolve finer detail than one enormous dish between them?
- AST·33Radio spectrum crowding of the skyWhy does every operator's perfectly legal transmitter add up to a sky astronomers cannot hear?
- PHY·37Radioactive half-lifeIf a single atom never ages and cannot know when it was made, how can a jar of them decay on so dependable a schedule?
- HIS·34Radiocarbon calibration plateausWhy can a more precise radiocarbon measurement still leave several possible calendar dates?
- EAR·34Rain shadowWhy can one side of a mountain range be rainforest and the other desert, under the same weather?
- EAR·35Rainfall isotope distillationWhy does rain falling far inland carry lighter oxygen than the rain that fell near the coast?
- GOV·37Random auditsWhy does a tax authority that inspects a few returns at random collect more honest filings than one that inspects only suspicious ones?
- MAT·42Random walk recurrenceWhy is a wanderer stumbling at random across a plain certain to find home, while one wandering in three dimensions may never?
- TRV·33Randomized screeningWhy does picking travellers for extra screening at random catch more than screening the ones who look most suspicious?
- MED·46Randomized trialsWhy does deciding treatment by coin toss give more trustworthy answers than choosing carefully?
- CDA·174Rapidly changing attributesWhy does an attribute that changes constantly have to be moved out of the table describing the thing it belongs to?
- LAN·30Rare words in corporaWhy does a dictionary need vastly more text to settle a rare word than a common one?
- CDA·175Rate limitingWhy does a service protect itself by turning away work it could have handled?
- CDA·176Re-identification of anonymized dataWhy can a dataset with every name removed still reveal exactly who is in it?
- EDU·30Reading acquisitionWhy is learning to read so much harder than learning to speak?
- ART·38Reciprocity failureWhy does doubling an already long film exposure fail to double what the negative records?
- CDA·177Recommendation narrowingWhy does a system built to show you what you like end up narrowing what you see?
- CDA·178Recording a change without losing the presentHow can a table show both what a customer's details are now and what they were when they ordered?
- CDA·179Recovering a schedule nobody wrote downHow do you reconstruct the order a nightly process runs in when no document describes it?
- CDA·180Recovering what the business meantHow do you work out what a rule was for when all that survives is the code that enforces it?
- CDA·181Recovery objectivesWhy does planning for disaster start with deciding how much data you are willing to lose?
- HOM·34Recycling contaminationWhy can one neighbour's careless bin send an entire lorry-load to landfill?
- PHY·38Redefining the kilogramWhy did the world's laboratories replace a real lump of metal with a fixed number?
- BIO·44Redox banding in sedimentWhy do the microbes in a jar of pond mud sort themselves into coloured bands that nobody arranged?
- LAN·31Redundancy of written textWhy can a sentence survive losing half its letters, yet resist being compressed below a fixed size?
- SPT·39Redundant climbing anchorsWhy does a climber build an anchor from several pieces when any one of them would hold?
- AST·34Reentry heatingWhy does a returning capsule glow white-hot in air far too thin for a person to breathe?
- MED·47Referred painWhy does a failing heart announce itself in the arm and jaw rather than only in the chest?
- CDA·182Refinement stagesWhy copy the same data three times instead of cleaning it once on the way in?
- PHI·33Reflective equilibriumWhen a cherished principle and a firm intuition collide, which one ought to give way?
- CHM·40Refrigerant changeoverWhy must a whole industry change refrigerants at once when any one firm could switch alone?
- GEO·35Regional incentive biddingWhy does every region offering a bigger subsidy to win the same factory leave them all poorer than offering none?
- MAT·43Regression to the meanWhy is an exceptional performance usually followed by a more ordinary one?
- GOV·38Regulatory captureWhy does an agency created to regulate an industry so often end up defending it?
- GOV·39Regulatory grandfatheringWhy do new safety rules so often exempt the very buildings that prompted them?
- GOV·40Regulatory ossificationWhy does an agency hedged about with safeguards against bad rules end up making almost no rules at all?
- ENG·38Reinforced concreteWhy does concrete need steel buried inside it to span a gap?
- SPT·40Relative age effectWhy are elite young players born disproportionately in the months just after the age-group cutoff?
- CDA·183Releasing to a few firstHow do you find out whether a change is safe for everyone without exposing everyone to it?
- TRV·34Remembered holidaysWhy can a two-week holiday be remembered almost entirely by its last afternoon?
- CDA·184Remembering the sub-answersWhy does writing down answers you have already worked out turn an impossible calculation into an instant one?
- FAM·32Reminiscence bumpWhy do people in old age recall their late teens and twenties far more vividly than the decades since?
- FAM·33Remittances and the children left behindWhy can money sent home by a migrant parent lift a child's school enrolment while lowering what they learn?
- HOM·35Repair economicsWhy is it so often cheaper to replace a broken device than to mend it?
- CDA·185Replacing a system you cannot turn offHow do you rebuild something while it continues to run every day without interruption?
- CDA·186Replay determinismWhy must code that will be re-run from the beginning be forbidden from asking what time it is?
- CDA·187Replication lagWhy can a system tell you something different one second after it told you it was saved?
- CDA·188Requests you did not makeHow can a site you are not even looking at act as you on one you are?
- EAR·36Reservoir operating dilemmaWhy can a reservoir not be ready for a drought and a flood at the same time?
- PHY·39ResonanceWhy can a series of small pushes destroy a structure that a single hard shove cannot?
- GOV·41Resource revenue and accountabilityWhy can a government funded by oil revenue end up less answerable to its citizens than one funded by taxes?
- TRV·35Restaurant districtsWhy do rival restaurants crowd onto one street instead of spreading across the city?
- ECO·43Retail clusteringWhy do competing shops crowd onto the same street instead of spreading across a town?
- ECO·44Retail seasonalityWhy does a shop earn most of its year in six weeks and then discount the same goods?
- WRK·39Retention moneyWhy would a builder agree to let a client hold back part of his payment?
- EDU·31Retrieval practiceWhy does trying to recall an answer improve learning more than rereading it?
- CDA·189Retrieval-augmented generationWhy does handing a model the source document work better than training the document into it?
- CDA·190Retry stormsWhy does every client politely trying again turn a brief hiccup into an outage that will not end?
- SPT·41Return-to-play decisionHow can a doctor clear an athlete when no test can show the injury has healed?
- TRV·36Return-trip effectWhy does the journey out feel longer than the identical journey home?
- HOM·36Review polarizationWhy do online ratings pile up at five stars and one star with almost nothing in between?
- HIS·35Revolution timingWhy do revolutions so often break out after conditions have started to improve?
- HOM·37Rice cooker cutoffWhy does a rice cooker with no timer or sensor switch itself off exactly when the rice is done?
- ENV·38Ripening by contagionWhy does one ripe apple in a bowl hurry along everything sitting beside it?
- PHI·34Ritual legal fictionsWhy do religious legal traditions build devices that satisfy a commandment's letter while plainly sidestepping its point, and why do the devout accept them?
- PHI·35Ritual meaningHow can a repeated ritual strengthen a group even when its practical purpose is unclear?
- PHI·36Ritual purity and contagionWhy does touching an impure thing spread impurity when touching a holy thing rarely spreads holiness?
- GEO·36River boundaries that shiftWhy does a boundary set in midriver follow the water when the channel creeps but stay behind when it jumps?
- GEO·37River captureWhy can the divide between two river basins creep across the land, handing one river's headwaters to its neighbour?
- EAR·37River meandersWhy do rivers develop looping bends instead of flowing in straight lines?
- GEO·38River name survivalWhy do a region's river names outlast the language of every people who have ruled it?
- ENG·39Road crackingWhy do roads crack in regular patterns even where no vehicle ever drives?
- AST·35Rocket stagingWhy does a rocket throw away most of itself on the way up?
- EAR·38Rogue wavesWhy can one wave twice the height of its neighbours rise out of an otherwise ordinary sea?
- CDA·191Roles as compressionWhy does a tidy set of roles turn, over years, into hundreds nobody can explain?
- HOM·38Rolling boil versus simmerWhy does a furious rolling boil cook potatoes no faster than a gentle simmer?
- TRV·37Room turnover windowWhy does a hotel leave its rooms standing empty for four hours in the middle of every day?
- EAR·39Rotation and storm sizeWhy does Earth's rotation steer a hurricane but not the water leaving a sink?
- WRK·40Rough-in inspectionWhy does an inspector sign off wiring and pipework before the walls go on rather than when the job is finished?
- MIL·39RoutWhy does a unit break and run after losing only a small fraction of its strength?
- TRV·38Route survival after downturnsWhy do some airline routes reappear after every crisis while others never come back?
- PHI·37Routinization of charismaWhy must a movement founded on one person's authority become a bureaucracy in order to survive?
- SPT·42Rowing crew scaleWhy does an eight travel faster than a single sculler when every rower in it produces no more power than the sculler does?
- ART·39Rubato's borrowed timeWhy must a performer who stretches one note give the time back somewhere else?
- CHM·41Rubber elasticityWhy does a stretched rubber band pull back, and why does it warm when you stretch it?
- CDA·192Rubber-stamped reviewWhy does a human reviewer who approves almost everything provide almost no safety?
- WRK·41Rules of thumb on siteWhy does a tradesman's rule of thumb, wrong in theory, keep beating the exact calculation on site?
- LAN·32Rumour sharpeningWhy does a story grow sharper and more dramatic each time it is passed along?
- AST·36Runaway planetesimal growthWhy do a few bodies become planets while trillions of their neighbors never grow at all?
- CDA·193Running both and comparingHow do you prove a replacement behaves like the original when nobody knows exactly what the original does?
- WRK·42Running-in wearWhy does new machinery last longer if its first hours are spent wearing itself down?
- ENV·39Runoff from dry groundWhy does a downpour on parched ground mostly run away instead of soaking in?
- GEO·39Rural depopulationWhy do people keep leaving places their families lived in for generations?
S
180- CHM·42Sacrificial anodesWhy does bolting a lump of soft zinc onto a steel hull stop the steel from rusting away?
- ECO·45Safety stockWhy is a shop that never once runs out of an item almost certainly ordering too much of it?
- CDA·194SagasHow do you undo half a transaction that spanned five systems, none of which can roll back?
- SPT·43Sailing upwindWhy can a sailing boat travel toward the very wind that is pushing against it?
- SPT·44Salary capWhy do leagues forbid their own clubs from spending money the clubs already have?
- ENV·40SalinizationWhy can irrigating a field for years eventually leave it barren?
- EAR·40Salt marsh accretionHow can a marsh keep its head above a sea that will not stop rising?
- HIS·36Salt trade routesWhy did caravans cross a desert to carry something people elsewhere could scrape off a shore?
- MAT·44Sample size versus populationWhy does a poll of a thousand people describe a nation of millions no less accurately than it describes a small town?
- FAM·34Sandwich-generation overlapWhy does having children later push care for parents and children into the very same years?
- HOM·39Savings commitment devicesWhy do people lock money into an account that pays nothing to give it back?
- WRK·43Scaffold tiesWhy is a scaffold that stands up perfectly well on its own still bolted back to the wall it surrounds?
- ENV·41Scaling a recipe upWhy does quadrupling a recipe ruin a dish that four separate batches make perfectly?
- CDA·195Scaling that overshootsWhy does a system that adds capacity by itself swing between far too much and far too little?
- HIS·37Scattered strip farmingWhy did villagers work many scattered strips instead of one consolidated field?
- TRV·39Schedule paddingWhy does the same flight take half an hour longer in the timetable than it did thirty years ago?
- EDU·32School catchment price premiumWhy does a house in the best catchment cost almost exactly what the school appears to be worth?
- PHI·38Scientific testabilityWhat makes a claim genuinely testable rather than merely compatible with any possible result?
- MED·48Screening false positivesWhy can a test that is right ninety-nine times in a hundred still flag mostly healthy people?
- HOM·40Screws in end grainWhy does a screw driven into the end of a board hold so much worse than the same screw in its face?
- HIS·38Scribal abbreviationWhy did scribes keep abbreviating words long after the parchment shortage that first made abbreviation worthwhile had passed?
- EAR·41Sea breeze reversalWhy does the wind at the coast blow inland during the day but out to sea at night?
- EAR·42Sea level fingerprintsWhy does a melting ice sheet make the sea fall near itself and rise most on the far side of the world?
- EAR·43Sea saltinessWhy is the ocean salty when nearly every river that feeds it runs fresh?
- EAR·44Sea-ice brine rejectionWhy does ice forming at the surface of a polar sea set the deep ocean in motion?
- CDA·196Search indexingHow can a search return results drawn from billions of pages in a fraction of a second?
- HIS·39Seasonal labour budgetWhy were the greatest ancient monuments built in the months when the fields needed nobody?
- AST·37SeasonsWhy does Earth have seasons when its distance from the Sun barely changes?
- EDU·33Seating arrangement and discussionWhy does moving the same students into a circle change what they are willing to say?
- TRV·40Seating by the windowWhy does a nearly empty restaurant seat its first customers where everyone in the street can see them?
- HIS·40Second serfdomWhy did serfdom tighten in eastern Europe at the very time it was dissolving in the west?
- FAM·35Second-earner insuranceWhy do households keep a second earner whose pay barely covers the childcare it requires?
- HOM·41Second-hand going rateWhy does a used item settle near a familiar price when nobody anywhere publishes one?
- GOV·42Secret ballotWhy must a vote be cast in secret when almost everything else in a democracy is done in public?
- MIL·40Security dilemmaWhy can two rivals both spend more on defence and both end up less safe?
- ENV·42Seed vigour versus germinationWhy does a seed lot that sprouts almost perfectly on a laboratory bench give a thin, ragged stand in the field?
- EAR·45Seismic shadow zoneWhy does a large earthquake leave a wide band of the planet where its shear waves never arrive?
- HIS·41Selection by lotWhy would a city hand its highest offices to whoever a drawing machine happened to pick?
- PHY·40Selective heatingWhy does a microwave oven heat the food but leave the plate cold?
- CDA·197Self-consistencyWhy does asking the same question five times and taking the most common answer beat asking once carefully?
- PHI·39Self-defeating aimsWhy do sleep, happiness and spontaneity retreat the harder a person aims at them?
- CHM·43Self-healing coatingsWhy does a paint deliberately filled with tiny bubbles of liquid protect steel better than a tougher, more perfect film?
- PHI·40Self-refuting claimsWhy does the claim that every truth is merely relative end up denying itself?
- MIN·41Self-ticklingWhy can nobody tickle themselves, however hard they try?
- MIN·42Semantic satiationWhy does a familiar word start to look wrong when you stare at it?
- CHM·44Semiconductor dopingWhy does adding one impurity atom per million transform a poor conductor into a useful one?
- BIO·45SenescenceWhy has evolution left bodies to fall apart with age when longer-lived individuals would leave more offspring?
- MIN·43Sense of timeWhy can the same amount of clock time feel short in one situation and long in another?
- CDA·198Separating the read model from the write modelWhy describe the same information twice, once for changing it and once for reading it?
- MED·49SepsisWhy can a defence that handles most infections quietly end up killing the patient?
- CHM·45Serial dilution limitWhy does diluting a solution a few dozen more times leave none of the substance at all?
- ENG·40Series reliability of many partsWhy does a machine built from a thousand excellent parts still fail almost every week?
- CDA·199Service discoveryHow do programs find each other when the addresses they live at change every few minutes?
- HOM·42Setting a stainWhy can washing a stain in hot water make it impossible to remove?
- WRK·44Setting blocksWhy is a heavy pane of glass set on two small blocks rather than supported evenly all along its frame?
- CHM·46Shape-memory alloysWhy does a bent metal wire snap back to its original shape when you warm it, when bending any other metal is permanent?
- CDA·200ShardingWhy does splitting data across machines make some previously trivial questions unanswerable?
- FAM·36Shared memory in couplesWhy do long-married people become unable to recall apart what they retrieve easily together?
- ENV·43Shared pesticide susceptibilityWhy does every farmer spraying the correct dose leave the whole district with a chemical that no longer works?
- WRK·45Shared schedule floatWhy does one task running late steal slack from tasks that were never late?
- HOM·43Shared water supply flowWhy does someone flushing a toilet on another floor turn your shower scalding?
- LAN·33Sharing cascadesWhy do a handful of posts reach millions while near-identical ones vanish?
- HIS·42Sharing under scarcityWhy do the peoples living with the least reliable food supply give away the most of what they catch?
- HOM·44SharpnessWhy does a sharp knife cut with so much less force than a dull one?
- ENV·44Shear-thickening food pastesWhy does a cornflour paste flow like cream until you stir it hard, then set solid under the spoon?
- WRK·46Shift handoverWhy do the worst mistakes in a hospital or plant cluster around the moment one shift hands over to the next?
- WRK·47Shift workWhy is a night shift harder on the body than the same number of hours worked by day?
- TRV·41Shipboard outbreakHow can one unwell passenger confine hundreds to their cabins within three days at sea?
- MIL·41Shoot-and-scoot artilleryWhy do modern gun crews displace after a handful of rounds when older batteries stayed put for hours?
- TRV·42Shoulder-season price cliffWhy does a room's price halve in the week either side of the peak when the town is still nearly full?
- HOM·45Shower curtain driftWhy does a shower curtain swing inward against your legs instead of being pushed away by the water?
- FAM·37Shrinking social circlesWhy does an older person let a wide circle of friends fall away while a young one keeps collecting new ones?
- CDA·201Shuffling before sortingWhy does deliberately disordering data first make a sorting method dependable?
- FAM·38Sibling deidentificationWhy does one sibling's success at something so often make the other quietly drop it?
- FAM·39Sibling differencesWhy can siblings raised in the same household develop very different personalities?
- FAM·40Sibling regressionWhy does an older child start behaving like a baby again once a new baby arrives?
- MIL·42Siege camp attritionWhy did a besieging army so often sicken and starve before the city it had surrounded?
- LAN·34Sign languageHow can a full language exist with no sound in it at all?
- CDA·202Signing out everywhereWhy is leaving harder than arriving?
- LAN·35Signing spaceHow can a signer point at empty air and have everyone present know exactly who is meant?
- CDA·203Silent data corruptionWhy does keeping three copies of a file still not guarantee you can get the original back?
- EAR·46Silicate weathering thermostatWhy has Earth kept liquid oceans for billions of years while the Sun grew steadily brighter?
- GEO·40Silted harboursWhy do the oldest quays of many port cities now stand well inland from the working docks?
- FAM·41Similar partnersWhy do partners so reliably come from similar backgrounds even when nobody is looking for that?
- MAT·45Simpson's paradoxHow can a treatment help every subgroup and still appear to harm the population as a whole?
- LAN·36Simultaneous interpretingWhy does a simultaneous interpreter start speaking before the sentence being translated has finished?
- TRV·43Single-queue serviceWhy does one long queue serve people better than several short ones?
- GEO·41Sinking streams in karstWhy does a stream in limestone country sink into the ground and rise again in a valley it never flowed toward?
- CDA·204Six names for one fieldWhy does the same piece of information end up with six different names and six slightly different meanings?
- MAT·46Sizes of infinityHow can one infinite set contain more members than another?
- WRK·48Skilled diagnosisHow does an experienced technician notice the source of a fault before a novice does?
- AST·38Sky-background limitWhy does leaving the shutter open twice as long not let a telescope reach twice as faint?
- PHY·41SkyglowWhy can every outdoor lamp be individually reasonable and yet nobody can see the stars?
- MED·50SleepWhy would an animal spend a third of its life unable to notice a predator?
- MIN·44Sleeping on a problemWhy does a night's sleep so often solve a problem that hours of trying could not?
- PHY·42Slippery iceWhy is ice slippery when most other cold solids are not?
- EDU·34Small disruptions in a classroomWhy does a teacher who stops to address trivial interruptions end up losing less lesson time than one who ignores them?
- MAT·47Small-world networksWhy can a message reach a stranger on the far side of the world in only a handful of steps?
- MIN·45Smell and memoryWhy can a passing smell drag back a childhood scene more sharply than a photograph of it ever does?
- CHM·47Smell codingHow can a nose tell thousands of smells apart using only a few hundred kinds of receptor?
- MIL·43Smuggling under sanctionsWhy does tightening a sanctions regime often enrich the very people it targets?
- CHM·48Soap cleaningHow does soap enable water to carry away grease?
- PHY·43Soap film coloursWhy does a colourless soap film show bands of colour that shift as it drains?
- MIN·46Social loafingWhy does each person pull less hard on the rope as more hands join the tug-of-war?
- HIS·43Societal collapseWhy do complex societies sometimes collapse rather than simply shrink?
- CDA·205Software agingWhy does a phone or laptop grow slower over years when not one component has physically changed?
- ENV·45Soil carbon loss under ploughingWhy does turning the soil every year, which looks like feeding it, steadily empty it of carbon?
- EAR·47Soil formationHow does bare rock become soil deep enough to support a forest?
- ENV·46Soil test extractantsWhy does a chemical bath no root would ever perform predict what a crop needs?
- AST·39Solar cycleWhy does the Sun's spot count rise and fall on a roughly eleven-year beat?
- PHY·44Solar sail propulsionHow can sunlight you cannot even feel push a spacecraft faster than a rocket can?
- ART·40Song intros and streaming payoutsWhy did pop songs lose their long introductions the year streaming began paying by play?
- PHY·45SonoluminescenceHow can ordinary sound in a glass of water squeeze a bubble hard enough to make it emit flashes of light?
- CDA·206Sorting more than fitsHow do you put a file in order when you cannot hold even a tenth of it at once?
- ENV·47Sourdough stabilityWhy does a jar of flour and water left on the counter for years stay wholesome when the same mixture left alone would rot?
- TRV·44Souvenir craft convergenceWhy do the handicrafts sold in tourist towns a thousand miles apart end up resembling each other rather than their own regions?
- AST·40Spacecraft coolingWhy is dumping heat, not staying warm, the hard problem for a spacecraft sitting in freezing space?
- EDU·35Spacing effectWhy does the same total study time work better spread out than done in one sitting?
- GEO·42Spare transport linksWhy does a region maintain a road almost nobody uses until the day the main one closes?
- LAN·37Speaking in noiseWhy does a speaker in a noisy room reshape vowels rather than merely getting louder?
- PHI·41Speaking of the unspeakableWhy do traditions that declare every positive statement about God false still go on speaking about God at length?
- HOM·46Specialised cleaning agentsWhy does one bottle that claims to clean everything struggle with both limescale and grease?
- GOV·43Specialized courtsWhy do some disputes get their own court instead of going to the ordinary one?
- CDA·207Speculative decodingWhy can a large model produce its text faster when a smaller, less capable model writes the first draft?
- MIN·47Speed-accuracy tradeoffWhy does answering faster make you reliably more wrong, no matter how skilled you are?
- LAN·38Spelling reformWhy does English spelling stay irregular when almost everyone agrees it is a burden?
- AST·41Spiral armsWhy do a galaxy's spiral arms not wind themselves into a blur after a few rotations?
- EDU·36Split attention in materialsWhy does a diagram with its labels in a separate key teach less than the same diagram labelled in place?
- CDA·208Split-brainWhat happens when a system that must have exactly one leader briefly has two?
- PHI·42Splitting a person in twoIf your brain were divided and each half woke up with your memories in a different body, which one is you -- and why can no answer satisfy?
- CDA·209Splitting a system into servicesWhy does breaking one program into thirty make it slower, more fragile, and easier to run?
- SPT·45Stadium waveWhy does a stadium wave travel smoothly around the ring when nobody is leading it?
- ART·41Stage lighting angleWhy does lighting an actor squarely from the front make them look flatter than lighting from two oblique sides?
- WRK·49Standard stud spacingWhy do boards from one supplier land exactly on framing built by another?
- GOV·44Standards of proofWhy can the same disputed act count as proven in a civil court and unproven in a criminal one?
- GOV·45Standing to sueWhy can a court refuse to rule on a plain injustice because the person raising it was not the one harmed?
- AST·42Star colorsWhy do stars have different colors?
- AST·43Star formationWhy must a cloud of gas get colder before it can collapse into something as hot as a star?
- PHY·46Static electricityWhy can removing a sweater make your hair stand up?
- GOV·46Statutes of limitationWhy does the law stop prosecuting a serious wrong merely because enough years have gone by?
- GOV·47Statutory interpretation canonsWhy do judges settle an ambiguous statute with shared rules of thumb rather than by asking what the legislature meant?
- MED·51Steady-state dosingWhy does a drug that acts within an hour still take days to reach its full effect?
- MIL·44Stealth tradeoffWhy does making an aircraft hard for radar to see make it worse at nearly everything else?
- AST·44Stellar hydrostatic balanceWhy has a sphere of gas releasing nuclear energy neither blown itself apart nor collapsed in billions of years?
- TRV·45Step climbWhy does an airliner climb higher partway through a long flight instead of settling at its best altitude from the start?
- FAM·42Stepparent acceptanceWhy can a stepparent who does everything right still take years to be accepted by a child?
- BIO·46Sterile worker castesWhy do worker bees raise a queen's offspring instead of having their own?
- ECO·46Stockout demand censoringWhy can a shop's sales records never tell it how much it could have sold?
- ART·42Story shapeWhy do stories from unconnected cultures fall into such similar shapes?
- MIL·45Strategic deceptionWhy can gathering more independent confirmations of an enemy's plan leave you more certain of a lie?
- MAT·48Stratified samplingWhy can splitting a population into groups before sampling beat sampling the whole at random?
- MIN·48Streaks in random sequencesWhy does a genuinely random sequence look far streakier than people expect it to?
- GEO·43Street network topologyWhy can two neighbourhoods with the same length of road move traffic so differently?
- ENG·41Stress concentrationWhy does a scratch far too small to weigh anything cut a steel plate's strength so sharply?
- FAM·43Stress spillover at homeWhy does a hard day at work so often end up landing on the youngest person at home?
- EDU·37Subject specialists in primary schoolWhy can four teachers who each know one subject outteach one who knows the child all day?
- HOM·47Subscription inertiaWhy do people keep paying every month for a service they know they no longer use?
- EDU·38Substitute teacher coverWhy must a school pay to keep teachers it hopes never to need?
- PHI·43Substitutionary sacrificeHow can an offering that owes nothing discharge a debt that someone else has incurred?
- EDU·39Summer learning lossWhy do identical school holidays leave some children further ahead and others further behind?
- ECO·47Sunk costWhy do people keep pouring money into a project they already believe will fail?
- PHY·47Superconducting levitationWhy can a magnet hover motionless above a chilled superconductor when no arrangement of ordinary magnets can hold anything stably in mid-air?
- PHY·48Supercooled waterWhy can water sit below freezing as a liquid for hours and then turn solid the instant it is knocked?
- CHM·49SupercoolingWhy can very pure water sit well below freezing as a liquid, and then turn to ice the instant you tap the bottle?
- PHI·44SupererogationWhy is the heroic act merely praised rather than required, if more good is always better?
- ENV·48Supermarket tomato flavourWhy does a tomato bred by experts and grown at scale taste of so much less than one from a garden?
- BIO·47Supernormal stimuliWhy will a bird abandon its own egg to sit on an absurd oversized fake?
- MED·52Surgical volume-outcome relationshipWhy does the same operation carry less risk in a hospital that does little else?
- CDA·210Surrogate keysWhy does a sales record point at a number that means nothing rather than at the customer's own identifier?
- AST·45Survey and follow-up telescopesWhy build one telescope that cannot study anything deeply and another that cannot find anything?
- MAT·49Survivorship biasWhy did reinforcing the bullet holes on returning bombers armour exactly the wrong part of the plane?
- ENG·42Suspension bridge cablesWhat lets a suspension bridge span far more than a solid beam of the same material could?
- ENG·43Swarm roboticsHow can a hundred simple robots assemble a shape that none of them holds a plan for?
- BIO·48Sweet fruit, guarded seedWhy does a plant make its fruit delicious and the seed inside it bitter or poisonous?
- BIO·49SymbiosisHow can two unrelated species come to depend on each other for survival?
- MIN·49Synaptic pruningWhy does a developing brain build far more connections than it intends to keep?
- ENV·49Synchronised planting windowsWhy must every neighbouring farmer sow in the same week for any one of them to escape the pest?
- MIN·50Synchronized applauseWhy does an audience's clapping sometimes fall into unison when nobody is leading it?
- CDA·211Synthetic versus real usersWhy does a test that runs perfectly every minute miss the failure your users are living through?
- CDA·212System prompt priorityWhy can instructions the user never sees outrank the ones they type, and why is that still not security?
T
122- CDA·213Tags versus digestsWhy can the same name fetch two different things a week apart?
- CDA·214Tail latencyWhy does a service that answers almost every request instantly still feel slow to use?
- PHI·45Taking moral advice on trustWhy do we accept a doctor's word about a diagnosis yet distrust accepting someone's word about whether an act is wrong?
- CDA·215Talked out of its own rulesWhy can a system trained to refuse be persuaded to agree?
- PHI·46Talking about what does not existHow can a sentence about Sherlock Holmes be true when there is nothing for the name to pick out?
- ECO·48Tax competitionWhy do countries keep cutting the same tax when none of them ends up ahead?
- GOV·48Tax incidenceWhy does the person who writes the tax cheque often not bear its cost?
- EDU·40Teacher attrition in hard schoolsWhy do the schools that most need experienced teachers keep losing them fastest?
- EDU·41Teacher expectationsWhy can a teacher's private guess about a pupil end up matching that pupil's later results?
- EDU·42Teaching to the testWhy does a school measure stop meaning what it once did as soon as everyone is judged by it?
- PHY·49Tears of wineWhy does a ring of droplets climb the inside of a wine glass and run back down with nobody disturbing it?
- CDA·216Technical debtWhy does a shortcut that saves a day cost more every week it survives?
- ENG·44Technical standardsWhy does a plug made by one company fit a socket made by another that never consulted it?
- HIS·44Technology lossWhy have societies forgotten skills their ancestors clearly possessed, with no disaster to explain it?
- FAM·44Teenage sleep phaseWhy does a teenager who cannot fall asleep at ten find it just as hard to wake at seven?
- LAN·39Telephone bandwidthWhy does a voice stay intelligible on a line that removes the very pitch you hear it at?
- HIS·45Tell moundsWhy do ancient Near Eastern towns sit on hills that no geological process ever built?
- CDA·217TemperatureWhy does making a model's word choice more random make it more useful for some jobs?
- CHM·50Tempered glassWhy does glass locked in permanent internal stress break less easily than unstressed glass?
- SPT·46Tendon rehabilitation loadingWhy does resting a damaged tendon completely leave it weaker than carefully loading it while it still hurts?
- GOV·49Term limitsWhy can forcing legislators out after a fixed term hand more power to lobbyists and permanent staff?
- PHY·50Terminal velocity of raindropsWhy does a raindrop falling from a kilometre up arrive gently instead of at bullet speed?
- EDU·43Test validityWhy can a scrupulously fair test still misjudge what a student knows?
- CDA·218Testability as a design propertyWhy is code that is hard to test usually badly designed rather than just hard to test?
- MAT·50Testing many questions at onceWhy does a careful study asking twenty harmless questions usually turn up one striking result?
- LAN·40Text message toneWhy does a plain text message so often read as colder than the same words spoken aloud?
- HIS·46Textual criticismHow can scholars reconstruct a lost original from surviving copies that all disagree with each other?
- CDA·219The agent loopWhy can a system that only writes text end up changing things in the world?
- CDA·220The audit record as the productWhen an automated system acts on your behalf, why is the log of what it did worth more than the result?
- AST·46The backwards magnitude scaleWhy do astronomers still call the brightest stars first magnitude and faint ones sixth?
- CDA·221The blocking commitWhy can one coordinator crashing leave every other participant waiting indefinitely?
- CDA·222The CAP theoremWhy must a system spanning several machines give something up the moment the network between them breaks?
- TRV·46The dish nobody ordersWhy does a menu carry a dish priced so high that almost nobody orders it?
- CDA·223The distributed monolithWhy can a system split into services still have to be deployed all at once?
- BIO·50The error threshold on genome lengthWhy can a genome never grow longer than its own copying accuracy permits?
- CDA·224The first processWhy does a program that stops cleanly on your laptop refuse to stop inside a container?
- EDU·44The fourth-grade slumpWhy do children who read fluently at seven begin to fail at reading by twelve?
- WRK·50The informal org chartWhy is the person everyone asks for help rarely near the top of the chart?
- PHI·47The liturgical calendarWhy retell the same sacred story on a fixed date every year rather than once and for all?
- ART·43The loudness warWhy did every record label mastering louder leave listeners with music nobody enjoyed more?
- CDA·225The middleman that reduces connectionsWhy does adding something in the middle leave fewer links than before, not more?
- CDA·226The noisy neighbourWhy does every tenant using no more than their fair share still degrade the service for all of them?
- MIL·46The nuclear triadWhy field three separate delivery systems when one could carry the same warheads?
- CDA·227The occasionally expensive operationWhy is an operation that sometimes has to copy everything still cheap on average?
- CDA·228The outboxHow do you save a record and send a message about it without either happening alone?
- CDA·229The paved roadWhy does making one route easy work better than forbidding all the others?
- CDA·230The price of being able to leaveWhy does keeping the freedom to change supplier often cost more than being tied to one?
- PHI·48The problem of other mindsWhat entitles you to believe that anyone besides yourself has an inner life at all?
- CDA·231The publisher that knows no subscribersHow does a system stay extendable by making the sender ignorant of who is listening?
- CDA·232The semantic layerWhy do two dashboards built from the same warehouse disagree about revenue?
- EDU·45The silent classroomWhy does a room full of confused students fall silent when asked whether anyone has a question?
- CDA·233The singleton regretWhy is the design pattern people learn first the one they later work hardest to remove?
- CDA·234The small files problemWhy does a query slow to a crawl when the data it reads is split into too many pieces?
- FAM·45The small last strawWhy does a long relationship often end over something far smaller than what was forgiven before?
- BIO·51The soil seed bankWhy does a burned hillside green up with plants nobody has seen there for decades?
- CDA·235The sorting floorWhy can no method that works by comparing pairs ever sort faster than a certain speed?
- PHI·49The state of natureWhy would people who all sincerely want peace still rationally arm themselves against each other?
- CDA·236The test pyramidWhy do the tests that most resemble real use catch the fewest problems worth catching?
- PHI·50The two-witness ruleWhy refuse to convict on one truthful witness when a second one adds nothing new?
- CDA·237The untidy shape that answers fasterWhy does the arrangement that looks less orderly return answers more quickly?
- WRK·51The wire that carries nothingWhy is the wire that carries no current in normal use the one an electrician takes most care over?
- ART·44The workshop's many handsWhy did a master painter's finest works pass through half a dozen other hands?
- EDU·46The zero-sum timetableWhy does every extra hour of reading instruction quietly cost some other subject an hour?
- PHY·51Thermal conductivity of touchWhy does a metal handle feel colder than a wooden one in the same room?
- ENG·45Thermal noise floorWhy can no amplifier ever reveal a signal quieter than its own warmth?
- ENG·46Thermal throttlingWhy does a laptop slow itself down at exactly the moment you are asking most of it?
- HOM·48Thermostat overshootWhy does turning the thermostat far above the temperature you want not heat the room any faster?
- CDA·238Thinking budgetWhy can a model get a hard problem right by being given more time rather than more knowledge?
- CDA·239Three kinds of responsible personWhy does one dataset need someone who owns it, someone who tends it, and someone who merely holds it?
- CDA·240Three questions people treat as oneWhy are 'who are you', 'prove it', and 'may you' three separate problems?
- ENG·47Three-bladed turbinesWhy do wind turbines almost all have exactly three blades when more blades would catch more wind?
- CHM·51Three-way catalytic converterWhy does one exhaust brick need three different precious metals doing three different jobs?
- AST·47Tidal lockingWhy does the Moon keep nearly the same face turned toward Earth?
- MAT·51Time average versus ensemble averageWhy can a bet with a favourable average outcome still ruin nearly everyone who keeps taking it?
- CDA·241Time to first tokenWhy do two answers that take exactly the same time feel instant and broken?
- GEO·44Time zonesWhy does the world keep clocks that deliberately disagree by whole hours?
- SPT·47Time-of-day performance peakWhy are so many records set in the early evening rather than in the morning?
- SPT·48Timing resolution in racingWhy do swimming records stop at hundredths when the clock can read thousandths?
- TRV·47Tipping customsWhy does paying extra for service that nobody can require of you persist in some countries and vanish in others?
- FAM·46Toddler tantrumsWhy do tantrums peak in the third year and then fade without anyone teaching a child to stop?
- CDA·242TokenizationWhy can a model that writes flawless prose fail to count the letters in a single word?
- ENG·48Tolerance stack-upWhy can a machine assembled entirely from parts that passed inspection still refuse to fit together?
- CDA·243Tool calling boundaryWhy does a model that calls a tool never actually run it?
- CDA·244Tool granularityWhy does giving an assistant fewer, broader actions often beat giving it many precise ones?
- TRV·48Tourism seasonalityWhy does a resort town's population multiply and then collapse every year?
- GEO·45Town spacingWhy do towns on an open plain space themselves out at surprisingly regular distances?
- HOM·49Tracing a leakWhy does the wet patch on a ceiling so rarely sit under the actual hole?
- ECO·49Trade creditWhy does a supplier short of cash itself agree to let its customers pay ninety days late?
- WRK·52Trade demarcationWhy does a building site split the work among a dozen trades that each stand idle waiting for the others?
- HIS·47Trade diasporasWhy did long-distance trade so often pass through settled communities of resident foreigners?
- LAN·41Trade jargonWhy does every occupation grow a private vocabulary that plain words could seemingly replace?
- SPT·49Trail braidingWhy does a footpath across a wet meadow end up ten times wider than the line anyone actually walked?
- EDU·47Train-the-trainer cascadesWhy can training ten teachers reach a whole country faster than training a thousand?
- MIL·47Training cadre bottleneckWhy does doubling an army's size take far longer than doubling its equipment?
- SPT·50Training taperWhy does resting before a competition make an athlete stronger than training through it?
- CDA·245Transactions on immutable storageHow can a store that only ever writes whole files support a transaction that can be rolled back?
- LAN·42Transcribed speechWhy does an ordinary conversation look ungrammatical the moment it is written down word for word?
- EDU·48Transfer of learningWhy does something learned thoroughly in one setting so often fail to help in another?
- ENG·49Transformer inrushWhy can switching on an idle transformer trip a breaker that its full running load never comes close to troubling?
- CDA·246Transformer parallelismWhy did reading every word of a sentence at once beat reading them in order?
- GEO·46TranshumanceWhy do herders climb the mountain on a schedule set by snowmelt rather than the calendar?
- LAN·43Translation equivalenceWhy can a faithful translation differ greatly from the wording of its source?
- MED·53Transplant rejectionWhy must a person given a life-saving organ stay deliberately vulnerable to infection?
- TRV·49Traveler herdingWhy do travellers crowd into the same few places while equally good ones stay empty?
- TRV·50Traveler's stomachWhy does the same tap water sicken a visitor while the residents drink it happily?
- EAR·48Tree-ring evidenceHow can the width and chemistry of tree rings reveal past environmental conditions?
- ENV·50Trophic cost of meatWhy does a field feeding cattle support so many fewer people than the same field sown with grain?
- FAM·47Trust asymmetryWhy does one broken promise cost more than many kept ones earn?
- EAR·49Tsunami shoalingWhy does a wave that a ship at sea never notices rise into a wall of water at the shore?
- ENG·50Tuning to the test cycleWhy do engines that pass every certification test still pollute heavily on real roads?
- EAR·50Turbidity currentsWhy do seafloor cables snap hundreds of kilometres from an earthquake, hours after the shaking has stopped?
- EDU·49Tutoring versus class sizeWhy does one-to-one tutoring transform results when cutting a class from thirty to twenty-five barely helps?
- CDA·247Twenty-five acronyms, nine piecesWhy do dozens of competing frameworks for the same task turn out to be rearrangements of one short list?
- EAR·51Twice-daily tidesWhy does the sea rise twice a day when there is only one Moon pulling on it?
- FAM·48Twin language delayWhy do twins begin talking later than single-born children despite growing up amid more speech?
- AST·48Two gravitational-wave detectorsWhy is a perfectly clear signal in one detector treated as no detection at all?
- CDA·248Two stores for one truthWhy does the same data need one database to record it and a different one to answer questions about it?
- CDA·249Two systems, one recordHow can two systems both own the same record for a year without drifting apart?
- ECO·50Two-sided market launchWhy does a new marketplace often have to pay one side of the market to show up at all?
- CDA·250Two-stage retrievalWhy fetch fifty candidates only to throw away forty-five of them with a slower method?
- TRV·51Two-way ratingsWhy do guest and host ratings both drift up to near-perfect once each side can rate the other?
- ART·45Typeface voiceWhy can the same sentence read as trustworthy or cheap depending only on the shape of its letters?
U
21- MAT·52Ubiquity of the bell curveWhy do measurements of completely unrelated things pile up into the same bell-shaped curve?
- LAN·44Unavoidable ambiguityWhy can no language avoid words that carry more than one meaning?
- CDA·251Undefined behaviourWhy can a program that ran correctly for years break the moment the compiler is asked to optimise it?
- PHI·51Underdetermination of theoryWhy can two incompatible theories fit every observation ever recorded, and how does a science choose between them anyway?
- ART·46UnderstudiesWhy does a production pay actors who may never once appear on stage?
- FAM·49Undifferentiated infant cryWhy can a newborn's cry not tell a parent which of its many needs is unmet?
- MIN·51Unfinished tasksWhy does a task you were interrupted in the middle of keep returning to mind when a finished one is gone by evening?
- LAN·45Uninformative advertisingWhy does an advertisement that tells you nothing about a product still make it more believable?
- MIL·48Unit combat learning curveWhy is a unit's first battle far deadlier for it than its fifth?
- HOM·50Unit-price inversionWhy does the larger pack on the shelf sometimes cost more per unit than the small one?
- CDA·252Unknown unknownsWhy can a system with every dashboard green still be failing in a way nobody thought to chart?
- LAN·46Unnamed sourcesWhy does a reporter's promise never to name a source yield more truth rather than less?
- HIS·48Unplanned settlement formWhy do old towns on different continents share street patterns that nobody ever designed?
- MAT·53Unstable averagesWhy can the average income in a room change completely when one more person walks in?
- MIL·49Unusable intelligenceWhy would a commander deliberately not act on information they know to be correct?
- EDU·50Unused curriculumWhy does a curriculum keep teaching material almost no student will ever use?
- FAM·50Unwritten household rulesWhy does every household end up with rules nobody ever agreed to?
- LAN·47Unwritten vowels in abjadsWhy can a script leave most of its vowels unwritten without leaving fluent readers lost?
- GEO·47Urban growth boundariesWhy does drawing a line to stop a city sprawling sometimes push building even further out?
- GEO·48Urban heat islandsWhy is a city several degrees warmer than the countryside surrounding it?
- HIS·49Urban mortalityWhy did cities kill more people than they birthed for most of recorded history?
V
24- ECO·51Vacancies alongside unemploymentWhy do unfilled jobs and jobless workers persist side by side instead of clearing each other away?
- PHI·52VaguenessHow many grains must you take away before a heap stops being a heap?
- ART·47Value of the originalWhy does a perfect copy of a painting feel worthless when no one can tell it from the original?
- EDU·51Value-added ranking instabilityWhy can the same teacher rank near the top one year and near the bottom the next?
- ART·48Varnish removalWhy can stripping a painting's yellowed varnish take the artist's own final glazes with it?
- AST·49Venus superrotationWhy does Venus's atmosphere circle the planet in four days when the planet itself takes 243?
- MIL·50Verified disarmamentWhy can a weapons treaty be enforced by counting things that are not the weapons themselves?
- GEO·49Vernacular house formWhy do houses built before air conditioning suit their climates better than newer ones do?
- BIO·52VernalizationWhy must some plants sit through weeks of cold before they will flower, when the warmth of spring is what they are waiting for?
- CDA·253Vertical and horizontal scalingWhy does a point arrive where buying a bigger machine stops being an option at any price?
- ENG·51Vibration isolator resonanceWhy can putting a machine on soft rubber mounts make it shake the floor harder than bolting it down did?
- SPT·51Video review boundariesWhy did adding video review, which settles exactly what happened, make offside decisions feel more arbitrary than the linesman's guess ever did?
- HIS·50Village pasture stintingWhy did shared village grazing survive for centuries when each family gained by adding one more animal?
- ART·49Vinegar syndromeWhy does a decaying reel of film destroy itself faster the longer it has already been decaying?
- MED·54Viral load kineticsWhy can someone feel perfectly well for days after catching a virus and then fall ill within hours?
- BIO·53Virulence and transmissionWhy are diseases we catch by touch usually milder than those carried to us by mosquitoes?
- TRV·52Visa reciprocityWhy does a country make visitors from one place wait months for a visa while waving through visitors who spend exactly the same money?
- CHM·52Viscoelastic puttyWhy does the same lump of putty bounce like rubber off the floor yet spread into a puddle if left out overnight?
- ART·50Visual groupingWhy do two items on a page read as a pair simply because they sit closer together than anything else?
- EDU·52Vocabulary gap wideningWhy does a small early gap in vocabulary widen every year instead of closing?
- ART·51Voice recording mismatchWhy does your own recorded voice sound like a stranger's while everyone else says it sounds normal?
- PHY·52Vortex sheddingWhy does a steady, tuneless wind make a wire or a mast sing at one definite pitch?
- GOV·50Voting rulesHow can the same set of votes elect different winners under different counting rules?
- LAN·48Vowel chain shiftsWhy does one vowel drifting out of place drag a whole set of unrelated vowels along with it?
W
72- ECO·52Wage stickinessWhy do firms lay off a tenth of their staff in a slump rather than cut everyone's pay a tenth?
- MIL·51WargamingHow can a war fought on a map teach real lessons while quietly hiding others?
- CDA·254Warm reuse leaksWhy does a system that reuses its own leftovers to go faster start returning one user's data to another?
- EAR·52Warming hiatusWhy did a decade of flat temperatures not mean the planet had stopped warming?
- HOM·51Warranty timingWhy do appliances seem to fail just after the warranty runs out?
- MIL·52Wartime turnover of commandersWhy do the generals who begin a war so rarely finish it?
- HOM·52Washing machine odourWhy does a washing machine used only on cool cycles begin to smell?
- ENG·52Water hammerWhy can closing a valve slowly protect a pipe that closing it quickly would burst?
- MIN·52WayfindingHow do people build a mental map of an unfamiliar place?
- PHI·53Weakness of willWhy do people knowingly do the very thing they have already judged to be worse for them?
- EAR·53Weather observing networkWhy can no single instrument replace the mix of balloons, buoys and satellites behind a forecast?
- ENV·51Weed seed banksWhy does a thoroughly weeded field sprout the same weeds again the next year, and the next?
- SPT·52Weight cuttingWhy do fighters starve and dehydrate to reach a weight limit and then put the weight straight back on before the bout?
- WRK·53Welding distortionWhy does a welder deliberately set two plates out of line before joining them straight?
- CDA·255What a list of numbers remembersWhy can a row of numbers made from a sentence be turned back into the sentence?
- CDA·256What an assistant should forgetHow does a system remember you usefully without accumulating everything you ever said?
- AST·50What is a black hole?What is a black hole?
- ECO·53What is inflation?What is inflation?
- PHI·54What makes an argument logically valid?What makes an argument logically valid?
- ENV·52What makes bread rise?What makes bread rise?
- AST·51What meteorite collections over-representWhy do the rocks in museum drawers misrepresent what actually falls out of the sky?
- ART·52What notation cannot recordWhy can no amount of scholarship recover exactly how a 1600s piece was played?
- CDA·257What one row stands forWhy is the first question to ask about a table what a single row of it actually represents?
- ART·53What survived from antiquityWhy does ancient sculpture look like an art of marble when its makers prized bronze?
- CDA·258When removing duplication hurtsWhy does merging two identical pieces of code sometimes make a system harder to change?
- CDA·259When responsibility transfersAt what exact moment does a message stop being the sender's problem?
- CDA·260When the best step now is safeWhen is taking whatever looks best at this moment guaranteed to end up best overall?
- CDA·261Where a fact lives in a modelIf a model holds no table of facts, where is anything it knows actually stored?
- GEO·50Where a river beginsWhy can two atlases disagree about where a river begins without either being wrong?
- GEO·51Where parks end upWhy do a country's protected wildernesses sit almost entirely on land nobody wanted to farm?
- CDA·262Where the time actually goesWhy is most of the time a piece of work takes not spent working on it?
- CDA·263Where the transform sitsWhy did loading raw data first and cleaning it later become the better order?
- GOV·51Which disputes reach trialWhy do the cases that reach trial look nothing like the disputes people actually have?
- CDA·264Which record is the real oneWhen four systems each hold a different address for the same person, how do you decide which is true?
- PHY·53Whip crackWhy does the crack of a whip come from its tip rather than from the hand that swung it?
- GOV·52Whistleblower protectionWhy does wrongdoing stay hidden until the law shields the person who reports it?
- LAN·49Whistled languagesWhy can a whistled message carry a full sentence across a valley without a single consonant in it?
- WRK·54Who leaves firstWhy are the first people to leave a struggling organisation the ones it can least afford to lose?
- CDA·265Why a code sent to your phone does not stop phishingWhy does a second factor still let an attacker who built a convincing fake page straight in?
- CDA·266Why adding a worker stops the othersWhy does bringing another consumer online briefly halt every consumer already running?
- GOV·53Why do democracies separate powers?Why do democracies separate powers?
- EAR·54Why do earthquakes happen?Why do earthquakes happen?
- LAN·50Why do languages change over time?Why do languages change over time?
- BIO·54Why do leaves change color?Why do leaves change color?
- MIN·53Why do we procrastinate?Why do we procrastinate?
- PHY·54Why is the sky blue?Why is the sky blue?
- CDA·267Why the average recovery time liesWhy is the mean time to recover almost never the time it takes to recover?
- ENG·53Wi-Fi channel congestionWhy does every router shouting a little louder leave every network in the building slower?
- AST·52Widmanstatten patternHow can the crystal figure inside an iron meteorite reveal how slowly its parent body cooled?
- FAM·51Widowhood and healthWhy does losing a spouse damage a survivor's health more than losing almost anyone else does?
- ENG·54Wind farm wake lossesWhy does the second row of a wind farm earn far less than the first from exactly the same wind?
- BIO·55Wind-hardened tree formWhy does a sheltered sapling snap in its first storm while its exposed neighbor bends?
- GEO·52Windward wealth divideWhy is the poorer half of so many old industrial cities the eastern half?
- ECO·54Winner's curseWhy does the bidder who wins a hard-fought auction so often wish they had lost it?
- HIS·51Witch-hunt cascadesWhy did accusations of witchcraft multiply fastest in the years a community was already suffering?
- HOM·53Wobbly tableWhy does a four-legged table rock on an uneven floor when a three-legged stool never does?
- LAN·51Word lengthWhy are the words people use most often the shortest ones in every language?
- LAN·52Word orderWhy does word order carry the meaning in some languages and barely matter in others?
- LAN·53Word spacing in writingWhy did scribes write for centuries without spaces between words if spaces make reading so much easier?
- WRK·55Word-of-mouth trade pipelineWhy can a tradesman's diary go from empty to booked for years without any advertising?
- LAN·54Wordless instructionsWhy do assembly instructions drop words entirely when a written sentence could explain the step faster?
- CDA·268Words stored by their beginningsHow can looking up a word take the same time whether the dictionary holds a thousand entries or a billion?
- CHM·53Work hardeningWhy does bending a paperclip make it stiffer exactly where you bent it, right up until the moment it breaks there?
- WRK·56Working to ruleWhy does a workplace grind to a halt when everyone follows the written rules exactly?
- FAM·52Worst behaviour at homeWhy does a child who is impeccably behaved at school save the tantrums for the parent who cares for them most?
- MED·55Wound healingWhy does a wound itch as it heals rather than while it is fresh?
- CDA·269Wrapping without changingHow do you add behaviour to something without altering it or anything that calls it?
- CDA·270Write amplificationWhy does saving a few kilobytes to a solid-state drive sometimes force it to rewrite far more than that?
- CDA·271Writing down what you could not determineWhy is a record of the questions you failed to answer worth as much as the answers?
- HIS·52Writing inventionHow did visible marks become systems capable of representing spoken language?
- CDA·272Writing the test firstWhy write a test for code that does not exist yet?
- CDA·273Wrong with nothing missingWhat does it mean for data to be wrong when every field is filled in and every rule passes?
Y
3- AST·53Yarkovsky effectWhy can an asteroid's own afternoon warmth shift its orbit more than any collision it has suffered?
- ENV·53Yield and protein in wheatWhy does the same wheat variety make fine bread on one farm and only biscuits on the next?
- CDA·274You cannot un-issue a signatureWhy is it so hard to withdraw permission you have already granted in writing?
Z
3- AST·54Zodiacal dust replenishmentWhy must the dust glowing between the planets be far younger than the solar system holding it?
- EDU·53Zone of proximal developmentWhy do a task that is too easy and a task that is too hard both leave a learner unchanged?
- GEO·53Zoning envelope architectureWhy do so many buildings in one city taper in the same peculiar way?