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102 entries. Combine any filters — "beginner and probability", "ancient and philosophy", "impossibility results in computer science".
- 1974★Anchoring EffectA random wheel-of-fortune spin changes your estimate of how many African nations are in the UN. The spin was meaningless. The effect was real. Why?
- 1968★Bystander EffectIf you collapse on a busy street, your chances of getting help may be worse than on a quiet one. Why does a crowd of witnesses make you less safe?
- 1999★Dunning-Kruger EffectThe less you know, the more confident you feel. The more you know, the more you see how much you don't. Why?
- 1920★Halo EffectWhy does being attractive make you seem smarter, or sounding confident make you seem right — even when neither is true?
- 1924 (lectures), 1947 (popularised)★Hilbert's Grand HotelA hotel with infinitely many rooms is completely full. At two in the morning, one more guest arrives. The manager finds them a room.
- 1965★Moore's LawA pattern that held for fifty years: every two years, computers got twice as powerful for the same price. What happens when it stops?
- 1949★Murphy's LawIf anything can go wrong, will it? The saying is a joke — but the engineering principle behind it is dead serious.
- c. 1320★Occam's RazorWhen two explanations fit the evidence equally, which should you believe? The one that assumes less.
- 1896★Pareto Principle80% of results come from 20% of effort. 80% of bugs from 20% of code. Is this a law of nature, or a coincidence with a catchy ratio?
- 1955★Parkinson's LawGive yourself a week for a task that takes an hour, and it will take a week. Why does work expand to fill available time?
- 1955★Placebo EffectA sugar pill reliably reduces pain in clinical trials — measurably, not just subjectively. How does a fake treatment produce real healing?
- 1985★Sunk Cost FallacyYou paid for a concert ticket and now feel terrible. If you hadn't paid, you'd stay home. You paid, so you go. Why does a sunk cost change anything?
- 1939 (first published), circulating from the 1920s★The Birthday ProblemHow many people must be in a room before two of them probably share a birthday? The answer is far smaller than you expect.
- 1963 (discovery), 1972 (butterfly metaphor coined)★The Butterfly EffectCan a butterfly in Brazil cause a tornado in Texas? Not by force — but by changing everything that follows.
- 1975 (posed), 1990 (made famous)★The Monty Hall ProblemThree doors, one car. The host opens a losing door and offers you the swap. Does it make any difference whether you take it?
- 1969★The Peter PrincipleWhy does every organisation seem to be run by people who are bad at their jobs? Because the good ones got promoted until they weren't.
- 1950★The Prisoner's DilemmaTwo people can each do better by betraying the other — and end up worse off than if neither of them had.
- c. 450 BCE★Achilles and the TortoiseThe fastest runner alive can never catch a tortoise with a head start. The argument is airtight. So where does it go wrong?
- 1975 (Goodhart's formulation), 1997 (Strathern's phrasing)★Goodhart's LawThe moment you measure something and start rewarding the number, the number stops telling you what it used to.
- 1968★Pygmalion EffectCan a teacher's expectation — with no basis in fact — make a student smarter? The data say yes. The mechanism is more unsettling than the result.
- 1935★Schrödinger's CatA cat sealed in a box, neither alive nor dead until somebody looks. The story was invented to show the idea was absurd.
- 1903 (Yule), 1951 (Simpson), 1972 (named)★Simpson's ParadoxA treatment does better for men, and better for women, and worse for people. None of the arithmetic is wrong.
- 1950 (Fermi's remark), 1975 (Hart's argument)★The Fermi ParadoxThe universe is ancient, enormous, and full of ordinary stars much like ours. So where is everybody?
- 1943 (Barjavel's novel), with antecedents from the 1920s★The Grandfather ParadoxTravel back in time and stop your own grandparents from ever meeting. Then who was it that went back?
- 2004 (the book); 2000 (the jam study)★The Paradox of ChoicePut out twenty-four kinds of jam instead of six and fewer people buy any jam at all. More options, fewer decisions.
- 1945★The Paradox of ToleranceA society that tolerates absolutely everything, including those working to end it, does not remain tolerant for long.
- c. 75 CE (Plutarch's report of an older dispute)★The Ship of TheseusReplace a ship's planks one at a time until not one original piece is left. Is it still the same ship?
- 1968★The Tragedy of the CommonsEvery herder gains by putting one more animal on the shared field. The field is destroyed by people behaving reasonably.
- 1905 (implicit in Einstein), 1911 (Langevin's traveller)★The Twin ParadoxOne twin flies away and comes home younger than the other. Yet each of them saw the other's clock running slow.
- 1867 (letter to Tait), 1871 (published in Theory of Heat)★Maxwell's DemonA tiny creature sorting fast molecules from slow ones appears to make heat flow the wrong way, for free, forever.
- 1901 (discovered), 1902 (letter to Frege), 1903 (published)★Russell's ParadoxConsider the set of all sets that do not contain themselves. Does that set contain itself? Either answer is wrong.
- 1936★The Halting ProblemNo program can ever be written that reliably tells you whether another program will finish running. This is not a limit of our cleverness.
- c. 600 BCE (the Epimenides line); c. 350 BCE (Eubulides' paradox)★The Liar Paradox"This sentence is false." Decide whether you are looking at something true or something false, and see how far you get.
- c. 450 BCE★Zeno's Dichotomy ParadoxTo cross a room you must first cross half of it, then half of what is left, and so on without end. So how does anyone move?
- 1931★Gödel's Incompleteness TheoremsIn any system of arithmetic strong enough to be useful, there are true statements it can never prove. Including this one.
- 1924★The Banach–Tarski ParadoxCut a solid ball into five pieces, move them around, and you have two balls the same size as the first. Nothing was stretched.
- 1977Amara's LawEvery major technology is overhyped on arrival and underestimated a decade later. Why does intuition fail in the same direction twice?
- 2006Baader-Meinhof PhenomenonYou learn a new word. Within a week, you hear it three times. Did the world start using it when you did — or did you just stop filtering it out?
- 2013Brandolini's LawA tweet spreads a false claim to a million people. Correcting it requires essays and citations. Why does the truth always have to work harder?
- c. 1340 (the attribution; the example is far older)Buridan's AssA donkey stands exactly halfway between two identical bales of hay. With no reason on earth to prefer either, does it starve?
- 1929Chesterton's FenceYou find a fence in the middle of a field with no obvious purpose. Remove it? Chesterton says no — and the reason reveals something about reform.
- 1900Cobra EffectThe British paid a bounty for dead cobras to reduce the snake population. When it ended, the population was higher than before. What went wrong?
- 2010Cunningham's LawAsk a question online and wait hours. Post the wrong answer and be corrected in minutes. Why is the urge to correct stronger than the urge to help?
- 1980Hanlon's RazorThey didn't do it to hurt you. Probably they just didn't think. How much does it matter?
- 1924–1932 (studies), 1958 (effect named)Hawthorne EffectWorkers became more productive every time the researchers changed conditions — even when they changed them back. What was the actual cause?
- 1979Hofstadter's LawIt always takes longer than you think — and that's still true even after you account for the fact that it always takes longer than you think.
- 1913Ringelmann EffectAdd more people to a task and each person works harder, right? Experiments show the opposite. Why does individual effort fall as the team grows?
- 1847Semmelweis ReflexA doctor proved handwashing saved lives. He had the data. The medical profession ignored him for twenty years. Why does evidence trigger resistance?
- 2003 (incident), 2005 (term coined)Streisand EffectThe most reliable way to ensure millions of people see something is to try to prevent anyone from seeing it.
- 1918 (Russell's lectures); the story circulated earlierThe Barber ParadoxThe barber shaves every man in town who does not shave himself, and no one else. So who shaves the barber?
- 1951 (Richardson), 1967 (Mandelbrot)The Coastline ParadoxHow long is the coastline of Britain? The answer depends on how you measure it. As the ruler gets shorter, the answer grows without bound.
- 1785The Condorcet ParadoxA majority prefers A to B, and B to C, and C to A. Every voter was honest and nobody made a mistake.
- 1991The Friendship ParadoxYour friends have more friends than you do. So do mine. This is true for almost everybody, all at the same time.
- 1938Benford's LawLook at the first digit of every number in a newspaper. You'll see 1 far more often than 9 — and it is a mathematical law, not a coincidence.
- 1975Brooks's LawA software project is six months late. You add more developers. Now it's eight months late. Why?
- 1968Conway's LawYour software will look like your org chart. Not because you planned it, but because you couldn't plan it otherwise.
- 1992Dunbar's NumberYou can maintain real relationships with about 150 people. Beyond that, a group becomes something different. Is this a law of human nature?
- 1984Flynn EffectIQ scores rise 3 points per decade worldwide. If the tests measure intelligence, are we smarter? Or is something wrong with the tests?
- 1641Gabriel's HornA shape you can fill with a finite bucket of paint but whose inside you could never finish painting. How?
- 1968Matthew EffectTwo equally talented people start. One gets a small early advantage. Decades later, the gap is enormous. Where did the extra distance come from?
- 1980Metcalfe's LawDouble the users of a network and the value quadruples. This simple mathematics is why some networks become monopolies and others die empty.
- 1988Moravec's ParadoxA computer beat the world chess champion in 1997. Getting one to pick up a cup it has not seen before is still hard.
- 1610 (Kepler), 1744 (de Chéseaux), 1823 (Olbers)Olbers' ParadoxIf the universe is infinite and full of stars, every line of sight should end on one. So why is the night sky dark?
- 1959 (posed), 1961 (retracted in part)The Boy or Girl ParadoxA family has two children and one of them is a boy. What are the odds the other is a girl? It depends on how you found out.
- 1961The Ellsberg ParadoxYou know exactly how many red balls there are, and nothing about how many are black. Does knowing more make a bet more attractive?
- 1865The Jevons ParadoxBuild an engine that burns less coal and the country ends up burning more coal. This was noticed in 1865 and has not stopped.
- 1963 (observed), 1969 (published)The Mpemba EffectA pot of boiling water and a pot of cold water go into the same freezer. Which freezes first?
- c. 420 BCE (traditional); earliest surviving account 2nd century CEThe Paradox of the CourtA student agrees to pay for his lessons the day he wins his first case. He never takes a case. His teacher sues him for the money.
- 1936The Paradox of ThriftEvery family starts saving more. The economy ends up with less saving. How can everyone doing the right thing produce the wrong outcome?
- 1975 (proved), 1978 (named)The Two Generals' ProblemTwo armies must attack at the same moment. Any message can be lost, including the one confirming the last one arrived.
- 1935Zipf's LawThe most common English word is twice as frequent as the second. Why does language obey the same mathematical law as city populations?
- 1968Braess's ParadoxAdd a new road to a congested city and every journey gets slower. Close the road again and the traffic speeds up.
- 1891Cantor's Diagonal ArgumentThere are more numbers between 0 and 1 than there are whole numbers in all of eternity. Both lists are infinite.
- c. 1960 (posed), 1969 (published)Newcomb's ProblemThe boxes are already filled. Does choosing one still change what is in them?
- 1952 (posed at the Paris colloquium), 1953 (published)The Allais ParadoxOffered the same improvement in odds twice, most people take it once and refuse it the second time. Both choices feel obviously right.
- 1982The Byzantine Generals ProblemSeveral generals must attack together or be destroyed. They can only send messengers, and some of the generals are traitors.
- 2000 (conjectured), 2002 (proved)The CAP TheoremA system spread across several machines can give you consistent answers, or always answer at all. The network makes you choose.
- 1997 (posed), 2000 (named and popularised)The Sleeping Beauty ProblemWoken with no memory of having been woken before, how confident should you be that the coin came up heads?
- c. 350 BCEThe Sorites ParadoxOne grain of sand is not a heap. Adding a single grain never turns a non-heap into a heap. So heaps do not exist.
- 1713 (posed by Nicolaus Bernoulli), 1738 (published by Daniel Bernoulli)The St. Petersburg ParadoxA coin-flipping game whose average winnings are infinite. How much of your own money would you actually pay to play?
- 1953 (Littlewood, crediting Schrödinger), 1989 (envelope form)The Two Envelopes ProblemOne envelope holds twice as much money as the other. The arithmetic says swap — then says swap back, forever.
- 1943 (in circulation), 1948 (first in print)The Unexpected Hanging ParadoxA prisoner is told he will hang next week, on a day he cannot possibly predict. He proves it cannot happen. It happens.
- 1950 (paper), 1951 (book), 1963 (corrected second edition)Arrow's Impossibility TheoremThere is no fair way to turn what a group of people each want into what the group wants. This is not a complaint about politics. It is a theorem.
- 1974/75 (Hawking radiation), 1976 (the paradox stated)The Black Hole Information ParadoxPhysics insists information can never be destroyed. Black holes appear to destroy it. Both of those cannot be true.
- 1935 (argument), 1964 (Bell's theorem), 2015 (loophole-free tests)The EPR ParadoxMeasure one particle here and you instantly know something about its partner light-years away. Einstein thought this proved physics was unfinished.
- 1889Bertrand's Box ParadoxYou reach into one of three boxes and pull out a gold coin. The chance the other coin in that box is gold is not one half.
- 1974The Abilene ParadoxEveryone at the table agreed to a trip that not one of them wanted to take. How does a group choose what every member is against?
- 1946Berkson's ParadoxTwo things with nothing whatever to do with each other can look strongly related — purely because of who ended up in the study.
- 1638Galileo's ParadoxThere are exactly as many square numbers as there are numbers, even though almost every number is not a square.
- c. 380 BCEMeno's ParadoxHow can you search for something you don't know? And how would you recognise it if you found it?
- 1975 (observation), 1977 (Peto's fuller statement)Peto's ParadoxA whale has a thousand times more cells than you and lives longer. It should be riddled with cancer. It is not.
- 1971 (named), 2001 (renamed the C-value enigma)The C-value ParadoxAn onion carries five times more DNA than you do. A single-celled amoeba carries a hundred times more. Nobody expected that.
- 1974The Easterlin ParadoxRicher people are happier than poorer people. Yet a whole country getting richer does not seem to get happier.
- 1908The Grelling-Nelson ParadoxIs the word "heterological" heterological? Either answer generates a contradiction.
- 1759 (novel), 1903 (paradox formulated)The Tristram Shandy ParadoxA man writes his autobiography but keeps falling behind. If he had infinite time, would he ever catch up?
- 1906 (published by Russell, crediting Berry); communicated c. 1904Berry's Paradox"The smallest number that cannot be described in fewer than twelve words." That description is eleven words long.
- 1968–1969Levinthal's ParadoxA protein has more possible shapes than the universe has atoms, yet it finds the right one in less than a thousandth of a second.
- 1895 (Marshall's third edition); 2008 (first credible field evidence)The Giffen ParadoxSome things sell more as the price goes up, and the people buying them are behaving perfectly sensibly.
- 1905 (the physics), 1961 (first prominent published version)The Ladder ParadoxA ladder too long to fit inside a barn fits inside it — and also does not — depending entirely on who is watching.
- 1987 (Solow's remark), debate ongoingThe Productivity ParadoxComputers arrived in every office through the 1970s and 80s. Measured productivity did not move for two decades.
- 1988The Ross-Littlewood ParadoxYou add ten balls and remove one, infinitely many times. At the end, the vase is empty. What happened to all the balls?
- 1985The FLP Impossibility ResultA handful of computers cannot be guaranteed to agree on a single value if even one of them might be slow. Not merely hard — impossible.
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