{
 "title": "UNSOLVED",
 "description": "A catalog of open questions.",
 "url": "https://unsolvedcatalog.org",
 "license": "CC BY 4.0",
 "updated": "2026-08-16",
 "entries": [
  {
   "number": "001",
   "title": "Why do we sleep?",
   "field": "Neuroscience",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Every animal with a nervous system does it. It is dangerous, costly, and non-negotiable, and nobody knows what it is buying.",
   "url": "https://unsolvedcatalog.org/001-why-do-we-sleep/"
  },
  {
   "number": "002",
   "title": "What is dark matter?",
   "field": "Cosmology",
   "posed": "1933",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Five independent lines of evidence say most of the matter in the universe is invisible. Fifty years of searching have not caught a single particle of it.",
   "url": "https://unsolvedcatalog.org/002-what-is-dark-matter/"
  },
  {
   "number": "003",
   "title": "Why does anesthesia work?",
   "field": "Medicine",
   "posed": "1846",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "We have been switching human consciousness off on demand since 1846. We still cannot say what the switch is.",
   "url": "https://unsolvedcatalog.org/003-why-does-anesthesia-work/"
  },
  {
   "number": "004",
   "title": "How did life begin?",
   "field": "Origins",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Somewhere on the early Earth, chemistry became biology. Every laboratory attempt to repeat the trick has stalled at the same gap.",
   "url": "https://unsolvedcatalog.org/004-how-did-life-begin/"
  },
  {
   "number": "005",
   "title": "Why is ice slippery?",
   "field": "Physics",
   "posed": "1850",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "A question a child can ask, studied since Faraday, still argued in physics journals. The textbook answer you learned is mostly wrong.",
   "url": "https://unsolvedcatalog.org/005-why-is-ice-slippery/"
  },
  {
   "number": "006",
   "title": "Does P equal NP?",
   "field": "Mathematics",
   "posed": "1971",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "If checking an answer is easy, is finding one easy too? A million-dollar question about the nature of difficulty itself.",
   "url": "https://unsolvedcatalog.org/006-does-p-equal-np/"
  },
  {
   "number": "007",
   "title": "How do birds sense magnetic fields?",
   "field": "Biology",
   "posed": "1966",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "A robin can feel a force you cannot. The leading explanation requires quantum mechanics operating inside a warm, wet eye.",
   "url": "https://unsolvedcatalog.org/007-how-do-birds-sense-magnetic-fields/"
  },
  {
   "number": "008",
   "title": "Why do we dream?",
   "field": "Neuroscience",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Every night you hallucinate vividly for about two hours, then forget most of it. No one can tell you what that is for, or whether it is for anything.",
   "url": "https://unsolvedcatalog.org/008-why-do-we-dream/"
  },
  {
   "number": "009",
   "title": "What is dark energy?",
   "field": "Cosmology",
   "posed": "1998",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "About two thirds of the universe is something that pushes space apart. The leading explanation misses by a factor with 120 zeros.",
   "url": "https://unsolvedcatalog.org/009-what-is-dark-energy/"
  },
  {
   "number": "010",
   "title": "Why do we age?",
   "field": "Biology",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Nothing in physics says a body must wear out. Some animals barely do. Ours does, on schedule, and the reason is still argued about.",
   "url": "https://unsolvedcatalog.org/010-why-do-we-age/"
  },
  {
   "number": "011",
   "title": "What is ball lightning?",
   "field": "Physics",
   "posed": "1638",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Thousands of people have watched a glowing sphere drift through a room during a storm. Physics still cannot say what they saw.",
   "url": "https://unsolvedcatalog.org/011-what-is-ball-lightning/"
  },
  {
   "number": "012",
   "title": "Is the Riemann hypothesis true?",
   "field": "Mathematics",
   "posed": "1859",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "One sentence from 1859 would, if proved, bring order to the prime numbers. It has been checked trillions of times and proved zero times.",
   "url": "https://unsolvedcatalog.org/012-is-the-riemann-hypothesis-true/"
  },
  {
   "number": "013",
   "title": "Why is the Sun's corona hotter than its surface?",
   "field": "Astrophysics",
   "posed": "1939",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Step back from a fire and the air gets cooler. Step off the Sun's surface into its atmosphere and the temperature rises three hundredfold.",
   "url": "https://unsolvedcatalog.org/013-why-is-the-suns-corona-so-hot/"
  },
  {
   "number": "014",
   "title": "What causes Alzheimer's disease?",
   "field": "Medicine",
   "posed": "1906",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "We can see the plaques, name the proteins, and now even slow the decline a little. The actual cause is still an open verdict.",
   "url": "https://unsolvedcatalog.org/014-what-causes-alzheimers-disease/"
  },
  {
   "number": "015",
   "title": "How does turbulence work?",
   "field": "Physics",
   "posed": "1883",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "We have had the exact equations for chaotic fluid flow since the 1840s. We still cannot solve them, and we cannot even prove they behave.",
   "url": "https://unsolvedcatalog.org/015-how-does-turbulence-work/"
  },
  {
   "number": "016",
   "title": "Where is everybody?",
   "field": "Astronomy",
   "posed": "1950",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Billions of old, sunlike stars. Planets around most of them. Six decades of listening. One universe, apparently silent.",
   "url": "https://unsolvedcatalog.org/016-where-is-everybody/"
  },
  {
   "number": "017",
   "title": "How did language begin?",
   "field": "Linguistics",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The defining human ability left no fossils. The question was once so hopeless that the field formally banned it.",
   "url": "https://unsolvedcatalog.org/017-how-did-language-begin/"
  },
  {
   "number": "018",
   "title": "Why do we hiccup?",
   "field": "Biology",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "A reflex with its own dedicated neural circuitry, present before birth, apparently good for nothing. It has a job or it is a souvenir. Nobody knows which.",
   "url": "https://unsolvedcatalog.org/018-why-do-we-hiccup/"
  },
  {
   "number": "019",
   "title": "What is consciousness, physically?",
   "field": "Neuroscience",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Three pounds of matter produces an inner life. Every fact in this catalog was experienced by someone. How that happens is unknown at the deepest level we can ask.",
   "url": "https://unsolvedcatalog.org/019-what-is-consciousness-physically/"
  },
  {
   "number": "020",
   "title": "How does the placebo effect work?",
   "field": "Medicine",
   "posed": "1955",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "A sugar pill, honestly labeled as nothing, can still relieve pain. The body runs a pharmacy that expectation can unlock, and we hold only a partial inventory.",
   "url": "https://unsolvedcatalog.org/020-how-does-the-placebo-effect-work/"
  },
  {
   "number": "021",
   "title": "Where did Earth's water come from?",
   "field": "Planetary science",
   "posed": "1951",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The planet formed close to a young star, hot and dry by every rule we know. Yet here are the oceans. The delivery route is still being argued.",
   "url": "https://unsolvedcatalog.org/021-where-did-earths-water-come-from/"
  },
  {
   "number": "022",
   "title": "Why is there more matter than antimatter?",
   "field": "Physics",
   "posed": "1928",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The Big Bang should have made matter and antimatter in equal amounts, which then annihilate to light. Something cheated, one part in a billion. You are made of the discrepancy.",
   "url": "https://unsolvedcatalog.org/022-why-is-there-more-matter-than-antimatter/"
  },
  {
   "number": "023",
   "title": "Does every number fall to one?",
   "field": "Mathematics",
   "posed": "1937",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Halve it if even, triple it and add one if odd, repeat. A child can play the game. Nobody alive can prove it always ends.",
   "url": "https://unsolvedcatalog.org/023-does-every-number-fall-to-one/"
  },
  {
   "number": "024",
   "title": "Why do zebras have stripes?",
   "field": "Biology",
   "posed": "1871",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Darwin and Wallace argued about it. A century and a half later the leading answer involves flies, and the mystery has moved rather than died.",
   "url": "https://unsolvedcatalog.org/024-why-do-zebras-have-stripes/"
  },
  {
   "number": "025",
   "title": "How do memories outlive their molecules?",
   "field": "Neuroscience",
   "posed": "1894",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The proteins storing your oldest memory were recycled thousands of times since it formed. Something persists. What, exactly, is the question.",
   "url": "https://unsolvedcatalog.org/025-how-do-memories-outlive-their-molecules/"
  },
  {
   "number": "026",
   "title": "What triggered the Cambrian explosion?",
   "field": "Origins",
   "posed": "1859",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Life spent three billion years as slime, then produced most animal body plans in a geological moment. Darwin called it a valid objection to his theory. The trigger is still not settled.",
   "url": "https://unsolvedcatalog.org/026-what-triggered-the-cambrian-explosion/"
  },
  {
   "number": "027",
   "title": "What are fast radio bursts?",
   "field": "Astronomy",
   "posed": "2007",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Millisecond flashes of radio from other galaxies, each briefly outshining its host. Thousands are catalogued. The engine is still not identified.",
   "url": "https://unsolvedcatalog.org/027-what-are-fast-radio-bursts/"
  },
  {
   "number": "028",
   "title": "Why does time flow one way?",
   "field": "Physics",
   "posed": "1876",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The laws of physics run fine in reverse. Eggs still refuse to unscramble. The one-wayness of time is real, measurable, and not yet explained at the bottom.",
   "url": "https://unsolvedcatalog.org/028-why-does-time-flow-one-way/"
  },
  {
   "number": "029",
   "title": "How do high-temperature superconductors work?",
   "field": "Physics",
   "posed": "1986",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Certain ceramics conduct electricity with zero loss at temperatures far too warm for the standard theory to allow. Four decades on, the mechanism is still contested.",
   "url": "https://unsolvedcatalog.org/029-how-do-high-temperature-superconductors-work/"
  },
  {
   "number": "030",
   "title": "Why do cats purr?",
   "field": "Biology",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The most familiar sound in domestic life, produced by a mechanism only recently glimpsed, for reasons that remain genuinely unclear.",
   "url": "https://unsolvedcatalog.org/030-why-do-cats-purr/"
  },
  {
   "number": "031",
   "title": "Why do humans cry emotional tears?",
   "field": "Biology",
   "posed": "1872",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Every animal with eyes lubricates them. Only humans weep at funerals, weddings, and films. The function of the most human fluid is unestablished.",
   "url": "https://unsolvedcatalog.org/031-why-do-humans-cry-emotional-tears/"
  },
  {
   "number": "032",
   "title": "Why is yawning contagious?",
   "field": "Biology",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "You may yawn while reading this entry. Nobody can tell you why, on either count: what yawns are for, or why they spread.",
   "url": "https://unsolvedcatalog.org/032-why-is-yawning-contagious/"
  },
  {
   "number": "033",
   "title": "What is the glass transition?",
   "field": "Physics",
   "posed": "1948",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Cool a liquid past crystallization without letting it crystallize and it quietly becomes solid without ever changing structure. Physics cannot say what kind of event that is.",
   "url": "https://unsolvedcatalog.org/033-what-is-the-glass-transition/"
  },
  {
   "number": "034",
   "title": "What happens to information that falls into a black hole?",
   "field": "Physics",
   "posed": "1976",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Quantum mechanics forbids information from being destroyed. Black holes looked like they destroy it. The verdict has shifted; the mechanism is still missing.",
   "url": "https://unsolvedcatalog.org/034-what-happens-to-information-in-a-black-hole/"
  },
  {
   "number": "035",
   "title": "How many species share the planet?",
   "field": "Biology",
   "posed": "1758",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Around 2.2 million species have names. The true total is unknown to within an order of magnitude, and possibly several.",
   "url": "https://unsolvedcatalog.org/035-how-many-species-are-there/"
  },
  {
   "number": "036",
   "title": "How does sound make a bubble glow?",
   "field": "Physics",
   "posed": "1934",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Squeeze a bubble in water with sound waves and it emits flashes of light, from a spot briefly hotter than the surface of the Sun. The lamp works; the manual is unfinished.",
   "url": "https://unsolvedcatalog.org/036-what-makes-sonoluminescence-glow/"
  },
  {
   "number": "037",
   "title": "How fast is the universe expanding?",
   "field": "Cosmology",
   "posed": "2016",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Two impeccable measurements of the universe's expansion rate disagree, and the disagreement has survived every attempt to blame the instruments.",
   "url": "https://unsolvedcatalog.org/037-how-fast-is-the-universe-expanding/"
  },
  {
   "number": "038",
   "title": "What causes migraines?",
   "field": "Medicine",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "A billion people carry a brain that periodically attacks them, complete with light shows and a warning phase. The full circuit has never been traced.",
   "url": "https://unsolvedcatalog.org/038-what-causes-migraines/"
  },
  {
   "number": "039",
   "title": "Why can salamanders regrow limbs and we cannot?",
   "field": "Biology",
   "posed": "1768",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "An axolotl rebuilds a severed leg, perfectly, bones and nerves and all. Mammals seal the wound and call it done. Both use nearly the same genes.",
   "url": "https://unsolvedcatalog.org/039-why-cant-humans-regrow-limbs/"
  },
  {
   "number": "040",
   "title": "What causes déjà vu?",
   "field": "Neuroscience",
   "posed": "1876",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "For a few seconds, the present moment feels like a memory, and you know it isn't. The glitch that watches itself has no confirmed mechanism.",
   "url": "https://unsolvedcatalog.org/040-what-causes-deja-vu/"
  },
  {
   "number": "041",
   "title": "How do rogue waves form?",
   "field": "Physics",
   "posed": "1995",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Sailors' tales of walls of water were dismissed for centuries, until a drilling platform measured one. The ocean makes monsters; the recipe is disputed.",
   "url": "https://unsolvedcatalog.org/041-how-do-rogue-waves-form/"
  },
  {
   "number": "042",
   "title": "Where do the highest-energy particles come from?",
   "field": "Astrophysics",
   "posed": "1962",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Single atomic nuclei arrive from space carrying the energy of a fast-pitched baseball. Nothing we know of should be able to throw them.",
   "url": "https://unsolvedcatalog.org/042-where-do-the-highest-energy-particles-come-from/"
  },
  {
   "number": "043",
   "title": "Why do we blush?",
   "field": "Biology",
   "posed": "1872",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "An involuntary broadcast of exactly the feeling you most want to hide, wired into one species only. Darwin called it the most human expression, and he could not explain it.",
   "url": "https://unsolvedcatalog.org/043-why-do-we-blush/"
  },
  {
   "number": "044",
   "title": "Where does the proton's spin come from?",
   "field": "Physics",
   "posed": "1987",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The proton spins. Its three quarks, added up, provide barely a third of the total. Most of the spin of ordinary matter is bookkept somewhere still unmeasured.",
   "url": "https://unsolvedcatalog.org/044-where-does-the-protons-spin-come-from/"
  },
  {
   "number": "045",
   "title": "What is ME/CFS?",
   "field": "Medicine",
   "posed": "1956",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "An illness that follows infection, worsens with exertion, and disables millions has no biomarker, no approved treatment, and no accepted mechanism. The patients were right; the science is late.",
   "url": "https://unsolvedcatalog.org/045-what-is-mecfs/"
  },
  {
   "number": "046",
   "title": "What is whale song for?",
   "field": "Biology",
   "posed": "1971",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Humpback males sing structured, evolving songs that sweep across oceans like hit records. Half a century of listening has not settled what the songs accomplish.",
   "url": "https://unsolvedcatalog.org/046-what-does-whale-song-mean/"
  },
  {
   "number": "047",
   "title": "What killed the ice-age giants?",
   "field": "Origins",
   "posed": "1796",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Mammoths, giant sloths, sabertooth cats: the large animals of every continent except Africa vanished in a geological instant. The suspects are climate and us.",
   "url": "https://unsolvedcatalog.org/047-what-killed-the-ice-age-giants/"
  },
  {
   "number": "048",
   "title": "Why do we have fingerprints?",
   "field": "Biology",
   "posed": "1892",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The ridges on your fingertips are famous for identifying you. That is a use humans invented. What they are actually for is still being tested.",
   "url": "https://unsolvedcatalog.org/048-why-do-we-have-fingerprints/"
  },
  {
   "number": "049",
   "title": "Does hot water freeze faster than cold?",
   "field": "Physics",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Aristotle said yes. A Tanzanian schoolboy insisted yes. Careful labs say maybe not. This entry is unusual: the open question is whether the effect exists at all.",
   "url": "https://unsolvedcatalog.org/049-does-hot-water-freeze-faster/"
  },
  {
   "number": "050",
   "title": "How does gravity fit with quantum mechanics?",
   "field": "Physics",
   "posed": "1916",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "Physics runs on two magnificent theories that contradict each other about what reality is. Every attempt to marry them remains unconfirmed by a single experiment.",
   "url": "https://unsolvedcatalog.org/050-how-does-gravity-fit-with-quantum-mechanics/"
  },
  {
   "number": "051",
   "title": "Where do European eels spawn?",
   "field": "Biology",
   "posed": "Antiquity",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "No one has ever seen a European eel egg, or a European eel spawning, in the wild. Aristotle guessed. We are still guessing better.",
   "url": "https://unsolvedcatalog.org/051-where-do-european-eels-spawn/"
  },
  {
   "number": "052",
   "title": "How does lightning get started?",
   "field": "Atmospheric science",
   "posed": "1925",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The electric fields measured inside thunderclouds are roughly ten times too weak to spark. Lightning strikes anyway, about a hundred times a second, worldwide.",
   "url": "https://unsolvedcatalog.org/052-how-does-lightning-get-started/"
  },
  {
   "number": "053",
   "title": "Why are the Moon's two faces so different?",
   "field": "Planetary science",
   "posed": "1959",
   "added": "2026-08-16",
   "status": "open",
   "teaser": "The side of the Moon we see is dark lava plains; the side we never see is pale, cratered, and thicker-skinned. Sixty years of spacecraft have not settled why.",
   "url": "https://unsolvedcatalog.org/053-why-are-the-moons-two-faces-so-different/"
  }
 ]
}