Problems

Open questions in science on Papex, each with the source that lists it and the public records that address it.

• Binding problem How does the brain combine separate features into a single experience?
• Biological ageing Why does biological ageing occur?
• Birch and Swinnerton-Dyer conjecture Does an elliptic curve’s L-function tell how many rational points it has?
• Cambrian explosion What caused almost all animal phyla to appear so rapidly at the start of the Cambrian?
• Causal classification of mental disorders Can mental disorders be classified by their causes rather than their symptoms?
• Cause of idiopathic pulmonary fibrosis What causes idiopathic pulmonary fibrosis?
• Chemistry of the transactinide elements How do relativistic effects change the chemistry of the heaviest elements?
• Collatz conjecture Does the 3n + 1 process always reach 1, whatever number it starts from?
• Complexity of matrix multiplication What is the fastest possible algorithm for multiplying two matrices?
• Coronal heating problem Why is the Sun’s corona hundreds of times hotter than its surface?
• Cosmological constant problem Why is the energy of empty space so much smaller than quantum theory suggests?
• Cosmological lithium problem Why do very old stars hold less lithium than Big Bang nucleosynthesis predicts?
• Darwin’s abominable mystery Why do flowering plants appear so suddenly, and nearly modern, in the fossil record?
• Evolution of sexual reproduction Why did sexual reproduction evolve, and why does it persist?
• Existence of one-way functions Do functions exist that are easy to compute but hard to invert?
• Exponential time hypothesis Does solving 3-SAT really require exponential time?
• Fast radio bursts What causes the millisecond radio flashes that arrive from distant galaxies?
• Fermi paradox Why is there no clear evidence of extraterrestrial civilisations?
• Final parsec problem How do pairs of supermassive black holes get close enough to merge?
• Function of sleep Why do animals need to sleep?
• Goldbach’s conjecture Is every even number greater than 2 the sum of two primes?
• Granite space problem How do large bodies of granite magma make room for themselves in the crust?
• Graph isomorphism problem Can it be decided in polynomial time whether two graphs are the same up to relabelling?
• High-temperature superconductivity What makes some materials superconduct at such high temperatures?
• Hodge conjecture Is every Hodge class on a projective variety a combination of algebraic cycles?
• How antidepressants work How do antidepressants improve the symptoms of depression?
• How general anaesthesia works How exactly do general anaesthetics switch off consciousness?
• How lithium stabilises mood How does lithium stabilise mood?
• How paracetamol works How does paracetamol relieve pain and fever?
• Hubble tension Why do early- and late-universe measurements of the expansion rate disagree?
• Light elements in Earth’s outer core Which light elements are alloyed with iron in Earth’s outer core?
• Matter–antimatter asymmetry Why is the universe made of matter rather than antimatter?
• Nature of dark energy What is driving the accelerating expansion of the universe?
• Nature of dark matter What is the matter that holds galaxies together but gives off no light?
• Navier–Stokes existence and smoothness Do smooth solutions of the 3D Navier–Stokes equations always exist?
• Neural basis of consciousness How does the brain give rise to conscious experience?
• Neural code How is information encoded in the activity of neurons?
• On-water reaction acceleration Why do some organic reactions run much faster on water?
• Origin of biological homochirality Why does life use only one mirror-image form of its amino acids and sugars?
• Origin of life How did life arise from non-living chemistry?
• P versus NP Can every problem whose answer is quick to check also be solved quickly?
• Quantum gravity How can general relativity and quantum mechanics be reconciled?
• Riemann hypothesis Do all non-trivial zeros of the Riemann zeta function have real part ½?
• RNA folding problem Can the three-dimensional structure of an RNA molecule be predicted from its sequence?
• Time-scale of topographic decay What controls how long mountain ranges keep their relief?
• Tropical cyclone frequency Why does Earth have as many tropical cyclones as it does?
• Twin prime conjecture Are there infinitely many pairs of primes that differ by 2?
• Ultra-high-energy cosmic rays Where do the most energetic cosmic rays come from?
• Unique games conjecture Is approximating Unique Games NP-hard?
• Yang–Mills existence and mass gap Does quantum Yang–Mills theory exist with a positive mass gap?