Cosmology
The expansion, history, and large-scale structure of the universe.
9 problemsPhysics
Matter, energy, physical phenomena, and the universe.
Explore Physics
Astrophysics
Stars, compact objects, and signals from space.
28 problemsParticle physics
Fundamental particles, interactions, and symmetries.
21 problemsQuantum physics
Quantum phenomena and the foundations of their description.
11 problemsCondensed matter
Collective behavior in materials and quantum matter.
17 problemsFluids and plasmas
The collective motion of gases, liquids, and charged matter.
8 problemsPlanetary science
The formation, interiors, and histories of planets and moons.
15 problemsEarth science
Earth’s interior, geological history, and physical systems.
21 problemsCollections
Browse collectionsMillennium Prize Problems
Five open problems from Clay’s famous prize program, linking mathematics with computation and mathematical physics.
5 problemsThe observed universe
Unseen matter, cosmic expansion, energetic particles, and brief radio flashes.
40 problemsQuantum foundations
Measurement, gravity, and black holes challenge our account of quantum physics.
10 problemsA few problems to explore
106 totalDark matter
Bent light and galaxy motions reveal gravity that known stars and gas cannot fully explain. What supplies the additional mass?
Dark energy
The universe's expansion is accelerating. “Dark energy” names the gap in our explanation, while several different physical accounts remain possible.
Quantum gravity
Gravity describes a changing spacetime. Quantum physics describes matter and its possibilities. How should they work together in a single physical account?
Room-temperature superconductivity
The goal is a material that conducts electricity without resistance at room temperature and normal atmospheric pressure. Achieving both conditions together remains a research target.
Matter–antimatter asymmetry
Matter and antimatter can annihilate each other. Yet the observable universe contains enough leftover matter to make stars, planets, and people. What produced that imbalance?
Strong CP problem
The theory of the strong nuclear force permits a kind of asymmetry that experiments find to be extraordinarily small. Why is nature so close to the symmetric case?