Unsolved problems in physics
This is an incomplete list of some of the unsolved problems in physics. Some of these problems are theoretical, meaning that existing theories seem incapable of explaining some observed phenomenon or experimental result. Others are experimental, meaning that there is a difficulty in creating an experiment to test a proposed theory or investigate a phenomenon in greater detail.
- Accretion disc jets: Why do the accretion discs surrounding certain astronomical objects, such as the nuclei of active galaxies, emit relativistic jets along their polar axes?
- Accelerating universe: Why is the expansion of the universe accelerating, as we have observed? What is the nature of the dark energy driving this acceleration? If it is due to a cosmological constant, why is the constant so small, yet non-zero? Why isn't it huge, as predicted by most quantum field theories, or zero for some yet unknown symmetry reason? What is the ultimate fate of the universe?
- Amorphous solids: What is the nature of the transition between a fluid or regular solid and a glassy phase? What are the physical processes giving rise to the general properties of glasses?
- Arrow of time: Why did the universe have such low entropy in the past, resulting in the distinction between past and future and the second law of thermodynamics?
- Baryon asymmetry: Why is there far more matter than antimatter in the universe?
- Cosmic inflation: Is the theory of cosmic inflation correct, and if so, what are the details of this epoch? What is the hypothetical inflaton field giving rise to inflation?
- Dark matter: What is the nature of the material observed via only its gravitational effects (for example, in the Galaxy rotation problem)? Or, does such matter exist at all? (An alternative explanation could be that the equations of General Relativity are subtly wrong, for example in Modified Newtonian Dynamics).
- Fusion power: Is it possible to construct a practical nuclear reactor that is powered by nuclear fusion rather than nuclear fission?
- Gamma ray bursts: What is the nature of these extraordinarily energetic astronomical objects?
- Gravitational waves: Is our universe filled with gravitational radiation from the big bang? From astrophysical sources, such as inspiralling neutron stars? What can this tell us about quantum gravity and general relativity?
- GZK paradox: Why is it that some cosmic rays appear to possess energies that are impossibly high, given that there are no sufficiently energetic cosmic ray sources near the Earth, and cosmic rays emitted by distant sources should have been absorbed by the cosmic microwave background radiation?
- High-temperature superconductors: Why do certain materials exhibit superconductivity at temperatures much higher than around 50 kelvins?
- Magnetic monopoles: Are there any particles that carry "magnetic charge", and if so, why are they so difficult to detect?
- Neutrino mass: What is the mass of the various neutrinos? Is the mass Dirac or Majorana in nature?
- Pioneer anomaly: What causes the apparent residual Sunward acceleration of the Pioneer spacecraft?
- Proton decay: Do protons decay? If so, then what is their half-life?
- Quantum chromodynamics (QCD) in the non-perturbative regime: The equations of QCD remain unsolved at energy scales relevant for describing atomic nuclei. How does QCD give rise to the physics of nuclei and nuclear constituents?
- Quantum computers: Is it possible to construct a practical computer that performs calculations on qubits (quantum bits)?
- Quantum gravity: How can the theory of quantum mechanics be merged with the theory of general relativity to produce a so-called "theory of everything"? Is string theory the correct step on the road to quantum gravity, or a blind alley? Is there any way to extract experimental information about the nature of physics at the Planck scale
- Quantum mechanics in the correspondence limit: Is there a preferred interpretation of quantum mechanics? How does the quantum description of reality, which includes elements such as the superposition of states and wavefunction collapse, give rise to the reality we perceive?
- Standard Model parameters: What gives rise to the Standard Model of particle physics? Why do its particle masses and coupling constants possess the values we have measured? Does the Higgs boson predicted by the model really exist? Why are there 3 classes of particles in the Standard Model? Is the Standard Model reality, a good approximation to reality or fatally flawed?
- Supersymmetry: Is supersymmetry a symmetry of Nature? If so, how is supersymmetry broken, and why? Can the new particles predicted by supersymmetry be detected?
- Turbulence: Is it possible to make a theoretical model to describe the behavior of a turbulent fluid (in particular, its internal structures)?
Problems solved recently:
- Physics News Update A weekly physics news bulletin hosted by the American Institute of Physics.
- Open Questions in Physics
- New Scientist: 13 things that do not make sense.
- Science Magazine: the most compelling puzzles and questions facing scientists today.
- List of links to unsolved problems in physics, prizes and research.
- Dark Matter - one problem solved
da:Fysikkens uløste gåder de:Ungelöste Probleme der Physik gl:Problemas por solucionar na física pt:Problemas não solucionados da Física sl:Nerešeni problemi v fiziki fi:Ratkaisemattomat fysiikan ongelmat zh:未解決的物理學問題