Unsolved problems in physics
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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. Lastly, some even border on the pseudo-sciences, e.g. the fringes of science which are widely discredited by today's community of physicists, but may some day show promise or conclusive evidence.
Contents
Phenomena or established occurrences in search of a scientific explanation
- 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?[Open Questions in Physics] Usenet Physics FAQ, 2006, Open Questions, Cosmology and Astrophysics item 5
- 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? Why does time flow in one direction at all, on macroscopic scales, when there does not seem to be an arrow of time on the scale of fundamental interactions?Open Questions item 4
- Ball lightning: Are these glowing, floating objects real? How to explain them?
- Baryon asymmetry: Why is there far more matter than antimatter in the universe?
- Cold fusion: What is the theoretical explanation for the apparent production of excess heat and helium in palladium metal when it is saturated with deuterium?
- Corona heating problem: Why is the Sun's Corona (atmosphere layer) so much hotter than the Sun's surface?
- Cosmological constant: Why doesn't the zero-point energy of vacuum cause a large cosmological constant? What cancels it out?
- Why does the cosmological constant have the value that it has, is it zero and is it really constant?[Physics Problems for the Next Millennium] University of Michigan Strings 2000 Conference
- Dark matter: What is dark matter?[13 things that do not make sense] newscientistspace, 19 March 2005, Michael Brooks, item 5 How is it generated? Is it related to supersymmetry? Do the phenomena attributed to dark matter really flow from some kind of matter at all, or are those phenomena in fact an indication of flawed physical laws? Sellwood and Kosowsky, "Does Dark Matter Exist?" [link]
- Electroweak symmetry breaking: What is the mechanism responsible for breaking the electroweak gauge symmetry, giving mass to the W and Z? Is it the simple Higgs mechanism of the Standard Model?Open Questions, Particle Physics, item 6
- Fundamental physical constants: Why do we observe these values, and not others?Open Questions, Particle Physics, item 12 Have the values of the so called "fundamental physical constants" varied at all over time?
- Gamma ray bursts: What is the nature of these extraordinarily energetic astronomical objects?Open Questions, Cosmology and Astrophysics, item 11
- High energy cosmic rays: Why is it that some cosmic rays appear to possess energies that are impossibly high (so called Oh-My-God particle), given that there are no sufficiently energetic cosmic ray sources near the Earth? Why is it that (apparently) some cosmic rays emitted by distant sources have energies above the Greisen-Zatsepin-Kuzmin limit?Open Questions, Cosmology and Astrophysics, item 12newscientistspace item 3
- General: What are the origins of asymmetries in general in the Universe?
- High-temperature superconductors: Why do certain materials exhibit superconductivity at temperatures much higher than around 50 kelvins?Open Questions, Condensed Matter and Nonlinear Dynamics, item 2
- Mass: What causes anything to have mass?
- Neutrino mass: What is the mechanism responsible for generating neutrino masses? Is the neutrino its own antiparticle?
- Pioneer anomaly: What causes the apparent residual sunward acceleration of the Pioneer spacecraft?Open Questions, Particle Physics, item 13newscientistspace item 8
- Turbulence: Is it possible to make a theoretical model to describe the behavior of a turbulent fluid (in particular, its internal structures)?Open Questions, Condensed Matter and Nonlinear Dynamics
Theoretical ideas in search of experimental evidence
- Axions: Is the Peccei-Quinn theory (i.e. mechanism) the solution to the strong CP problem? What are the properties of the predicted axion?
- 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?
- Emergent phenomena: Are there physical laws important at a particular scale of phenomena, which are impossible to deduce or derive from fundamental laws of physics at small and great scales such as quantum mechanics and general relativity?
- Extra dimensions: Does Nature have more than four spacetime dimensions?
- Faster-than-light: Is it possible to go faster than the speed of light? Is it possible to transmit information faster than the speed of light?
- Gravity: 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? Does gravity behave as predicted at very small distance scales?
- Information: Do physical phenomena irrevocably destroy information about their prior states?
- Magnetic monopoles: Are there any particles that carry "magnetic charge", and if so, why are they so difficult to detect?
- Matter: Why is there matter at all? What was here before the Big Bang? How did the four fundamental forces appear?
- Proton decay: Many theories beyond the Standard Model predict 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 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?
- Size of the universe: Is there anything beyond the limits of the theoretical boundaries of the observable universe?
- Standard Model Higgs mechanism: Does the Standard Model Higgs particle exist? More generally, does inertial mass have a basis or mechanism separate from gravitational mass?
- Supersymmetry: Is supersymmetry a symmetry of Nature? If so, what is the mechanism of supersymmetry breaking?
- Technicolor: Does Nature make use of strong dynamics in breaking electroweak symmetry?
Engineering challenges
- Fusion power: Is it possible to construct a practical nuclear reactor that is powered by nuclear fusion rather than nuclear fission?
- Quantum computers: Is it possible to construct a practical computer that performs calculations on qubits (quantum bits)? Is there a practical limit to the speed of a quantum computer?
- Oldest star: How old an object in space is it possible to observe (i.e. how greatly can light be redshifted and still observed)?
Problems solved recently
See also
References
External links
- [APS]
- [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]
- [Ideas Based On What We’d Like To Achieve]
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