Unsolved problems in physics

From Wikipedia, the free encyclopedia

This is a 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.

1 Phenomena lacking clear scientific explanation
2 Theoretical ideas in search of experimental evidence
3 Problems solved recently
4 Notes
5 See also
6 References
7 External links

[edit] Phenomena lacking clear 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: What is the source of the observed accelerated expansion of the universe? What is the nature of the dark energy driving this acceleration?
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?^[1] ***
Ball lightning: Are these glowing, floating objects real? How can they be explained? *
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? Is a non-total cancelation of the cosmological constant responsible for the observed accelerated expansion (deSitter phase) of the Universe?
Dark matter: What is dark matter?^[2] Is it related to supersymmetry? Do the phenomena attributed to dark matter point not to some form of matter but actually to an extension of gravity? (It should be stressed that while a modification of gravity is a technical possibility for an explanation of dark matter, observations strongly disfavor this alternative.)
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?^[3]
Fundamental physical constants: Can fundamental constants be predicted by a more complete theory? ^[4] Do "fundamental physical constants" vary over time?
Gamma ray bursts (short duration): What is the nature of these extraordinarily energetic astronomical objects that last less than two seconds?^[5]
High-temperature superconductors: Why do certain materials exhibit superconductivity at temperatures much higher than around 50 kelvins?^[6] **
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?^[7]^[8]
Sonoluminescence: What causes the emission of short bursts of light from imploding bubbles in a liquid when excited by sound?
Turbulence: Is it possible to make a theoretical model to describe the behavior of a turbulent flow (in particular, its internal structures)?^[9]
Ultra-high-energy cosmic ray: Why is it that some cosmic rays apparently appear to possess energies that are impossibly high (the 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?^[10]^[11]

[edit] 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? If inflation happened at one point, is it self-sustaining through inflation of quantum-mechanical fluctuations, and thus ongoing in some impossibly distant place?
Extra dimensions: Does nature have more than four spacetime dimensions?
Faster-than-light: Is it possible to go faster than the speed of light (create path that is locally timelike but globally spacelike)? Is it possible to transmit information faster than the speed of light? If so, what is the consequence for the principle of causality (i.e., does it make time machines possible), or why not? **
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?
Physical information: Are there physical phenomena which 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? (Related to inflation, above)
Multiple universes: Are there physical reasons to believe in other universes that are fundamentally non-observable? For instance: Are there quantum mechanical "alternate histories"? Are there "other" universes with physical laws resulting from alternate ways of breaking the apparent symmetries of physical forces at high energies, possibly incredibly far away due to cosmic inflation? Is the use of the anthropic principle to resolve global cosmological dilemmas justified? ***
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, superstring theory, M-theory, or some other variant on this theme, a 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 Higgs mechanism: Does the Standard Model Higgs particle exist with its predicted Standard Model interactions?
Supersymmetry: Is spacetime supersymmetry realized in nature? If so, what is the mechanism of supersymmetry breaking? Does supersymmetry stablize electroweak symmetry breaking?
Technicolor: Does nature make use of strong dynamics in breaking electroweak symmetry?

[edit] Problems solved recently

Long duration gamma ray bursts (2003): Long-duration bursts are associated with the deaths of massive stars in a specific kind of supernova-like event commonly referred to as a collapsar.
Solar neutrino problem (2002): Solved by a new understanding of neutrino physics, requiring a modification of the Standard Model of particle physics — specifically, neutrino oscillation.
Quasars (1980s): The nature of quasars was not understood for decades. They are now accepted as a type of active galaxy where the enormous energy output results from matter falling into a massive black hole in the center of the galaxy.

[edit] Notes

* Problems marked with one star result from alleged events, and thus are considered by some physicists to be pseudoscience.

** Problems marked with two stars are considered by a significant number of physicists to be resolved, though there is still significant debate about them.

*** Problems marked with three stars are considered by some physicists to be outside the purview of physics, more properly philosophical in nature.

[edit] See also

[edit] References

^ Open Questions item 4
^ 13 things that do not make sense newscientistspace, 19 March 2005, Michael Brooks, item 5
^ Open Questions, Particle Physics, item 6
^ Open Questions, Particle Physics, item 12
^ Open Questions, Cosmology and Astrophysics, item 11
^ Open Questions, Condensed Matter and Nonlinear Dynamics, item 2
^ Open Questions, Particle Physics, item 13
^ newscientistspace item 8
^ Open Questions, Condensed Matter and Nonlinear Dynamics
^ Open Questions, Cosmology and Astrophysics, item 12
^ newscientistspace item 3