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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.
Contents |
- 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?
- 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?
- Black hole structure
- Does a black hole have an internal structure, and if so, what is its nature?
- Black hole information
- Hawking radiation allows black holes to evaporate to (perhaps) nothing, and yet carries no information. Quantum mechanics does not allow information to be destroyed. Where does it go? Is Hawking's formula incorrect, and the radiation carries information? Or does it stop at some point leaving black hole remnants?
- 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 cancellation of the cosmological constant responsible for the observed accelerated expansion (deSitter phase) of the Universe? If it is, why is the energy density of the cosmological constant of the same magnitude as the density of matter at present when the two evolve quite differently over time; could it be simply that we are observing at exactly the right time?
- Dark matter
- What is dark matter?[1] 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?
- 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?[2]
- Fundamental physical constants
- Can fundamental constants be predicted by a more complete theory? [3] 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?[4]
- High-temperature superconductors
- What is the responsible mechanism that causes certain materials to exhibit superconductivity at temperatures much higher than around 50 kelvins?[5]
- Hipparcos Anomaly
- How far away are the Pleiades, exactly?
- Island of stability
- What is the largest theoretically possible stable atom?
- Minkowski space
- Why does the Minkowski metric describe the vacuum?
- 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?[6][7] ****
- Proton Spin Crisis
- As initially measured by the European Muon Collaboration, the quarks of the proton account for about 12% of its total spin. What accounts for the rest of it?
- 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 statistics of a turbulent flow (in particular, its internal structures)?[8]
- Ultra-high-energy cosmic ray
- Why is it that some cosmic rays 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?[9][10]
- 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?
- Emergent phenomena
- Is a complete understanding of particle physics sufficient to fully understand all physical phenomena, or are there emergent phenomena in physics whose existence cannot be definitively predicted from a complete understanding of the fundamental particles and forces that govern the universe?
- Extra dimensions
- Does nature have more than four spacetime dimensions? If so, why are they not easily observed? Are dimensions a fundamental property of the universe or an emergent result of other physical laws?
- 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? **
- Physical information
- Are there physical phenomena which irrevocably destroy information about their prior states?
- Magnetic monopoles
- Do particles that carry "magnetic charge" exist?
- 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
- As the lightest baryon, are protons absolutely stable? If current theoretical ideas are correct, quarks and leptons are ultimately unified and thus nothing in principle forbids proton decay. If so, then what is the proton's half-life? (This question is related to extracting experimental information about physics near the Planck scale.)
- 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 gravity be realized as a fully consistent quantum theory? Is string theory (M-theory) the correct approach? More pressing, how much experimental information can be extracted about physics near 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 stabilize electroweak symmetry breaking? Does the lightest supersymmetric particle make up the dark matter?
- Tachyons
- Do these hypothetical particles exist? If so, how do they travel FTL ignoring the laws of special relativity?
- Technicolor
- Does nature make use of strong dynamics in breaking electroweak symmetry?
- 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.
** 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.
**** Problems marked with four stars are disputed.
- ^ 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
- 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.
- Ideas Based On What We’d Like To Achieve
- 2004 SLAC Summer Institute: Nature's Greatest Puzzles