List of unsolved problems in physics

Source: Wikipedia, the free encyclopedia.

The following is a list of notable

unsolved problems grouped into broad areas of physics.[1]

Some of the major unsolved problems in physics are theoretical, meaning that existing theories seem incapable of explaining a certain observed phenomenon or experimental result. The 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.

There are still some questions

event horizon).[4]

General physics

  • Theory of everything: Is there a singular, all-encompassing, coherent theoretical framework of physics that fully explains and links together all physical aspects of the universe?
  • Dimensionless physical constants: At the present time, the values of various dimensionless physical constants cannot be calculated; they can be determined only by physical measurement.[5][6] What is the minimum number of dimensionless physical constants from which all other dimensionless physical constants can be derived? Are dimensional physical constants necessary at all?

Quantum gravity

  • Quantum gravity: Can quantum mechanics and general relativity be realized as a fully consistent theory (perhaps as a quantum field theory)?[7] Is spacetime fundamentally continuous or discrete? Would a consistent theory involve a force mediated by a hypothetical graviton, or be a product of a discrete structure of spacetime itself (as in loop quantum gravity)? Are there deviations from the predictions of general relativity at very small or very large scales or in other extreme circumstances that flow from a quantum gravity mechanism?
  • even exists
    ?
  • The
    naked singularities", arise from realistic initial conditions, or is it possible to prove some version of the "cosmic censorship hypothesis" of Roger Penrose which proposes that this is impossible?[9] Similarly, will the closed timelike curves which arise in some solutions to the equations of general relativity (and which imply the possibility of backwards time travel) be ruled out by a theory of quantum gravity which unites general relativity with quantum mechanics, as suggested by the "chronology protection conjecture" of Stephen Hawking
    ?
  • Holographic principle: Is it true that quantum gravity admits a lower-dimensional description that does not contain gravity? A well-understood example of holography is the AdS/CFT correspondence in string theory. Similarly, can quantum gravity in a de Sitter space be understood using dS/CFT correspondence? Can the AdS/CFT correspondence be vastly generalized to the gauge–gravity duality for arbitrary asymptotic spacetime backgrounds? Are there other theories of quantum gravity other than string theory that admit a holographic description?
  • Quantum spacetime or the emergence of spacetime: Is the nature of spacetime at the Planck scale very different from the continuous classical dynamical spacetime that exists in General relativity? In loop quantum gravity, the spacetime is postulated to be discrete from the beginning. In string theory, although originally spacetime was considered just like in General relativity (with the only difference being supersymmetry), recent research building upon the Ryu–Takayanagi conjecture has taught that spacetime in string theory is emergent by using quantum information theoretic concepts such as entanglement entropy in the AdS/CFT correspondence.[10] However, how exactly the familiar classical spacetime emerges within string theory or the AdS/CFT correspondence is still not well understood.
  • four-dimensional spacetime, and the flow of time changes depending on the curvature of spacetime and the spacetime trajectory of the observer. How can these two concepts of time be reconciled?[11]

Quantum physics

Cosmology and general relativity

Estimated distribution of dark matter and dark energy in the universe

High-energy/particle physics

Colour Confinement is the observed phenomenon that colored particles (quarks and gluons) can't be isolated and are always bound to color neutral groups (at low energies). Such bound states are generally called hadrons.
  • The QCD vacuum: Many of the equations in non-perturbative QCD are currently unsolved. These energies are the energies sufficient for the formation and description of atomic nuclei. How thus does low energy /non-pertubative QCD give rise to the formation of complex nuclei and nuclear constituents?[citation needed]
  • Yukawa couplings)?[31]
  • Neutrino mass: What is the mass of neutrinos, whether they follow Dirac or Majorana statistics? Is the mass hierarchy normal or inverted? Is the CP violating phase equal to 0?[32][33]
  • Reactor antineutrino anomaly: There is an anomaly in the existing body of data regarding the antineutrino flux from nuclear reactors around the world. Measured values of this flux appears to be only 94% of the value expected from theory.[34] It is unknown whether this is due to unknown physics (such as sterile neutrinos), experimental error in the measurements, or errors in the theoretical flux calculations.[35]
  • charge conjugation? Is Peccei–Quinn theory the solution to this problem? Could axions be the main component of dark matter
    ?
  • Anomalous magnetic dipole moment: Why is the experimentally measured value of the muon's anomalous magnetic dipole moment ("muon g − 2") significantly different from the theoretically predicted value of that physical constant?[36]
  • Proton radius puzzle: What is the electric charge radius of the proton? How does it differ from a gluonic charge?
  • Pentaquarks and other exotic hadrons: What combinations of quarks are possible? Why were pentaquarks so difficult to discover?[37] Are they a tightly bound system of five elementary particles, or a more weakly-bound pairing of a baryon and a meson?[38]
  • Mu problem: A problem in supersymmetric theories, concerned with understanding the reasons for parameter values of the theory.
  • Koide formula: An aspect of the problem of particle generations. The sum of the masses of the three charged leptons, divided by the square of the sum of the roots of these masses, to within one standard deviation of observations, is Q = 23. It is unknown how such a simple value comes about, and why it is the exact arithmetic average of the possible extreme values of  1 /3 (equal masses) and 1 (one mass dominates).
  • Heat Death of the Universe
    .
  • Glueballs: Do they exist in nature? What configurations of them are stable?

Astronomy and astrophysics

Nuclear physics

The "island of stability" in the proton vs. neutron number plot for heavy nuclei

Fluid dynamics

Condensed matter physics

A sample of a cuprate superconductor (specifically BSCCO). The mechanism for superconductivity of these materials is unknown.
Magnetoresistance in a u = 8/5 fractional quantum Hall state

Quantum computing and quantum information

Plasma physics

Biophysics

  • stochasticity? Certain models exist for genetic processes, but we are far from understanding the whole picture, in particular in development
    where gene expression must be tightly regulated.
  • Quantitative study of the immune system: What are the quantitative properties of immune responses? What are the basic building blocks of immune system networks?
  • biochemical systems
    ?
  • Magnetoreception: How do animals (e.g. migratory birds) sense the Earth's magnetic field?
  • Protein structure prediction: How is the three-dimensional structure of proteins determined by the one-dimensional amino acid sequence? How can proteins fold on microsecond to second timescales when the number of possible conformations is astronomical and conformational transitions occur on the picosecond to microsecond timescale? Can algorithms be written to predict a protein's three-dimensional structure from its sequence? Do the native structures of most naturally occurring proteins coincide with the global minimum of the free energy in conformational space? Or are most native conformations thermodynamically unstable, but kinetically trapped in metastable states? What keeps the high density of proteins present inside cells from precipitating?[96]
  • Quantum biology: Can coherence be maintained in biological systems at timeframes long enough to be functionally important? Are there non-trivial aspects of biology or biochemistry that can only be explained by the persistance of coherence as a mechanism?

Foundations of physics

  • many worlds interpretation
    resolve it?
  • entropy's arrow of time): Why does time have a direction? Why did the universe have such low entropy in the past, and time correlates with the universal (but not local) increase in entropy, from the past and to the future, according to the second law of thermodynamics?[44] Why are CP violations observed in certain weak force decays, but not elsewhere? Are CP violations somehow a product of the second law of thermodynamics, or are they a separate arrow of time? Are there exceptions to the principle of causality? Is there a single possible past? Is the present moment physically distinct from the past and future, or is it merely an emergent property of consciousness
    ? What links the quantum arrow of time to the thermodynamic arrow?
  • Locality: Are there non-local phenomena in quantum physics?[98][99] If they exist, are non-local phenomena limited to the entanglement revealed in the violations of the Bell inequalities, or can information and conserved quantities also move in a non-local way? Under what circumstances are non-local phenomena observed? What does the existence or absence of non-local phenomena imply about the fundamental structure of spacetime? How does this elucidate the proper interpretation of the fundamental nature of quantum physics?
  • quantum mechanical phenomena, such as entanglement and superposition, play an important part in the brain's function and can it explain critical aspects of consciousness?[100]

Problems solved in the past 30 years

General physics/quantum physics

Cosmology and general relativity

High-energy physics/particle physics

Astronomy and astrophysics

Nuclear physics

Rapidly solved problems

  • Existence of
    University of Maryland and a group led by Mikhail Lukin at Harvard University, who were both able to show evidence for time crystals in the laboratory setting, showing that for short times the systems exhibited the dynamics similar to the predicted one.[127][128]
  • Photon underproduction crisis (2014–2015): This problem was resolved by Khaire and Srianand.[129] They show that a factor 2 to 5 times large metagalactic photoionization rate can be easily obtained using updated quasar and galaxy observations. Recent observations of quasars indicate that the quasar contribution to ultraviolet photons is a factor of 2 larger than previous estimates. The revised galaxy contribution is a factor of 3 larger. These together solve the crisis.
  • Hipparcos anomaly (1997[130]–2012): The High Precision Parallax Collecting Satellite (Hipparcos) measured the parallax of the Pleiades and determined a distance of 385 light years. This was significantly different from other measurements made by means of actual to apparent brightness measurement or absolute magnitude. The anomaly was due to the use of a weighted mean when there is a correlation between distances and distance errors for stars in clusters. It is resolved by using an unweighted mean. There is no systematic bias in the Hipparcos data when it comes to star clusters.[131]
  • Faster-than-light neutrino anomaly (2011–2012): In 2011, the OPERA experiment mistakenly observed neutrinos appearing to travel faster than light. On 12 July 2012 OPERA updated their paper after discovering an error in their previous flight time measurement. They found agreement of neutrino speed with the speed of light.[132]

See also

Footnotes

  1. ^ "This problem is widely regarded as one of the major obstacles to further progress in fundamental physics ... Its importance has been emphasized by various authors from different aspects. For example, it has been described as a 'veritable crisis" ...] and even 'the mother of all physics problems' ... While it might be possible that people working on a particular problem tend to emphasize or even exaggerate its importance, those authors all agree that this is a problem that needs to be solved, although there is little agreement on what is the right direction to find the solution."[24]
  2. ^ When physicists strip neutrons from atomic nuclei, put them in a bottle, then count how many remain there after some time, they infer that neutrons radioactively decay in 14 minutes and 39 seconds, on average. But when other physicists generate beams of neutrons and tally the emerging protons — the particles that free neutrons decay into — they peg the average neutron lifetime at around 14 minutes and 48 seconds. The discrepancy between the “bottle” and “beam” measurements has persisted since both methods of gauging the neutron's longevity began yielding results in the 1990s. At first, all the measurements were so imprecise that nobody worried. Gradually, though, both methods have improved, and still they disagree.[26]

References

  1. .
  2. ^ Hammond, Richard (1 May 2008). "The Unknown Universe: The Origin of the Universe, Quantum Gravity, Wormholes, and Other Things Science Still Can't Explain". Proceedings of the Royal Society of London, Series A. 456 (1999): 1685.
  3. ^ Womersley, J. (February 2005). "Beyond the Standard Model" (PDF). Symmetry Magazine. Archived from the original (PDF) on 17 October 2007. Retrieved 23 November 2010.
  4. ^ Overbye, Dennis (11 September 2023). "Don't Expect a 'Theory of Everything' to Explain It All - Not even the most advanced physics can reveal everything we want to know about the history and future of the cosmos, or about ourselves". The New York Times. Archived from the original on 11 September 2023. Retrieved 11 September 2023.
  5. ^ "Alcohol constrains physical constant in the early universe". Phys Org. 13 December 2012. Archived from the original on 2 April 2015. Retrieved 25 March 2015.
  6. from the original on 17 January 2023. Retrieved 10 January 2020.
  7. ^ Sokal, Alan (22 July 1996). "Don't Pull the String Yet on Superstring Theory". New York Times. Archived from the original on 7 December 2008. Retrieved 17 February 2017.
  8. S2CID 7481797
    .
  9. ^ Joshi, Pankaj S. (January 2009). "Do Naked Singularities Break the Rules of Physics?". Scientific American. Archived from the original on 25 May 2012.
  10. .
  11. .
  12. ^ "Yang–Mills and Mass Gap". Clay Mathematics Institute. Archived from the original on 22 November 2015. Retrieved 31 January 2018.
  13. .
  14. .
  15. ^ Podolsky, Dmitry. "Top ten open problems in physics". NEQNET. Archived from the original on 22 October 2012. Retrieved 24 January 2013.
  16. ^ a b c d e Brooks, Michael (19 March 2005). "13 things that do not make sense". New Scientist. Issue 2491. Archived from the original on 23 June 2015. Retrieved 7 March 2011.
  17. ^ "Quanta Magazine". Archived from the original on 27 April 2020. Retrieved 10 May 2020.
  18. ^
    S2CID 247411131
    .
  19. .
  20. ^ .
  21. ^ from the original on 10 March 2022. Retrieved 25 March 2022.
  22. .
  23. ^ a b Wang, Qingdi; Zhu, Zhen;
    S2CID 119076077
    .
  24. (PDF) from the original on 20 May 2011. Retrieved 25 December 2010.
  25. ^ a b Wolchover, Natalie (13 February 2018). "Neutron lifetime puzzle deepens, but no dark matter seen". Quanta Magazine. Archived from the original on 30 July 2018. Retrieved 31 July 2018.
  26. S2CID 119246624
    .
  27. ^ Hansson, Johan (2010). "The "proton spin crisis" – a quantum query" (PDF). Progress in Physics. 3: 23. Archived from the original (PDF) on 4 May 2012. Retrieved 14 April 2012.
  28. .
  29. ^ Wu, T.-Y.; Hwang, W.-Y. Pauchy (1991). Relativistic Quantum Mechanics and Quantum Fields. .
  30. ^ Blumhofer, A.; Hutter, M. (1997). "Family structure from periodic solutions of an improved gap equation". Nuclear Physics. B484 (1): 80–96. .
  31. ^ "India-based Neutrino Observatory (INO)". Tata Institute of Fundamental Research. Archived from the original on 26 April 2012. Retrieved 14 April 2012.
  32. from the original on 23 April 2012. Retrieved 25 April 2012.
  33. from the original on 17 January 2023. Retrieved 2 October 2021.
  34. from the original on 2 October 2021. Retrieved 2 October 2021.
  35. ].
  36. ^ Muir, H. (2 July 2003). "Pentaquark discovery confounds skeptics". New Scientist. Archived from the original on 10 October 2008. Retrieved 8 January 2010.
  37. ^ Amit, G. (14 July 2015). "Pentaquark discovery at LHC shows long-sought new form of matter". New Scientist. Archived from the original on 8 November 2020. Retrieved 14 July 2015.
  38. S2CID 1547625
    .
  39. .
  40. S2CID 4689535. Archived from the original
    (PDF) on 3 February 2014. Retrieved 25 January 2013.
  41. .
  42. .
  43. ^ a b c d e f Baez, John C. (March 2006). "Open Questions in Physics". Usenet Physics FAQ. University of California, Riverside: Department of Mathematics. Archived from the original on 4 June 2011. Retrieved 7 March 2011.
  44. ^ "Scientists Find That Saturn's Rotation Period is a Puzzle". NASA. 28 June 2004. Archived from the original on 29 August 2011. Retrieved 22 March 2007.
  45. S2CID 120464396
    .
  46. .
  47. .
  48. .
  49. .
  50. .
  51. .
  52. .
  53. .
  54. .
  55. .
  56. .
  57. .
  58. .
  59. .
  60. .
  61. .
  62. .
  63. .
  64. .
  65. .
  66. ^ Charles Fefferman. "Existence and Uniqueness of the Navier-Stokes Equation" (PDF). Clay Mathematics Institute. Archived (PDF) from the original on 14 November 2020. Retrieved 29 April 2021.
  67. ^ Schlein, Benjamin. "Graduate Seminar on Partial Differential Equations in the Sciences – Energy and Dynamics of Boson Systems". Hausdorff Center for Mathematics. Archived from the original on 4 May 2013. Retrieved 23 April 2012.
  68. ^ Kenneth Chang (29 July 2008). "The Nature of Glass Remains Anything but Clear". The New York Times. Archived from the original on 14 September 2017. Retrieved 17 February 2017.
  69. S2CID 28052338
    . The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition.
  70. .
  71. .
  72. .
  73. ^ Cryogenic electron emission phenomenon has no known physics explanation Archived 5 June 2011 at the Wayback Machine. Physorg.com. Retrieved on 20 October 2011.
  74. from the original on 20 February 2020. Retrieved 20 April 2018.
  75. .
  76. .
  77. .
  78. .
  79. .
  80. ^ A. Yethiraj, "Recent Experimental Developments at the Nematic to Smectic-A Liquid Crystal Phase Transition" Archived 15 May 2013 at the Wayback Machine, Thermotropic Liquid Crystals: Recent Advances, ed. A. Ramamoorthy, Springer 2007, chapter 8.
  81. from the original on 27 April 2022. Retrieved 18 October 2020.
  82. .
  83. .
  84. .
  85. .
  86. from the original on 9 June 2020. Retrieved 8 February 2020.
  87. ^ Barton, G.; Scharnhorst, K. (1993). "QED between parallel mirrors: light signals faster than c, or amplified by the vacuum".
    S2CID 120489943
    .
  88. ^ a b c Aaronson, Scott. "Ten Semi-Grand Challenges for Quantum Computing Theory". ScottAaronson.com. Retrieved 1 September 2023.
  89. ^ Ball, Phillip (2021). "Major Quantum Computing Strategy Suffers Serious Setbacks". Quanta Magazine. Retrieved 2 September 2023.
  90. ^ Skyrme, Tess (20 March 2023). "The Status of Room-Temperature Quantum Computers". EE Times Europe. Retrieved 1 September 2023.
  91. .
  92. S2CID 498401. Archived from the original
    (PDF) on 23 February 2019..
  93. from the original on 17 January 2023. Retrieved 3 September 2015.
  94. .
  95. .
  96. .
  97. .
  98. .
  99. ^ Atmanspacher, Harald (2020), "Quantum Approaches to Consciousness", in Zalta, Edward N. (ed.), The Stanford Encyclopedia of Philosophy (Summer 2020 ed.), Metaphysics Research Lab, Stanford University, retrieved 12 April 2023
  100. .
  101. from the original on 31 July 2019. Retrieved 21 October 2015.
  102. .
  103. .
  104. ^ "Einstein papers at the Instituut-Lorentz". Archived from the original on 19 May 2015. Retrieved 30 April 2016.
  105. from the original on 24 December 2018. Retrieved 11 February 2016.
  106. .
  107. ^ "Gravitational waves detected 100 years after Einstein's prediction". www.nsf.gov. National Science Foundation. Archived from the original on 19 June 2020. Retrieved 11 February 2016.
  108. S2CID 23409406
    .
  109. .
  110. ^ .
  111. from the original on 27 April 2022. Retrieved 17 January 2013.
  112. ^ .
  113. from the original on 30 October 2021. Retrieved 16 October 2017.
  114. from the original on 16 October 2017. Retrieved 27 August 2017.
  115. ^ Shull, J. Michael, Britton D. Smith, and Charles W. Danforth. "The baryon census in a multiphase intergalactic medium: 30% of the baryons may still be missing." The Astrophysical Journal 759.1 (2012): 23.
  116. ^ "Half the universe's missing matter has just been finally found". New Scientist. Archived from the original on 13 October 2017. Retrieved 12 October 2017.
  117. S2CID 49347964
    .
  118. .
  119. .
  120. .
  121. .
  122. .
  123. .
  124. from the original on 24 June 2021. Retrieved 21 November 2021.
  125. .
  126. .
  127. .
  128. .
  129. .
  130. .
  131. .
  132. ^ Overbye, Dennis (23 July 2012). "Mystery Tug on Spacecraft Is Einstein's 'I Told You So'". The New York Times. Archived from the original on 27 August 2017. Retrieved 24 January 2014.

External links