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Quantum foam

October 21, 2023

For related articles, see Quantum vacuum (disambiguation).

Quantum foam or spacetime foam is a theoretical quantum fluctuation of spacetime on very small scales due to quantum mechanics. The theory predicts that at these small scales, particles of matter and antimatter are constantly created and destroyed. These subatomic objects are called virtual particles.[1] The idea was devised by John Wheeler in 1955.[2][3]

Background Edit

With an incomplete theory of quantum gravity, it is impossible to be certain what spacetime would look like at small scales. However, there is no definitive reason that spacetime needs to be fundamentally smooth. It is possible that instead, in a quantum theory of gravity, spacetime would consist of many small, ever-changing regions in which space and time are not definite, but fluctuate in a foam-like manner.[4]

Wheeler suggested that the uncertainty principle might imply that over sufficiently small distances and sufficiently brief intervals of time, the "very geometry of spacetime fluctuates".[5] These fluctuations could be large enough to cause significant departures from the smooth spacetime seen at macroscopic scales, giving spacetime a "foamy" character.

Experimental results Edit

The experimental proof of the Casimir effect, which is possibly caused by virtual particles, is strong evidence for the existence of virtual particles. The g-2 experiment, which predicts the strength of magnets formed by muons and electrons, also supports their existence.[1]

In 2005, during observations of gamma-ray photons arriving from the blazar Markarian 501, MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescopes detected that some of the photons at different energy levels arrived at different times, suggesting that some of the photons had moved more slowly and thus were in violation of special relativity's notion that the speed of light is constant, a discrepancy which could be explained by the irregularity of quantum foam.[6] More recent experiments were, however, unable to confirm the supposed variation on the speed of light due to graininess of space.[7][8]

Other experiments involving the polarization of light from distant gamma ray bursts have also produced contradictory results.[9] More Earth-based experiments are ongoing[10] or proposed.[11]

Constraints on the size of quantum fluctuations Edit

The fluctuations characteristic of a spacetime foam would be expected to occur on a length scale on the order of the Planck length (≈ 10−35 m),[12] but some models of quantum gravity predict much larger fluctuations.

Photons should be slowed down by quantum foam, with the rate depending on the wavelength of the photons. This would violate Lorentz invariance. But observations of radiation from nearby quasars by Floyd Stecker of NASA's Goddard Space Flight Center failed to find evidence of violation of Lorentz invariance.[13]

A foamy spacetime also sets limits on the accuracy with which distances can be measured because photons should diffuse randomly through a spacetime foam, similar to light diffusing by passing through fog. This should cause the image quality of very distant objects observed through telescopes to degrade. X-ray and gamma-ray observations of quasars using NASA's Chandra X-ray Observatory, the Fermi Gamma-ray Space Telescope and ground-based gamma-ray observations from the Very Energetic Radiation Imaging Telescope Array (VERITAS) showed no detectable degradation at the farthest observed distances, implying that spacetime is smooth at least down to distances 1000 times smaller than the nucleus of a hydrogen atom,[14][15][16][17][18] setting a bound on the size of quantum fluctuations of spacetime.

Relation to other theories Edit

The vacuum fluctuations provide vacuum with a non-zero energy known as vacuum energy.[19]

Spin foam theory is a modern attempt to make Wheeler's idea quantitative.

See also Edit

Notes Edit

  1. ^ a b Quantum Foam, Don Lincoln, Fermilab, 2014-10-24.
  2. ^ Wheeler, J. A. (January 1955). "Geons". Physical Review. 97 (2): 511–536. Bibcode:1955PhRv...97..511W. doi:10.1103/PhysRev.97.511.
  3. ^ Minsky, Carly (24 October 2019). "The Universe Is Made of Tiny Bubbles Containing Mini-Universes, Scientists Say – 'Spacetime foam' might just be the wildest thing in the known universe, and we're just starting to understand it". Vice. Retrieved 24 October 2019.
  4. ^ See Derek Leinweber's QCD animations of spacetime foam, as exhibited in Wilczek lecture
  5. ^ Wheeler, John Archibald; Ford, Kenneth Wilson (2010) [1998]. Geons, black holes, and quantum foam : a life in physics. New York: W. W. Norton & Company. p. 328. ISBN 9780393079487. OCLC 916428720.
  6. ^ "Gamma Ray Delay May Be Sign of 'New Physics'". 3 March 2021.
  7. ^ Vasileiou, Vlasios; Granot, Jonathan; Piran, Tsvi; Amelino-Camelia, Giovanni (2015). "A Planck-scale limit on spacetime fuzziness and stochastic Lorentz invariance violation". Nature Physics. 11 (4): 344–346. Bibcode:2015NatPh..11..344V. doi:10.1038/nphys3270.
  8. ^ Cowen, Ron (2012). "Cosmic race ends in a tie". Nature. doi:10.1038/nature.2012.9768. S2CID 120173051.
  9. ^ Integral challenges physics beyond Einstein / Space Science / Our Activities / ESA
  10. ^ Moyer, Michael (17 January 2012). "Is Space Digital?". Scientific American. Retrieved 3 February 2013.
  11. ^ Cowen, Ron (22 November 2012). "Single photon could detect quantum-scale black holes". Nature News. Retrieved 3 February 2013.
  12. ^ Hawking, S.W. (November 1978). "Spacetime foam". Nuclear Physics B. 144 (2–3): 349–362. Bibcode:1978NuPhB.144..349H. doi:10.1016/0550-3213(78)90375-9.
  13. ^ "Einstein makes extra dimensions toe the line". NASA. Retrieved 9 February 2012.
  14. ^ "NASA Telescopes Set Limits on Spacetime Quantum "Foam"". 28 May 2015.
  15. ^ "Chandra Press Room :: NASA Telescopes Set Limits on Space-time Quantum "Foam":: 28 May 15". chandra.si.edu. Retrieved 2015-05-29.
  16. ^ "Chandra X-ray Observatory - NASA's flagship X-ray telescope". chandra.si.edu. Retrieved 2015-05-29.
  17. ^ Perlman, Eric S.; Rappaport, Saul A.; Christensen, Wayne A.; Jack Ng, Y.; DeVore, John; Pooley, David (2014). "New Constraints on Quantum Gravity from X-ray and Gamma-Ray Observations". The Astrophysical Journal. 805 (1): 10. arXiv:1411.7262. Bibcode:2015ApJ...805...10P. doi:10.1088/0004-637X/805/1/10. S2CID 56421821.
  18. ^ "Chandra :: Photo Album :: Space-time Foam :: May 28, 2015". chandra.si.edu. Retrieved 2015-05-29.
  19. ^ Baez, John (2006-10-08). "What's the Energy Density of the Vacuum?". Retrieved 2007-12-18.

References Edit

  • Minkel, JR (24 November 2003). "Borrowed Time: Interview with Michio Kaku". Scientific American
  • Swarup, A. (2006). "Sights set on quantum froth". New Scientist, 189, p. 18, accessed 10 February 2012.

October 21, 2023
quantum, foam, related, articles, quantum, vacuum, disambiguation, spacetime, foam, theoretical, quantum, fluctuation, spacetime, very, small, scales, quantum, mechanics, theory, predicts, that, these, small, scales, particles, matter, antimatter, constantly, . For related articles see Quantum vacuum disambiguation Quantum foam or spacetime foam is a theoretical quantum fluctuation of spacetime on very small scales due to quantum mechanics The theory predicts that at these small scales particles of matter and antimatter are constantly created and destroyed These subatomic objects are called virtual particles 1 The idea was devised by John Wheeler in 1955 2 3 Contents 1 Background 2 Experimental results 2 1 Constraints on the size of quantum fluctuations 3 Relation to other theories 4 See also 5 Notes 6 ReferencesBackground EditWith an incomplete theory of quantum gravity it is impossible to be certain what spacetime would look like at small scales However there is no definitive reason that spacetime needs to be fundamentally smooth It is possible that instead in a quantum theory of gravity spacetime would consist of many small ever changing regions in which space and time are not definite but fluctuate in a foam like manner 4 Wheeler suggested that the uncertainty principle might imply that over sufficiently small distances and sufficiently brief intervals of time the very geometry of spacetime fluctuates 5 These fluctuations could be large enough to cause significant departures from the smooth spacetime seen at macroscopic scales giving spacetime a foamy character Experimental results EditThe experimental proof of the Casimir effect which is possibly caused by virtual particles is strong evidence for the existence of virtual particles The g 2 experiment which predicts the strength of magnets formed by muons and electrons also supports their existence 1 In 2005 during observations of gamma ray photons arriving from the blazar Markarian 501 MAGIC Major Atmospheric Gamma ray Imaging Cherenkov telescopes detected that some of the photons at different energy levels arrived at different times suggesting that some of the photons had moved more slowly and thus were in violation of special relativity s notion that the speed of light is constant a discrepancy which could be explained by the irregularity of quantum foam 6 More recent experiments were however unable to confirm the supposed variation on the speed of light due to graininess of space 7 8 Other experiments involving the polarization of light from distant gamma ray bursts have also produced contradictory results 9 More Earth based experiments are ongoing 10 or proposed 11 Constraints on the size of quantum fluctuations Edit The fluctuations characteristic of a spacetime foam would be expected to occur on a length scale on the order of the Planck length 10 35 m 12 but some models of quantum gravity predict much larger fluctuations Photons should be slowed down by quantum foam with the rate depending on the wavelength of the photons This would violate Lorentz invariance But observations of radiation from nearby quasars by Floyd Stecker of NASA s Goddard Space Flight Center failed to find evidence of violation of Lorentz invariance 13 A foamy spacetime also sets limits on the accuracy with which distances can be measured because photons should diffuse randomly through a spacetime foam similar to light diffusing by passing through fog This should cause the image quality of very distant objects observed through telescopes to degrade X ray and gamma ray observations of quasars using NASA s Chandra X ray Observatory the Fermi Gamma ray Space Telescope and ground based gamma ray observations from the Very Energetic Radiation Imaging Telescope Array VERITAS showed no detectable degradation at the farthest observed distances implying that spacetime is smooth at least down to distances 1000 times smaller than the nucleus of a hydrogen atom 14 15 16 17 18 setting a bound on the size of quantum fluctuations of spacetime Relation to other theories EditThe vacuum fluctuations provide vacuum with a non zero energy known as vacuum energy 19 Spin foam theory is a modern attempt to make Wheeler s idea quantitative See also EditGeon Hawking radiation Holographic principle Loop quantum gravity Lorentzian wormhole Planck time Stochastic quantum mechanics String theory Wormhole Virtual black holeNotes Edit a b Quantum Foam Don Lincoln Fermilab 2014 10 24 Wheeler J A January 1955 Geons Physical Review 97 2 511 536 Bibcode 1955PhRv 97 511W doi 10 1103 PhysRev 97 511 Minsky Carly 24 October 2019 The Universe Is Made of Tiny Bubbles Containing Mini Universes Scientists Say Spacetime foam might just be the wildest thing in the known universe and we re just starting to understand it Vice Retrieved 24 October 2019 See Derek Leinweber s QCD animations of spacetime foam as exhibited in Wilczek lecture Wheeler John Archibald Ford Kenneth Wilson 2010 1998 Geons black holes and quantum foam a life in physics New York W W Norton amp Company p 328 ISBN 9780393079487 OCLC 916428720 Gamma Ray Delay May Be Sign of New Physics 3 March 2021 Vasileiou Vlasios Granot Jonathan Piran Tsvi Amelino Camelia Giovanni 2015 A Planck scale limit on spacetime fuzziness and stochastic Lorentz invariance violation Nature Physics 11 4 344 346 Bibcode 2015NatPh 11 344V doi 10 1038 nphys3270 Cowen Ron 2012 Cosmic race ends in a tie Nature doi 10 1038 nature 2012 9768 S2CID 120173051 Integral challenges physics beyond Einstein Space Science Our Activities ESA Moyer Michael 17 January 2012 Is Space Digital Scientific American Retrieved 3 February 2013 Cowen Ron 22 November 2012 Single photon could detect quantum scale black holes Nature News Retrieved 3 February 2013 Hawking S W November 1978 Spacetime foam Nuclear Physics B 144 2 3 349 362 Bibcode 1978NuPhB 144 349H doi 10 1016 0550 3213 78 90375 9 Einstein makes extra dimensions toe the line NASA Retrieved 9 February 2012 NASA Telescopes Set Limits on Spacetime Quantum Foam 28 May 2015 Chandra Press Room NASA Telescopes Set Limits on Space time Quantum Foam 28 May 15 chandra si edu Retrieved 2015 05 29 Chandra X ray Observatory NASA s flagship X ray telescope chandra si edu Retrieved 2015 05 29 Perlman Eric S Rappaport Saul A Christensen Wayne A Jack Ng Y DeVore John Pooley David 2014 New Constraints on Quantum Gravity from X ray and Gamma Ray Observations The Astrophysical Journal 805 1 10 arXiv 1411 7262 Bibcode 2015ApJ 805 10P doi 10 1088 0004 637X 805 1 10 S2CID 56421821 Chandra Photo Album Space time Foam May 28 2015 chandra si edu Retrieved 2015 05 29 Baez John 2006 10 08 What s the Energy Density of the Vacuum Retrieved 2007 12 18 References EditMinkel JR 24 November 2003 Borrowed Time Interview with Michio Kaku Scientific American Swarup A 2006 Sights set on quantum froth New Scientist 189 p 18 accessed 10 February 2012 Retrieved from https en wikipedia org w index php title Quantum foam amp oldid 1177740930, wikipedia, wiki, book, books, library,

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