Quantum foam
Quantum foam (also referred to as spacetime foam), is a concept in quantum mechanics devised by John Wheeler in 1955. The foam is supposed to be conceptualized as the foundation of the fabric of the universe.[1]
Additionally, quantum foam can be used as a qualitative description of subatomic spacetime turbulence at extremely small distances (on the order of the Planck length). At such small scales of time and space, the Heisenberg uncertainty principle allows energy to briefly decay into particles and antiparticles and then annihilate without violating physical conservation laws. As the scale of time and space being discussed shrinks, the energy of the virtual particles increases. According to Einstein's theory of general relativity, energy curves spacetime. This suggests that - at sufficiently small scales - the energy of these fluctuations would be large enough to cause significant departures from the smooth spacetime seen at larger scales, giving spacetime a "foamy" character.
With an incomplete theory of quantum gravity, it is impossible to be certain what spacetime would look like at these small scales, because existing theories of gravity do not give accurate predictions in that regime. Therefore, any of the developing theories of quantum gravity may improve our understanding of quantum foam as they are tested. However, observations of radiation from nearby quasars by Floyd Stecker of NASA's Goddard Space Flight Center have placed strong mathematical limits on the possible violations of Einstein's special theory of relativity implied by the existence of quantum foam.[2] Thus experimental evidence so far has given us a range of values in which scientists can test for quantum foam.
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[edit] Relation to other theories
Quantum foam is theorized to be created by virtual particles of very high energy. Virtual particles appear in quantum field theory, arising briefly and then annihilating during particle interactions in such a way that they affect the measured outputs of the interaction, even though the virtual particles are themselves space. These "vacuum fluctuations" affect the properties of the vacuum, giving it a nonzero energy known as vacuum energy, itself a type of zero-point energy. However, physicists are uncertain about the magnitude of this form of energy.[3]
The Casimir effect can also be understood in terms of the behavior of virtual particles in the empty space between two parallel plates. Ordinarily, quantum field theory does not deal with virtual particles of sufficient energy to curve spacetime significantly, so quantum foam is a speculative extension of these concepts which imagines the consequences of such high-energy virtual particles at very short distances and times.
Some physicists[4] theorize the formation of wormholes therein, and speculation arising from this includes the possibility of hyperspatial links to other universes. This theory was employed by author Michael Crichton in the fiction novel Timeline.
[edit] See also
[edit] Footnotes
- ^ "Quantum foam". New Scientist. http://ldolphin.org/qfoam.html. Retrieved 29 June 2008.
- ^ "Einstein makes extra dimensions toe the line". NASA. http://www.nasa.gov/centers/goddard/news/topstory/2003/1212einstein.html. Retrieved 9 February 2012.
- ^ Baez, John (2006-10-08). "What's the Energy Density of the Vacuum?". http://math.ucr.edu/home/baez/vacuum.html. Retrieved 2007-12-18.
- ^ Klotz, Irene (2010-05-07). "Stephen Hawking's time machine". http://www.msnbc.msn.com/id/37018725/ns/technology_and_science-science/. Retrieved 2010-05-07.
[edit] References
- John Archibald Wheeler with Kenneth Ford. Geons, Black Holes, and Quantum Foam. 1995 ISBN 0-393-04642-7.
- Reginald T. Cahill. Gravity as Quantum Foam In-Flow. June 2003.
- http://www.scientificamerican.com/article.cfm?id=borrowed-time-interview-w
- Swarup, A 2006, 'Sights set on quantum froth', New Scientist, 189, p. 18, Science Full Text Select (H.W. Wilson), EBSCOhost, viewed 10 February 2012.
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