Quantum foam, also referred to as
spacetime foam, is a concept in
quantum mechanics, devised by
John Wheeler in 1955. The
foam is supposedly the foundations of the fabric of the universe, but it can also be used as a qualitative description of subatomic spacetime turbulence at extremely small distances of the order of the
Planck length. At such small scales of time and space the
uncertainty principle allows particles and energy to briefly come into existence, and then
annihilate, without violating
conservation laws. As the scale of time and space being discussed shrinks, the energy of the
virtual particles increases. Since energy curves
spacetime according to
Einstein's theory of
general relativity, this suggests that at sufficiently small scales the energy of the fluctuations would be large enough to cause significant departures from the smooth spacetime seen at larger scales, giving spacetime a "foamy" character. However, without a theory of
quantum gravity it is impossible to be certain what spacetime would look like at these scales, since it is thought that existing theories do not give accurate predictions in this domain. However, observations of radiation from nearby quasars by Floyd Stecker of NASA's Goddard Space Flight Center in Greenbelt, Md., have placed strong limits on the possible violations of Einstein's
special theory of relativity implied by the existence of quantum foam.
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, where they arise briefly and then annihilate during particle interactions, in such a way that they affect the measured outputs of the interaction even though the virtual particles are themselves space, and these "
vacuum fluctuations" affect the properties of the vacuum, giving it a nonzero energy known as
vacuum energy, a type of
zero-point energy (however, physicists are uncertain about the magnitude of this energy). 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 theorize the formation of wormholes therein; 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.
See also
Dirac sea
Hawking radiation
Hyperspace theory
Planck time
"Rolling ball" topology
Vacuum energy
Wormhole
Invariance mechanics
sub-Planck
Footnotes
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
Category:Quantum gravity
Category:Quantum field theory
Category:Wormhole theory
Category:Foams
