- Quantum foam
**Quantum foam**, also referred to as**spacetime foam**, is a concept inquantum mechanics , devised by John Wheeler in1955 . The "foam" is supposedly the foundations of the fabric of the universe, [*cite web|url=http://ldolphin.org/qfoam.html|title=Quantum foam|publisher=New Scientist|accessdate=29 June|accessyear=2008*] but it can also be used as a qualitative description of subatomic spacetime turbulence at extremely small distances of the order of thePlanck length . At such small scales of time and space theuncertainty principle allows particles and energy to briefly come into existence, and then annihilate, without violatingconservation laws . As the scale of time and space being discussed shrinks, the energy of thevirtual particles increases. Since energy curvesspacetime according toEinstein 's theory ofgeneral 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 ofquantum gravity it is impossible to be certain what spacetime would look like at these scales, since it is thought that existing theories would no longer give accurate predictions in this domain.**Relation to other theories**Quantum foam is theorized to be created by

virtual particle s of very high energy. Virtual particles appear inquantum 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 never directly observed. They can also appear and annihilate briefly in empty space, and these "vacuum fluctuations" affect the properties of the vacuum, giving it a nonzero energy known asvacuum energy , a type ofzero-point energy (however, physicists are uncertain about the magnitude of this energy [*cite web*] ). The

url = http://math.ucr.edu/home/baez/vacuum.html

title = What's the Energy Density of the Vacuum?

accessdate = 2007-12-18

last = Baez

first = John

authorlink = John C. Baez

date = 2006-10-08Casimir 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.The "foamy" spacetime would look like a complex turbulent storm-tossed sea. Some physicists theorize the formation of

wormhole s therein; speculation arising from this includes the possibility of hyperspatial links to other universes.**ee 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.

* [*http://www.scieng.flinders.edu.au/cpes/people/cahill_r/HPS15.pdf Reginald T. Cahill. "Gravity as Quantum Foam In-Flow." June 2003.*]

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2010.*

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