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Quantum foam, also referred to as spacetime foam, is a concept in quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
, devised by John Wheeler
John Archibald Wheeler

John Archibald Wheeler was an eminent United States theoretical physicist. One of the later collaborators of Albert Einstein, he tried to achieve Einstein's vision of a unified field theory....
 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
Planck length

In physics, the Planck length, denoted , is unit of length, equal to about 1.6 × 10-33 centimeters. It is a base unit in the system of Planck units, the most widely used system of natural units....
. At such small scales of time and space the uncertainty principle
Uncertainty principle

In quantum physics, the Werner Heisenberg uncertainty principle states that certain physical quantities, like the position and momentum, cannot both have precise values at the same time....
 allows particles and energy to briefly come into existence, and then annihilate
Annihilation

Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil . A literal translation is "to make into nothing"....
, without violating conservation laws.






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Quantum foam, also referred to as spacetime foam, is a concept in quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
, devised by John Wheeler
John Archibald Wheeler

John Archibald Wheeler was an eminent United States theoretical physicist. One of the later collaborators of Albert Einstein, he tried to achieve Einstein's vision of a unified field theory....
 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
Planck length

In physics, the Planck length, denoted , is unit of length, equal to about 1.6 × 10-33 centimeters. It is a base unit in the system of Planck units, the most widely used system of natural units....
. At such small scales of time and space the uncertainty principle
Uncertainty principle

In quantum physics, the Werner Heisenberg uncertainty principle states that certain physical quantities, like the position and momentum, cannot both have precise values at the same time....
 allows particles and energy to briefly come into existence, and then annihilate
Annihilation

Annihilation is defined as "total destruction" or "complete obliteration" of an object; having its root in the Latin nihil . A literal translation is "to make into nothing"....
, 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
Spacetime

In physics, spacetime is any mathematical model that combines space and Time in physics into a single continuum . Spacetime is usually interpreted with space being Three-dimensional space and time playing the role of a fourth dimension that is of a different sort than the spatial dimensions....
 according to Einstein's theory of general relativity
General relativity

General relativity or the general theory of relativity is the Geometry Theoretical physics of gravitation published by Albert Einstein in 1916....
, 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
Quantum gravity

Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the Fundamental interaction , with general relativity, the theory of the fourth fundamental force: Gravitation....
 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
Virtual particle

In physics, a virtual particle is a particle that exists for a limited time and space, introducing uncertainty in their energy and momentum due to the Heisenberg Uncertainty Principle....
s of very high energy. Virtual particles appear in quantum field theory
Quantum field theory

Quantum field theory or QFT provides a theoretical framework for constructing quantum mechanics models of systems classically described by field or of Many-body problem....
, 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 as vacuum energy
Vacuum energy

Vacuum energy is an underlying background energy that exists in space even when devoid of matter . The vacuum energy is deduced from the concept of Virtual particle#Virtual particles in the vacuum, which are themselves derived from the Uncertainty principle#Energy-time uncertainty principle....
, a type of zero-point energy
Zero-point energy

In physics, the zero-point energy is the lowest possible energy that a quantum mechanical physical system may have and is the energy of the ground state....
 (however, physicists are uncertain about the magnitude of this energy ). The Casimir effect
Casimir effect

In physics, the Casimir effect and the Casimir-Polder force are physical force arising from a quantum field theory. The typical example is of two electric charge metallic plates in a vacuum, placed a few micrometers apart, without any external electromagnetic field....
 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
Wormhole

In physics, a wormhole is a hypothetical topology feature of spacetime that is fundamentally a 'shortcut' through space and time. Spacetime can be viewed as a 2D surface, and when 'folded' over, a wormhole bridge can be formed....
s therein; speculation arising from this includes the possibility of hyperspatial links to other universes
Multiverse (science)

The multiverse is the hypothetical set of multiple possible universes that together comprise all of reality. The different universes within the multiverse are sometimes called parallel universes....
.

See also

  • Dirac sea
    Dirac sea

    The Dirac sea is a theoretical model of the vacuum as an infinite sea of particles possessing negative energy. It was invented by the United Kingdom physicist Paul Dirac in 1930 to explain the anomalous negative-energy quantum states predicted by the Dirac equation for theory of relativity electrons....
  • Hawking radiation
    Hawking radiation

    Hawking radiation is a thermal radiation with a black body predicted to be emitted by black holes due to quantum physics effects. It is named after the physicist Stephen Hawking who provided the theoretical argument for its existence in 1974, and sometimes also after the physicist Jacob Bekenstein who predicted that black holes should have a...
  • Hyperspace theory
  • Planck time
    Planck time

    In physics, the Planck time , is the unit of time in the system of natural units known as Planck units. It is the time required for light to travel, in a vacuum, a distance of 1 Planck length....
  • "Rolling ball" topology
    Rolling ball

    In topology, quantum mechanics and geometrodynamics, rolling-ball arguments are used to describe how the perceived geometry and connectivity of a surface can be scale-dependent....
  • Vacuum energy
    Vacuum energy

    Vacuum energy is an underlying background energy that exists in space even when devoid of matter . The vacuum energy is deduced from the concept of Virtual particle#Virtual particles in the vacuum, which are themselves derived from the Uncertainty principle#Energy-time uncertainty principle....
  • Wormhole
    Wormhole

    In physics, a wormhole is a hypothetical topology feature of spacetime that is fundamentally a 'shortcut' through space and time. Spacetime can be viewed as a 2D surface, and when 'folded' over, a wormhole bridge can be formed....
  • Invariance mechanics
    Invariance mechanics

    In physics, invariance mechanics, in its simplest form, is the rewriting of the laws of quantum field theory in terms of invariant quantities only....
  • sub-Planck
    Planck scale

    In particle physics and physical cosmology, the Planck scale is an energy scale around 1.22 ? 1028 eV at which quantum mechanics of gravity become strong....


Footnotes