Quantum foam

Quantum foam is a term from physics that describes what happens when the two great theories of physics, quantum field theory and general relativity , are applied on an extremely small scale of 10 ⁻³⁵  meters (so-called Planck length ). Here, small "bubbles" would constantly arise in space-time and collapse again. In 1955, John Archibald Wheeler gave this phenomenon the name, initially casually meant, quantum foam, which later found its way into specialist literature (English Quantum foam or Spacetime foam ).

theory

Quantum effects mix up space-time at small distances to form quantum foam. From the point of view of quantum theory, the vacuum is not empty, but filled with virtual particles . The basis of the processes in the quantum vacuum is Heisenberg's uncertainty principle , especially its fundamental relationship between energy and time . According to the following formula, these two quantities are not determined at the same time as precisely as desired: ${\displaystyle E}$ ${\displaystyle t}$

${\displaystyle \Delta E\cdot \Delta t\geq {\frac {h}{4\pi }}={\frac {\hbar }{2}}}$,

where is Planck's quantum of action and . ${\displaystyle h=6{,}6261\cdot 10^{-34}\mathrm {Js} }$ ${\displaystyle \hbar ={h \over {2\pi }}}$

This relationship says that particles of energy can arise spontaneously and exist for a time , but then have to disappear again. ${\displaystyle E}$ ${\displaystyle \Delta t<\hbar /E}$

The short-term creation of virtual particle pairs, each consisting of a matter particle and an antimatter particle, is called vacuum fluctuation . The Heisenberg uncertainty principle allows the conservation of energy to be violated for a short time . For sufficiently short times, particles with any large energy or mass ( ) can arise. The greater the energy required, i.e. the heavier the particle pairs, the shorter the period of their existence. Because according to quantum theory, the universe can "borrow" energy in a certain way. The more energy is borrowed, the faster it has to be "paid back". All of this takes place in the order of magnitude of 10 ⁻²⁷ seconds. The emerging and passing particles can already be called quantum foam. According to the general theory of relativity (ART), however, the particle masses also bend the surrounding space-time. The consequence for spacetime is sometimes referred to by the term spacetime foam: space is no longer smooth and the equations of general relativity no longer apply. ${\displaystyle m_{0}=E/c^{2}}$

For a complete description of the phenomenon a quantum gravity theory would be necessary, which combines quantum theories and the general theory of relativity. The hypothetical loop quantum gravity is based, for example, on a spin foam . According to a speculative notion of quantum cosmology , the “bubbles” that are formed from quantum foam could be entire mini-universes that can expand into large-scale macro-universes in an “era of inflation”. Most of these bubbles, however, are likely to have "burst": It is assumed that the inflation phase cannot start for everyone.

So far, however, there is no evidence for the existence of the quantum foam. An attempt was made to prove the influence of the quantum foam on cosmic gamma radiation. For this purpose, the gamma radiation of the blazars Markarjan 421 and Markarjan 501 was examined, but no signs were found that would suggest the existence of the quantum foam.

literature

• John A. Wheeler , K. Ford : Geons, black holes, and quantum foam - a life in physics. Norton, New York / London 1998, ISBN 0-393-04642-7 (introducing the term quantum foam ).

Individual evidence

1. ↑ Again no references to the quantum foam of space-time - image of science ( Memento from December 31, 2016 in the web archive archive.today )

See also

Quantum geometry

Web links

• Quantum Foam - Video (2 min) - Max Planck Institute for Gravitational Physics
• Spacetime foam - video (1 min, spoken in English)