**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 a range of values in which scientists can test for quantum foam.