quantum fluctuations

Quantum fluctuations are a seemingly-odd consequence of quantum physics (as described by QFT): ongoing, ubiquitous random fluctuations of energy levels, which can be seen as the appearance and disappearance of short-lived pairs of particles (termed virtual particles, of the usual particle types, but which disappear quickly through annihilation) at random, even within a vacuum. They can be thought of as a consequence of the Heisenberg uncertainty principle: an example where it is clear the principle says more than "we don't know what's going on at a small scale", but something more like "reality is uncertain". (Quantum fluctuations might also be termed the same thing as the uncertainty principle: the randomness at a very small scale resulting in successive measurements producing some randomness in their results.) Among the connections of quantum fluctuations to astrophysics:

• Quantum fluctuations are an explanation of Hawking radiation at the event horizon of black holes.
• Modern cosmological theories generally credit the structure of the present universe to early universe quantum fluctuations that somehow persisted (i.e., the initial fluctuations), resulting in sufficient density-variation to evolve into galaxy clusters, galaxies, and ultimately stars, but not so large as to prevent large portions of the universe in different directions from looking roughly the same. Inflation is cited as smoothing the results of earlier quantum fluctuations that would make things too varied, and quantum fluctuations in the field that drove inflation (inflation field) are presumed to have created the density variations inherent in the current state of things, which were also a major contributor toward observed CMB anisotropies.