The quantum in quantum foam comes from quantum mechanics, and the foam comes from the idea that at extremely small distances (of the order of the Planck length), spacetime itself ceases to be smooth, and resembles instead a kind of rapidly changing foam. This is all thanks to the uncertainty principle.
The importance of quantum foam is that it is thought to give rise to a sea of virtual particles that pop into existence for an instant, that is, for a period of time that is less than the period of time known as Planck time. These virtual particles make their existence known by the Casimir effect.
Reginald Cahill has developed a theory called Process Physics, which describes space as a quantum foam system in which gravity is an inhomogeneous flow of the quantum foam into matter. According to this theory, the so-called spiral galaxy rotation-velocity anomaly may be explained without the need for dark matter.
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