Davies, P. (1985). Superforce. A Touchstone Book. Simon & Schuster. стр. 105. ISBN978-0-671-60573-5. LCCN84005473. „What might appear to be empty space is, therefore, a seething ferment of virtual particles. A vacuum is not inert and featureless, but alive with throbbing energy and vitality. A 'real' particle such as an electron must always be viewed against this background of frenetic activity. When an electron moves through space, it is actually swimming in a sea of ghost particles of all varieties – virtual leptons, quarks, and messengers, entangled in a complex mêlée. The presence of the electron will distort this irreducible vacuum activity, and the distortion in turn reacts back on the electron. Even at rest, an electron is not at rest: it is being continually assaulted by all manner of other particles from the vacuum.”
Tadokoro, M. (1968). „A Study of the Local Group by Use of the Virial Theorem”. Publications of the Astronomical Society of Japan. 20: 230. Bibcode:1968PASJ...20..230T. This source estimates a density of 6971700000000000000♠7×10−29 g/cm³ for the Local Group. An atomic mass unit is 6973166000000000000♠1,66×10−24 g6973166000000000000♠1,66×10−24 g, for roughly 40 atoms per cubic meter.
Davies, P. (1985). Superforce. A Touchstone Book. Simon & Schuster. стр. 105. ISBN978-0-671-60573-5. LCCN84005473. „What might appear to be empty space is, therefore, a seething ferment of virtual particles. A vacuum is not inert and featureless, but alive with throbbing energy and vitality. A 'real' particle such as an electron must always be viewed against this background of frenetic activity. When an electron moves through space, it is actually swimming in a sea of ghost particles of all varieties – virtual leptons, quarks, and messengers, entangled in a complex mêlée. The presence of the electron will distort this irreducible vacuum activity, and the distortion in turn reacts back on the electron. Even at rest, an electron is not at rest: it is being continually assaulted by all manner of other particles from the vacuum.”
Genz, Henning (1994). Nothingness, the Science of Empty Space (translated from German by Karin Heusch изд.). New York: Perseus Book Publishing (објављено 1999). ISBN978-0-7382-0610-3. OCLC48836264.
