# Zero-point energy

Zero-point energy (ZPE) or ground state energy is the lowest possible energy that a quantum mechanical system may have. Unlike in classical mechanics, quantum systems constantly fluctuate in their lowest energy state as described by the Heisenberg uncertainty principle. As well as atoms and molecules, the empty space of the vacuum has these properties. According to quantum field theory, the universe can be thought of not as isolated particles but continuous fluctuating fields: matter fields, whose quanta are fermions (i.e., leptons and quarks), and force fields, whose quanta are bosons (e.g., photons and gluons). All these fields have zero-point energy. These fluctuating zero-point fields lead to a kind of reintroduction of an aether in physics, since some systems can detect the existence of this energy; however, this aether cannot be thought of as a physical medium if it is to be Lorentz invariant such that there is no contradiction with Einstein's theory of special relativity.

## Quotes

    Quotes are arranged alphabetically by author
* The light-quantum has the peculiarity that it apparently ceases to exist when it is in one of its stationary states, namely, the zero state, in which its momentum and therefore also its energy, are zero. When a light-quantum is absorbed it can be considered to jump into this zero state, and when one is emitted it can be considered to jump from the zero state to one in which it is physically in evidence, so that it appears to have been created. Since there is no limit to the number of light-quanta that may be created in this way, we must suppose that there are an infinite number of light quanta in the zero state...
** Paul Dirac (1927). "The Quantum Theory of the Emission and Absorption of Radiation". Proc. Roy. Soc. A114 (767): 243–265. DOI:10.1098/rspa.1927.0039. Retrieved on 17 October 2016.
* One hopes Debye will soon demonstrate the incorrectness of the hypothesis of zero-point energy, the theoretical untenability of which became glaringly obvious to me soon after the publication of the paper I coauthored with Mr. Stern.
** Albert Einstein, letter to Ludwig Hopf. 1913. Albert Einstein (1995). Klein, Martin J.; Kox, A. J.; Renn, Jürgen et al.. eds. The Collected Papers of Albert Einstein Vol. 5: The Swiss Years: Correspondence, 1902-1914. Princeton: Princeton University Press. pp. 562-563. ISBN 978-0-691-03322-8. OCLC 928803111.
* Zero-point energy is now dead as a doornail.
** Albert Einstein, letter to Paul Ehrenfest. 1913. Albert Einstein (1995). Klein, Martin J.; Kox, A. J.; Renn, Jürgen et al.. eds. The Collected Papers of Albert Einstein Vol. 5: The Swiss Years: Correspondence, 1902-1914. Princeton: Princeton University Press. p. 564. ISBN 978-0-691-03322-8. OCLC 928803111.
* In his Theorie der Wärmestrahlung, Planck emphasized that the existence of a zero-point energy was completely foreign to classical physics. However, it seemed to be a ghost-like entity which it was difficult to connect to experiments.
** Helge Kragh: (2012). "Preludes to dark energy: zero-point energy and vacuum speculations". Archive for history of exact sciences 66 (3): 199–240. DOI:10.1007/s00407-011-0092-3. arXiv.org preprint, page 8
* I fear that your hatred of the zero-point energy extends to the electrodynamic emission hypothesis that I introduced and that leads to it. But what’s to be done? For my part, I hate discontinuity of energy even more than discontinuity of emission.
** Max Planck, letter to Paul Ehrenfest. 1913. Thomas Kuhn (1978). Black-Body Theory and the Quantum Discontinuity, 1894-1912. New York: Oxford University Press. p. 253. ISBN 0-19-502383-8. OCLC 803538583.
* We here face a fundamental problem of outstanding importance. Its solution may still require a radical change in our theories beyond our present imagining.
** Dennis Sciama (1991). "The Physical Significance of the Vacuum State of a Quantum Field". in Saunders, Simon; Brown, Harvey R.. The Philosophy of Vacuum. Oxford: Oxford University Press. p. 157. ISBN 0198244495. OCLC 774073198.
* From quantum theory there follows the existence of so called zero-point oscillations; for example each oscillator in its lowest is not completely at rest but always is moving about its equilibrium position. Therefore electromagnetic oscillations also can never cease completely. Thus the quantum nature of the electromagnetic field has as its consequence zero point oscillations of the field strength in the lowest energy state, in which there are no light quanta in space... The zero point oscillations act on an electron in the same way as ordinary electrical oscillations do. They can change the eigenstate of the electron, but only in a transition to a state with the lowest energy, since empty space can only take away energy, and not give it up. In this way spontaneous radiation arises as a consequence of the existence of these unique field strengths corresponding to zero point oscillations. Thus spontaneous radiation is induced radiation of light quanta produced by zero point oscillations of empty space.
** Victor Weisskopf (1935). "Probleme der neueren Quantentheorie des Elektrons". Naturwissenschaften 23: 631–637. DOI:10.1007/BF01492012.