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The Scharnhorst effect is a hypothetical phenomenon in which light signals travel slightly
faster than ''c'' between two closely spaced conducting plates. It was first predicted in a 1990 paper by
Klaus Scharnhorst of the
Humboldt University of Berlin
Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative ...
,
Germany
Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
. He showed using
quantum electrodynamics
In particle physics, quantum electrodynamics (QED) is the relativistic quantum field theory of electrodynamics. In essence, it describes how light and matter interact and is the first theory where full agreement between quantum mechanics and spec ...
that the effective
refractive index
In optics, the refractive index (or refraction index) of an optical medium is a dimensionless number that gives the indication of the light bending ability of that medium.
The refractive index determines how much the path of light is bent, or ...
''n'', at low frequencies, in the space between the plates was less than 1. Barton and Scharnhorst in 1993 claimed that either signal velocity can exceed ''c'' or that imaginary part of ''n'' is negative.
[
A more recent follow-up paper is ]
Explanation
Vacuum fluctuation
In quantum physics, a quantum fluctuation (also known as a vacuum state fluctuation or vacuum fluctuation) is the temporary random change in the amount of energy in a point in space, as prescribed by Werner Heisenberg's uncertainty principle. ...
s exist even in a perfect vacuum. The vacuum fluctuations are influenced by conducting plates nearby. As a
photon
A photon () is an elementary particle that is a quantum of the electromagnetic field, including electromagnetic radiation such as light and radio waves, and the force carrier for the electromagnetic force. Photons are massless, so they a ...
travels through a vacuum its propagation is influenced by these vacuum fluctuations.
A prediction made by this assertion is that the speed of a photon will be increased if it travels between two
Casimir plates
In quantum field theory, the Casimir effect is a physical force acting on the macroscopic boundaries of a confined space which arises from the quantum fluctuations of the field. It is named after the Dutch physicist Hendrik Casimir, who predi ...
. The ultimate effect would be to increase the apparent speed of that photon. The closer the plates are, the stronger the change in the vacuum fluctuations, and the higher the speed of light.
The effect, however, is predicted to be minuscule. A photon traveling between two plates that are 1 micrometer apart would increase the photon's speed by only about one part in 10
36.
[
] This change in light's speed is too small to be detected with current technology, which prevents the Scharnhorst effect from being tested at this time.
Causality
The possibility of
superluminal photons has caused concern because it might allow for the violation of
causality by sending information faster than ''c''.
[
] However, several authors (including Scharnhorst
[) argue that the Scharnhorst effect cannot be used to create causal paradoxes.][
][
]
Possible experimentation
It may be possible to amplify the Scharnhorst effect by replacing Casimir plates with event horizons, an idea informally suggested by American physicist Timothy Retter. In this space, even fewer virtual particles will be present than between Casimir plates thus magnifying the effect. He suggests that rather than light becoming superluminal, that the speed of light c should be redefined to account for this improved medium.
References
{{Reflist, 2
Quantum electrodynamics