Scharnhorst effect

Last updated

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, Germany. [1] He showed using quantum electrodynamics that the effective refractive index n, at low frequencies, in the space between the plates was less than 1. Gabriel Barton and Scharnhorst in 1993 claimed that either signal velocity can exceed c or that the imaginary part of n is negative. [2]

Contents

Explanation

Vacuum fluctuations exist even in a perfect vacuum. The vacuum fluctuations are influenced by conducting plates nearby. As a photon 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. [3] 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. [4]

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 1036. [5] 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. [6] However, several authors (including Scharnhorst [2] ) argue that the Scharnhorst effect cannot be used to create causal paradoxes. [6] [7] [8]

Related Research Articles

Faster-than-light travel and communication are the conjectural propagation of matter or information faster than the speed of light. The special theory of relativity implies that only particles with zero rest mass may travel at the speed of light, and that nothing may travel faster.

<span class="mw-page-title-main">Speed of light</span> Speed of electromagnetic waves in vacuum

The speed of light in vacuum, commonly denoted c, is a universal physical constant that is exactly equal to 299,792,458 metres per second. According to the special theory of relativity, c is the upper limit for the speed at which conventional matter or energy can travel through space.

A tachyon or tachyonic particle is a hypothetical particle that always travels faster than light. Physicists believe that faster-than-light particles cannot exist because they are inconsistent with the known laws of physics. If such particles did exist they could be used to send signals faster than light and into the past. According to the theory of relativity this would violate causality, leading to logical paradoxes such as the grandfather paradox. Tachyons would exhibit the unusual property of increasing in speed as their energy decreases, and would require infinite energy to slow to the speed of light. No verifiable experimental evidence for the existence of such particles has been found.

<span class="mw-page-title-main">Alcubierre drive</span> Hypothetical FTL transportation by warping space

The Alcubierre drive is a speculative warp drive idea according to which a spacecraft could achieve apparent faster-than-light travel by contracting space in front of it and expanding space behind it, under the assumption that a configurable energy-density field lower than that of vacuum could be created. Proposed by theoretical physicist Miguel Alcubierre in 1994, the Alcubierre drive is based on a solution of Einstein's field equations. Since those solutions are metric tensors, the Alcubierre drive is also referred to as Alcubierre metric.

<span class="mw-page-title-main">Zero-point energy</span> Lowest possible energy of a quantum system or field

Zero-point energy (ZPE) 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. Therefore, even at absolute zero, atoms and molecules retain some vibrational motion. Apart from atoms and molecules, the empty space of the vacuum also 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, and force fields, whose quanta are bosons. 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.

<span class="mw-page-title-main">Quantum vacuum state</span> Lowest-energy state of a field in quantum field theories, corresponding to no particles present

In quantum field theory, the quantum vacuum state is the quantum state with the lowest possible energy. Generally, it contains no physical particles. The term zero-point field is sometimes used as a synonym for the vacuum state of a quantized field which is completely individual.

<span class="mw-page-title-main">Two-photon physics</span> Branch of particle physics concerning interactions between two photons

Two-photon physics, also called gamma–gamma physics, is a branch of particle physics that describes the interactions between two photons. Normally, beams of light pass through each other unperturbed. Inside an optical material, and if the intensity of the beams is high enough, the beams may affect each other through a variety of non-linear effects. In pure vacuum, some weak scattering of light by light exists as well. Also, above some threshold of this center-of-mass energy of the system of the two photons, matter can be created.

<span class="mw-page-title-main">Schwinger effect</span> Decay of strong electromagnetic fields into particles

The Schwinger effect is a predicted physical phenomenon whereby matter is created by a strong electric field. It is also referred to as the Sauter–Schwinger effect, Schwinger mechanism, or Schwinger pair production. It is a prediction of quantum electrodynamics (QED) in which electron–positron pairs are spontaneously created in the presence of an electric field, thereby causing the decay of the electric field. The effect was originally proposed by Fritz Sauter in 1931 and further important work was carried out by Werner Heisenberg and Hans Heinrich Euler in 1936, though it was not until 1951 that Julian Schwinger gave a complete theoretical description.

PVLAS aims to carry out a test of quantum electrodynamics and possibly detect dark matter at the Department of Physics and National Institute of Nuclear Physics in Ferrara, Italy. It searches for vacuum polarization causing nonlinear optical behavior in magnetic fields. Experiments began in 2001 at the INFN Laboratory in Legnaro and continue today with new equipment.

Delbrück scattering, the deflection of high-energy photons in the Coulomb field of nuclei as a consequence of vacuum polarization, was observed in 1975. The related process of the scattering of light by light, also a consequence of vacuum polarization, was not observed until 1998. In both cases, it is a process described by quantum electrodynamics.

<span class="mw-page-title-main">Günter Nimtz</span> German physicist

Günter Nimtz is a German physicist, working at the 2nd Physics Institute at the University of Cologne in Germany. He has investigated narrow-gap semiconductors and liquid crystals. His claims show that particles may travel faster than the speed of light when undergoing quantum tunneling.

Shengwang Du is a professor in the department of physics at The University of Texas at Dallas.

<span class="mw-page-title-main">Modern searches for Lorentz violation</span> Tests of special relativity

Modern searches for Lorentz violation are scientific studies that look for deviations from Lorentz invariance or symmetry, a set of fundamental frameworks that underpin modern science and fundamental physics in particular. These studies try to determine whether violations or exceptions might exist for well-known physical laws such as special relativity and CPT symmetry, as predicted by some variations of quantum gravity, string theory, and some alternatives to general relativity.

In physics, a tachyonic field, or simply tachyon, is a quantum field with an imaginary mass. Although tachyonic particles are a purely hypothetical concept that violate a number of essential physical principles, at least one field with imaginary mass, the Higgs field, is believed to exist. Under no circumstances do any excitations of tachyonic fields ever propagate faster than light—the presence or absence of a tachyonic (imaginary) mass has no effect on the maximum velocity of signals, and so unlike faster-than-light particles there is no violation of causality. Tachyonic fields play an important role in physics and are discussed in popular books.

Measurements of neutrino speed have been conducted as tests of special relativity and for the determination of the mass of neutrinos. Astronomical searches investigate whether light and neutrinos emitted simultaneously from a distant source are arriving simultaneously on Earth. Terrestrial searches include time of flight measurements using synchronized clocks, and direct comparison of neutrino speed with the speed of other particles.

<span class="mw-page-title-main">Schwinger limit</span> Energy scale at which vacuum effects become important

In quantum electrodynamics (QED), the Schwinger limit is a scale above which the electromagnetic field is expected to become nonlinear. The limit was first derived in one of QED's earliest theoretical successes by Fritz Sauter in 1931 and discussed further by Werner Heisenberg and his student Hans Heinrich Euler. The limit, however, is commonly named in the literature for Julian Schwinger, who derived the leading nonlinear corrections to the fields and calculated the rate of electron–positron pair production in a strong electric field. The limit is typically reported as a maximum electric field or magnetic field before nonlinearity for the vacuum of

Searches for Lorentz violation involving photons provide one possible test of relativity. Examples range from modern versions of the classic Michelson–Morley experiment that utilize highly stable electromagnetic resonant cavities to searches for tiny deviations from c in the speed of light emitted by distant astrophysical sources. Due to the extreme distances involved, astrophysical studies have achieved sensitivities on the order of parts in 1038.

<span class="mw-page-title-main">Augusto Sagnotti</span> Italian theoretical physicist

Augusto Sagnotti is an Italian theoretical physicist at Scuola Normale.

<span class="mw-page-title-main">Light-front quantization applications</span> Quantization procedure in quantum field theory

The light-front quantization of quantum field theories provides a useful alternative to ordinary equal-time quantization. In particular, it can lead to a relativistic description of bound systems in terms of quantum-mechanical wave functions. The quantization is based on the choice of light-front coordinates, where plays the role of time and the corresponding spatial coordinate is . Here, is the ordinary time, is a Cartesian coordinate, and is the speed of light. The other two Cartesian coordinates, and , are untouched and often called transverse or perpendicular, denoted by symbols of the type . The choice of the frame of reference where the time and -axis are defined can be left unspecified in an exactly soluble relativistic theory, but in practical calculations some choices may be more suitable than others. The basic formalism is discussed elsewhere.

In quantum chromodynamics, heavy quark effective theory (HQET) is an effective field theory describing the physics of heavy quarks. It is used in studying the properties of hadrons containing a single charm or bottom quark. The effective theory was formalised in 1990 by Howard Georgi, Estia Eichten and Christopher Hill, building upon the works of Nathan Isgur and Mark Wise, Voloshin and Shifman, and others.

References

  1. Scharnhorst, K. (February 1990). "On propagation of light in the vacuum between plates". Physics Letters B. 236 (3): 354–359. Bibcode:1990PhLB..236..354S. doi:10.1016/0370-2693(90)90997-K.
  2. 1 2 Barton, G.; Scharnhorst, K. (1993). "QED between parallel mirrors: light signals faster than c, or amplified by the vacuum". Journal of Physics A . 26 (8): 2037. Bibcode:1993JPhA...26.2037B. doi:10.1088/0305-4470/26/8/024. A more recent follow-up paper is Scharnhorst, K. (1998). "The velocities of light in modified QED vacua". Annalen der Physik . 7 (7–8): 700–709. arXiv: hep-th/9810221 . Bibcode:1998AnP...510..700S. doi:10.1002/(SICI)1521-3889(199812)7:7/8<700::AID-ANDP700>3.0.CO;2-K.
  3. Chown, M. (1990). "Can photons travel 'faster than light'?". New Scientist . 126 (1711): 32. Bibcode:1990NewSc.126...32B.
  4. Cramer, J. G. (December 1990). "FTL Photons". Analog Science Fiction & Fact Magazine. Retrieved 2009-11-26.
  5. "Secret of the vacuum: Speedier light". Science News . 137 (19): 303. 1990.
  6. 1 2 Liberati, S.; Sonego, S.; Visser, M. (2002). "Faster-than-c signals, special relativity, and causality". Annals of Physics . 298 (1): 167–185. arXiv: gr-qc/0107091 . Bibcode:2002AnPhy.298..167L. doi:10.1006/aphy.2002.6233.
  7. Bruneton, J.-P. (2007). "On causality and superluminal behavior in classical field theories. Applications to k-essence theories and MOND-like theories of gravity". Physical Review D . 75 (8): 085013. arXiv: gr-qc/0607055 . Bibcode:2007PhRvD..75h5013B. doi:10.1103/PhysRevD.75.085013.
  8. Milonni, P. W.; Svozil, K. (1990). "Impossibility of measuring faster-than-c signalling by the Scharnhorst effect" (PDF). Physics Letters B . 248 (3–4): 437. Bibcode:1990PhLB..248..437M. doi:10.1016/0370-2693(90)90317-Y.