Vacuum energy
The vacuum energy is the energy of " empty space " in the complete absence of particles of the Standard Model of elementary particle physics.
Observations and delimitation
As an experimental indication of the vacuum energy and the resulting vacuum fluctuations of the Casimir effect and the Lamb shift are often interpreted. However, it is possible to derive the Casimir effect, even without the use of vacuum fluctuations. The Lamb shift is a phenomenon in an interacting quantum field theory, which therefore can not be attributed to the vacuum energy; the misunderstanding arises from the fact that although he is a consequence of virtual particle-antiparticle pair production, but which do not take place in the vacuum, but is due to interactions of fields.
The vacuum energy is considered as a possible candidate for dark energy, which would provide an explanation for the observed accelerated expansion of the universe in astronomy. The amount of vacuum energy represents in this context, one of the biggest problems of modern physics, as found experimentally and vary the theoretically predicted values for the vacuum energy as dark energy from each other: the basis of observation, the energy density of the vacuum to a value of the order of 10 - 9 is estimated to 10-11 J/m3, it is thus by a factor of approximately 10,120 lower than the theoretical calculations.
Historical development
After the abandonment of the empty space fulfilling the ether as a medium for the propagation of waves and frame of reference for motion of bodies prevailed in classical physics the idea of neither matter, nor any form of energy containing vacuum.
But already the law of radiation discovered by Max Planck in 1911 his " second theory " suggested a zero-point energy of the electromagnetic field in a vacuum, as an independent on the temperature size ½ occurred. However, Planck measured the first no importance in terms of experimental proof.
With similar considerations Albert Einstein and Otto Stern in 1913 came to the conclusion that the zero- point fluctuations of the electromagnetic field would be in the absolute zero of temperature.
Building on the work of Planck suggested Walther Nernst before and at the other to a zero-point fluctuations of the electromagnetic field to the value ½, that the entire universe is filled with zero-point energy.
In 1927, Werner Heisenberg formulated his uncertainty principle, which is the basis of the zero-point energy in each quantum mechanical system.
Georges Lemaître had done, the pioneering theoretical work on the Big Bang and the expansion of the universe, found in 1934 a match of the vacuum energy with the cosmological constant of Einstein (1917 ), the introduction of Einstein but later than the designated "biggest blunder " of his life.
In a study of the van der Waals forces used in colloid solutions Hendrik Casimir together with Dirk Polder 1947 a quantum mechanical approach, which led to a discussion with Niels Bohr. Bohr expressed this, "it must have something to do with zero point fluctuations ". Casimir was the idea after, the attraction between neutral atoms could perhaps only be based on vacuum fluctuations, and published in 1948 his fundamental work about the attraction between two perfectly conducting plates. In it he described a theoretical test arrangement with two metal plates in a vacuum, which should attract due to the vacuum energy of the electromagnetic quantum field to his calculations ( Casimir effect).
Getting the appropriate tests to demonstrate the Casimir force in vacuum were carried out in 1958 by Marcus Spaarnay, but with a measurement error of about 100%. Gradually, the measurements of the Casimir force reached ( value for two levels of 1 cm ² area at a distance 1 micron: 10-7 N ) has a higher accuracy, for example, the measurement error was at van Blokland and Oveerbeeks 1978 25% and in 1996, only Steven Lamoreaux 5%.
In recent years, also found the cosmological constant, which is closely related to the curvature of space-time, again more attention, especially since it is now considered small positive energy density of the vacuum. A more recent explanation for the cosmological constant, for example, provides a cyclic universe.
Details
The quantum field theory is not considered a vacuum as completely empty. Even in the ground state, the lowest possible energy level, the Heisenberg uncertainty principle allows the formation of so-called " virtual particles " and fields. Virtual particle pairs are particle-antiparticle pairs that exist only briefly and then wipe again. The vacuum energy can thus allow particles of the Standard Model arise in this otherwise empty space. The constantly taking place mutual destruction ( annihilation) of the resulting particle pairs prevents global violation of applicable energy conservation.
Stephen Hawking has the particle generation of the vacuum energy. Well as a mechanism for the " evaporation " of black holes described ( Hawking radiation)
Some researchers also suggest that the vacuum energy is discussed in cosmology dark energy has a significant impact on the cosmological constant and thus the temporal evolution of the universe. There is but still no convincing theoretical basis. John Archibald Wheeler calculated taking into account the requirements in force up to the Planck length of 10-33 cm quantum laws have an energy density of the vacuum of 10108 J/cm3.
Others
Vacuum energy has been explored in the Breakthrough Propulsion Physics Project of NASA.