Hughes–Drever experiment

Hughes - Drever experiments ( also watches comparison, Uhrenanisotropie, Massenisotropie, or Energieisotropie experiments ) are used for the spectroscopic examination of the isotropy of the mass or of space. These experiments test fundamental statements of both the special and the general theory of relativity., As with the Michelson Morley experiments by the presence of a preferred reference system or variations are examined by the Lorentz, which also relates to the validity of the equivalence principle. In contrast to the Michelson-Morley Hughes - Drever experiments, however, the matter relating to the isotropy of the interaction itself, ie of protons, neutrons, and electrons. The accuracy of scoring makes this type of analyzes performed to date experiments with the most precise measurements of the theory of relativity at all (see tests of special relativity ). [A 1] [A 2] [A 3] [A 4] [A 5] [ A 6 ]

Experiments by Hughes and Drever

Giuseppe Cocconi and Edwin Salpeter (1958 ) pointed out that the inertia of matter depends on the distribution of the surrounding masses, when the Mach principle is correct. This would lead to an anisotropy of inertia in different directions and could be detected by spectroscopic observation of Zeeman effects in atomic nuclei.

Vernon Hughes et al. (1960) and Ronald Drever (1961 ) conducted independently as similar experiments. The core of lithium -7 was used, which has a ground state spin 3/ 2, and are thus exist in accordance with the allowable magnetic speed in a magnetic quantum four magnetic energy levels. In Massenisotropie occurs no shift of the energy levels, and hence only a single resonance line should exist in anisotropy there is a triplet resonance line or widening. Indeed, it was found there is no frequency shift in the energy levels, the maximum anisotropy could be limited to 0.04 Hz = 10-25 GeV due to the high degree of accuracy.

Robert H. Dicke (1961 ), however, showed that the null result is quite compatible with the Mach's principle, as long as the spatial anisotropy for all particles is the same. The null result therefore shows that the Massenanisotropieeffekte, where they exist, for all particles are the same and hence not locally observable.

Modern interpretation

During this experiment was originally based on the Mach principle, it is often interpreted in modern works as an important verification of Lorentz invariance and thus the special theory of relativity. Because anisotropy must (usually the CMB rest frame as ether ) are present even in the presence of a preferred reference frame, therefore, the negative results of the Hughes - Drever experiment - such as the Michelson -Morley experiments - as refutations of the existence of such a system are considered. In particular, the physicist Mark P. Haugan and Clifford Will were able to show that these experiments can be interpreted as testing whether the limit velocity of matter with the speed of light matches as required by the special theory of relativity. If they are different, the characteristics and frequency of the interactions of matter change. And since it is a basic statement of the equivalence principle of general relativity, that locally in a freely falling reference frames, the Lorentz invariance is valid = Local Lorentz invariance ( LLI), concerning the results of this experiment, both the special and the general theory of relativity. [A 1] [ A 2 ]

Due to the fact that different frequencies can be compared here, and these in turn can be regarded as a watch, these experiments are also called " clock comparison" - means (clock comparative ) experiments [A 3], [ A-4 ].

More recent experiments

In addition to violations of Lorentz invariance by the presence of a preferred reference system or the Mach 's principle, also possible spontaneous breaks the Lorentz invariance and related to the CPT theorem have come into view in the wake of developments in quantum gravity. To check all these effects and more precise variations of the original experiments are conducted to date. These measurements refer to neutrons and protons, and ( can thereby suppressing magnetic influences ) through the use of spin-polarized systems and the accuracy Komagnetometern could be increased considerably. In addition, with the aid of the spin-polarized electrons and the torsion sector is verified. [ A-5 ] [ A6 ]

All results were negative so far, so still there is no indication of the existence of a preferred reference system, or otherwise violate the Lorentz invariance. The values ​​of the following table refer to the parameters, which is given by the standard model extension (SME, one of the test theories of special relativity ). This model contains several parameters for each deviation from the Lorentz invariance. Since in each of these experiments a number of parameters is checked, only the value of the maximum sensitivity is represented (for the detailed statement see the individual items): [ A-3 ] [A 7], [ A-4 ]