According to Einstein’s theory of relativity, the speed of light in a vacuum is an absolute constant, and modern physics is based on this assumption. Not surprisingly, early measurements of the speed of light varied considerably, but by 1927, the measured values had converged to 299,796 kilometers per second. . . . However, all around the world from about 1928 to 1945, the speed of light dropped by about 20 kilometers per second. . . . In the late 1940s the speed of light went up again by about 20 kilometers per second and a new consensus developed around the higher value. In 1972, the embarrassing possibility of variations in c was eliminated when the speed of light was fixed by definition. In addition, in 1983 the unit of distance, the meter, was redefined in terms of light. Therefore if any further changes in the speed of light happen, we will be blind to them because the length of the meter will change with the speed of light. (The meter is now defined as the length of the path traveled by light in a vacuum in 1/ 299,792,458 of a second.) The second is also defined in terms of light: it is the duration of 9,192,631,770 periods of vibration of the light given off by cesium 133 atoms in a particular state of excitation (technically defined as the transition between the two hyperfine levels of the ground state).
How can the drop in c between 1928 and 1945 be explained? This remarkable episode in the history of physics is now generally attributed to the psychology of metrologists. Brian Petley, a leading British metrologist, explained it thus: The tendency for experiments in a given epoch to agree with one another has been described by the delicate phrase “intellectual phase locking.” Most metrologists are very conscious of the possible existence of such effects; indeed ever-helpful colleagues delight in pointing them out! Aside from the discovery of mistakes, the near completion of the experiment brings more frequent and stimulating discussion with interested colleagues and the preliminaries to writing up the work add a fresh perspective. All of these circumstances combine to prevent what was intended to be “the final result” from being so in practice, and consequently the accusation that one is most likely to stop worrying about correction when the value is closest to other results is easy to make and difficult to refute.
Originally posted by DJW001
reply to post by primalfractal
You are already making the assumption that light is a wave that propagates in a medium. It is true that light displays behaviors that are analogous to such waves, eg; polarization and interference, and they can be treated mathematically as though they were. However, they are not. A photon's "wavelength" is a measure of the particles' energy, not its physical extension. It is a massless particle's equivalent to mass.
Kind of create a fold in the movement of light.
Superluminal speeds are associated with a phenomenon known as anomalous dispersion,
Originally posted by primalfractal
Every physicist is taught that information cannot be transmitted faster than the speed of light. Yet laboratory experiments done over the last 30 years clearly show that some things appear to break this speed limit without upturning Einstein's special theory of relativity. Now, astrophysicists in the US have seen such superluminal speeds in space – which could help us to gain a better understanding of the composition of the regions between stars. . . .
Superluminal speeds are associated with a phenomenon known as anomalous dispersion, whereby the refractive index of a medium (such as an atomic gas) increases with the wavelength of transmitted light. When a light pulse – which is comprised of a group of light waves at a number of different wavelengths – passes through such a medium, its group velocity can be boosted to beyond the velocity of its constituent waves. However, the energy of the pulse still travels at the speed of light, which means that information is transferred in agreement with Einstein's theory.