Albert Einstein published his special theory of relativity in 1905. This theory has been used to explain the odd behavior of electrons and radioactive particles in particle accelerators, the strange behavior of atomic clocks and radioactive particles in motion, and other curious phenomenon involving photons. I will come back to these observations after I discuss the origin of the equation that forms the backbone of special relativity.
The theory of relativity has its roots in an experiment carried out by A. Michelson and E. W. Morley in 1887. They demonstrated experimentally that the velocity of light appears to be the same regardless of the direction it is aimed from a moving source. In this experiment, the velocity of light was measured in reference to Earth’s motion as it orbits the Sun. The instrument used was an interferometer they built on a large slab of sandstone which was floated on a sea of mercury. This made it possible to change the orientation of the instrument and the direction the photons are ejected from their source, and subsequently their direction moving through the interferometer, without disturbing its adjustment. By this means they could compare the velocity of light traveling in various directions. If Earth’s rotation did indeed affect the velocity of the photon, this instrument was easily capable of detecting Earth’s orbital velocity of 29,786 meters per second. The final result of this sensitive experiment indicated that light leaving a source was not influenced by Earth’s rotation as measured in their interferometer.
Of course, this is far different than a bullet short from a moving train. If a bullet is shot in the same direction the train is moving, its velocity is the combined sum of mussel velocity and train velocity; whereas, a bullet shot in the opposite direction is slower because the train’s velocity must be subtracted from mussel velocity. All of this is perfectly reasonable, which caused the scientists at the time to ask why it doesn’t apply to the velocity of light?
The Irish physicist, G. Fitzgerald, suggested that the velocity of light is modified by Earth’s velocity, but cannot be detected in the Michelson-Morley experiment because the length of the instrument (slab of sandstone) shrinks in the direction it is moving. A Dutch physicist by the name of Hendrik Lorentz derived an equation that makes it possible to calculate what the shrinkage would have to be for a given velocity. This article was published in 1892. This equation is known as the Lorentz contraction, and it is always less than one.
Where v is the velocity of the instrument and c is the velocity of light.
Thus, the length of the interferometer would vary according to its velocity with respect to the normal velocity of light as shown in the following equation:
Because the Lorentz contraction is always less than one, the length in motion is always less than the length at rest.
This equation, along with other uses of the Lorentz contraction, forms the basis of the special theory of relativity. I will continue with this discussion in my next blog. Till then be safe and in good health. Kelland—www.vestheory.com
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