Physics
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Relativistic time
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Relativistic time
The measurement of time represents in relativity (special and general) an operation strictly dependent on the kinematic and/or gravitational conditions in which the observer performs it.
For example, μ particles, or muons, present in the swarms of particles produced by cosmic ray impacts in the atmosphere, hit the Earth’s surface at speeds very close to that of light after a flight time of the order of 200 microseconds. Muons are unstable particles that – in the laboratory – spontaneously decay in only 2 microseconds. The increase of their average lifetime in atmospheric swarms is justified by the time dilation provided by special relativity for moving observers.
Time dilation phenomena also occur for the theory of general relativity. In this theory, Einstein effect consists in a red shift manifested by electromagnetic radiation radiated by celestial bodies with considerable gravitational field (gravitational red shift).
Near the Sun, this shift reaches 0.01 Å, equivalent in frequency – and therefore in the local time scale – to a time dilation of \(2\times 10^{-6}\) seconds per second. However, the time dilation would increase to 15 times larger values if the star were a compact white dwarf with very strong surface intensity of the attractive field, such as Sirius B. Finally, the complete zeroing of the time course (infinitely large dilation) would occur at the “event surface” surrounding a black hole.
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