Galilean Relativity


Einstein says in The Evolution of Physics:

We really have no choice. We tried to save the Galilean relativity principle by assuming that systems carry the ether along in their motion, but this led to a contradiction with experiment. The only way out is to abandon the Galilean relativity principle and try out the assumption that all bodies move through the calm ether-sea.


Galilean relativity (see Wikipedia) states that the laws of motion are the same in all inertial frames. Galileo Galilei first described this principle in 1632 using the example of a ship travelling at constant velocity, without rocking, on a smooth sea; any observer doing experiments below the deck would not be able to tell whether the ship was moving or stationary.

It is assumed that the medium should move with the motion of inertial frame along with the disturbance, as in the case of sound waves, for Galilean relativity to work. Thus, ether as the medium of light is expected to move with the inertial frame, but there is no experimental evidence found for that.

This can be explained by observing that the inertia associated with the medium of light is several orders of magnitude smaller than the inertia associated with the medium of sound. An object cannot move through a “medium” having the same order of inertia. But such restriction need not apply when the “medium” has a level of inertia several orders of magnitude smaller.

Galilean relativity applies only to objects and medium that has the same order of inertia. We simply have to be aware of this limitation. We need not abandon the Galilean relativity principle.

The error has been in viewing everything physical from the inertial frame of matter.


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