The Apparent Incompatibility of the Law of Propagation of Light with the Principle of Relativity

As a result of an analysis of the physical conceptions of time and space, it became evident that in reality there is not the least incompatibility between the principle of relativity and the law of propagation of light, and that by systematically holding fast to both these laws a logically rigid theory could be arrived at.

The law of the propagation of light in vacuo would then have to be replaced by a more complicated law conformable to the principle of relativity.

Every child at school knows, or believes he knows, that this propagation takes place in straight lines with a velocity c = 300,000 km./sec.

Prominent theoretical physicists were therefore more inclined to reject the principle of relativity, in spite of the fact that no empirical data had been found which were contradictory to this principle.

But this result comes into conflict with the principle of relativity set forth in Section V. For, like every other general law of nature, the law of the transmission of light in vacuo must, according to the principle of relativity, be the same for the railway carriage as reference-body as when the rails are the body of reference.

Every child at school knows, or believes he knows, that this propagation takes place in straight lines with a velocity c = 300,000 km./sec.

By means of similar considerations based on observations of double stars, the Dutch astronomer De Sitter was also able to show that the velocity of propagation of light cannot depend on the velocity of motion of the body emitting the light.

The development of theoretical physics shows, however, that we cannot pursue this course.

If a ray of light be sent along the embankment, we see from the above that the tip of the ray will be transmitted with the velocity c relative to the embankment.

At all events we know with great exactness that this velocity is the same for all colours, because if this were not the case, the minimum of emission would not be observed simultaneously for different colours during the eclipse of a fixed star by its dark neighbour.

The assumption that this velocity of propagation is dependent on the direction “in space” is in itself improbable.

At this juncture the theory of relativity entered the arena.

The assumption that this velocity of propagation is dependent on the direction “in space” is in itself improbable.

At all events we know with great exactness that this velocity is the same for all colours, because if this were not the case, the minimum of emission would not be observed simultaneously for different colours during the eclipse of a fixed star by its dark neighbour.

By means of similar considerations based on observations of double stars, the Dutch astronomer De Sitter was also able to show that the velocity of propagation of light cannot depend on the velocity of motion of the body emitting the light.

The epoch-making theoretical investigations of H. A. Lorentz on the electrodynamical and optical phenomena connected with moving bodies show that experience in this domain leads conclusively to a theory of electromagnetic phenomena, of which the law of the constancy of the velocity of light in vacuo is a necessary consequence.

Who would imagine that this simple law has plunged the conscientiously thoughtful physicist into the greatest intellectual difficulties?

In short, let us assume that the simple law of the constancy of the velocity of light c (in vacuum) is justifiably believed by the child at school.

In short, let us assume that the simple law of the constancy of the velocity of light c (in vacuum) is justifiably believed by the child at school.

At this juncture the theory of relativity entered the arena.

If every ray of light is propagated relative to the embankment with the velocity c, then for this reason it would appear that another law of propagation of light must necessarily hold with respect to the carriage—a result contradictory to the principle of relativity.

At all events we know with great exactness that this velocity is the same for all colours, because if this were not the case, the minimum of emission would not be observed simultaneously for different colours during the eclipse of a fixed star by its dark neighbour.

In view of this dilemma there appears to be nothing else for it than to abandon either the principle of relativity or the simple law of the propagation of light in vacuo.

But this result comes into conflict with the principle of relativity set forth in Section V. For, like every other general law of nature, the law of the transmission of light in vacuo must, according to the principle of relativity, be the same for the railway carriage as reference-body as when the rails are the body of reference.

At all events we know with great exactness that this velocity is the same for all colours, because if this were not the case, the minimum of emission would not be observed simultaneously for different colours during the eclipse of a fixed star by its dark neighbour.

Every child at school knows, or believes he knows, that this propagation takes place in straight lines with a velocity c = 300,000 km./sec.

At all events we know with great exactness that this velocity is the same for all colours, because if this were not the case, the minimum of emission would not be observed simultaneously for different colours during the eclipse of a fixed star by its dark neighbour.

THERE is hardly a simpler law in physics than that according to which light is propagated in empty space.

THERE is hardly a simpler law in physics than that according to which light is propagated in empty space.

THERE is hardly a simpler law in physics than that according to which light is propagated in empty space.

THERE is hardly a simpler law in physics than that according to which light is propagated in empty space.