The Einstein Theory of Relativity | Page 4

developed by Albert Einstein, and thus reinforced the
conviction that the defining of this theory is one of the most important

steps ever taken in the domain of natural science. In response to a
request by the editor, I will attempt to contribute something to its
general appreciation in the following lines.
For centuries Newton's doctrine of the attraction of gravitation has been
the most prominent example of a theory of natural science. Through the
simplicity of its basic idea, an attraction between two bodies
proportionate to their mass and also proportionate to the square of the
distance; through the completeness with which it explained so many of
the peculiarities in the movement of the bodies making up the solar
system; and, finally, through its universal validity, even in the case of
the far-distant planetary systems, it compelled the admiration of all.
But, while the skill of the mathematicians was devoted to making more
exact calculations of the consequences to which it led, no real progress
was made in the science of gravitation. It is true that the inquiry was
transferred to the field of physics, following Cavendish's success in
demonstrating the common attraction between bodies with which
laboratory work can be done, but it always was evident that natural
philosophy had no grip on the universal power of attraction. While in
electric effects an influence exercised by the matter placed between
bodies was speedily observed--the starting-point of a new and fertile
doctrine of electricity--in the case of gravitation not a trace of an
influence exercised by intermediate matter could ever be discovered. It
was, and remained, inaccessible and unchangeable, without any
connection, apparently, with other phenomena of natural philosophy.
Einstein has put an end to this isolation; it is now well established that
gravitation affects not only matter, but also light. Thus strengthened in
the faith that his theory already has inspired, we may assume with him
that there is not a single physical or chemical phenomenon--which does
not feel, although very probably in an unnoticeable degree, the
influence of gravitation, and that, on the other side, the attraction
exercised by a body is limited in the first place by the quantity of
matter it contains and also, to some degree, by motion and by the
physical and chemical condition in which it moves.
It is comprehensible that a person could not have arrived at such a
far-reaching change of view by continuing to follow the old beaten
paths, but only by introducing some sort of new idea. Indeed, Einstein
arrived at his theory through a train of thought of great originality. Let

me try to restate it in concise terms.

THE EARTH AS A MOVING CAR
Everyone knows that a person may be sitting in any kind of a vehicle
without noticing its progress, so long as the movement does not vary in
direction or speed; in a car of a fast express train objects fall in just the
same way as in a coach that is standing still. Only when we look at
objects outside the train, or when the air can enter the car, do we notice
indications of the motion. We may compare the earth with such a
moving vehicle, which in its course around the sun has a remarkable
speed, of which the direction and velocity during a considerable period
of time may be regarded as constant. In place of the air now comes, so
it was reasoned formerly, the ether which fills the spaces of the
universe and is the carrier of light and of electro-magnetic phenomena;
there were good reasons to assume that the earth was entirely
permeable for the ether and could travel through it without setting it in
motion. So here was a case comparable with that of a railroad coach
open on all sides. There certainly should have been a powerful "ether
wind" blowing through the earth and all our instruments, and it was to
have been expected that some signs of it would be noticed in
connection with some experiment or other. Every attempt along that
line, however, has remained fruitless; all the phenomena examined
were evidently independent of the motion of the earth. That this is the
way they do function was brought to the front by Einstein in his first or
"special" theory of relativity. For him the ether does not function and in
the sketch that he draws of natural phenomena there is no mention of
that intermediate matter.
If the spaces of the universe are filled with an ether, let us suppose with
a substance, in which, aside from eventual vibrations and other slight
movements, there is never any crowding or flowing of one part
alongside of another, then we can imagine fixed points existing in it;
for example, points in a straight line, located