The Einstein Theory of Relativity | Page 2

nature; it was found, however, that
they would not conform to the rapid motions apparent in
electrodynamics.
"This led the Dutch professor, Lorentz, and myself to develop the
theory of special relativity. Briefly, it discards absolute time and space
and makes them in every instance relative to moving systems. By this
theory all phenomena in electrodynamics, as well as mechanics,

hitherto irreducible by the old formulae--and there are multitudes--were
satisfactorily explained.
"Till now it was believed that time and space existed by themselves,
even if there was nothing else--no sun, no earth, no stars--while now
we know that time and space are not the vessel for the universe, but
could not exist at all if there were no contents, namely, no sun, earth
and other celestial bodies.
"This special relativity, forming the first part of my theory, relates to all
systems moving with uniform motion; that is, moving in a straight line
with equal velocity.
"Gradually I was led to the idea, seeming a very paradox in science,
that it might apply equally to all moving systems, even of difform
motion, and thus I developed the conception of general relativity which
forms the second part of my theory."
As summarized by an American astronomer, Professor Henry Norris
Russell, of Princeton, in the Scientific American for November 29,
Einstein's contribution amounts to this:
"The central fact which has been proved--and which is of great interest
and importance--is that the natural phenomena involving gravitation
and inertia (such as the motions of the planets) and the phenomena
involving electricity and magnetism (including the motion of light) are
not independent of one another, but are intimately related, so that both
sets of phenomena should be regarded as parts of one vast system,
embracing all Nature. The relation of the two is, however, of such a
character that it is perceptible only in a very few instances, and then
only to refined observations."
Already before the war, Einstein had immense fame among physicists,
and among all who are interested in the philosophy of science, because
of his principle of relativity.
Clerk Maxwell had shown that light is electro-magnetic, and had
reduced the whole theory of electro-magnetism to a small number of
equations, which are fundamental in all subsequent work. But these
equations were entangled with the hypothesis of the ether, and with the
notion of motion relative to the ether. Since the ether was supposed to
be at rest, such motion was indistinguishable from absolute motion.
The motion of the earth relatively to the ether should have been
different at different points of its orbit, and measurable phenomena

should have resulted from this difference. But none did, and all
attempts to detect effects of motions relative to the ether failed. The
theory of relativity succeeded in accounting for this fact. But it was
necessary incidentally to throw over the one universal time, and
substitute local times attached to moving bodies and varying according
to their motion. The equations on which the theory of relativity is based
are due to Lorentz, but Einstein connected them with his general
principle, namely, that there must be nothing, in observable phenomena,
which could be attributed to absolute motion of the observer.
In orthodox Newtonian dynamics the principle of relativity had a
simpler form, which did not require the substitution of local time for
general time. But it now appeared that Newtonian dynamics is only
valid when we confine ourselves to velocities much less than that of
light. The whole Galileo-Newton system thus sank to the level of a first
approximation, becoming progressively less exact as the velocities
concerned approached that of light.
Einstein's extension of his principle so as to account for gravitation was
made during the war, and for a considerable period our astronomers
were unable to become acquainted with it, owing to the difficulty of
obtaining German printed matter. However, copies of his work
ultimately reached the outside world and enabled people to learn more
about it. Gravitation, ever since Newton, had remained isolated from
other forces in nature; various attempts had been made to account for it,
but without success. The immense unification effected by
electro-magnetism apparently left gravitation out of its scope. It seemed
that nature had presented a challenge to the physicists which none of
them were able to meet.
At this point Einstein intervened with a hypothesis which, apart
altogether from subsequent verification, deserves to rank as one of the
great monuments of human genius. After correcting Newton, it
remained to correct Euclid, and it was in terms of non-Euclidean
geometry that he stated his new theory. Non-Euclidean geometry is a
study of which the primary motive was logical and philosophical; few
of its promoters ever dreamed that it would come to be applied in
physics. Some of Euclid's axioms were felt to be not