The Einstein Theory of Relativity | Page 3

"necessary truths,"
but mere empirical laws; in order to establish this view, self-consistent
geometries were constructed upon assumptions other than those of

Euclid. In these geometries the sum of the angles of a triangle is not
two right angles, and the departure from two right angles increases as
the size of the triangle increases. It is often said that in non-Euclidean
geometry space has a curvature, but this way of stating the matter is
misleading, since it seems to imply a fourth dimension, which is not
implied by these systems.
Einstein supposes that space is Euclidean where it is sufficiently remote
from matter, but that the presence of matter causes it to become slightly
non-Euclidean--the more matter there is in the neighborhood, the more
space will depart from Euclid. By the help of this hypothesis, together
with his previous theory of relativity, he deduces gravitation--very
approximately, but not exactly, according to the Newtonian law of the
inverse square. The minute differences between the effects deduced
from his theory and those deduced from Newton are measurable in
certain cases. There are, so far, three crucial tests of the relative
accuracy of the new theory and the old.
(1) The perihelion of Mercury shows a discrepancy which has long
puzzled astronomers. This discrepancy is fully accounted for by
Einstein. At the time when he published his theory, this was its only
experimental verification.
(2) Modern physicists were willing to suppose that light might be
subject to gravitation--i.e., that a ray of light passing near a great mass
like the sun might be deflected to the extent to which a particle moving
with the same velocity would be deflected according to the orthodox
theory of gravitation. But Einstein's theory required that the light
should be deflected just twice as much as this. The matter could only be
tested during an eclipse among a number of bright stars. Fortunately a
peculiarly favourable eclipse occurred last year. The results of the
observations have now been published, and are found to verify
Einstein's prediction. The verification is not, of course, quite exact;
with such delicate observations that was not to be expected. In some
cases the departure is considerable. But taking the average of the best
series of observations, the deflection at the sun's limb is found to be
1.98'', with a probable error of about 6 per cent., whereas the deflection
calculated by Einstein's theory should be 1.75''. It will be noticed that
Einstein's theory gave a deflection twice as large as that predicted by
the orthodox theory, and that the observed deflection is slightly larger

than Einstein predicted. The discrepancy is well within what might be
expected in view of the minuteness of the measurements. It is therefore
generally acknowledged by astronomers that the outcome is a triumph
for Einstein.
(3) In the excitement of this sensational verification, there has been a
tendency to overlook the third experimental test to which Einstein's
theory was to be subjected. If his theory is correct as it stands, there
ought, in a gravitational field, to be a displacement of the lines of the
spectrum towards the red. No such effect has been discovered.
Spectroscopists maintain that, so far as can be seen at present, there is
no way of accounting for this failure if Einstein's theory in its present
form is assumed. They admit that some compensating cause may be
discovered to explain the discrepancy, but they think it far more
probable that Einstein's theory requires some essential modification.
Meanwhile, a certain suspense of judgment is called for. The new law
has been so amazingly successful in two of the three tests that there
must be some thing valid about it, even if it is not exactly right as yet.
Einstein's theory has the very highest degree of aesthetic merit: every
lover of the beautiful must wish it to be true. It gives a vast unified
survey of the operations of nature, with a technical simplicity in the
critical assumptions which makes the wealth of deductions astonishing.
It is a case of an advance arrived at by pure theory: the whole effect of
Einstein's work is to make physics more philosophical (in a good sense),
and to restore some of that intellectual unity which belonged to the
great scientific systems of the seventeenth and eighteenth centuries, but
which was lost through increasing specialization and the overwhelming
mass of detailed knowledge. In some ways our age is not a good one to
live in, but for those who are interested in physics there are great
compensations.

THE EINSTEIN THEORY OF RELATIVITY
A Concise Statement by Prof. H. A. Lorentz, of the University of
Leyden
The total eclipse of the sun of May 29, resulted in a striking
confirmation of the new theory of the universal attractive power of
gravitation