March 29, 1919, there was an eclipse of
the Sun. It was a particularly
important eclipse. For years astronomers
had eagerly awaited it, since it would enable them to check a
revolutionary new theory in physics,
proposed four years earlier by a scientist named Albert Einstein.
the day of the eclipse one group of astronomers was stationed in
northern Brazil, another on an island of the western coast of
Africa. Delicate cameras were set up and waiting.
Pictures would be taken during the eclipse — not of the eclipsed Sun,
but of the stars
that appear in the suddenly darkened sky around the Sun.
had said that the position of the stars would be somewhat
changed, since the rays of starlight passing near the Sun
would be bent by the Sun's mass.To many
scientists this sounded impossible. How could light, which
was immaterial, they argued, be affected by gravity?
If Einstein were correct, the picture of the Universe
built up by the great Newton more than two hundred
years earlier would have to be considerably
came. The pictures were taken and developed. The
distances of the stars from the Sun and from one another
were carefully measured. There could be no doubt about
the results. Einstein was right. The light rays had been
bent by the attraction of the Sun. One of the key
points of Einstein's theory had been
It was said that
only twelve persons in the world really understood exactly at that time
meant in his theory of relativity. Yet throughout the civilized world everyone
who read the newspapers knew that Einstein was
a genius, that he had overthrown
the foundations on which physics, chemistry,and
astronomy had rested for two hundred years, and upset all earlier
concepts of the Universe. Later they learned that this revolution had
made possible the development of the
photoelectric cell, television, a whole series of
electronic inventions, and, finally, the harnessing of atomic energy.
More than fifty years
have now passed since Einstein
put forward the principle of relativity. His theory, which seemed a mere
flight of the imagination to many at first, is now the cornerstone of
modern physics. Indeed,
cannot exist without the theory of relativity, just as
it cannot exist without the concept of atoms and molecules.
A vast number of physical phenomena could never be explained without the
relativity. Particle accelerators and calculations of nuclear reactions are
based on it.
It is not too difficult to grasp the simpler aspects of the theory of
relativity. We have little difficulty in understanding
that a fly walking along the top of a moving train
moves at one speed relative to the train and at another
relative to the ground. It would appear to be moving at
still another speed from the point ofview of an
observer in space who could consider the motion of the Earth' in addition to the motion
of the train and the fly. From these facts it is not hard to go on
to Einstein's contention that there is no absolute motion and no
absolute rest: that all motion in the
Universe is relative to some
other motion. Indeed, the very notions of space and time
are relative. The interval
between two events, like the distance between them in space, has to refer to
some frame if it is to have meaning. The simple words "at one and the same time" are just as
meaningless as the words "in one and the same place".
From here on, however, the way becomes more difficult.
Our story must stop before it reaches the point where sentences
turn into equations. If some of you, however, feel
determined to learn more about this
remarkable theory, there is a very good book about it,
written in simple and
understandable language. It is a short book of only 60 pages,
with many pictures, and
is called "What Is the Theory of Relativity?". The authors are the late
Academician Lev Landay and Y. Rumer. An English edition
of the book was published by the Foreign Languages Publishing
House in Moscow.