FROM COPERNICUS TO EINSTEIN
*
From Coper KLICTULS JL
BY HANS REICHENBAGH Translated by Ralph B.
Winn
NEW YORK PHIL...
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FROM COPERNICUS TO EINSTEIN
*
From Coper KLICTULS JL
BY HANS REICHENBAGH Translated by Ralph B.
Winn
NEW YORK PHILOSOPHICAL LIBRARY, MCMXL I I
INC.
FROM
COPERNICUS
TO
EINSTEIN
COPYRIGHT MCMXLII BY
PHILOSOPHICAL 15
INC. LIBRARY, EAST 40TH STREET, NEW YORK
Composed and Printed in the United States of America By Steingould Corp., New York
TYPOGRAPHY BY SIDNEY SOLOMON
CONTENTS CHAPTER
World
1.
The Copernican View
2.
Ether
29
3.
49
4.
The The
5.
General Theory of Relativity
6.
Space and Time
of the
Special Theory of Relativity Relativity of
Motion
6201251
11
73 85
107
ILLUSTRATIONS FIGURE 1.
A Tycho
2.
Roemer s Observation
3.
The Phenomenon
4.
The Total Spectrum The Diagram of Michelson s Experiment
5. 6.
A
Brahe s Sextant
7.
A Diagram of
8.
Einstein
9.
The Curvature
s
32
Measurement
38
46
54
of the
59 63
86
Experiment"
of Light-Rays in Einstein
10.
The
11.
Major Segrave s at
Moon
the Course of a Light-Signal
"Box
Einstein
s
of Interference
of the of Speed Light
Diagram
of Jupiter
20
Tower
Full Speed
in
1,000
Potsdam
s
Box
95 100
Horsepower Auto 1
10
Chapter
1
:
THE COPERNICAN VIEW OF THE WORLD
THIS
little book purports to serve as an introduction to the great problems of space, time and motion. The in
concerned with are very old. Men have been forming ideas concerning space and time since times im memorial, and curiously enough, have been writing and quiries
it is
fighting about these things with the greatest interest, even fanaticism. This has been a strange strife, indeed, having little to
do with economic
necessities
;
it
has always dealt
with abstract things, far removed from our daily life and with no direct influence upon our daily activities. Why
do
we need
earth or
Can
know whether the sun revolves around the vice versa? What business of ours is it, anyway? to
knowledge be of any use to us? No sooner have we uttered these questions than we become aware of their foolishness. It may not be of any use to us, but we want to know something about these problems. We do not want to go blindly through the world. We desire more than a mere existence. We need this
these cosmic perspectives in order to be able to experi ence a feeling for our place in the world. The ultimate
the meaning of our actions and as to the questions as to meaning of life in general always tend to involve astro nomical problems. Here lies the mystery surrounding 11
From Copernicus To
Einstein
wonder we experience at the sight of the starry sky, the wonder growing in proportion to our understanding of immense distances of space and of the stars inner nature. Here is the source of scientific astronomy, here
as well as
lies
the
popular astronomy.
These two branches have diverged
in the course of
Astronomy, as a science, has come to primitive wonder: instead, it approaches the
their development.
forget
its
realm of
stars
with sober research and calculation. This
disenchantment with
its
subject-matter,
which
scientific
study invariably entails, has permeated astronomy to a greater degree than the layman realizes. In observing the
astronomers of today, culate,
how
lations,
one
nothing
is
little
how
they measure, take notes, cal
attention fiiey
pay
to
mysterious specu be the find wonderful struc to may surprised ture of learning so cut and dry at a close range. Yet
feeling of
more wrong and more objectionable than the a heartbreaking loss, with which some people
regard the vanishing mysticism of the skies. Although science may have destroyed a few naive fantasies, what she has put in their place can well bear the loss.
is
so
immensely greater that we
perseverance and energy, of course, to com prehend the discoveries of science; but whoever under takes the study is bound to learn many more surprising It takes
from
than a naive study of nature can disclose. Scientific astronomy has always exercised, in fact, a great
things
influence
it
upon everyday thinking and upon
conception of the universe. If 12
it is difficult
the popular
today to pro-
The Copernican View
of the
World
nounce the name of Copernicus without thinking of a turning point of history,
it is
name
not only because the
connected with a profound transformation in the science, but also because all our knowledge and thinking have been deeply affected by his discovery. The statement is
that the earth does not occupy the center of the
means more than an astronomical asserting that
man
is
fact;
we
world
interpret
as
not the center of the world, that
to us everything which appears large and mighty
reality of the smallest significance,
cosmic standards.
it
The
statement has
as a result of scientific
thousands of years, yet
is
in
when measured by been made possible
of development in the course it definitely contradicts our im
mediate experience. It takes a great deal of training in no to believe in it at all Nowadays we are thinking because we have been longer conscious of these things, since childhood in the Copernican view of
brought up
the world. However,
it
cannot be denied that the view
our senses, that every immediate the evidence shows the earth as standing still while
belies the testimony of
heavens are moving. And who among us can declare in the tremendous all seriousness that he is able to imagine
comprehend the cosmic distances The signifi earthly ways of measurement? in the fact that he lies
size of the sun or to
defying all cance of Copernicus
precisely
all broke with an old belief apparently supported by immediate sensory experiences. He could do it only be
cause he had at his disposal a considerable
accumulated
scientific
thought and
amount of
scientific data,
only 13
From Copernicus To
Einstein
because he himself had followed the road of disillusion
ment
knowledge before he glimpsed new and broader
in
perspectives.
If
we
endeavor
to trace, in the
following pages, the
development of the problems of space and time, begin ning with the discovery of Copernicus and closing with the still less accessible theory of the Copernicus of our day, we have no other alternative than to apply hard scientific
to
thought
every step of the way.
that the discoveries of
modern
s
doctrines are by no
add
made new scientific materials.
science have been
possible only by the abundance of
Einstein
We must
means an outgrowth
of
astronomical reflections alone; they are grounded in the facts of the theory of electricity
able to
quainted with
all of their sources.
several sources tivity.
and light
comprehend them only insofar
While
is
the
as well. as
we
We are get ac
This derivation from
characteristic of the theory of rela
modern source gave
rise to the special
theory of relativity, the older sources provided the terial for the construction of the tivity,
in
ma
general theory of rela
which the old and new knowledge became
blended in a magnificent unity. In this chapter we shall deal with old material in the next two chapters we shall present the special theory of ;
and its origin; and the last three chapters will be devoted to the blending of the material and, therefore, relativity
to the general theory of relativity.
The
world-picture found by Copernicus goes back to the ancient Greeks. It was systematized about 140 A.D. 14
The Copernican View
of the
World
by Ptolemy Claudius of Alexandria and outlined in his famous work Almagest. The most important feature of the Ptolemaic scheme of the universe is the principle that the earth
is
the center of the world.
The heavenly
globe revolves around it; and Ptolemy knew full well that it has the same spherical shape below the horizon,
which
knew
it
assumes above the horizon. In
fact,
Ptolemy
a sphere. His proofs to this knowledge of astronomy. He shows, the existence of curvature from north to south.
even that the earth
is
effect reveal a great first
As
of
all,
the Polar Star stands higher in the north and lower
in the south, the surface of the earth
The. proof
ingly curved.
from west
to east reveals
must be correspond
of the existence of curvature
even better observation.
When
the clocks are set by the sun in two places located west and east, and when an eclipse of the moon is thus ob served,
it
eclipse
is
will be seen at different times. However, the a single objective event and should be seen
everywhere
same time. Hence we conclude that the two places are not in accord. This can
at the
the clocks at
*
be accounted for by the curvature of the earth in the west-east direction the sun passes the line of the meridian :
at different
moments
in different places.
In spite of the recognition of the spherical shape of the earth, Ptolemy was far from admitting its movement
He contended,
on the contrary, that
it
was impossible for
the earth to be
moving at all, either in a rotating or in a progressive manner. As far as the former is concerned, he admitted the
possibility of such
an opinion, as long 15
From
as the
movement
Copernicus
of the stars
To
Einstein
was considered. However,
when we
take into consideration everything that happens around us and in the air, this view so he argues be
comes obviously absurd. For the earth, during its rota in the tion, would have to leave the air behind. Objects not being able to follow the rotation, would have to be also left behind. pro in is equally impossible for, gressive motion of the earth
atmosphere, such
as flying birds,
A
that case, the earth
sphere, and
would leave the center
we would
see
of the heavenly
by night a smaller part of the
sphere) and
by day a larger one. One can see from these arguments that the great
astronomer has devoted
much
serious
thought
to
the of
problem. In the light of his rather limited knowledge mechanics and of the heavenly spaces, his reasoning must
have seemed quite conclusive. As far as his last objection was concerned, he could .not have suspected that the interstellar distances shift of the earth
were
so great as to
make
the lateral
completely unnoticeable.
The planets are characterized, according to Ptolemy, in the by common movements. Their path, as observed circular orbits. As sky, is determined by superimposed One must a result, there arise the so-called "epicycles."
admit that Ptolemy has deeply understood the nature of with the planetary movements. When one gets acquainted
Copernican conception, one discovers the facts revealed behind Ptolemy s epicycles: the loop of the planets course mirrors their double motion as regards the earth.
In the 16
first
place, they
move
in a circle
around the sun,
The Copernican View
and
in the second place, this
the earth which, in
its
of the
World
movement
turn, revolves
is
observed from
around the sun.
The Ptolemaic
conception of the universe dominated the learned people s minds for more than one thousand years.
The man who undermined
this firm tradition
of required great independence an thought as well as great scientific knowledge, for only nature could give insight into the ultimate relations of
Nicholas Copernicus
him
the ability to discern
new approaches
to truth.
Frauenburg was long known as a learned astronomer before his new ideas were presented; he had studied in Italy all branches of science, he had
The canon
of
acted as doctor and church administrator in his home so well recog town, and his astronomic knowledge was nized that in 1514 he was asked by the Lateran Coun for his opinion on questions of calendar reform. His new ideas concerning the system of the universe were cil
he formed, in their essence, at the age of 33, However, the did not promulgate them at that time, but devoted and demon following years to a thorough elaboration
Only excerpts of his doctrine were published during his lifetime. His main work en stration of his theories.
titled
"Of
the Rotation of Celestial
Bodies"
appeared
read the proofs only on
only after his death in 1546. He his death-bed and thus failed to notice that his friend Osiander supplied the work with a foreword which con tained a cautious compromise with the opinions of the
Church. If
we examine
the proofs given by Copernicus of his 17
From
new theory, we
find
Copernicus
To
them quite
Einstein
of view of present-day knowledge. to cite as a distinct
of his system.
He
from the point was able, in fact,
insufficient
He
advantage only the greater simplicity
regards
improbable that the stars their large orbits and finds it
it
move with
as
great speed in mo)re likely that the earth rotates
on,