I
Essentially, Einstein's theory of relativity has its roots
in the questions: Where are we? How are we moving?
In connection with our present purposes, these ques-
tions posed no profound problems so long as men
believed that the earth is the fixed center of the uni-
verse. With the astronomical hypothesis of a moving
earth, however, the questions began to become dis-
turbing, not only theologically but also scientifically.
This article is concerned with the scientific aspects of
the problem.
In the seventeenth-century concepts of Galileo, and
more sharply in those of Newton, one already finds
a “principle of relativity,” though the phrase itself did
not come into being until late in the nineteenth cen-
tury. We can say that the principle has to do with the
impossibility of detecting absolute motion. But to this
statement we have to attach changing caveats whose
nature will not become apparent until we have dis-
cussed the matter in detail.
In the nineteenth century, optical and electromag-
netic theory had seemed to invalidate the principle.
Reaffirming it and later generalizing it were thus revo-
lutionary acts. Their drastic scientific consequences,
affecting the basic concepts of time and space, were
worked out in the twentieth century, principally by
Einstein.
