Chapter 9: Einstein and Relativity Theory (319 KB) - D Cassidy Books

3637_CassidyTX_09 6/14/02 12:08 PM Page 406
406 9. EINSTEIN AND RELATIVITY THEORY
effects, and currents all fit within the physics of Newton, Maxwell, and their
contemporaries. In addition, their work made possible the many wonders
of the new electric age that have spread throughout much of the world
since the late nineteenth century. No wonder that by 1900 some distinguished
physicists believed that physics was nearly complete, needing only
a few minor adjustments. No wonder they were so astonished when, just
5 years later, an unknown Swiss patent clerk, who had graduated from the
Swiss Polytechnic Institute in Zurich in 1900, presented five major research
papers that touched off a major transformation in physics that is still in
progress. Two of these papers provided the long-sought definitive evidence
for the existence of atoms and molecules; another initiated the development
of the quantum theory of light; and the fourth and fifth papers introduced
the theory of relativity. The young man’s name was Albert Einstein,
and this chapter introduces his theory of relativity and some of its
many consequences.
Although relativity theory represented a break with the past, it was a
gentle break. As Einstein himself put it:
We have here no revolutionary act but the natural continuation of
a line that can be traced through centuries. The abandonment of
certain notions connected with space, time, and motion hitherto
treated as fundamentals must not be regarded as arbitrary, but only
as conditioned by the observed facts.*
The “classical physics” of Newton and Maxwell is still intact today for
events in the everyday world on the human scale—which is what we would
expect, since physics was derived from and designed for the everyday world.
However, when we get away from the everyday world, we need to use relativity
theory (for speeds close to the speed of light and for extremely high
densities of matter, such as those found in neutron stars and black holes)
or quantum theory (for events on the scale of atoms), or the combination
of both sets of conditions (e.g., for high-speed events on the atomic scale).
What makes these new theories so astounding, and initially difficult to
grasp, is that our most familiar ideas and assumptions about such basic concepts
as space, time, mass, and causality must be revised in unfamiliar, yet
still understandable, ways. But such changes are part of the excitement of
science—and it is even more exciting when we realize that much remains
to be understood at the frontier of physics. A new world view is slowly
emerging to replace the mechanical world view, but when it is fully revealed
* Ideas and Opinions, p. 246.