D O C . 3 3 2 O N T H E E T H E R 3 3 5
surrounded by a magnetic field whose energy in first approximation depends qua-
dratically on the velocity. What would suggest itself more immediately than to con-
ceive of all kinetic energy as electromagnetic energy? That way one could hope to
trace mechanics back to electromagnetism, after the previous
[10]
endeavor to trace
electromagnetic processes back to mechanical ones had failed. This seemed the
more hopeful, the more it was becoming probable that all ponderable matter was
built out of charged elementary particles. Yet two difficulties could not be mas-
tered. Namely, first, the Maxwell-Lorentz equations could not make comprehensi-
ble why the electric charge constituting a charged elementary particle can exist at
equilibrium despite electrostatic forces of repulsion. Second, the electromagnetic
theory was incapable of explaining gravitation in any somewhat natural and satis-
factory manner. Despite this, the successes that the electromagnetic theory afforded
physics were so significant that it came to be regarded as a completely secure part
and parcel of physics, indeed, as its most well-founded achievement.
The Maxwell-Lorentz theory ultimately influenced our attitude toward the is-
sues regarding the theoretical foundations by leading to the creation of the special
theory of relativity. It was realized that the electromagnetic equations in truth do
not prefer any definite state of motion; rather that, according to those equations,
just as according to classical mechanics, an infinite manifold of mutually uniformly
moving coordinate systems were equally legitimate, if only one applies suitable
transformation formulas for the spatial coordinates and for time. It is well known
that this insight bore in its train a profound modification of kinematics and
dynamics.[11]
Henceforth a definite state of motion was no longer assigned to the
ether of electrodynamics. Its effect now—like the ether of classical mechanics—
was not the preference for a defined state of motion, but just the preference for a
defined state of acceleration. Because simultaneous states could no longer be spo-
ken of in an absolute sense, the ether became four-dimensional, so to speak, as
there was no objective order to its states by time alone. Even according to the spe-
cial theory of relativity, the ether was absolute since its
influence[12]
on inertia and
the propagation of light was thought of as independent of any kind of physical in-
fluences. While in classical physics the geometry of bodies is presupposed to be
independent of the state of motion, according to the special theory of relativity the
laws of Euclidean geometry for the configuration of bodies at rest relative to one
another are relevant only if these bodies are at rest relative to an inertial
frame;*)
[13]
*)
For bodies which, although at rest relative to one another, are rotating as a whole
against the inertial frame, for example (according to the special theory of relativity),
Euclidean geometry is not valid.
[p. 90]