1 3 0 D O C . 3 1 I D E A S A N D M E T H O D S
The inertial mass of a body increases by if one adds (in a state of rest) the
energy (e.g., in the form of heat, chemical energy, etc.).
This result, which is derivable with complete rigor from the premises of the the-
ory (in connection with Maxwell’s electrodynamics) states that at least part of the
inertial mass of a body consists of energy. There cannot be much doubt that the
mass of a body is nothing else than latent energy.
This reflection also shows that the theorem of the conservation of mass can no
longer claim a place independent of the theorem of the conservation of energy.
13. Theory of Special Relativity and Ether
It is obvious that an ether at rest has no place in the theory of relativity. Because,
if two systems and are of completely equal value for the formulation of the
laws of nature, then it is inconsistent to put a concept into the foundations of a the-
ory such that it distinguishes one system over all the others. After all, if one as-
sumes an ether that is at rest relative to , it is moving relative to , a feature that
does not agree with the equivalence of the two systems.
For this reason, my opinion in 1905 was that one should no longer talk about the
ether in physics. But this judgment was too radical, as we shall see in the following
considerations on the theory of general relativity. Rather, it is still permissible to
assume a space-filling medium whose states may be imagined as electromagnetic
fields (and perhaps also as matter). But it is not permissible to attribute to this me-
dium states of motion in every point, like in an analogy to ponderable matter. This
ether must not be imagined as consisting of particles whose identity could be traced
in
time.[26]
14. Minkowski’s
Method[27]
In an era of classical dynamics it would have been idle play to combine time and
space into a four-dimensional continuum. Because for that era, the chronological
order of events was independent of everything spatial, i.e., independent of the
choice of the coordinate system. In the theory of relativity, however, time is de-
prived of its separate existence; the Lorentz transformation demonstrates that spa-
tial and chronological coordinates depend on each other according to the state of
m
E
c2
---- -
E
K K′
K K′
[p. 16]