3 3 4 D O C . 3 3 2 O N T H E E T H E R
We see that, for Newton, “space” was something physically real, despite the
strangely indirect way in which this realness makes itself known to us. Ernst Mach,
who was the first after Newton to subject the foundation of mechanics to profound
analysis, recognized this
He sought to elude the hypothesis of the “ether
of mechanics” by trying to attribute inertia to an unmediated interaction between
the considered mass and all the rest of the masses of the
This concep-
tion is logically possible; however, as action-at-a-distance, it no longer comes seri-
ously under consideration for us
The mechanical ether, designated by
Newton as “absolute space,” must therefore be considered by us as a physical real-
ity. Yet, the expression “ether” must not lead us to think of something analogous to
the 19th century’s physics concept of ponderable matter.
When Newton denotes the space of physics as “absolute,” he is still thinking of
another property of what we here call the “ether.” Every physical object influences
others and conversely is generally influenced by others. This latter point does not,
however, apply to the ether of Newtonian mechanics. The latter’s property of ex-
pending inertia, according to classical mechanics, cannot be influenced by any-
thing, neither by the configuration of matter nor by anything else; to that extent it
can be described as “absolute.”
It became clear to physicists only in the past few years that a real thing must be
presupposed as the cause for the preference of inertial frames over non-inertial
Historically, the ether hypothesis in its present form emerged by subli-
mation out of the mechanical ether hypothesis in optics. After long, fruitless ef-
forts, the conviction was reached that light should not be comprehended as the mo-
tion of an inert, elastic medium; that the electromagnetic fields of Maxwell’s theory
could not be interpreted mechanically at all. Thus, under the pressure of these fail-
ures, the electromagnetic fields were gradually regarded as the last, irreducible
physical realities, as still inexplicable states of the ether. What initially remained of
the ether of the mechanical theory was its definite state of motion; it embodied to
some extent an “absolute rest.” Whereas in Newtonian mechanics all inertial
frames were at least equivalent, in the Maxwell-Lorentz theory it seemed that the
state of motion of the legitimate coordinate system (rest against the ether) was fully
determined. It was silently assumed that this preferred system was an inertial frame
at the same time, i.e., that the principle of inertia was valid relative to the electro-
magnetic ether.
The basic conception of physicists shifted in a second way as well under the in-
fluence of the Maxwell-Lorentz theory. After electromagnetic fields had been
conceived as fundamental, irreducible entities, they seemed to be called upon to rob
ponderable, inert mass of its fundamental importance in mechanics as well. It was
concluded from Maxwell’s equations that a moving electrically charged body is
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[p. 89]
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