Time and the Metaphysics of Special RelativityEinstein, Relativity, and Absolute Simultaneity

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14 Νοε 2013 (πριν από 4 χρόνια και 6 μήνες)

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potentially important development that it is irresistible. I actually did an audio
-
blog on this
exciting news, but our sound equipment failed and so, for better o
r worse, I’ll address it here.

This is a very welcome development, confirmatory of the position I defended concerning the
proper physical interpretation of the Special Theory of Relativity (STR) in my books
Time and
the Metaphysics of Special Relativity

(Kluwer, 2001) and
Einstein, Relativity, and Absolute
Simultaneity

(co
-
edited with Quentin Smith) (Routledge, 2007). It is a dramatic empirical
confirmation of the physical interpretation of the mathematical equations of

STR by the great
Dutch physicist Hendrik Antoon Lorentz.

You see, a physical theory comprises a mathematical core and a physical interpretation of those
core equations. The mathematical core of STR is the Lorentz transformation equations, which
tell you h
ow to calculate the spatio
-
temporal co
-
ordinates of an object relative to different frames
of reference. But there are at least three different physical interpretations of those equations:

1. The original
Einsteinian interpretation,

which denied the exist
ence of absolute space and time
and envisioned physical deformations of 3
-
dimensional, physical objects enduring through time.

2. The
Minkowskian interpretation,

which denied the existence of 3
-
dimensional, physical
objects enduring through time in favor o
f 4
-
dimensional objects existing tenselessly in
spacetime. Once Minkowski proposed his spacetime interpretation in 1908, Einstein immediately
abandoned his original interpretation for Minkowski’s, which has since become the standard
textbook version of STR
.

3. The
Lorentzian interpretation
, which like the original Einsteinian interpretation, affirmed the
existence of 3
-
dimensional objects enduring through time but which, unlike the Einsteinian view,
affirmed the existence of absolute space and absolute simu
ltaneity, even if we cannot detect them
empirically. Clocks and measuring rods in motion relative to the absolute reference frame (the
“aether”) run slowly and shrink up as Einstein suggested.

These three interpretations have been until recently empirical
ly equivalent, so that it has been
impossible scientifically to choose between them. During the heyday of positivism, theories
which were empirically equivalent tended to be regarded as just the same theory, despite the
vastly different views of space and
time they might involve, because there was no way to verify
the differing interpretations. With the collapse of verificationism, philosophers of science are
once more appreciative of the vast differences ontologically between the interpretations of
Einstei
n, Minkowski, and Lorentz, differences that cannot be glossed over.

In recent years experimental results concerning the predictions of a quantum mechanical theorem
called Bell’s Theorem have made the Lorentzian interpretation, so long ignored by the
positi
vists, once more a serious option. John Bell himself, who formulated the theorem,
advocated going back to Lorentz’s view, since the experimental results seemed to indicate the
objective reality of relations of absolute simultaneity in the universe.

These m
ost recent results at CERN continue this pattern. Let me explain.

STR does not really prohibit the existence of particles traveling at superluminal velocities. What
it prohibits is the acceleration of a particle from subluminal velocity to superluminal ve
locity.
But it doesn’t rule out particles which always travel at superluminal speeds. Indeed, there has
been much discussion of such theoretical particles, which are called “tachyons” (from the Greek
word for
swift
), even though none has yet been found. If

these new results hold up, then these
neutrinos are, in fact, tachyons, and somebody is probably in line for a Nobel Prize!

Now if tachyons are compatible with STR, then, you may ask, what’s the fuss all about? Just
this: in the vocabulary of the Einstein
ian interpretation of STR, simultaneity of distant events is
relative to reference frames, which are the inertial frames of observers in relative motion. To
determine the simultaneity of two spatially separated events, you send a light signal to a distant
observer, who reflects it back to you. Assuming light’s velocity is the same both going and
returning, you figure that the event simultaneous with the distant reflection event is the event at
your location which is halfway between the time you sent the sig
nal and the time you got it back.
So you can draw a line of simultaneity, as it were, between those two events, and use that as the
basis for figuring which other events in the two locations are simultaneous. This sounds fine; but
it has the consequence th
at simultaneity becomes relative. For which event is halfway between
the time you sent the signal and the time you received it back depends on the relative motion of
the two observers. Observers at those same locations who have different reference frames w
ill
determine different events to be simultaneous. There is no absolute (
i.e
., frame independent)
simultaneity.

But if tachyons exist, then you can send signals between the two observers
faster

than the speed
of light. But then here’s the rub: that implies

that relative to some reference frames,
the tachyons
will be going backward in time
! For if there is no absolute simultaneity, some observers will
draw the line of simultaneity between the two distant events in such a way that the tachyon is
reflected bac
k
before
it is even sent! Such behavior is pathological. This is what is in mind when
it is said that faster than light particles would violate causality: an effect could occur (like the
reception of a signal) before it is caused (the signal is sent).

The

easiest and most natural way to avoid such pathological behavior is to say that the line of
simultaneity drawn by the relatively moving observers is just wrong. The use of light signals to
calculate simultaneity works only in the fundamental reference fra
me but not between relatively
moving frames. In other words, Lorentz was right all along! If there do exist relations of absolute
simultaneity, then there’s just no problem with faster than light signals. Indeed, if we had infinite
velocity tachyons, we co
uld use them to measure absolute simultaneity. The reason for the panic
you sense in the press releases on the CERN results is that the scientists interviewed implicitly
assume either an Einsteinian or Minkowskian interpretation of STR. But Lorentz would b
e
rejoicing.

In fact, Lorentz himself predicted that something like this might happen. In 1913 he wrote,

According to Einstein it has no meaning to speak of motion relative to the aether. He likewise
denies the existence of absolute simultaneity.

It is ce
rtainly remarkable that these relativity concepts, also those concerning time, have found
such a rapid acceptance.

The acceptance of these concepts belongs mainly to epistemology . . . It is certain, however, that
it depends to a large extent on the way on
e is accustomed to think whether one is attracted to one
or another interpretation. As far as this lecturer is concerned, he finds a certain satisfaction in the
older interpretations, according to which the aether possesses at least some substantiality, sp
ace
and time can be sharply separated, and simultaneity without further specification can be spoken
of. In regard to this last point, one may perhaps appeal to our ability of imagining arbitrarily
large velocities. In that way, one comes very close to the
concept of absolute simultaneity.

Finally, it should be noted that the daring assertion that one can never observe velocities larger
than the velocity of light contains a hypothetical restriction of what is accessible to us, [a
restriction] which cannot be

accepted without some reservation.
1

Here Lorentz clearly discerns the crucial role played by Einstein's verificationist theory of
meaning and rejects it. In defense of
absolute simultaneity, he appeals to the use of arbitrarily
fast signals, even though they were not presently observable. He quite rightly expresses caution
about our never being able to detect empirically such superluminal velocities.

Lorentz’s interpreta
tion, like the original Einsteinian interpretation, presupposes an A
-
Theory of
time. But it enjoys the advantage over Einstein’s interpretation in making the physical
deformations suffered by objects in motion relative to the fundamental frame intelligible
.

I hope you’ll forgive the triumphalism of my title for this Question of the Week. Lorentz is one
of my scientific heroes. The results obtained at CERN may not hold up. But I sure hope that they
do.

Notes

1

H. A. Lorentz, A. Einstein, H. Minkowski Das Relativitätsprinzip, Fortschritte der
mathematischen Wissenschaften 2, mit Anmerkungen von A. Sommerfeld und Vorwort von O.
Blumenthal (Leipzig: B. G. Teubner, 1920),

p. 23 (Pais translation).