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[To article:“Relativity of Simultaneity” and “Time Dilation” Issues - Revisited]
Dear Editor,
In the paper, " 'Relativity of Simultaneity' and 'Time Dilation' Issues - Revisited," by Rafy Milo, the author examines a version of Einstein's famous train-embankment gedanken experiment and reaches a conclusion at odds with that demanded by the postulates of relativity.
Specifically, the author writes:
"A railway car of length, L0 = 2l =2cτ, (in the railway car 'rest system') is moving with velocity v relative to the laboratory system. A light pulse is sent at time, τ0 = t0 = 0, from a light source at the center of the railway car towards detectors at both rear and front ends.
"Obviously, in the railway car reference system, the detection of the light pulses at both ends will occur simultaneously at time τ. It should be emphasized that all clocks in the railway car frame are synchronized and thus, any clock at any point in this frame presents the common time of all the clocks in the railway car reference system.
"The observer in the laboratory system should agree about the simultaneity of detection events, since for him, the detection time, τ, in the rest frame, presented by any clock, is equivalent to detection time t in the laboratory frame, given by the 'time dilation' effect:
(3.1) t = γτ."
The paragraph before Eq. 3.1 is where the author's argument goes off the tracks (so to speak.) The author's claim that "[t]he observer in the laboratory system should agree about the simultaneity of detection events" stands in stark contradiction to the conclusion that is readily demonstrated to be demanded by the postulate of constant light speed, indeed, the conclusion drawn by generations of physicists.
Truth in physics is not determined by majority rule, however, as Carl Sagan once said, "extraordinary claims require extraordinary evidence." Yet, in support of this genuinely extraordinary claim, the author provides only the following argument: "the detection time, τ, in the rest frame, presented by any clock, is equivalent to detection time t in the laboratory frame, given by the 'time dilation' effect ... t = γτ."
The problem with the argument is not even so much that it is wrong as that it makes no sense. First, and possibly foremost, it erroneously presupposes that there *is* "a detection time" in the laboratory frame. Second, it makes use of an equation appropriate for determining the translation of certain time *intervals* and applies it to the translation of (ill-defined) *times* (i.e., clock readings.)
In any event, because the conclusion the author purports to reach is so readily demonstrated by completely elementary considerations to be false, the argument itself is certainly invalid. To the extent that the conclusions reached throughout the rest of the paper depend on this and other similar mistakes, they too are invalid.
A. John Mallinckrodt
Professor of Physics
Cal Poly Pomona
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