One of the following statements is a valid deduction from Einstein's 1905 two postulates; the other statement is, accordingly, non sequitur (does not logically follow from the postulates):
(A) The moving clock lags behind the stationary one AS JUDGED FROM THE STATIONARY SYSTEM, and the stationary clock lags behind the moving one AS JUDGED FROM THE MOVING SYSTEM (symmetric time dilation).
(B) The moving clock lags behind the stationary one AS JUDGED FROM BOTH SYSTEMS (asymmetric time dilation).
Which statement, (A) or (B), is the valid deduction, theoretical physicists? The "peculiar consequence" in Einstein's text below is equivalent to (A) or to (B)? Is the "peculiar consequence" non sequitur?
Albert Einstein, On the Electrodynamics of Moving Bodies, 1905: "From this there ensues the following peculiar consequence. If at the points A and B of K there are stationary clocks which, viewed in the stationary system, are synchronous; and if the clock at A is moved with the velocity v along the line AB to B, then on its arrival at B the two clocks no longer synchronize, but the clock moved from A to B lags behind the other which has remained at B by tv^2/2c^2 (up to magnitudes of fourth and higher order), t being the time occupied in the journey from A to B."
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