Re: .Simple SR question...


"Jim Hutton" <nogods@xxxxxxxxxxxx> wrote in message news:ep8rvr$g2u$1@xxxxxxxxxxxxxxxxxxx
I have come to understand that the effects of time
dilation, length contraction, etc are *not* due to the
time it takes light to travel to an observer in frame
S as opposed to the one in frame S'.

Correct.

In other words, both observers have an infinite number
of clocks and measuring sticks that are spread out
over their respective frame coordinates so that all
measurements are "local" and don't have to wait for
light to travel from an event to the observer, who is
say, sitting at the origin.

Correct.

I also understand that there are *additional* effects
that can complicate matters that are directly due to
the time it takes light to travel to the observer. (I
believe one of these might be the observed rotation of
a moving cube that is not rotating in its rest frame.)

Am I correct so far?

Yes


If this be the case, why do so many textbook
discussion start with an observer on a train with two
flashes of light, one in the front (*toward* which the
observer is moving) and one from the back (*away* from
which the observer is moving)?
Is this the root cause of the downfall of
simultaneity? Or is it more subtle?

A bit.

The point is that light is measured to travel at c
in all inertial frames. In particular it travels at
c in the train's frame and at c the trackside frame.

Clearly this is impossible if the universe is Galilean,
that is to say three dimensions of space and one of
universal time. Something has to give, and it is
simultaneity.

Martin Hogbin


.

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