Re: Understanding SR - simultaneity


"Dirk Van de moortel" <dirkvandemoortel@xxxxxxxxxxxxxxxxxxxxxxxxxxx> schreef
in bericht news:gOeeg.451927$dg7.12080230@xxxxxxxxxxxxxxxxxxxxxxxx

"Nicolaaas Vroom" <nicolaas.vroom@xxxxxxxxxx> wrote in message
news:A%aeg.451604$dg7.12080230@xxxxxxxxxxxxxxxxxxxxxxxx

For Experiment 3 there is also no problem.
For spacetime diagram see http://users.pandora.be/nicvroom/dirk1.htm

The problem comes in Experiment 4.
When you synchronise the Left mirror, Observer R does
not see the signal and the front of the train together.
That is what the spacetime diagram tells you. See above url.

Indeed. The front of the train arrives at R before the
light signal does.


But is the spacetime diagram correct ?
Is the spacetime diagram in agreement with observations ?

Yes, it represents and demonstrates the situation you have
in mind.

Sort of.
It represents the situation I have in mind
but it does not demontrates this by performing an experiment.

That is my problem.
When I perform experiment 3 for any speed
does the observer R see the signal and front simultaneous ?

IMO Observer A (L and R) in experiment 1 and 2 represents
an person/object that has a speed 0 * c.

Yes, with respect to the ground.

Does that mean that when I stay on the ground my speed is 0 * c ?
And when I stay on a moving train,
(which has a speed of 10 km / hour)
does that mean that my speed is also 0 * c ?
Is that something I have to accept ?

Is that person the same as when
"I" would perform experiment 2,
being Observer R and measure no difference ?
I expect "your" answer is Yes.
But how would you convince "me".

I made the same mistake twice. Sorry.
This should have been experiment 3.

The correct text is:

Is that person the same as when "I" would perform experiment 3,
being Observer R and measure no difference ?
I expect "your" answer is Yes.
But how would you convince "me".

I think this problem runs parallel with Length Contraction.
You cannot perform an actual experiment that proves that
Length Contraction is involved.

In actual fact IMO in experiment 3 Length Contraction is involved.
Observer A at the centre between the mirrors is not influenced.
He will See the reflected signals always simultaneous.
The problem comes with the right observer because he has to observe
the front of a moving train.
Accordingly to SR (IMO) he will only see the signal simultaneous
with the "front of the train" for v = small.

Is this true or wrong ?
Again the problem is you cannot perform an actual experiment to
demonstrate this.

This leaves me in Limbo.
What is the true argument that should convince "me" that SR is correct
related to this problem ?
http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html
Accordingly to Tom Roberts:
"Similarly in SR, "length contraction" is purely a geometrical effect"
Is that "The" answer ?


By the way, do you realize that for the train observer (for instance
at B, but also at the moving mirror places a and b) the events
where the signals hit the mirrors are simultaneous? I.o.w. you can
draw a line between the place where you marked t1 on mirror a,
and t4 on mirror b. This line is parallel to the x'-axis of the train.
You can also look at the a-line (or the B-line, or the b-line, or
any other line parallel with it) as the t'-axis. It helps when you
explicitly draw these lines.

Dirk Vdm



Nicolaas Vroom
http://users.pandora.be/nicvroom/


.

Relevant Pages

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