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From: someone2 on 14 Jul 2010 08:31
I was wondering if anyone could help me understand issues of
simultaneity under relativity.

I was thinking of a circular track in space, which a vechile moving at
100mph takes 2 years to make a circuit, and there being a mirror in
the middle of the track, and an observer 1.5 light years from the
track, travelling towards it at near light speed, while firing a beam
of light at the mirror.

Would I be correct in thinking that after 1 year the observer would be
0.5 light years from the track, and be receiving back a reflection of
the fired light beam from the mirror, and the light from when the
vehicle was quarter of the way around the track (assumes the vehicle
to have started its journey from the start of the track, as the
observer started start its journey towards the track & mirror).

If I am not correct, could you please state what the correct
observations would be expected to be.
From: harald on 14 Jul 2010 08:47
On Jul 14, 2:31 pm, someone2 <glenn.spig...(a)btinternet.com> wrote:
> I was wondering if anyone could help me understand issues
> of simultaneity under relativity.

Please allow me first to test: Do you understand that "simultaneity"
in relativity theory is largely a matter of convention?

> I was thinking of a circular track in space, which a vechile moving at
> 100mph takes 2 years to make a circuit, and there being a mirror in
> the middle of the track, and an observer 1.5 light years from the
> track,  

You mean NOT on the track? Then where?

> travelling towards it at near light speed, while firing a beam
> of light at the mirror.
>
> Would I be correct in thinking that after 1 year the observer would be
> 0.5 light years from the track, and be receiving back a reflection of
> the fired light beam from the mirror, and the light from when the
> vehicle was quarter of the way around the track (assumes the vehicle
> to have started its journey from the start of the track, as the
> observer started start its journey towards the track & mirror).

I'm afraid that this is too complex without a little sketch. Please
try, ASCII is better than nothing!

Harald

> If I am not correct, could you please state what the
> correct observations would be expected to be.

From: someone2 on 14 Jul 2010 08:54
On 14 July, 13:31, someone2 <glenn.spig...(a)btinternet.com> wrote:
> I was wondering if anyone could help me understand issues of
> simultaneity under relativity.
>
> I was thinking of a circular track in space, which a vechile moving at
> 100mph takes 2 years to make a circuit, and there being a mirror in
> the middle of the track, and an observer 1.5 light years from the
> track,  travelling towards it at near light speed, while firing a beam
> of light at the mirror.
>
> Would I be correct in thinking that after 1 year the observer would be
> 0.5 light years from the track, and be receiving back a reflection of
> the fired light beam from the mirror, and the light from when the
> vehicle was quarter of the way around the track (assumes the vehicle
> to have started its journey from the start of the track, as the
> observer started start its journey towards the track & mirror).
>
> If I am not correct, could you please state what the correct
> observations would be expected to be.

Actually I think I might be wrong in my expectations there, since
although the light would be travelling away from the observer at the
speed of light, and thus be 0.75 light years in front of the observer
after 0.75 of a year (and thus have reached the mirror by the time the
observer is about 0.75 light years from the mirror), it would only
have travelled 0.25 light years back towards the observer, after the 1
year. Such that the observation after 1.125 years travelling would be
of the reflection, and a vehicle being 5/16ths of the way around the
track.

Though it is likely I am simply carrying a big misunderstanding about
what is being said, which is why I asked the question in the hope that
it would be cleared up.
From: someone2 on 14 Jul 2010 09:06
On 14 July, 13:47, harald <h...(a)swissonline.ch> wrote:
> On Jul 14, 2:31 pm, someone2 <glenn.spig...(a)btinternet.com> wrote:
>
> > I was wondering if anyone could help me understand issues
> > of simultaneity under relativity.
>
> Please allow me first to test: Do you understand that "simultaneity"
> in relativity theory is largely a matter of convention?
>

I hadn't really thought about it, though am not suprised.

> > I was thinking of a circular track in space, which a vechile moving at
> > 100mph takes 2 years to make a circuit, and there being a mirror in
> > the middle of the track, and an observer 1.5 light years from the
> > track,  
>
> You mean NOT on the track? Then where?
>


If you were to think of a graph where there is a circle (the track)
around the centre point x=0, y=0, and z=0 (where the mirror is), such
that for all points on the circle, z = 0 and x-squared + y-squared =
radius-squared and the circumferance is such that a vechile moving at
100mph would take 2 years to make a circuit.

The observer is approaching along the z axis where x=0 and y = 0.


> > travelling towards it at near light speed, while firing a beam
> > of light at the mirror.
>
> > Would I be correct in thinking that after 1 year the observer would be
> > 0.5 light years from the track, and be receiving back a reflection of
> > the fired light beam from the mirror, and the light from when the
> > vehicle was quarter of the way around the track (assumes the vehicle
> > to have started its journey from the start of the track, as the
> > observer started start its journey towards the track & mirror).
>
> I'm afraid that this is too complex without a little sketch. Please
> try, ASCII is better than nothing!
>

Hopefully the description above will help.

>
>
>
> > If I am not correct, could you please state what the
> > correct observations would be expected to be.- Hide quoted text -
>


From: Mathal on 14 Jul 2010 09:34
On Jul 14, 5:31 am, someone2 <glenn.spig...(a)btinternet.com> wrote:
> I was wondering if anyone could help me understand issues of
> simultaneity under relativity.
>
> I was thinking of a circular track in space, which a vechile moving at
> 100mph takes 2 years to make a circuit, and there being a mirror in
> the middle of the track, and an observer 1.5 light years from the
> track,  travelling towards it at near light speed, while firing a beam
> of light at the mirror.
>
> Would I be correct in thinking that after 1 year the observer would be
> 0.5 light years from the track, and be receiving back a reflection of
> the fired light beam from the mirror, and the light from when the
> vehicle was quarter of the way around the track (assumes the vehicle
> to have started its journey from the start of the track, as the
> observer started start its journey towards the track & mirror).
>
> If I am not correct, could you please state what the correct
> observations would be expected to be.

After one year from the frame of the mirror the observer would be
lagging just behind the photons travelling towards the mirror. Neither
the observer or the light would have arrived yet.
From the observer's travelling just below light speed's point of view
a few microseconds have transpired. He can't see the light but it's on
it's way just a few light micro-seconds ahead of him.
Mathal
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