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Natural Science Forum / Physics / Relativity / October 2006



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yet another paradox (?)

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nobody1357@operamail.com - 28 Oct 2006 05:21 GMT
Please bear with me again. Consider a spaceship with two people at
front and back ends. The person at the front resets his clock and sends
a light signal to the person at the back, who resets his clock when he
receives the signal. Then, they both move to the center of the ship to
compare clocks. Due to the delay of the signal, there will be a certain
offset in time that the clocks show. Next, the same scenario is
repeated, except it's the person at the back who initiates the reset.
If one way speed of light is the same in both directions, the offset
between the clocks must the same. The effect of moving the clocks to
the center of the ship is the same in both cases, only difference can
come from one way speed of light. Paradox is, according to a stationary
observer, the light signal in two directions is not the same relative
to the spaceship, therefore the offsets in two cases cannot be the
same, but the people on spaceship cannot explain this difference. How
is this resolved? Thanks in advance.
Androcles - 28 Oct 2006 05:42 GMT
| Please bear with me again.

No.

| Consider a spaceship with two people at
| front and back ends. The person at the front resets his clock and sends
[quoted text clipped - 11 lines]
| same, but the people on spaceship cannot explain this difference. How
| is this resolved? Thanks in advance.

It isn't resolved, Einstein was a fuckwit. You'll find any number of
pair-o'-dorkses.  Move on.
  http://www.androcles01.pwp.blueyonder.co.uk/Rocket/Rocket.htm
Androcles
Brian Kennelly - 28 Oct 2006 05:50 GMT
> Please bear with me again. Consider a spaceship with two people at
> front and back ends. The person at the front resets his clock and sends
[quoted text clipped - 11 lines]
> same, but the people on spaceship cannot explain this difference. How
> is this resolved? Thanks in advance.

This is not too hard to see qualitatively:
Moving the clocks to the centre of the ship requires a non-zero
velocity, which implies time dilation.

The effect of time dilation in the ship frame is not the same as
in the stationary observer.

In the ship frame, the time dilation is entirely due to the
motion of the clocks.  In the stationary frame, there is already
a time dilation effect, and the motion of the clocks is
compounded with it (the rear clock is moving faster than the
ship so it is dilated more, while the front clock is moving
slower, so it is dilated less).  The overall effect can be shown
to exactly compensate for the difference perceived by the
stationary observer.
nobody1357@operamail.com - 28 Oct 2006 05:55 GMT
> > Please bear with me again. Consider a spaceship with two people at
> > front and back ends. The person at the front resets his clock and sends
[quoted text clipped - 27 lines]
> to exactly compensate for the difference perceived by the
> stationary observer.

Yes, but this can only cause a fixed amount of offset between the two
clocks, it cannot compansate in both cases with this fixed amount.
nobody1357@operamail.com - 28 Oct 2006 06:06 GMT
> > > Please bear with me again. Consider a spaceship with two people at
> > > front and back ends. The person at the front resets his clock and sends
[quoted text clipped - 30 lines]
> Yes, but this can only cause a fixed amount of offset between the two
> clocks, it cannot compansate in both cases with this fixed amount.

sorry, I think you're right
dlzc - 28 Oct 2006 06:07 GMT
Dear nobody1357:

> Please bear with me again. Consider a spaceship
> with two people at front and back ends.
...
> If one way speed of light is the same in both
> directions, the offset between the clocks must the
> same.

The act of moving the clocks erases any offset.  Experiment dies.
Nature will not allow you to measure OWLS.

...
> Paradox is, according to a stationary observer,
> the light signal in two directions is not the same
> relative  to the spaceship,

It is always c.  Spaceship measurements are ancillary.

> therefore the offsets in two cases cannot be the
> same,

It is, because all measurements of c are TWLS.

> but the people on spaceship cannot explain this
> difference. How is this resolved?

The stationary observer will also determine that the spaceship adhered
observers will measure c.  That is the second postulate, after all.

David A. Smith
Martin Hogbin - 28 Oct 2006 10:31 GMT
> Please bear with me again.

Have you understood your last paradox yet?

Why not try learning about relativity so you can answer your own paradoxes?

Martin Hogbin
Androcles - 28 Oct 2006 15:59 GMT
Learn
tau = (t-vx/c^2)/sqrt(1-v^2/c^2)
xi = (x-vt)/sqrt(1-v^2/c^2)
Now learn where it comes from.
http://www.androcles01.pwp.blueyonder.co.uk/Rocket/Rocket.htm
http://www.androcles01.pwp.blueyonder.co.uk/Smart/Smart.htm

Now that you've learnt about Santa Claus, grow up.

Ignore Hogbin, the imbecile doesn't take is own advice.

| > Please bear with me again.
|
[quoted text clipped - 3 lines]
|
| Martin Hogbin
wugi - 28 Oct 2006 12:57 GMT
<nobody1357@operamail.com> /:

> Please bear with me again. Consider a spaceship with two people at
> front and back ends. The person at the front resets his clock and sends
[quoted text clipped - 11 lines]
> same, but the people on spaceship cannot explain this difference. How
> is this resolved? Thanks in advance.

How, do you think, come both clocks ticking "in pace"? Right, by
synchronising them with each other or with one or more other clocks
belonging to their system. And synchronisations are two-way procedures.
And once the clocks tick in pace, the reset delays are the same.

--
guido
http://home.scarlet.be/~pin12499/paratwin.htm
wugi - 29 Oct 2006 13:00 GMT
"wugi" :

> How, do you think, come both clocks ticking "in pace"? Right, by
> synchronising them with each other or with one or more other clocks
> belonging to their system. And synchronisations are two-way procedures.
> And once the clocks tick in pace, the reset delays are the same.

....so that, remembering the relativity of simultaneity,
when the signal emitted at the front arrives "in advance" at the back, the
clock there will compare it with an "earlier" event, and
when the signal emitted at the back arrives "retardedly" at the front, the
clock there will compare it with a "later" event,
earlier and later to be understood "than emission time", from the viewpoint
of a "rest" system,
and resulting in equal transmission intervals to and fro, in the moving
system.

> --
> guido
> http://home.scarlet.be/~pin12499/paratwin.htm
same:-)
 
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