Speed Of Light

[ll_billym]

My question is obviously totally theoretical but I think it makes sense and I'd just like an explanation of the effect please, I don't know if it's relativity or Doppler or something else:

You are in space and had two clocks set up, one at your location and one that was 1 light hour away, you can see both of them and they are synchronised.

The clock where you are reads 2pm, the clock 1 light hour away also reads 2pm but because the light from it has taken an hour to reach you, you see it as showing 1pm.

If you travel towards the remote clock at half the speed of light it will take you 2 hours to get there, so as the remote clock ACTUALLY reads 2pm when you leave, by the time you get there it will read 4pm, and you will see this correctly because you will be next to it.

So, throughout your journey you will observe it going from the 1pm you SAW when you left and the 4pm it reads when you arrive, so you will see it progress 3 hours in what is only actually 2 hours.

The clock that you left will also read 4pm but you will only see it read 3pm because you are now 1 light hour away, so looking back at it throughout your journey would mean you will see it progress only 1 hour during the two hours of your journey.

Thanks.

[bert_h]

Those both sound right to me. And if you could travel away from a clock at the speed of light, it would look as though it had stopped. You're in good company thinking about it, because it was by thinking his way through apparent paradoxes, like these, that Einstein came up with Special Relativity.

[mibn2cweus]

That's all correct, except -

//If you travel towards the remote clock at half the speed of light it will take you 2 hours to get there//

- the watch you're wearing would read 3:44 because only 1 hour and 44 minutes have elapsed for you due to time dilation within you're reference frame when travelling @ 1/2c

[ll_billym]

Thanks for your answers! Relativity it is then!

I just thought Doppler may have an effect but then thinking about it it may just affect the 'colour' of the clock as you see it as you are travelling towards it?

[mibn2cweus]

ll_billym
Question Author
Thanks for your answers! Relativity it is then!

I just thought Doppler may have an effect but then thinking about it it may just affect the 'colour' of the clock as you see it as you are travelling towards it?
14:42 Fri 18th Jan 2013

Red turns to green at less than 1/4 c. This is attributable almost entirely to the Doppler effect . . . relativistic effects are minimal (2~3%) at such velocities.

You would however probably begin to notice some other rather bizarre modifications (other than colour shift) in your external surroundings travelling at 1/2c, among them, a contraction of the field of view ahead of you.

http://math.ucr.edu/home/baez/physics/Relativity/SR/Spaceship/spaceship.html