If the speed of light is constant time must be constant too?

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Offline Chuck F

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The theory of relativity states that everything is relative to the observer. I understand that and it makes sense.  The problem I have is that say you have 3 planets

      (a)                  (b)                   (c)

Planets (a) and (c) are moving away from each other at just under the speed of light.  Planet (b) is always halfway between them.  According to reletivity an observer on planet (a) would see time neary stopped on planet (c) and slowed down to 1/2 on planet (b).  But an observer on planet (c) would see time nearly stopped on (a) and 1/2 on (b).  Planet (b) would see time being 1/2 on both (a) and (c) ie time would appear to be the same on both planets.  This is due the the fact we are observing the light and because the distance is changing it is stretching the observed time and slowing it down.  In reality time has passed the same on all 3 planets.  The same would hold for the person on the event horizon of a black hole.  We would observe him as if time had stopped.  but he would observe us the same.  Because to him we are moving away at the speed of light.  The speeding up or slowing down of time only occurs because the speed of light is constant therfore the time appears squished or stretched.  So if we sent a ship to a planet 10 light years away at 1/2 the speed of light it would take 40years round trip they would age 40 years we would age 40 years both planets would age 40 years.  It would appear that it took them 30 years to get there but only 10 to get back.  In reality it takes 20 years both ways.

I could very well be wrong on this but every thing I have seen on reletivity is from the point of view of the observer.  And from the observers stand point time is not constant. But the actual time passing is constant.


Offline graham.d

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If the speed of light is constant time must be constant too?
« Reply #1 on: 31/01/2011 16:39:29 »
It is more complicated than you realise, Chuck. I could explain, but it would be easier if you got a book on special relativity from the library. The time dilation effects are not simply because of the Doppler effect on light. You also have to do the maths more rigorously. The nearest problem to the one you describe is referred to as the "Twin Paradox" (it is not actually a paradox but it can seem that way until you understand Special Relativity); you can find lots of references and explanations on the internet.