Einstein's Special Relativity and "twin paradox" applied to stars.?

Question

A set of twins. One boards a space ship traveling near the speed of light. He returns to earth and finds his twin brother has aged more than he. Time dialation, got it.

It takes light from a star 4 billion light years away 4 billion years to reach earth, thus we are looking back into time the way the star was 4 billion years ago. But are we really? Does light from stars go through time dialation? Does the star 4 billion light years away really appear to us the way it looked 4 billion years ago? Or is it more like 2 billion years ago? Is the star aging slower because it, or the light from it, is traveling so fast? I assume, given the fact that stars/galaxies experience redshift, that they are moving at a speed comparable to the speed of light and are thus subject to extreme cases of time dialation like those expressed in the twin paradox.

Could this too then mean that every other star could essentially appear to live longer than our Sun because they're traveling so fast?

Answer 1

Well...to make this whole thing simpler....

You're watching the superbowl live on TV. There is a 5 seconds delay on that live image. You're watching a game that happened 5 seconds ago. The game is the same the image is the same. I would say the same thing for the stars. We're watching the star with a 4 billion years delay......

Answer 2

Remember that the twin paradox is a *paradox* and only resolved because one twin turned around. While the twin is racing away from Earth, he looks back and it looks like his twin is moving in slow motion, but the Earth twin sees the space twin also as moving in slow motion (the whole 'everything is relative' thing).

That star light that we see from the star 4 billion ly away, that light took 4 billion ly to get to us - no time dilation effects or anything. You can complicate things if that star is moving relative to us, but if it isn't then there is no time dilation of any sort. And that's still *relative* motion.

The Sun is 8 light-minutes away from Earth, so we see the Sun as it was 8 minutes ago - again, no time dilation there.

Answer 3

As was pointed out the star doesn't age more slowly but in a sense you're on the right track. Since the time dilation effect increase as you approach the speed of light, photons since they travel AT the speed of light can be thought of to have infinite time dialation from out point of view. At least until they impact something. But the star itself would have to be moving at light speed to have the effect you are looking for not just the light from it.

Answer 4

Yes, there are subtleties when talking about distance stars. The appropriate theory is not special relativity, for this, it is general relativity. The redshift then turns out to be related to the ratio of the 'expansion factors' for when the light started out and when it was observed. Unlike in special relativity, there are preferred observers in general relativity: those who are at rest relative to the average of motion in their local area. it turns out that galaxies are very close to being such preferred observers. The expansion factor turns out to be directly related to the proper time of the preferred observers. The result is that when you look at a galaxy with a particular red-shift, the distance and age are computed via these relationships, so you *do* see it as it was billions of years ago.

Answer 5

The stars are not traveling fast (relatively speaking) it is the light from the star that is traveling, coincidentally at the speed of light.

There are issues with relativity, but that is not one of them.

Answer 6

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