# What are peoples thoughts on the fact that at the exact limit of our universe.

1. Nov 5, 2014

### jbander

What are peoples thoughts on the fact that at the exact limit of our universe. the stars are moving at just less then the speed of light away from us. If there wasn't a limit to the speed of light , isn't that what we would be seeing but the real fact then would be that it isn't the boundaries of our universe.

2. Nov 5, 2014

### Matterwave

What's the "exact limit of our universe"? For objects very distant to us, a measurement of speed relative to us, is no longer simple. This is because on large scales, one must consider general relativistic effects and not just simple special relativity. Objects very far away have red shifts greater than 1 which makes their "recessional velocities" greater than the speed of light. But that's simply because we are not performing a local measurement of speed (how can we, they are billions of light years from us). In the general relativistic sense, these far away galaxies are approximately "stationary" with respect to us, since both our galaxy and these far away galaxies are in the rest-frame of the CMBR, it is only the space in between these galaxies and us that is expanding. See: http://en.wikipedia.org/wiki/Metric_expansion_of_space

3. Nov 5, 2014

### Staff: Mentor

Do you mean the observable universe? Then it is by definition that we can only observe stars from which the light can reach us. The actual universe is bigger than the observable universe.

4. Nov 5, 2014

### phinds

Your "fact" is erroneous. The objects out close to the edge of our observable universe are receding from us at about 3c, not "just less than c"

5. Nov 5, 2014

### jbander

I'm really interested in this but really have very little knowledge of this subject but I hope you can respond to these very simple questions by a willingness to advise a raw beginner

So is the influence of time just a matter of the difference between the period of deceleration and the acceleration now. And does that mean then that at some time these observed stars will blink out when the deceleration/ acceleration time balance is reached as far as our relationship to this observable star at our perceived maximum visibility.
If you also would respond to one more question. Is there a Idea on what is making the expanding universe increase in acceleration. The idea that at one time it was decelerating and now accelerating is a idea that is wonderful just because of the question why.
If anyone could advise me of literature that may be helpful for a interested beginner. I would appreciate it.

6. Nov 5, 2014

### Matterwave

I have no idea what you are asking here. You can perhaps rephrase your question?

You can try Ned Wright's cosmology tutorial page: http://www.astro.ucla.edu/~wright/cosmolog.htm

Currently it is unknown why the universe is accelerating in its expansion. Nothing deeper than "it's a cosmological constant of integration that appears in Einstein's equations" has been unveiled as of yet.

7. Nov 5, 2014

### jbander

Thanks for the response, I may not understanding this but I'll try again , The early universe at one time was decelerating , I believe because of the gravity of the concentration of mass of the early universe ,then it changed and started to accelerate, because of the reduction in the gravity from the less concentration of the mass of the universe as it expanded and got older and the increased influence of the X factor (the thing we don't know about that makes the universe accelerate). it ultimately was more of a influence then the gravity. .you could be viewing a distance object at either the time it was decelerating or accelerating(depending on how far away it is),. I see that within the acceleration and deceleration period that the two objects can be separated ultimately in space by more than the distance light could have travelled, right when that happens, does the star just disappear, I mean from our ability to see it . Thank you for the suggestion on reading material.

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