Cosmology question: After the Big Bang

[Glyptus]

We're all familiar with the theory of the Big Bang. As we look out into the universe, we observe that all the galaxies are speeding away from each other. This leads us to conclude that, at some time in the past, the universe must have begun with a tremendous, explosive event- a "Big Bang".

According to this scenario, it's possible that the collective gravity of all matter will eventually cause the expansion to slow down, and perhaps even reverse, resulting in a "Big Crunch" at the end of time.

Here's my question. Let's say you are a civilization that has been born into a collapsing universe. As you observe the cosmos, you see that all the galaxies are getting closer and closer to each other. The question: Would there be any way for you to know that the universe was once expanding, unless you had a history book that told you so?

To put the problem another way: In an expanding universe, it's easy to deduce what must have happened in the past. But in a collapsing universe, how could you deduce what happened in the past? Would there be any telltale evidence?

A question for the scientists.

[Saeltari]

Though I am not a scientist it seems to me that by studying where something is you can find where it has been. Stephen Hawking puts things in laymans terms and his stuff is pretty good. You might also check out The Holographic Universe by Michael Talbot, if you haven't already.
If you could measure how much something has changed you can get an idea of where it came from and if it hasn't changed much you can figure it might not have come from far away. You could also look at the pieces and perhaps like a puzzle see that they were all a part of one thing previously. Finding the same make up in one object or material that is the same in a material that you don't think could have possible been the same might lead you to the conclusion that they came from the same place no matter how improbable it seems.
Again, I am not a quantum physicist, though I love reading about it and I enjoy cosmology.
Check out this site; http://www.hawking.org.uk/home/hindex.html hope this stuff helps. It is interesting to think about. I like the question

[bendoran]

even in a collapsing universe if you looked far enough out into space you would far back into time as the light would take time to reach you. Therefore if you looked far enough out you would see that the universe was larger than you expected if it had been collapsing since it began, so at one point it must have been expanding. This could lead to your discovery of a big bang effect.

[Green Knight]

The consensus these days does seem to be that the universe will never collapse - there simply isn't enough matter in it to create the necessary gravity. In fact, with the mysterious 'dark energy' taken into account, expansion may actually be speeding up.

But, you might say, it might conceivably be possible to have a universe that DID have enough mass in it. Perhaps, but I am doubtful... there is strong evidence to suggest that a universe with so much mass in it would have failed to get going properly at all... too many black holes would have formed too early on (when everything was much closer together) and caused collapse before galaxies had time to form.

(The above is all based on my reading of various pop-science works, though, so I could be spectacularly, embarrassingly wrong...)

[chrispenycate]

Actually, it would be possible to tell by the relative age of the elements and their distribution patterns, if you were working from the same physical theories as us. However, a life form evolved to fit a universe where the sky was white with infalling energy, where most of the stars were dead heat sinks largely made of iron, where for many interactions, both physical and chemical, time appears to run backward macroscopically, and forward locally, who knows what their picture of the universe would resemble? What bizarre theories would they come up with? But the data would be there- if they chose to see it- which leaves me wondering what data we overlook every day of the week, telling us our universe is not what we have been lead to believe.

[Glyptus]

Originally Posted by bendoran

even in a collapsing universe if you looked far enough out into space you would far back into time as the light would take time to reach you. Therefore if you looked far enough out you would see that the universe was larger than you expected if it had been collapsing since it began, so at one point it must have been expanding. This could lead to your discovery of a big bang effect.

Certainly, as you look farther out in space, you're also looking farther back in time. You’re right, this would surely be the most reliable way to learn about conditions in the distant past. So, let me make the question more specific: Let's say you live in a universe that has been collapsing for a considerable length of time- (in this hypothetical model, about 15 billion years). All you could see, even with your most powerful telescope, would be galaxies advancing towards you, as if your own world were at the center of this cosmic contraction. If that was your reality, if that was the only way you had ever observed the universe, how would you know there had once been a “Big Bang”, followed by an expansion? What would be the proof?

[Glyptus]

Originally Posted by chrispenycate

Actually, it would be possible to tell by the relative age of the elements and their distribution patterns, if you were working from the same physical theories as us.

That’s closer to what I was looking for, but our future scientists need a way to correctly deduce what happened before the collapse began, and I’m not sure how the examples you mentioned would enable them to do this. Can you be more specific? It’s really more of a thought exercise, anyway, and you definitely understand the implications, and the cosmic misunderstandings that might arise under these circumstances.

[bendoran]

Originally Posted by Glyptus

Certainly, as you look farther out in space, you're also looking farther back in time. You’re right, this would surely be the most reliable way to learn about conditions in the distant past. So, let me make the question more specific: Let's say you live in a universe that has been collapsing for a considerable length of time- (in this hypothetical model, about 15 billion years). All you could see, even with your most powerful telescope, would be galaxies advancing towards you, as if your own world were at the center of this cosmic contraction. If that was your reality, if that was the only way you had ever observed the universe, how would you know there had once been a “Big Bang”, followed by an expansion? What would be the proof?

Unless they were in the centre of the universe not everything would be coming toward them. Somethings would be moving oser but at a slower rate as the matter toward the centre would move faster than that at the edges. Well they must assume the universe began somehow, otherwise why would it still exist? it couldnt come into being one day and have these galaxies all over the place that suddenly just exert pull on each other and collapse. Now given that you have an estimate on contraction you could in theory work out the minimum mass of the universe by tracking the farthest out distance and the time it has taken for contraction. Hevier galaxies would already be in the melting point of the centre and you could work probably estimate how much time your galaxy has left. Given that you have an idea how long the universe has been contracting for you could then estimate the position of your galaxy before it began its journey inward. Given that you could work out a minimum mass for the universe to contract on itselve and the energy required to send matter beyond you. Nothing would be exact, but it would be possible.

in a few words, clutching at straws

[Glyptus]

Cosmology takes the perspective that there is no special place, no "center", in the universe. That's why it appears that all distant galaxies are speeding away from us at a velocity relative to their distance away from us. In the same manner, I believe that a collapsing universe would look very much the same- that everything would appear to be rushing towards us, equally in all directions. Take a sheet of rubber, draw a bunch of dots to represent galaxies, and then stretch out the sheet of rubber. No matter which dot you're sitting on, it looks like all the other dots are moving away from you. It's the same for the universe, except in three dimensions instead of two, like on the rubber sheet.

Anyhoo, it's all theoretical physics to me. As for the math, I'll let someone else do it, thank you very much! :>)

[Áréwn'tháwr]

If the only way we know that the universe is expanding is based on red shift in distant galaxies, this information has been travelling to us for billions of years at the speed of light, therefore this information must be out of date as we are seening the universe in the past. How do we know then, that the universe has not already slowed, stopped, or is now contracting?

[Glyptus]

Good question. My reply can be found in your new thread, "Cosmology Question: Expansion Theory". It seems like a good time to move the discussion over there.