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Infinitenight2093
2010-Nov-03, 03:35 PM
While I understand that the "big bounce" isn't given much credit since the release of WMAP data, I would still like to know something. If all galaxies in the universe are moving radially towards us, then wouldn't that soon create a black hole and then a supermassive black hole that all matter is racing towards? or do I have this all wrong? Is it just the space between points that would be decreasing so that the distance between every galaxy decreases by the same amount with time until there is no distance between anything and all things become part of a whole again? and exactly how then does the universe "bounce" back into another big bang?

Infinitenight2093
2010-Nov-03, 03:37 PM
Also I was wondering if there are any theories that claim time might start to go in reverse, which would lead us to a big crunch and then suddenly revert again?

astromark
2010-Nov-03, 07:27 PM
NO. 'Infinitenight' I do not know from where you got the idea that Galaxies are moving towards us.

Andromeda is on a intersecting path... While others are moving away.

That idea of a shrinking universe is not what we see as ever happening. Your shrinking universe is not.

kevin1981
2010-Nov-03, 08:53 PM
Also I was wondering if there are any theories that claim time might start to go in reverse, which would lead us to a big crunch and then suddenly revert again?

I don't know, i don't think time will go in reverse though. I would imagine if the universe started to contract and get smaller, then their would be "less" time the smaller it gets. If the universe started to contract now, time as we perceive it would still "flow" forwards.

kevin1981
2010-Nov-03, 09:05 PM
Is it just the space between points that would be decreasing so that the distance between every galaxy decreases by the same amount with time until there is no distance between anything and all things become part of a whole again?

I would imagine so as it is the other way round at the moment. Galaxy's are not moving though space-time per se, rather the space-time in between them is increasing separating them from each other. So like you say, if we reverse that, using common sense, it would seem that space-time contracts until everything is on top of it's self in a very hot, dense state.

Also, from the mathematics in general relativity, the universe has to be either, expanding or contracting it can not be in a "steady state".

Infinitenight2093
2010-Nov-04, 02:21 AM
NO. 'Infinitenight' I do not know from where you got the idea that Galaxies are moving towards us.

Andromeda is on a intersecting path... While others are moving away.

That idea of a shrinking universe is not what we see as ever happening. Your shrinking universe is not.

I understand that the universe is accelerating in its expansion, I am not concerned with that. My question is only about the "big bounce" or "big crunch" in which the expansion of the universe would slow and stop like the path of a rock thrown into the air on earth, the expansion will reverse and all galaxies will be moving towards us. I am also aware that these theories are not supported by recent data (WMAP)

Infinitenight2093
2010-Nov-04, 02:27 AM
kevin1981 could you explain what you mean by "less time"?

kevin1981
2010-Nov-04, 03:24 AM
kevin1981 could you explain what you mean by "less time"?

Well, if we could measure the universe starting to contract, getting smaller with time, and we worked out the parameters such as how quick it is contracting and the smaller it gets, the denser it becomes, increasing the speed of the contraction and so on then we could make predictions.

For example we could say, in 5 billion years time, the universe will be half it's size, and in another 5 billion it will be squashed to a point. So if we only had 5 billion years left before the squash or big crunch, then the smaller the universe is getting the "less time" we will have to do anything.

I have a feeling that could be some sort of paradox :/ !

caveman1917
2010-Nov-04, 05:53 AM
I am also aware that these theories are not supported by recent data (WMAP)

In what way exactly is a big bounce not supported by WMAP data, do you have a reference at hand?

WayneFrancis
2010-Nov-04, 06:12 AM
While I understand that the "big bounce" isn't given much credit since the release of WMAP data, I would still like to know something. If all galaxies in the universe are moving radially towards us, then wouldn't that soon create a black hole and then a supermassive black hole that all matter is racing towards? or do I have this all wrong? Is it just the space between points that would be decreasing so that the distance between every galaxy decreases by the same amount with time until there is no distance between anything and all things become part of a whole again? and exactly how then does the universe "bounce" back into another big bang?

The problem with comparing the universe to a black hole is there is a very definite inside and outside of a black hole. For the universe you have no "outside".

Think of it this way.
Take a ball and attach a string to it. Now pull the string. What happens to the ball? It moves right? That is a simple model of gravity. The object moves in the direction of gravity. 1 string is like a black hole or any amount of mass for that matter.
Now attach another string to it but have it lead off in the opposite direction. Now grab a string in each hand and pull away from the ball. The ball doesn't move. The force you are exerting is the same in both direction so the net effect is zero.

Even though the universe was in a state where the mass/energy per unit volume was much higher in the past and we typically associate something with a mass/energy per unit volume with higher gravity it is only because there is a difference in the mass/energy per unit volume from one location to another.

In the early universe this was not the case. The mass/energy per unit volume was very high but also very uniform. So the net result as far as gravity is concerned was zero.

WayneFrancis
2010-Nov-04, 06:14 AM
Also I was wondering if there are any theories that claim time might start to go in reverse, which would lead us to a big crunch and then suddenly revert again?

There is no indication that the time component of space time would reverse if the universe started to collapse back down. The 2 don't seem to be directly correlated in that way.

WayneFrancis
2010-Nov-04, 06:31 AM
Well, if we could measure the universe starting to contract, getting smaller with time, and we worked out the parameters such as how quick it is contracting and the smaller it gets, the denser it becomes, increasing the speed of the contraction and so on then we could make predictions.

For example we could say, in 5 billion years time, the universe will be half it's size, and in another 5 billion it will be squashed to a point. So if we only had 5 billion years left before the squash or big crunch, then the smaller the universe is getting the "less time" we will have to do anything.

I have a feeling that could be some sort of paradox :/ !

I don't see any paradox. Say the universe was in a cyclic state where it expanded and contracted then it would be reasonable to think that it would do it at similar rates. IE takes 20 billion years to expand to its maximum then it might take 20 billion to contract.

Sure in the year 35 billion we'd say "Crap we've only got 5 billion more years before things get REALLY hot"

WayneFrancis
2010-Nov-04, 06:41 AM
In what way exactly is a big bounce not supported by WMAP data, do you have a reference at hand?

I'm not complete sure but he might mean how they used WMAP data to determine the hubble parameter which matches other older methods in a independent manner. Combine that with other techniques showing that the hubble parameter show that expansion is getting faster then you could indirectly infer that WMAP supports an increasingly expanding universe. Though, as I understand it, it only confirms a smaller set then what is needed to say that Omega < 0.

loglo
2010-Nov-04, 08:24 AM
There is no indication that the time component of space time would reverse if the universe started to collapse back down. The 2 don't seem to be directly correlated in that way.

Hawking discusses just such a possibility here:-
Arrow of time in cosmology (http://prd.aps.org/abstract/PRD/v32/i10/p2489_1)

I think this was the inspiration of the Red Dwarf episode "Backwards".

astromark
2010-Nov-04, 08:55 AM
I am pleased we are the same page 'Infinitenight' but then I see both 'caveman' and 'loglo' are back there...

Let this be rested and clear... The Universe is continuing to accelerate as it expands. That this is the mainstream view is a fact.

Some of us accept this as fact. I see some do not... shame really. Because I want to make a point.

Which will be completely wasted if you do not accept as fact the expansion we are so sure of...

It being that; If the alleged bounce were the fact and a shrinking of the universe were to occur. Would time reverse.

No.

loglo
2010-Nov-04, 09:06 AM
Astromark...the OP wasn't about the current mainstream, it was about a specific model of cosmology. When the Big Crunch was still a possible outcome there was a bit of work done on the turnaround point. Hawking's arguments come from similar ones he used in his theory of black hole radiation. So forgive me but I will be siding with Mr Hawking on matters cosmological over your opinions of the facts.

astromark
2010-Nov-04, 09:22 AM
I am pleased by this... As I also hold Doctor Hawking's words as paramount in regards to cosmology.
I now understand the conversation and its context. Just 'caveman' to bring up to speed then... How do we do this ?

Have I understood you correctly 'caveman' Do you not accept the expansion infinitum. As the best yet explanation available.

caveman1917
2010-Nov-04, 06:39 PM
I'm not complete sure but he might mean how they used WMAP data to determine the hubble parameter which matches other older methods in a independent manner. Combine that with other techniques showing that the hubble parameter show that expansion is getting faster then you could indirectly infer that WMAP supports an increasingly expanding universe.

Ah I see. As in a prediction of a future big bounce. I was thinking in the sense of an explanation for the past big bang.

caveman1917
2010-Nov-04, 06:44 PM
I don't see any paradox. Say the universe was in a cyclic state where it expanded and contracted then it would be reasonable to think that it would do it at similar rates. IE takes 20 billion years to expand to its maximum then it might take 20 billion to contract.

Interestingly, if a cosmological constant is presumed for dark energy, it will act in reverse for contraction - it will slow it down. So you would get a period of rapid expansion, and then a slow retreat backwards.

astromark
2010-Nov-04, 07:33 PM
I find it confusing and a bit of a conundrum... That there is this line of thinking that tolerates a reversal of the great expansion we see.

We have not the slightest clue to the acceleration and expansion rate ever subsiding. Where does this enquire come ?

WayneFrancis
2010-Nov-05, 04:35 AM
I find it confusing and a bit of a conundrum... That there is this line of thinking that tolerates a reversal of the great expansion we see.

We have not the slightest clue to the acceleration and expansion rate ever subsiding. Where does this enquire come ?


Agreed, I put it in a similar bucket as being asked "What would happen if the Earth's orbit would reverse?"