View Full Version : Gravity and the Big Bang

AriAstronomer

2010-Jun-25, 01:11 PM

This is kind of on the subject of another thread, but a different question, so I thought I'd start a different one. Is the following question grounds to believe that the universe may indeed be finite (in matter at least):

If the universe had infinite matter, then the 'gravity well' at the instant after the big bang would have also been infinite, and therefore the time dilation would have also been infinite, and therefore nothing else would have happened afterward; we would simply be frozen in time in the first instant after the big bang.

korjik

2010-Jun-25, 01:13 PM

only to an outside observer, which by definition dosent exist

Ken G

2010-Jun-25, 04:40 PM

What's more, any theory that takes the model right back to the singularity achieves an infinite degree of time dilation at t=0, not just those that use an infinite universe. But we know our physics breaks down before the time dilation reaches infinity, so when we are faced with a theory that cannot support a certain reality, do we say the reality cannot have happened, or just that the theory cannot work there? We should use theories to understand reality, not to legislate reality.

What's more, I don't even know if an infinite time dilation would have to "freeze time"-- there are functions that go infinite at t=0 that can still be integrated to yield a finite result when integrated up from t=0.

cosmocrazy

2010-Jun-25, 05:13 PM

This is part of the problem with dealing with infinities, especially at the origin of the BB. Our current math and theory suggests that the BB possibly came from an infinitely dense point that occupied no space or time (Singularity). Whether or not this physically happened or is possible is not known. What we can take from this though is that quite possibly the laws which govern our universe came into existence very shortly after the initial BB and quite possibly the laws were set dependent on the out come of the initial BB. So you could say anything was possible at the point of the BB. And as all the laws we observe seem to be a function of space-time and what it contains, anything prior (if that term makes any sense) to the BB would have no definition, so time dilation and such would not apply and make no sense.

korjik

2010-Jun-25, 06:08 PM

What's more, any theory that takes the model right back to the singularity achieves an infinite degree of time dilation at t=0, not just those that use an infinite universe. But we know our physics breaks down before the time dilation reaches infinity, so when we are faced with a theory that cannot support a certain reality, do we say the reality cannot have happened, or just that the theory cannot work there? We should use theories to understand reality, not to legislate reality.

What's more, I don't even know if an infinite time dilation would have to "freeze time"-- there are functions that go infinite at t=0 that can still be integrated to yield a finite result when integrated up from t=0.

If you understood the reality, you would know that it dosent legislate the reality. The theory breaks down bacause it is not complete enough to handle the situation. This is a well known property of current theory.

forrest noble

2010-Jun-26, 12:53 AM

AriAstronomer,

Gravity and the Big Bang

This is kind of on the subject of another thread, but a different question, so I thought I'd start a different one. Is the following question grounds to believe that the universe may indeed be finite (in matter at least):

If the universe had infinite matter, then the 'gravity well' at the instant after the big bang would have also been infinite, and therefore the time dilation would have also been infinite, and therefore nothing else would have happened afterward; we would simply be frozen in time in the first instant after the big bang.

There might be good arguments that the universe is infinite in matter but to my knowledge there are no well-known BB proposals that assert infinite mass. In general most BB models propose that the universe is finite in three different ways: That it is finite in its quantity of mass energy; finite in its volume or extension of space; and finite in its age and elapsed time since its beginning: it accordingly would have a definite age concerning a beginning before which nothing existed.

If you wish to consider models involving infinities, most of these models do not include a Big Bang. There are however a number of other models the propose a finite beginning and finite extensions separate from the Big Bang model.

The logic of your argument seems valid based upon common sense, which is a good thing in my opinion.

Ken G

2010-Jun-26, 04:57 AM

The theory breaks down bacause it is not complete enough to handle the situation. This is a well known property of current theory.Exactly, and that is why it is completely moot on the issue of the potential infiniteness of the universe. There are no physical or observational objections to an infinite universe, the objections are purely philosophical. Without philosophy, we can only go with the observations, and they are completely moot on the four possibilities:

1) the universe is infinite and obeys the cosmological principle

2) the universe is compact and obeys the cosmological principle, so closes on itself

3) the universe does not obey the cosmological principle, so can have finite mass without being compact

4) the universe is something different from any of these in ways our imagination has not even entertained.

Take your pick.

AriAstronomer

2010-Jun-28, 08:24 AM

Yeah, I think I secretly knew this already from other posts I had personally responded to on other people's question boards, but I think I need to be reminded often that theories simply try to do the best job it can in explaining current phenomena we see, and the extreme predictions of the theories shouldn't always be taken too literally. Theories try to explain reality, not the other way around. Take QM for example. Should we believe that me making a typo on this forum suddenly creates a new universe where the only distinction between the two, out of everything in the universe that has happened, is that I didn't make the typo error? I'm personally against the thought.

Jens

2010-Jun-28, 08:37 AM

Take QM for example. Should we believe that me making a typo on this forum suddenly creates a new universe where the only distinction between the two, out of everything in the universe that has happened, is that I didn't make the typo error? I'm personally against the thought.

I don't think that's a logical conclusion of GM, just the description of one explanation of QM. It's not the viewpoint of the so-called Copenhagen interpretation (that there is a mermaid who sits around all day throwing dice).

Infinitenight2093

2010-Jun-29, 05:53 AM

This is kind of on the subject of another thread, but a different question, so I thought I'd start a different one. Is the following question grounds to believe that the universe may indeed be finite (in matter at least):

If the universe had infinite matter, then the 'gravity well' at the instant after the big bang would have also been infinite, and therefore the time dilation would have also been infinite, and therefore nothing else would have happened afterward; we would simply be frozen in time in the first instant after the big bang.

Excuse me if I am wrong but doesn't general relativity break down at those scales? how can we even say that the universe behaved according to GR if we don't have a quantum theory of gravity?

WayneFrancis

2010-Jun-29, 02:03 PM

AriAstronomer,

There might be good arguments that the universe is infinite in matter but to my knowledge there are no well-known BB proposals that assert infinite mass. In general most BB models propose that the universe is finite in three different ways: That it is finite in its quantity of mass energy; finite in its volume or extension of space; and finite in its age and elapsed time since its beginning: it accordingly would have a definite age concerning a beginning before which nothing existed.

If you wish to consider models involving infinities, most of these models do not include a Big Bang. There are however a number of other models the propose a finite beginning and finite extensions separate from the Big Bang model.

The logic of your argument seems valid based upon common sense, which is a good thing in my opinion.

Where do you see the BB model say anything about the universe being finite in volume and energy? Even the claim of finite in time is only a generalisation as the details of the actual models can't go back to T0 so can't really say much about the first instances.

The universe could, from my understanding, have come forth from a point of no volume and transitioned straight into a infinite volume with a total infinite amount of energy. All we can say is shortly after T0, if the models are right, the universe was very dense but not infinitely dense.

For the OP, there are other posts that explain why there is no problem with the time dilation. Basically the dilation can only be infinite with respect to an outside observer. Just like a free faller going into a black hole doesn't freeze in time with respect to themselves. Its the nuances of a theory that are really interesting.

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