raindropple

Will the universe just burn out and be pieces of cold high density iron ever expanding etc.or will there be a big crunch?

Will the process start over if there is a big crunch?

Aquila ka Hecate

Hi raindropple(?),

Two directions of research and speculation tend toward the idea that, no, we won't experience a big crunch.


In one, the 'flatness' of the universe is now thought to be such that we escape the topological closure,
and in the other,Turok at Cambridge has been playing with string theory, and reckons that maybe the universe has never had a beginning, and thus won't have an ending-a sort of cyclical reformulation of everything.

At least, that is my latest take on the situation-probably there are members here who keep a little more up to date than I do...it's tough these days!

(edited because its the afternoon before a long weekend and I'm dropping off at the console)

[ August 08, 2002: Message edited by: Aquila ka Hecate ]</p>

raindropple

Could you please explain a little more what is meant by "escape the topological closure,"?

eh

The universe is not only expanding, but accelerating, so no big crunch seems possible. So the stars of the universe will all die, but the fundemental energy will exist forever.

Since forever is a long time, there is always the chance another inflation event could happen and led to the creation of more galaxies. So we have a universe that expands forever with an infinite potential for the creation of life.

Bill

My personal understanding (from <a href="http://zebu.uoregon.edu/~js/ast123/lectures/lec28.html" target="_blank">Professor Shombert's Astronomy 123 on-line class</a>) is that the "heat death" condition of the universe occurs after roughly 10**100 years, after which no matter will exist: Once the state of quantum vacuum is reached, or even at an earlier stage in the process, there might well be a quantum fluctuation, and from that fluctuation, the entire process can begin all over again (so say some physicists, anyway) with the creation of yet-another "Big Bang."

Another possibility is to finally demonstrate that the expansion of the universe is due to pressure applied from the total matter and energy within the universe, so that once the state of quantum vacuum is achieved, there will be literally nothing holding the universe up to its fully-expanded size, and at that point there will be a catastrophic collapse of the universe, probably into a "big crunch" of some sort. Thus, it may well be that we will have a cyclical universe without having enough matter to force an "early" collapse.

All-in-all, I would not reject the idea of a cyclical universe or a "Big Crunch" just because our present experimental evidence seems to indicate that we will not have an EARLY "Big Crunch."

== Bill

Aquila ka Hecate

Sorry about that-out of sync with most of the board!

By the 'topological closure' I was meaning to say, in my less than lucid fashion, the 'shape of the universe being closed'

Umm, that is, we've long thought that we could be in one of three 'shapes', topologically.

one is a four-dimensional open, or hyperbolic sine shape similar to a saddle shape in three dimensions.

The second is a four-dimensional closed,or sine related shape roughly corresponding to a sphere in three dimensions.

Lastly a non-curved (in four dimensions) or flat shape.

This last is probably the state we are in.

It has been thought that for the universe to acheive a four-dimensional closed sphere, we would have to find about ten times the amount of mass we already have tracked down.
Possibly we may never find all the so-called missing, or dark, matter.

We seem to have accounted for about enough mass to ensure that the universe, if not hyperbolically shaped, is at least flat.

I hope this makes some kind of sense-I'm not the world's greatest communicator!

(Edited because by no stretch of the imagination is 'sin' equal to 'sine' in written English!)

[ August 08, 2002: Message edited by: Aquila ka Hecate ]</p>

ohwilleke

The current estimates of the density of matter in the universe based upon what we have observed is insufficient for gravity to pull the universe back together into a big crunch. Moreover, we have not observed areas of mass positive and negative electrical charge, allowing for long range action of that force of nature, and the only other two non-contact forces we have discovered in nature (weak and strong nuclear forces), only work at very short ranges and hence couldn't explain universe level dynamics. If any big crunch is in the offing, it could only happen because of distributions of matter and energy we have not yet observed or non-contact forces that have not yet been discovered.

To the extent that the results of experiment differ from the predictions of gravity acting alone on observed matter and energy, they show that predictions based on gravity acting alone overestimate the apparent strength of the forces tending towards a big crunch. In short, there may be something wrong with current versions of the theory gravity at long range with huge masses through apparent vacuums, or there may be another repelling non-contact force we don't know about. There is not experimental evidence for any kind of force that could create a big crunch.

Observation, based on cosmic ray observations, for example, also shows no evidence of concentrations of gravity sufficient to "wrinkle space-time" by curling the shape of the universe towars high concetrations of mass on the scale of the universe at large. While there are local distortion, observations do not reveal any material distortion of the universe as a whole by gravity it is thus "flat" to a very high degree. There is no observational indication, for example, that the universe will allow you to travel in one direction in a straight line and end up coming back to the same place from another direction as you can on a globe.

[ August 09, 2002: Message edited by: ohwilleke ]</p>

Answerer

Hi, guys, I had a pretty nasty imagination of the inevitable fate of the future of our universe. Since our universe is expanding faster and faster, it may come to point where the stretching of our spacetime fabric will come to its limit and tore apart, resulting in a line of event horizon or sort. I guess all of you know what will happen next.

Aquila ka Hecate

We'll ask for a towel?

eh

Hey Bill,

This topic came up in another thread, but I guess you must have missed it.
GR predicts spacetime can not only exist without matter, it can also expand. If you were to create a universe full of matter, it would start to contract, not expand. Even though it was once thought the expansion was caused from the initial energy from the big bang, this need not mean the expansion would stop after all matter is gone.

In fact, the discovery that the expansion is speeding up seems to do away with the idea. The energy of the vaccuum should be enough to explain why the expansion is getting faster. The more empty space you have, the more vaccuum energy comes into play. As the universe gets bigger, the effects of the energy increase and you get an increasing rate of expansion.

So without matter, the universe should still continue to expand. If eternal inflation is correct, then some regions of spacetime will 'inflate' to a massive, expanding fireball, laying the seeds to galaxy creation. It does not require the entire universe to contract, and could happen without end. If this is true, then I suppose we would have no way of knowing if our local big bang truely was the beginning.