luvluv

I hope this hasn't been addressed, but I would like to comment on the notion that time before the universe began is an impossibility.

Doesn't this beg the question, a bit? If one holds that "the universe is all there is, all there was, and all there ever will be", then yes it is nonsensical to speak of time before time. But suppose someone doesn't believe that, or doesn't see any good reason why they should?

This is not simply a theist argument. Even given the many universe hypothesis, isn't it perfectly reasonable that there was a time, in another universe, temporally prior to our Big Bang?

eh

Keep in mind, that space is something rather than nothing. Space is just another name for the gravitational field, so there is no reason it can't be finite. But cosmologists say the universe is spatially infinite, so I guess the point is moot.

But if it helps, try using a 2D analogy to understand how space can fold over itself. Humans can't imagine an object with 4 spatial dimensions, so the best we can do is start with a 2D sheet of paper, and wrap it around. Take the sheet, and draw some galaxies on it. Then roll it up into a cylinder, and join the ends together. You can see that any 2D stick person on this sheet would eventually travel in one direction forever without reaching an edge. The same idea applies to a closed universe, but with a 3D sheet folding over.

Hawkingfan

The statement that "time did not exist before the big bang" actually holds true much better when you use them model of an ever-expanding universe beginning at a finite time in the past and where time is relative then in the one where an infinitely static universe always existed.
Between ten and twenty thousand million years ago, distances between neighboring galaxies was zero. At that time, which is called the big bang, the density of the universe and the curvature of space-time would have been infinite. However, mathematics cannot truly deal with infinite numbers, so the theory of relativity concludes that there's a point in the universe where the theory "breaks down". In math, this is what is called a "singularity". All theories of science are based upon the assumption that space-time is nearly flat and level, so they "break down" at the big bang singularity, an area where curvature is infinite.
So, if there was an event or seies of events prior to the big bang, we could not use them to determine what would happen afterward, because predictability "breaks down" at the big bang.
We are therefore limited to only know what has happened after the big bang.
In fact, events taking place before the big bang would have no consequences whatsoever, so they do not form any part of a rational scientific model of the universe. Scientists therefore exise them out of the model and declare that time had a beginning at the big bang.
Our universe began at the big bang. You therefore would not be able to say that the big bang was apart of a prior universe, because the first universe would be the actual universe.

Stephen T-B

I like the fact that the big mysteries are still out there.
Some people can solve them using their gods.
Some people can sit back and wait patiently for science to come up with an answer.
Some people can enjoy the speculation which ignorance permits.
What is clear to me, and I am not even remotely scientifically orientated, is that the Big Bang did not occur without a precedent.
In the no-time zone of a pre-Big Bang Nothingness, there is no moment at which something can begin to happen.
Right?

Oxymoron

Me too.

Not right, not necessarily wrong, but definitely impossible to verify. More in the realm of the speculation you mention. In that vein, we might like to base an informed view of what the pre-BB might have been like when we get a better understanding of what time is in the first place (see other threads in the forum). Then we might be in a position to speculate upon its absence!

Steven S

Uh, no. The gravitational field is given by the curvature of spacetime. Spacetime is given by a smooth manifold funished with a metric and the Einstein tensor is a measure of the intrinsic curvature of your spacetime and also the field strength.
As to the question that started this thread...
In the BB cosmology all world lines are traced back to the Big Bang, the initial singularity. The common analogy to this is to trace all the latitude lines from the equater to the north pole and then ask what is north of the north pole. So the geometry of the situation renders the question
of what event preceded the BB somewhat meaningless.

Steven S

eh

I'm not sure what you're trying to say here. Space itself is a gravitational field, by why again can't it be finite?

Steven S

I didn't write that space cannot be finite I pointed out that your statement 'space is another name for the gravitational field' is wrong.

eh

Then I must be reading something wrong:

<a href="http://itss.raytheon.com/cafe/qadir/q2330.html" target="_blank">http://itss.raytheon.com/cafe/qadir/q2330.html</a>

What do cosmologists mean when they say 'space' is just the gravitational field of the universe?

Answerer

Somehow, I feel that everything in our universe is quantized and that there is a ground state(or minimum value) for every matter(charge, 'colour' and mass), energy and spacetime. Hehe, maybe I got too much quantum in my head.