Recreating the Big Bang. | Page 2 | The Physics and Mathematics Guild | Guild Forums

Dewdew

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Posted: Mon Aug 27, 2007 10:23 pm

Layra-chan

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How do you know there was no time before the Big Bang? Has it been proven? I'm just asking because I really can't understand the concept of something coming from nothing.

According to General relativity and what we see from astronomical observations, if we run the universe backwards then we end up with everything coming together to a single point (this is the Big Bang in reverse). Because of the increase of the matter/energy density as we approach the Big Bang, this coming together also forces time to bend quite severely, and at the point of the Big Bang, there is no more backwards because every direction away from that point is "forward" in time.

Consider the north pole. If you're at the north pole, every direction is south; there is no "north" of the north pole. Similarly, because of the time bending, the Big Bang is a time pole, the "past" pole, if you will; every direction away from this past pole is "south" or forward, into the future.

What is time? How can there be no time?
And still even if there was no time before the Big bang, why was there suddenly time?
Anyway, I'm someone who believes in eternity, though not neccesairly that time as we know it is eternal, but that there is some kind of eternity.

Maybe, (as some theories suggest) the Universe is forever contracting and expanding. therefor the Big bang, was only one big bang in a series of big bang's.

Posted: Tue Aug 28, 2007 7:23 am

Layra-chan

WormHole

How do you know there was no time before the Big Bang? Has it been proven? I'm just asking because I really can't understand the concept of something coming from nothing.

According to General relativity and what we see from astronomical observations, if we run the universe backwards then we end up with everything coming together to a single point (this is the Big Bang in reverse). Because of the increase of the matter/energy density as we approach the Big Bang, this coming together also forces time to bend quite severely, and at the point of the Big Bang, there is no more backwards because every direction away from that point is "forward" in time.

Consider the north pole. If you're at the north pole, every direction is south; there is no "north" of the north pole. Similarly, because of the time bending, the Big Bang is a time pole, the "past" pole, if you will; every direction away from this past pole is "south" or forward, into the future.

Thank you for the explanation, I think I understand what you're saying. However, if there was no time, how can the Big Bang occur in the first place? Also, how do you know that the Big Bang was a 'time pole'? A beam of light will bend significantly when close to a large mass, but it still came from somewhere.

Sorry if I come off as uh...a word that sort of means 'snotty' but I can't think of it. I was up at 1:30 am, watching the FREAKING AWESOMESAUSE lunar eclipse.

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Posted: Tue Aug 28, 2007 8:24 am

Dewdew

What is time? How can there be no time?

Using the prescription for SR/GR, the framework for describing the universe, it is the reversed dimension in the Minkowski metric. You can describe any point in space-time using four co-ordinates: (t,x,y,z) where the absolute distance between two points in space-time is ds² = dt² - dx² - dy² - dx².

It is merely another part of space-time, albeit one with slightly different properties compared with the spatial dimensions.

Dewdew

And still even if there was no time before the Big bang, why was there suddenly time?

The idea of there being "no time" before the Big Bang is that time, itself, is a component of the universe: it is brought into being when the spatial dimensions of the universe are brought into being. However, and I cannot stress this enough, we have no known way of going from a state of no-universe to universe. As Layra states, we can run GR backward in time and we find that the universe becomes compressed into what appears to some sort of singularity. The orthodox Big Bang theory states that this pre-existing super-dense universe expanded and cooled down forming the universe we now observe. The same way in that as the universe expands the dimensions of space stretch out and we can traverse them, time expands.

Dewdew

Anyway, I'm someone who believes in eternity, though not neccesairly that time as we know it is eternal, but that there is some kind of eternity.

It is possible for there to have been something "before" the Big Bang, but it cannot be "before" using the time we experience, it would need to be some temporal higher dimension.

Dewdew

Maybe, (as some theories suggest) the Universe is forever contracting and expanding. therefor the Big bang, was only one big bang in a series of big bang's.

The cycle of bang and crunches. That's not so popular because we do not believe there to be enough matter to slow down the universe so that it would contract upon itself. In fact, we find that it is accelerating away from itself. If we do not believe this cycle to crunch upon itself, how can we propose that there were previous cycles?

Nevertheless, there are solutions to GR that permit a previous universe collapsing before rebounding into this one — particular instanton solutions — it is just not very parsimonious to propose it for we have no data before the Big Bang.

That's about as much GR as I can help with [now, Big Bang from a HEP perspective I know more about].

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