1. Jul 25, 2004

### niranjan

Hi,
i had a query bout big bang which i guess even u guys would have thought of at some time or the other.....
big bang theory says that this primordial atom was a "small point" which had infinite density and contained all the matter n energy needed to fuel n run todays universe.....agreed.....it is possible for this whole universe and its energy (keep on compressing, i guess )to be gotten at a single point ....agreed......but how can one say that time n space was created at the time of big bang!!!!
when u r saying that before the big bang some "primordial atom" was present then it just goes on to prove that some process must have been happening to "create" that atom....it just cannot come out of nothing! now when some process was being done....how can u say that time was created at the big bang??at what time was the process being done? was the process being done in negative time??even so time was present! also the theory that space was created has got the same questions......if space was created at the time of big bang ,then where was the atom placed at the time of big bang.....it can be agreed that "inside" this atom space was and is continuously being created but even at the boundary of this atom(now turned into our universe) space has and should still be present.....in which case once we reach the boundaries of our universe we should not be stopping but just be going into that space which was present before the big bang.....
these r just my views....i am an amateur and really am not aware if these questions have already been answered by somebody....anyways please be kind to tell ur views...
thanks, niranjan

2. Jul 25, 2004

### urtalkinstupid

The theory of the big bang starting off from a single point (singularity) has been thrown out, for the most part. Now, they are saying that the big bang was a small string that was about $10^{-33}cm$ in length. This was said to have "finite" mass but no volume. It had no volume, because it only had length. My question is: How can the big bang happen, when the pull of gravity towards this string was so great that nothing could get out? Does this have anything to do with Hawking's new idea on black holes? How can space not exist before the big bang even happened? Where was this singularity or string positioned at? If there is no space, there was nothing that could contain. If space was created at the big bang, what was there before space? The idea of a big bang is just repugnant.

3. Jul 25, 2004

### Mike2

Well actually, wouldn't time slow to a stop as the universe crunched to a point so that in essense we would never actually reach the singularity itself?

4. Jul 25, 2004

### urtalkinstupid

Mike2, are you also asking if space would not exist if the universe were to crunch?

How can the universe expand or cave in on itself? I really want to know how the big bang actually happened. If something has finite density, woudln't it have finite gravitational pull? This would make it impossible for expansion?

5. Jul 25, 2004

### Jim Beam

yes, ask yourself how long this string existed before the big bang occurred, and what caused it to actually bang, instead of continue its existence as a super small string

6. Jul 25, 2004

### Chronos

The volume of the universe has always been infinite. Mass density is the only property that has varied over time. The big bang singularity represents the point at which the mathematical model breaks down, not physical reality.

7. Jul 25, 2004

### Mean-Hippy

Haaa, Welcome to the mind bending world of astrophysic ! :rofl:
I am not really qualified to answer your question but here are some articles that you might find very helpfull in your rflections
- SCIENTIFIC AMERICAN Vol. 290 no. 5 (may 2004) :"The Myth of teh Beginning of Time"
- DISCOVER magazine vol. 25 no. 2 ( feb 2004 ): "Before the Big Bang".

I can also invit eyou to look into the researchs about the Cosmic Radiation Backgroung. The predictions of the Big Bang theory about the characteristics of the CBR have been confirmed to an amazing degree of precision by later observations.
See SCIENTIFIC AMERICAN Vol. 290 no. 2 ( feb 2004 ) : "Four keys to Cosmology"
It is of course to early to close the books on the birth of our universe but we are certainly on the right track.

8. Jul 25, 2004

### Mike2

How can space curve back on itself, you ask? Imagine a balloon. If you were a bug on the surface, you could walk in any direction and end up back you were you started. The surface of the balloon is "closed" which means it has no boundary. A bowl is a surface which has a boundar, and a cylindar is a surface that has two boundaries. The surface of a balloon is 2 dimensional, you can walk in any combination of east and north but you can't walk up - thus 2 dimensions. The universe is supposed to be a multidimensional version of these concepts.

It is supposed that all of space started from a singularity and then started to grow with time as a closed manifold, a closed geometry with dimensions that curve back on themselves. All of spacetime started this way with nothing at all beyond the initial closed manifold that defines the initial dimensions of the universe.

9. Jul 25, 2004

### niranjan

hi mike,
agreed what u r saying -that due to some reasons with time space started to grow-but my point is:space started to grow for OUR universe and not for the actual thing that was present before it - also what must have been the "trigger" for such an expansion ? one really needs to think-whether it was an external trigger or an internal trigger? if external then the very theory of time starting with big bang should go out of thw window because for that very existance of an external trigger some other process should have taken place...if an internal trigger then again we have to ponder that what was it inside the system which caused it to go over the threshold?
i know one might say it is very easy to put such questions for the sake of argument!- but what i am surprised is that how we have chosen to accept a theory with such confidence without suceesfully answering these simple ques!!
in a way i too am a big supporter of a big bang sort of creation for our universe - but only for OUR universe - i quite firmly beleive that once the boundaries of our universe is reached it will just open out to a newer super universe - one might ask when does this new universe end ? what r its boundaries ?n what beyond that.........
lets hope one day we know the answer!!
regards, niranjan

10. Jul 25, 2004

### urtalkinstupid

It is only "supposed" that all of space started from a singularity. How did this singularity come into existance if there was nothing before space? Ask yourself, "Is it legit to say that everything arose from a single point of existence?" Space was always here. It never arose from a point. Energy emerged as a way to try and make space symmetrical. Energy is made in different densities. When an energy of a lower density meets an energy of a higher density, it is absorbed. This is how the first particles became to form. Just a theory. Everything wants perfect symmetry, space is just like everything but nothing at the same time.

11. Aug 2, 2004

### Phobos

Staff Emeritus
FWIW, string theory has not replaced big bang theory (at least not yet). But it sure is an interesting development of ideas. For now, big bang theory (as modified by inflation theory, etc.) is still the standing explanation...although the concept of the singularity is certainly being scrutinized as suggested here.

I hope to have more time to discuss this soon. So for now, I'll just bump this back to the top of the topic list because I think there is a lot that can be discussed here.

12. Aug 2, 2004

### Nereid

Staff Emeritus
There are a number of 'big bang' cosmology models, with various kinds of 'inflation' for example to address the 'flatness' problem.

Big bang cosmologies which stick to 'confirmed physics' - General Relativity and Quantum Mechanics - cannot model the first Planck 'second' of the universe, ~10-43 s. This is because GR and QFT are inconsistent with each other in the dense early universe.

There are some theories of physics which seek to unite, or supersede, GR+QFT - String/M Theory is one huge class of such theories. In principle, within such theories, a consistent description of the first Planck second of the universe is possible.

So what to do? IMHO, it depends on what you're interested in. If it's views consistent with confirmed physics, then 'What happened in the first Planck second?' is question that cannot be answered. This has the advantage of being sound physics (consistent with observational and experimental results), but may be annoying (what *did* happen??).

If it's speculation, loosely based on some new theories for which there's essentially no observational evidence, then take a look at string cosmologies, etc. I would recommend that you spend some time on the Strings & Branes sub-forum.

13. Aug 5, 2004

### whydoyouwanttoknow

Was it Hawkings who said, "Asking what happened before the Big Bang is like asking what is north of the North Pole?"

14. Aug 5, 2004

### marcus

Carlo Rovelli said that.
(It could be folklore, it might not actually be known who said it first. And several people may AFAIK have made the saying up, Rovelli being one of them.)
He uses that one-liner in the introduction to his book "Quantum Gravity".

In Loop Quantum Gravity one does study what could have preceded the big bang, because the singularity has been removed, so this quip about the north pole has become somewhat dated.

It's a witty saying, but one doesnt know how seriously to take it.

15. Aug 5, 2004

### whydoyouwanttoknow

I do know though that Hawkings said that whatever was before the Big Bang would have no bearing on the universe after the Big Bang.

16. Aug 5, 2004

### marcus

he could also have made up the north pole quip too
but if he did he wasnt the only one

cosmology is in the whitewater rapids just now and sayings
get out of date so fast

what was before the big bang seems not to have quite a lot of bearing on our universe----I will give you some links to check out----and this isnt Hawking's fault, it is just that things change

I have to go get the links

17. Aug 5, 2004

### marcus

http://arxiv.org/gr-qc/0407097
"Disappearance of the Black Hole Singularity in Quantum Gravity"

http://arxiv.org/gr-qc/0407074
"Genericity of Big Bounce in isotropic loop quantum cosmology"

http://arxiv.org/abs/gr-qc/0407069
"Genericity of inflation in isotropic loop quantum cosmology"

An overview given by John Baez 20July at the GR17 conference in Dublin
"Loop Quantum Gravity, Quantum Geometry and Spin Foams"
It is online at his website
http://math.ucr.edu/home/baez/lectures.html#lqg

This is all recent work. Removing the Big Bang singularity goes back to Bojowald in 2001.
the point is there was no singularity at BB
and what preceded it could have been somebody else's black hole
because black holes do not contain singularities either (see Modesto and also forthcoming Bojowald paper)
and if so there are testable predictions
so the hypothesis that our universe proceeded from a black hole somewhere else can, surprisingly enough, be tested and shot down if
some things can be observed which astronomers are looking for
and so, curiously enough, this strange idea is empirical---testable--part of scientific discourse.

And so what came before actually does have some bearing on what is, and what we can test and observe. what preceded the big bang now is meaningful (although if you had asked me 5 years ago I might very well have agreed with what you say hawking said). Sayings get old.

18. Aug 5, 2004

### meteor

Where in the hell have you read it? I don't know of any string theoretical model that says that the universe started from a string

19. Aug 5, 2004

### Chronos

I kind of like the notion the universe was a pure quantum state 'prior' to the initial expansion [big bang]. Like all well behaved quantum states, it was in a continuous state of fluctuation. The inevitable result is that one of those fluctuations had the right properties to result in this universe.

This allows for the possibility of an infinite number of other 'universes', most of which either quickly collapsed or expanded so rapidly that no complex structures could form. I don't see that as a problem so long as each universe is causally isolated [i.e., unable to interact with other universes]. This is similar to Gott's bubble universe idea. His theory bogged down, in part, due to perceived problems involving collisions between different bubbles. This objection, however, assumes the bubbles all arose at the same 'time'. I would argue that prior to 10-43 seconds, the concept of time ceases to be meaningful, hence so does the concept of simultaneity. More likely, it would seem, each universe, by its own clock, is infinitely distant in time from all other universes. Anyways, this is one way to solve the problem of 'why is the universe the way it is?' without appealing to the anthropic principle. The answer is 'one of them had to be like this one'.

20. Aug 7, 2004

### Mike2

This is a contradiction of terms. If there never is any causal link between two things, then you could never use one to prove the other. In other words, there could never be any evidence or proof derived in this world that would prove the existence of the other. If it never has an effect, then it does not exist.