Originally posted by 3.14159265
...i am really interested in astrophysics and cosmology.
..., what existed before the big bang? please state theories or even your own...
If you are interested in cosmology that means you probably are or will be interested in mathematical models of the universe
and you indicate you are willing to consider different theories, you invite people to state alternatives
this is a can of worms but fun too
I disagree with Nereid in a subtle way. I would say that we cannot know there was nothing before BB, or that there was no time.
I would emphasize that the prevailing mathematical model (the cosmologists' favorite for now) breaks down and will not compute at a certain point when you push it back in time.
This gives the impression that there was no time and that nothing existed, but what it means is simply that the model starts dividing by zero, predicting infinities, and gives meaningless results.
But recently it has been found that without doing violence to that model one can fix it so it does not break down, and can be pushed back before the instant that expansion began. And then the model predicts a prior contraction phase. So the prevailing model can be fixed in such a way that the "singularity" or failure of the original model is eliminated, but it still predicts the same story of expansion----coinciding with the original model except right around that critical instant.
Several groups of researchers have done this. A recent paper is by Viqar Husain and Oliver Winkler "On singularity resolution in quantum gravity"
http://arxiv.org/gr-qc/0312094
An interesting feature of their article is that it belongs to an older research line from before "string theory" and "loop quantum gravity" were invented.
It uses long-established "ADM" (Arnowitt-Deser-Misner") variables
and the most widely accepted cosmology model, the "FRW" (Friedmann-Robertson-Walker) model.
So there is not much novelty in Husain/Winkler's approach. FRW has been the standard model since the 1930s and ADM has been standard since 1961. They quantize the FRW model and the singularity goes away.
It is hard to argue with because the FRW-ADM picture has been unchallenged for so long.
A similar result was obtained in 2001, but not using the ADM variables. This was by Martin Bojowald. A number of other people have
derived the same results since then, removing the BB singularity and running the quantized FRW model back through the moment when the prior contraction ended and the present expansion phase began.
There are also exotic cosmologies which are not based on quantizing the FRW model. (colliding braneworlds etc.) But pretty much all of contemporary cosmology uses the FRW model of the universe, so certainly the most obvious and direct approach to dealing with the model-failure at BB is to fix that model by quantizing it.
If you want to read more I will try to find some links. The Husain Winkler article is just one I happened to have handy because it is recent. It is short, but not the easiest to read.
