Before the big Bang?

What is the evidence to prove that the universe was extremely small and extremely dense before the Big bang?
- Shanti
Bangalore, Karnataka, India

Well, we don't know what the state of the Universe was before the big bang since there is no remnant evidence that would allow us to observe it.    There is plenty of evidence from astrophysical observations that there was an extremely hot and dense beginning of our observable universe.  These observations include the CMB (cosmic microwave background),the observed Hubble expansion rate, the abundance of light elements, etc. 
Take a look at for more information.

LeeH

(published on 07/31/2008)

If we say that our universe is expanding there must be a space in which it is contained--?
- nimish (age 16)
india

You might think that at first but it isn't necessary. The mathematical description of a space in which the distances between all objects keeps growing in time is self-consistent. It doesn't require any reference to a hypothetical larger space.

Mike W.

(published on 08/15/2008)

The big bang must have begun from something right?? According to scientists everything,time energy etc came into existance from the big bang...But why did the big bang occur any way???
- Souptik
trichy,tn,india

This question is one of the most important ones in cosmology.  The short answer is that we simply don't know why it came about or where did all that energy come from.  Many pieces of astronomical evidence point to such a happening taking place 13.7 Billion years ago. An important clue is the current presence of the 'Cosmic Microwave Background', called the CMB in the literature.  This ever present radiation is consistent with the Big Bang hypothesis and subsequent expansion of the universe.  The physics of Big Bang becomes a bit murky.  The reason is that it was so dense and energetic one needs to use both quantum mechanics and general relativity to characterize the situation.   This is very difficult but the problem is being vigorously pursued these days.     The best I can do to help you is to point to an article:      http://en.wikipedia.org/wiki/Big_Bang

LeeH

(published on 06/13/2009)

I just watched a program about Stephen Hawkings in which was stated that before the big bang there was no previous time or existence. So my question is time must have existed before the big bang, because if it didn't, the big bang would never had happened?
- Ian Bailey (age 58)
london

That show stated too much. We don't know what to make of spacetime right around the Big Bang, because to describe it we'd need a quantum theory of gravity. None has been fully developed yet. So there may have been a "before" or at least some sort of extension of spacetime beyond that vicinity, although not necessarily in a way that would be called "before". We just don't know.

Mike W.

See also  and our other many "before the big bang" answers.

(published on 12/07/2013)