Saying that all atheists believe in creation from nothing is wrong. Please consider a rebuttal for what many atheists really believe in:
What was in the beginning?:
What will be in the end?:
It's really amazing how advanced the school of though was in Ancient Greece.
The Greek believed in a creation from Chaos. (We have the word "Chaos" from them)
In Greek mythology this Chaos gave birth to the first gods who then created the Cosmos (the order, in the Greek understanding the Cosmos stood against the Chaos.
The Ancient Greek had no understanding of advanced physics and therefor had to make the mistake with the Gods. If the Greek would have known the stunning simplicity of the universe shortly after its formation I guess they would have become formidable atheists.
In a time-bound universe you need to have a beginning (and an end). The Indians (South Asia) thought up the idea that time is an everyspinning wheel. (Which actually begs the question who made it spin)
If you don't have a universe in a time-loop you have the problem of what was before.
You have 3 principle options how this could happen.
a) Creation from nothing: Nothing causes nothing. If nothing would cause something it wouldn't have been nothing.
b) Creation from a static entity (God). Before the universe there was no time. Without time there is no movement or change. An entity that does not move can't create. It would be 'frozen' in a timeless existence.
And if there was a non-moving entity (God) why did it create the universe about 6000 years ago? Why not 5 minutes earlier?
If this entity (God) was everlasting, why did it wait to create the universe?
What caused it to create the universe after an infinity of waiting? -Keep in mind that it was the only thing existing and a cause would need to be an external influence on the system.
what lasts is option 3:
Creation from Chaos
A perfect Chaos can't have a cause since a cause would be an impossition on this Chaos that would spoil it. A Chaos is defined as a system that is without rules applying to it or a system upon an infinte number of orders apply.
A little experiment of though:
Imagine your desk: You bring your order to this desk. Then comes another person and adds his order to your desk, and then a this person who adds her order to the desk too... and so on. Just imagine your desk after lets say 100 persons adding their orders to it.... it will already look pretty untidy.
The great thing about a Chaos - that's existing - is that everything can happen. If not everything could happen it wouldn't be perfectly chaotic. The more complex the things are that happen the less likely they become. If you throw dice the chance that you throw a one is 1 to 6. The chance that you throw 10 ones in a row is 1 to 60,466,176. And a perfect chaos would keep on throwing dice forever...
At one point in this process of throwing dice it had to end up with the singularity and the physical laws who gave birth to our universe.
- And since the Greek did understand logic but not physics as we do today they had to end up with simple Gods who then created the further order that we see today
Our universe still ressembles it's creator - the Chaos -: The 2nd Law of Thermodynamics. On the grand scheme entropy always increases. (Which does not mean that entropy can't decrease in local systems upon the entropic cost of its environment - see your fridge). Entropy is a messurement of thermic disorder. The higher the entropy the higher the disorder. And with every moment the entropy of the universe increases.
The universe was given birth by Chaos and it will end in Chaos.