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I'm just copying this over from another thread, it will be a useful way for me to refer back to it and anyone who looks at my journal can become a little more informed about science as I, apparently, did a pretty good job of explaining it all in layman's terms.






You did a terrible job of describing the big bang theory so I'm going to clarify- hopefully a few people will read this and decide not to post anything~

The big bang concept was derived out of several mathematical equations approximately a century ago. Mainly the Hubble's law redshift, the cosmological principal, and the Friedmann-Lemaître model of general relativity. Basically if you put them all together the big bang theory says that the universe used to be very small and very hot.
Now, thirty or so years after the theory had been created we discoverred something so powerful that it wiped out all other theories at the time about this subject- the cosmic microwave background radiation. The big bang theory predicted this (through complicated physics) and nothing else has had so much as a guess as to why it would be there and at such a specific frequency (which was also predicted by the big bang theory.)

So, a lot of people thing that the big bang just says that all of the matter was all in this tiny dot and then exploded. Well, that might be an acceptable way of explaining it to second graders but that is by no means what scientists think happened. Rather than that, it is thought that there was just an unimaginably large ammount of energy in a small galaxy- basically it was so hot that any matter forming would have been torn apart and converted right back into energy. Where did it come from? It doesn't matter, the big bang doesn't say anything about it (though there are several other theories about this. Personally I like M theory.)

So, for some reason, that the BBT doesn't make any claim to know, space started expanding. It's not that there was some kind of explosion but that the distance between any two points started to become greater. It's not that the points were being pushed away from each other at all (in this way it's possible for distant galaxies to appear to be moving away faster than the speed of light. Now- it sounds like the light would never reach us but as it travels towards us there could be less distance between us and it for expanding space to appear to push it back so basically it can slowly catch up some of the time. Other times it's just too far away to ever reach us- I believe the dstance where this starts to happen is called the event horizon.

Anyway, after things expanded quite a bit that energy was spread out more and allowed for matter and antimatter particles to start forming. This is actually an aspect of the big bang that we can repeat ourselves- there are some people who do it quite often. All it requires is a particle accelerator (which is a very large facility that uses magnetic fields to accelerate particles around it's perimeter inside of a tube- once they are going fast enough we let them smash into something else and they convert right into energy and produce some enormous temperatures- and then shortly after matter and anti matter can form out of this.)

Then, at some point after that 1 out of about every 1000000000 antimatter particles dissapeared. Well, maybe they never formed in the first place but either way we havent figured out why there was more matter than antimatter- this doesn't invalidate the big bang theory, it just leaves room for some other theory (though, once we figure it out we'd probably lump it together with the big bang theory because it would be convenient.)

And from there on a bunch of hydrogen was pulled together by gravity to form stars and from there on you know the rest well enough and it all makes sense in terms of things we can experience and see with just our eyes.