The Big Bang Theory: how did we get here?

So recently I posted in a different thread about this, but it's not quite the same topic so am making this thread to separate the discussion.

My post in the other thread:

Quote:

Originally Posted by Ambrosia (Post 12135779) I've never believed in the Big Bang as the origin of our universe. It just never made sense to me. I'm also not a physicist and am happy to be proved wrong, but: We know the universe is expanding and AIUI Big Bang Theory goes that if you wind the clock back far enough then at some point in time the universe was contained in a very small area and something caused a rapid expansion and then 13.8billion years later here we are. How do we know that the universe expanded all this time at a constant rate? If there was a rapid expansion (inflation) and then since then a slower expansion, doesn't that suggest the universe doesn't expand at a constant rate at all? If the maths breaks down at the point of the singularity, then wouldn't that be a good clue that that explanation isn't correct? The universe we can see is huge and has a LOT of stuff in it, from normal stars and planets to Pulsars and Magnataurs and other things that are already impossibly dense. I have a very very hard time wrapping my head around the idea that all of this stuff was contained in a very small space at some previous point in time.

and a reply from Crossbow:

Quote:

Originally Posted by Crossbow (Post 12135812) First, the universe did not expand at a constant rate. Second, there are quite a few good books and good documentaries about the Big Bang if you actually do desire to learn more about the Big Bang.

I've watched a number of videos on this and recently rewatched this one:

[yt]G_MFhAoUUmQ[/yt] (Lawrence Krauss and Michio Kaku on the Big Bang)

At about 4:30 in the above video the narrator states:

"If galaxies are speeding away from each other, at some point they must have all been together"

That is basically the main problem I have with BBT. Why *must* all the galaxies have been together?

I don't see how we know that at some point in time everything must have occupied the same space.

How do we know for example that a version of the universe didn't exist ~13.8bn years ago that was smaller, say about the size of our galaxy that was a hot soup of elemental particles and something happened that then birthed the universe as we know it?

How do we know that the cosmic microwave background is the remnants of the big bang? That in the first fraction of plank time that the laws of physics sprang into being and time started?

I'm not saying BBT is wrong. I'm saying that it doesn't make a lot of sense to me and I don't understand it.

Also a lot of science docs are dumbed down a lot. There's loads of really basic introductory stuff, and I can find lectures and things that you need a maths degree to understand and not so much inbetween.

If anyone has suggestions for books/docs that aren't really basic and don't need a degree in advanced maths to understand I'd appreciate them.

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