h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

"The most beautiful thing we can experience is the mysterious. It is the source of all true art and science."

"The important thing is not to stop questioning."

Two quotes I live my life by. They are by the greatest mind of the 20th century - Albert Einstein.

Now I've read a number of articles about the "Big Bang" theory. I am aware of the proposed doppler effect. However I am not sure why this is taken as the accepted norm.

Admittedly, I am not an expert - I simply haven't got that kind of time. But like to think my knowledge and interest covers a lot of fields.

Before you start I'm afraid I haven't got time to read long articles from other web-sites about the "big bang" theory. Sorry, I'm very busy at the moment.

But I am curious about the subject.

Can anyone tell me why they believe in the "Big Bang" Theory?

I too am no expert but is'nt it true that everything in the universe that we can see is travelling away from a central point that sometime in the past it must have all occupied?

I believe in the Big Bang theory because it's the best explanation science has came up with as to how the universe began and how it reached its present state. As for why or by whom the universe was created, frankly, hell if I know. Stephen Hawking said in A Brief Histroy of Time that all the laws of science break down there because of infinities, so there's apparently no way for us to ever know.

If you're keeping score, I'm an agnostic, but only because of what I said above: we really never will know what exactly did happen on the day of the Big Bang minus one, but there is good enough evidence for me to believe the Big Bang happened.

I must say i believe in the Big Crunsh (also called Gnab Gib) theory, and in that case i must believe in the Big Bang also. It's a quite interesting theory, it sais that the Universe is like a pulsing heart, wich contracts and expands over a great period of time. Now the universe is at the end of the expansion, and will soon start to contract.

This might sound a rather naive question, but then I don't have a scientific background.

We are told that the universe began as a single point, and expanded rapidly. The expansion has continued ever since. We are told that one ten-trillionth (or something very small) of a second after the creation the universe was the size of a grapefruit, and another ten-zillionth of a second later it was the size of the earth, etc.

What I can't understand is how it is even possible to talk about size in relation to the universe. From the point of view of an object *in* the universe (i.e. everything) the universe can only be one size - universe sized. Surely to talk about an expanding universe we have to create an imaginary viewpoint *outside* the universe?

Well, at least I can answer the question about the size of the Universe. What grew (and still grows) during the expansion of the Universe is not the size of anything in it, but rather the three-dimensional space containing it.

Easiest analogy is to imagine yourself as a two-dimensional bug (no offence intended ) on a three-dimensional ball. You see your 'Universe as infinite, because you can walk forever without meeting any barriers. However, if you mark your starting point, you will return to after walking in a straight line for long enough.

Now, the expansion is the same as inflating your ball-Universe. Everything moves further away from everything else, but you absolutely cannot determine where the expansion occurs, since it actually occurs everywhere. You can't determine the center of your 'Universe', either.

In our Universe, the expansion occurs in a fourth spatial dimension that you can't see, and everything moves away from everything else. So the size of the Universe is determined by the distance you (theoretcally) would have to travel in a straight line to get back home.