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Well, the "Big Bang" according to a theory of 1916, by Einstein's theory of General Relativity, as worked out in more detail by Friedman and others later on, the " Big Bang" is not an expansion of matter into empty space. Every cosmologist, every experimental scientist who is working this field uses the same paradigm, the same picture. It is that the Big Bang is an expansion of space, with the matter not moving. In fact the math reflects this when you learn General Relativity and you do this mathematically, these galaxies are fixed. They don't move; they have fixed coordinates, and the expansion that takes place is that even though they are not moving more space is appearing between them. It is called the metric, the metric tensor is what changes in General Relativity, and space is increasing between these objects whose coordinates are not moving.

Sometimes this is illustrated in some of the elementary books by having students imagine you are blowing up a balloon and you have dots on the balloon and as you blow up the balloon the dots get further apart from each other. That is actually an excellent model. The trouble with it is that most students imagine that the three dimensional space is space and that the galaxies are somehow on this surface. What was really meant by that is to imagine a two dimensional space, the surface, which is the entire universe. This two dimensional surface is the universe, there is no three dimensions, and that the size of the balloon is getting bigger. In other words, the universe may be finite and if it is the geometry is very similar to that of a balloon, at least the three dimensional geometry in the sense that if you go out that way and go far enough you come back to the same spot.

In the "Big Bang" what is happening is that space is increasing, not that the objects are moving. Now this gives a lot of people trouble to have space increasing. Another analogy that is often made is I can stand here and you can stand there and the distance it takes for me to get from me to you is a certain amount. Someone can dig a hole between us, a ditch, and now it is a longer distance as measured along the ground to get from me to you. That is, even if we don't move the amount of distance between us can change. The trouble is that the student says "yeah, yeah, but that is only because you are not a bird, you can't fly, you go down the ditch and up again." But the space between us actually does increase, if you are confined to that surface. In general relativity theory the same thing happens. If we don't move, then a black hole is placed in between us, the distance between us is vastly increases. To get from me to you it would have to go way down into that space. It is a huge amount of space crowded in around the black hole. It is not so bad if I go around it but if I go through it, it is a very long distance. Space is a flexible tangible thing in modern physics.

Now I talk about teaching this to kids. When I was six, I was sort of mystified by this idea that space was so fixed, I mean the distances between things seemed to change every year. The hills got smaller, the apartment buildings got smaller. By the time I was ten, there were no longer giants around, well that's cause I had grown up. Everything was relative to me. I had to be taught that space was fixed and that I was growing.


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