Re: i say universe is contracting.reason is in comments,what's wrong with it.

The expanding universe is a difficult concept to understand (and explain!) so it's not easy to grasp how all the pieces fit together. Your theory could describe the universe - the "Big Crunch," in which there is enough matter in the universe to halt the expansion and cause it to recollapse, would be very similar to the scenario you describe. However, it doesn't appear to describe our universe.

First, there is no "center" to the universe. This is tough to grasp. The reason is that observations show that almost all the other galaxies are flying away from us. This certainly makes it appear that we are at the center, but that's not necessarily true. Consider a balloon. While it's empty, paint spots all over the balloon. As you blow up the balloon, the spots will get farther and farther apart. In fact, from the perspective of each individual spot, the others all appear to be moving away from it - just like galaxies appear to be doing from our perspective. But, because every single galaxy sees the same thing, no one of them can legitimately call their location the center.

The balloon analogy is not perfect, of course, because the balloon is a two- dimensional surface while the universe has three spatial dimensions. But the same principle applies.

Now, what would happen if the universe were contracting? That would be like the balloon deflating: from the perspective of each spot, all the other spots would be moving toward it. This is incompatible with our observations of the real universe, in which the galaxies in fact move away from us.

I believe that you are thinking of something like a whirlpool, with us on the edge. In that case, objects closer to the center of the whirlpool would appear to move faster as they were sucked in. However, there would also be objects which are farther from the whirlpool's center than us - and these would appear to be moving away from us as well, as we accelerate toward the center away from them. So far we'd be compatible with observations of galaxies, at least if we arranged things very carefully so that the whirlpool caused an apparent expansion like Hubble's law (which would not be easy, by the way). However, what about the galaxies that are the same distance as us from the center, just displaced around the rim of the whirlpool? The would not be moving toward the center any faster than we do, and so they wouldn't appear to follow Hubble's law for the expansion. This scenario would therefore violate observations - something that we don't like to see. Also, the galaxies on the other side of the whirlpool would appear to move towards us, which again we do not see.

On another level, cosmologists believe quite strongly in the "cosmological principle." This says that there is no special location in the universe - this is something that astronomers cannot prove, but so far it is consistent with everything we know and is a basis for all of our cosmological models. Therefore we don't want to throw it out without a very good reason! In your model, the point to which everything is contracting is special, so it would not be consistent with this principle. Thus, for better or worse, astronomers would be very hesitant to accept a theory like yours without very good evidence!