# Big Bang

Simple question:

Where is the center of the universe?

I have always been told that the universe is expanding in all directions. I would have to assume that by detecting this expansion, we can also measure the relative rate of expansion.

In that case, if we look around and everywhere is expanding at the same rate, we (the earth) would be the center in that case. However, if we detect a slower rate in one direction, we can offset that center mathematically.

Next question:

Is the shape of the universe spherical?

Where is the center of the universe?
She lives in Medfor, NJ now. Bitch.

Many teaching models of the big bang ask you to imagine the galaxies on the surface of a ballon that is inflating.

However, what many of them fail to remind you of is that you need to imagine that the galaxies are all two-dimensional and that you live on the surface of the balloon and can only see things that are on the surface of the balloon, i.e., that light travels only on the surface of the rubber, and you are incapable of perceiving anything either “outside” or “inside” the balloon.

Because the entire surface of the balloon expands as it inflates, if you lived in one of the flat galaxies, the other galaxies would all appear to move away, with the speed of their recession increasing with the distance they are away from you.

The “center of the universe” in this model is of course somewhere in the middle of the balloon, which is beyond your perception in this model.

Because this model presupposes a spherical shape to the universe, some propose an alternate model in which the galaxies are distributed on an infinite rubber sheet being stretched in two direections, which of course, unless it were curved into a spherical shape, would have no center.

The idea, which, again, many fail to teach when presenting this model, is to exptrapolate the insight you get from thinking about it in two dimensions into the real world observations in three dimensions. Three-dimensional galaxies are moving away from us in every direction because the universe is expanding in three dimensions, much like the surface of the balloon or sheet is expanding in two.

Some propose a model for thinking about this in the form of the galaxies being the raisins in an infinite loaf of raisin bread which is rising, spreading the raisins out in all directions.

We perceive ourselves to be a the center, but those who may be observing in a different galaxy will percieve themselves to be in the center.

The upshot is that there is no observable center. The whole thing is expanding.

Some people think the universe may be shaped like a horn:

http://www.newscientist.com/news/news.jsp?id=ns99994879

Philosophically, any notion of a “shape” to the universe is meaningless. A shape implies boundaries.

Not necessarily. The most common everyday understanding of “shape” is dependant upon boundaries, but then, most common everyday folks lack familiarity with unbounded objects. There are, however, at least two mathematical concepts which could be considered the “shape” of an object which are independent of the object’s boundaries or lack thereof. A 3-torus, for instance, is, in a very real sense, a different shape than a 3-sphere, even though neither of those manifolds has a boundary (and in fact, both of them are reasonable proposals for the shape of our actual Universe, though it seems to be to large to detect either of these shapes).

The illustration of the expansion of the Universe I like best uses a pair of transparancies. Draw some random pattern of dots on an overhead transparency: Each dot will represent a galaxy. Now, make a photocopy of that transparency at 110% magnification. The original transparency represents the Universe at one time, and the magnified one represents the Universe at some later time. Now, overlay the two transparencies, and line them up so that one particular dot matches. From the point of view of that dot, it will look like all other dots are moving away from that dot. But if we line it up on any other dot, then from the point of view of that other dot, it still appears that all galaxies are moving away. It doesn’t matter which dot you choose, they all equally look like the center.