The Shape of the Universe

by Adam Frank for McGraw-Hill

What is the shape of the Universe? Is it round like a ball, flat like a sheet of paper or doubly curved like a western saddle? This may seem like a pretty abstract question. Most people struggle just to make sense of how the words "shape" and "Universe" can end up in the same sentence. While it may seem like an abstract issue fit only for philosophers, to scientists and wooly-headed ex-hippies it is, in fact, the strange issue of "shape" which can determine the entire fate of the Universe.

Cosmology (the science of the Universe as a whole) is not an easy subject to wrap your mind around. It is worth the effort though. The issues are so mind boggling that it can become the intellectual equivalent of skydiving. Perhaps the hardest part of Cosmology is learning to imagine the Universe as one giant entity. The question that almost always rears its ugly head in dealing with cosmological questions is the nature of the Universe's edge. In dealing with Everything-ness it is natural to run head long into the problem of what, exactly, is Everything in? Does the Universe go on forever? If not is there some kind of giant brick wall at the edge of the Universe (imagine the graffiti opportunities). In asking these questions, a problem arises in the way most people imagine space itself. It's natural to imagine Space to be emptiness or nothingness, a kind of giant shoebox into which the contents of the Universe are poured. Nothing, it seems, could be further from the truth. Space is not the empty stage on which the drama of the Universe is played. It is one of the leading actors.

Our modern ideas of space (and time) come from none other than Albert Einstein. The good Dr. Einstein's Theory of Relativity is a potent set of physics ideas that gives us a completely new view of the nature of space. It also turns out to be the principal piece of physics needed for cosmology. Einstein, in all his genius, recognized that Space was not just emptiness but had its own separate reality. Space and time are a kind of "fabric" of reality and like any fabric they can stretch, bend and even fold. Yes, this is a completely freaky idea but let us just accept for now and see where we can go with it in terms of cosmology.

One of the first things Einstein did after he finished his theory of relativity was start thinking about space, time and the Universe as a whole. He knew that all the beautiful equations he derived could describe the stretching of the entirety of space. Now that is certainly a wild idea. There are actually equations that can describe the stretching, the shape, of all space. After years of working on the problem, Einstein and other scientists found that this cosmological stretching of space and time would determine how the physics of the entire Universe plays out. To get a glimmer of how this works you have to go back to the beginning.

In the beginning there was the Big Bang, a cataclysmic explosion that initiated the expansion of all that is. I am not kidding about the "all" here. Space was part of the explosion too. The big bang was not an explosion into space; it was an explosion of space. There was no Universe outside the Big Bang then or now. When we talk about the expansion of the Universe we are talking about all the space that ever existed. That is why we have to give up the idea that there is an "edge" where space just runs out. There cannot be anything outside of the Universe's space. It is existence! That is all. Imagine the Universe to be the stretched rubber of an inflated balloon. As the balloon is blown up, space expands but there is no edge. "Ah", you say "what about the inside and outside of the balloon?" My answer is there is no such thing. Existence is the skin of the balloon. The inside and outside are "fictions" we use to visualize the whole picture but they are not real. In the real world there is no inside or outside of space and time.

The round balloon picture is okay because it gives your mind something to hold on to. Unfortunately the Universe can have shapes other than round. These are more difficult to imagine. The Universe's space could be flat or even saddle shaped. In the classic versions of cosmology there is a direct relation between these shapes and the eventual fate of the Universe. A round Universe eventually stops expanding and collapses into a "Big Crunch". Other shaped Universes never collapse and may go on expanding forever. "Shape" is destiny in cosmology. Even in the infinitely expanding Universes, however, the idea of an edge never comes into play because, once again, space is all there is.

If all this still bothers you, you are not alone. It still bothers me too and after years of working on it I am just starting to get used to the idea. What is really remarkable however is that we have gobs of experimental evidence which supports Einstein's ideas about space and time and Big Bang cosmology. This tells you something very important about the Universe. The key thing about Big Bang Cosmology and Einstein's Theory of Relativity is they are clear, rational mathematical pieces of physics. What they are not is easy to reconcile with our everyday experience. That is not however a problem. Our everyday experience is very limited. So all this goes to show a critical feature of the Universe: just because something seems weird doesn't mean it can't be true.

Questions to Ponder

  1. Cosmology is not an easy subject to get a hold of without the mathematics. Can you make a list of the three things that seem most difficult to conceive in the ideas discussed above? How do you think scientists deal with these problems?

  2. Think about the relation between our human "common sense" and science. How can they end up departing from each other? What happens when they do?

Check Out These Websites

The Shape of the Universe
http://ngst.gsfc.nasa.gov/science/shape.html

Origin and Destiny of the Universe
http://imagine.gsfc.nasa.gov/docs/science/mysteries_l1/origin_destiny.html

Ask the Space Scientist (Big Bang Cosmology)
http://image.gsfc.nasa.gov/poetry//ask/acosmexp.html


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