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Q: The ultimate fate of the universe. ( No Answer,   3 Comments )
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 Subject: The ultimate fate of the universe. Category: Science > Astronomy Asked by: buffycat-ga List Price: \$25.00 Posted: 02 Mar 2006 20:32 PST Expires: 01 Apr 2006 20:32 PST Question ID: 703109
 ```In terms of the size and future of the universe, could someone explain to me, in simple terms, the concepts of a closed, flat, and an open universe? Am I correct in believing they refer to whether the universe is expanding, and at what rate, and to the ultimate fate of the universe?```
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 ```You're mostly correct! There's a contest going on between the expansion of the universe, started by the big bang, and gravity, which is trying to stop it. There are three possibilities:- if there's enough mass/energy then gravity wins, the expansion will stop, and the universe will collapse in on itself - "The Big Crunch". The universe is "closed". If there isn't enough mass/energy the big bang wins and the expansion goes on forever. The universe is "open". The third possibility is that the ammount of mass/energy is just enough to stop the expansion, but it will take an infinite time to do it. The universe is "flat". There are theoretical reasons, based on a model called inflation, for believing that the universe is flat, and so far the experimental results are supporting the theory. The terms "open", "closed" and "flat" describe the general shape of the universe. If you draw a triangle on a flat piece of paper the angles add up to 180 degrees. If you draw one on a ball, which is a closed shape, the angles add up to more than 180 while doing it on an open shape like a saddle gives less than 180. Everyday experience shows that triangles have 180 degrees, but imagine you were to start drawing *realy big* triangles - wherever you happened to be they'd look flat, but because they're drawn on the Earth's surface they're realy closed. You'd only find that out by measuring the angles. Now imagine drawing triangles on a cosmic scale. If the universe isn't flat, the angles wont add up to 180! Drawing them on that scale is obviously impossible, but by looking at the results of cosmic microwave background experiments like COBE and Boomerang we can see other indications that the universe is flat. Until the late 1990s it was thought that the ultimate fate of the universe was indicated by its shape. Along came the discovery of dark energy, and we now have the possibility that the expansion of the universe will accelerate to the point where it's torn apart! We live in interesting times! Ian G.```
 ```If you use the analogy of an escape velocity - The velocity needed to escape from the gravitational field forever - For example if you fire a rock in to space from the earth if it is going faster than 11000 km per second it will escape from the earths orbit. A similar thing happened with the big bang only instead of the rock being thrown it is the expansion of the universe. If we imagine this as a balloon being blown up then all objects can be thoght of as our rock on the surface of the balloon and they will all be moving away from one another. Instead of our rock escaping from the earth it will be all galaxies planets and matter in general trying to escape from everything else. Recent supernovae data shows however that an added factor of dark energy which acts to push apart all objects and accounts for ~70% of everything in the universe. Due to this it appears that on large scales everything in the universe is accelerating away from one another. This does not mean however that eventually it will rip it apart just that in a long time all objects will be so far away from everything that it will essentially be floating around in its own private universe - pretty lonely!```
 ```>This does not mean however that eventually it will rip it apart Some people think that it does, though they're probably in a minority - there's not enough data yet. Have a look at http://www.newscientist.com/article.ns?id=dn3461 Ian G.```