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Subject: Re: Why are the differences between both Big Bang and Big Crunch theories?

Date: Thu Oct 1 04:05:48 1998
Posted by Ricky J. Sethi
Position: PhD

Hi Erwin,

The Big Bang and the Big Crunch are concerned with the beginning and the end of the universe, so to speak. As you're probably aware, the Big Bang is the currently accepted theory for the origin and evolution of the Universe. Briefly, it states that the Universe started as a point that was smaller than an atomic nucleus about 15 billion years ago. That point of energy "exploded", and this instantaneously expanding point created space, time, and matter... basically the Universe as we know it.

The Big Bang is tremendously more complicated than I've led you to believe. Luckily for me, however, your question concerns the Big Crunch. The Big Crunch is actually significantly easier to understand than the Big Bang. The Big Bang describes how the Universe started. The Big Crunch, however, deals with how the Universe might end. And this rests simply on one thing: how much matter there is in the Universe.

Around 1920, a Russian mathematician by the name of Aleksander Friedmann proposed a theory about the end of the Universe. There were three possibilities for us in that theory, each relying on a critical density of matter in the Universe.

  1. If the matter in the Universe were higher than the critical density, then the matter would exert enough gravitational forces to eventually cause the Universe to stop expanding and start falling back in upon itself. When this happens, the Universe will end in an event as cataclysmic as its creation, namely, the so-called Big Crunch.
  2. If there isn't enough matter to exert enough gravitational force to pull it back in on itself (i.e., amount of matter in the Universe is less than the critical density), then the Universe will continue to expand and end in the Big Chill.
  3. Finally, if the amount of matter were exactly the same as the critical density, the universe would still expand indefinitely, resulting, once again, in the Big Chill.
The proof for the Big Bang is quite abundant. And recently, there has been mounting evidence that there might not be enough matter in the Universe to result in the Big Crunch and that the Big Chill is the most likely fate for our Universe. However, this is an incredibly hot (pardon the pun) field and the subject is also, as I mentioned before, much more complicated than how I've presented it. A good introductory book on all this is Scientific American's From Quarks to the Cosmos (availble at any good library). Of course, there's plenty of stuff available on the Web, too. Just point your favourite browser to any search engine and search for either "big bang" or "big crunch". One great site that I found was Scott Siegel's Creation of a Cosmology. Give them a look and if you have any further questions, please don't hesitate to drop me a line.



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