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Author Topic:   what is the big bang and how do i understand it?
Chiroptera
Inactive Member


Message 3 of 122 (229494)
08-03-2005 9:45 PM
Reply to: Message 1 by mick
08-03-2005 9:08 PM


Actually, mick, I have a master's degree in physics, but I don't have any experience in astrophysics, cosmology, or even high energy particle physics, so, believe it or not, I'm no better off than you!
However, here is my "cartoon" (read: over simplified explanation) of Big Bang.
It is observed that the spectra of distance galaxied pretty systematically exhibit "red-shifts". That is, the spectral lines that identify particular elements are all shifted toward longer wavelengths ("redder" colors). This usually indicates movement away from the earth at a particular velocity. The further the galaxy is, the greater the red shift. The obvious interpretation is that the galaxies are moving away from the earth, and the further a galaxy is, the faster it is moving away.
Actually, a more satisfactory interpretation is that space is expanding, and carrying the galaxies along with it. Think of (classic analogy) raisins in a loaf of bread that is rising -- the raisins are moving away from one another, and the further apart two raisins are, the faster the distance between them is increasing.
Now we think of the implications. If the universe is expanding, then if we "run the clock backwards", all of the galaxies must have been closer together -- go back far enough, and everything must have been packed together -- physics tells us that the universe must have been hotter, too, so the temperature was higher. If we run the clock backwards, the universe must have been infinitely hot and dense -- what is called the singularity.
We can use the laws of physics to tell us what the conditions were like in the past when things were hotter and denser. Often there are several possible models, and we use the observations of the current universe to decide which models are correct -- different models will predict different distributions of galaxies and such.
Also, at some point the universe gets too hot and dense for our current laws of physics to work -- for the time between the singularity and about 10^-40 sec later, our laws of physics are completely inadequate to describe what the universe was completely like.
This is what Big Bang is -- the observation that the universe was much denser in the past, and the use of the laws of physics to determine what the universe was like at these earlier epochs.
What the Big Bang is not is a theory of the origin of the universe. Big Bang is a model (or several competing models) of the early universe after its origin. In fact, since the singularity is when "time began", it makes no sense to speak of "before" the singularity, and so speaking of "causes" poses, in my opinion, something of a philosophical problem.
There are ideas of the origin of the universe, the origin of the singularity, but as far as I know none of these ideas are as yet even close to being observationally verified even in principle.
If this doesn't answer your query, then maybe it's enough to start some questions.

This message is a reply to:
 Message 1 by mick, posted 08-03-2005 9:08 PM mick has not replied

  
Chiroptera
Inactive Member


Message 10 of 122 (230794)
08-07-2005 8:37 PM
Reply to: Message 9 by Omnivorous
08-07-2005 8:28 PM


Re: tall stack of earths
Google "big rip".

This message is a reply to:
 Message 9 by Omnivorous, posted 08-07-2005 8:28 PM Omnivorous has not replied

Replies to this message:
 Message 16 by RAZD, posted 08-11-2005 11:08 PM Chiroptera has not replied

  
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