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Entropy and Bigbang.

by aaryan0077
Tags: big bang, chaos, properties, time
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aaryan0077
#1
Apr19-09, 10:01 AM
P: 70
First I don't understand that what is order and disorder, as said that thermal equilibrium is disorder, but for equilibrium there is only one state, but 1st law of themodynamics says that a state with larger no. of microstate is much probable than one with less no. So equilibrium can be only in one way, so should not it be order.
Now big bang is said to be most ordered state, as chaos started after it, but if it was ordered what the 2.73 K microwave background? This is same everywhere so there must be equilibrium, so we must be in state of disorder. Also, to measure chaos, we need two different states to compare, means we need "time" for chaos to be meaningful. Does this means chaos is property of time? And as time started at big bang so rather say chaos is property of big bang?
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Chronos
#2
Apr20-09, 12:01 AM
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The temperature of the CMB is not the same everywhere, it was hotter in the past. See http://spaceflightnow.com/news/n0012/24vlthot/
Chalnoth
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Apr20-09, 11:06 AM
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Quote Quote by aaryan0077 View Post
First I don't understand that what is order and disorder, as said that thermal equilibrium is disorder, but for equilibrium there is only one state, but 1st law of themodynamics says that a state with larger no. of microstate is much probable than one with less no. So equilibrium can be only in one way, so should not it be order.
Now big bang is said to be most ordered state, as chaos started after it, but if it was ordered what the 2.73 K microwave background? This is same everywhere so there must be equilibrium, so we must be in state of disorder. Also, to measure chaos, we need two different states to compare, means we need "time" for chaos to be meaningful. Does this means chaos is property of time? And as time started at big bang so rather say chaos is property of big bang?
The reason why this is an issue is that if you look carefully at the way the universe expanded, and just assume the classical big bang for a moment (no inflation), then different parts on the sky that are now at 2.73K were never in causal contact with one another. Having never been in contact, there was no way for the different parts of the sky to come to equilibrium. This is known as the "horizon problem" of the classical big bang theory.

Something, therefore, must have set up our region of the universe at this uniform temperature, as it couldn't have happened within the classical big bang theory. This is one of the problems that cosmic inflation resolves: by proposing a different expansion history at early times, it allows widely-separated parts of the sky to have been in contact with one another, which allows them to come in equilibrium with one another.

But, if you look carefully at inflation, it is still a highly ordered state, one with fantastically low entropy. Anyway, if you want to read more on this, I highly recommend Sean Carroll's take on the subject. Here's a popular article he wrote not too long ago:
http://www.sciam.com/article.cfm?id=...of-times-arrow


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