Quote:
Originally Posted by snas
The veterinarian's view (ie: my assumptions on the physics of astronomy may very well be very wrong)
In the beginning (not trying to sound biblical) there was a singularity which was highly ordered (very low entropy). 1 second later there was a massively expanding universe which now had a much higher entropy. Since the 2nd law of thermodynamics dictates that entropy can only increase over time, would that not mean that the universe can only expand as time passes? (This is perhaps where my biologist's view may come unstuck). I know that this is not directly concerned with acceleration of the universe, but it has just always struck me that in the days when it was believed that the universe may eventually stop expanding , or even begin to implode/shrink, wouldn't the 2nd law of TD have been there saying, hey dudes, entropy always increases and therefore a shrinking universe appears unlikely/impossible.
If I'm wrong I'll go to work and spey a dog
Stuart
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Aah, entropy. A mind-bending topic.
Here's the out-of-date physicist turned banker's view.
What you're suggesting isn't wrong, but I think it's not exactly how most physicists would put it.
Firstly, the 2'nd law of thermodynamics (which is essentially about entropy) is not really a law like most physical laws. It's a statistical law which is an inevitable consequence of fundamental physical processes and the laws of probability. In fact it can be violated from time to time, it's just that the chances of a violation in any decent-sized system are negligibly small. Think about a chamber of gas, and the chance that (briefly) all the particles turn out to be in the left half of the chamber. It would be a decrease in entropy, it could happen, and the chances of it happening are so close to zero you can forget about ever seeing it.
So, in your contracting universe, it's not actually clear that the fact entropy would increase is a problem.
But, physicists seem to generally view the 2'nd law as about the most fundamental there is, and the universe seems to go to a great deal of trouble to not violate it. (Hawking's work on the entropy of black holes is a good example.) As a result, one line of thinking people have gone through is to look at the directionality of time. This pulls together a few observations:
- Underlying physical processes are generally 'blind' to whether time is going forwards or backwards;
- Nevertheless, we perceive time as going in a particular direction;
- The 2'nd law provides a directionality for time - it's the direction in which entropy increases;
- When we remember things, we increase entropy - that's why we remember the past not the future;
- Then the big leap - Someone observed that the expansion of the universe can be thought of as a second directionality for time. As time moves forward, the universe expands, which coincides with entropy increasing. So - if the universe started contracting, would time appear to reverse?
Personally I think the last point reads way too much into the coincidence, however much smarter people than me think there is a real point here.
Finally, I mentioned the trouble the universe seems to go to to preserve the 2'nd law. Is that why things are arranged so that the universe will expand forever?
Anyone else more up to date on this?