Date: 3/12/2018 11:23:22
From: The Rev Dodgson
ID: 1311055
Subject: Is the 2nd Law a law?
I thought this was interesting:
I thought this was interesting:
>Is the 2nd Law a law?
It seems to be. It’s certainly a strong tendency :)
Bubblecar said:
>Is the 2nd Law a law?It seems to be. It’s certainly a strong tendency :)
The guy who wrote the link says it’s not a proper law because it can be derived from other more basic laws.
BTW, for non-link followers, we are talking thermodynamics here.
The Rev Dodgson said:
Bubblecar said:
>Is the 2nd Law a law?It seems to be. It’s certainly a strong tendency :)
The guy who wrote the link says it’s not a proper law because it can be derived from other more basic laws.
BTW, for non-link followers, we are talking thermodynamics here.
I’m certainly no expert but although the 2nd Law can be explained by (and derived from) statistical mechanics:
>Irreversibility in thermodynamic processes is a consequence of the asymmetric character of thermodynamic operations, and not of any internally irreversible microscopic properties of the bodies. Thermodynamic operations are macroscopic external interventions imposed on the participating bodies, not derived from their internal properties.<
and furthermore:
>Due to Loschmidt’s paradox, derivations of the Second Law have to make an assumption regarding the past, namely that the system is uncorrelated at some time in the past; this allows for simple probabilistic treatment. This assumption is usually thought as a boundary condition, and thus the second Law is ultimately a consequence of the initial conditions somewhere in the past, probably at the beginning of the universe (the Big Bang), though other scenarios have also been suggested.
Given these assumptions, in statistical mechanics, the Second Law is not a postulate, rather it is a consequence of the fundamental postulate, also known as the equal prior probability postulate, so long as one is clear that simple probability arguments are applied only to the future, while for the past there are auxiliary sources of information which tell us that it was low entropy. The first part of the second law, which states that the entropy of a thermally isolated system can only increase, is a trivial consequence of the equal prior probability postulate, if we restrict the notion of the entropy to systems in thermal equilibrium.<
https://en.wikipedia.org/wiki/Second_law_of_thermodynamics
The Rev Dodgson said:
I thought this was interesting:
I’m one of many people who tried to design a thermomechanical system that broke the second law using a Brownian motion ratchet. For a few weeks I thought I’d succeeded. I hadn’t.
Some people have hypothesised that since the second law is necessary to give a directionality to time, it reverses when the expansion of the universe reverses direction. That is false.
Negative entropy does exist, but only in closed artificial systems with a temperature hotter than infinity.
Will read link later. In the meantime:
It doesn’t matter. This is a discussion about words, not physics.
The Rev Dodgson said:
I thought this was interesting:
The second law is more fundamental than Boltzmann’s statistical mechanics.
Statistical mechanics assumes baryon number conservation. The second law requires no such assumption. In the earliest times of the universe, during the inflationary epoch and even a bit afterwards, the second law still holds but statistical mechanics does not.
I’m beginning to think that the second law is actually mathematically identical to the law that “there is no travel backwards in time”. This can be broken locally for artificial systems (in quantum mechanics for the second law and in general relativity for time travel) but not outside such artificial local bubbles.
dv said:
It doesn’t matter. This is a discussion about words, not physics.
The writer’s flogging a book.