Examining the Second Law a little closer

[sophiaserpentia]

One of the things I've been pondering lately is the second law of thermodynamics, which asserts that entropy will always tend to increase.

I've never thought before to examine the experimental basis on which this law is based. My question is this: if this law is based on observations that have all involved the examination of isolated systems -- gas or liquid in an airtight jar, etc. -- then how do we know for certain that it will always tend to increase in systems that are not isolated? I'm not doubting that it is a tendency for the entropy of a given system to increase, but what I'm curious about is the logical leap from laboratory work to the assertion of a law that applies globally everywhere in the universe. I'm not even sure I doubt that... but I just want to look a little closer.

Comments

[inkyblue2.livejournal.com]

The entire first half of The User Illusion by Tor Norretranders is a wonderful examination of the second law of thermodynamics. I think this topic is covered, and also the fact that entropy is at heart a subjective concept.

[anosognosia.livejournal.com]

This is a good question; and an important one because the laws of thermodynamics have acted as unquestioned assumptions underlying alot of theoretical science.

We should keep in mind, though, that the second law doesn't deny that there are cases where entropy decreases -- just that those cases are necessarily accompanied by a paired circumstance where entropy increases as much or more.

This can be tied, perhaps ironically, to cosmology: if you assume an eternally expanding universe and finite matter/energy, it follows that entropy is generally increasing and the universe will eventually suffer a cold death.

The natural corollary which unfortunately seems to go unnoticed is that if you posit a contracting universe, it follows that entropy would generally decrease.

And as you posit increasingly complex cosmological models where uniform expansion or contraction are not so easily spoken of, so too does the entropy issue become complicated.

[adityanath.livejournal.com]

It is said that life is based on a temporary decrease in entropy, also known as negentropy. This is thought to be due to the open nature of an organism, which of course takes in nourishment from its enviroment and also disposes of its waste products as well.

[discoflamingo.livejournal.com]

My understanding is that the basis for the Second Law is almost entirely statistical mechanics for closed systems.

In the immortal words of MC Hawking:

Defining entropy as disorder's not complete,
'cause disorder as a definition doesn't cover heat.
So my first definition I would now like to withdraw,
and offer one that fits thermodynamics second law.
First we need to understand that entropy is energy,
energy that can't be used to state it more specifically.
In a closed system entropy always goes up,
that's the second law, now you know what's up.

Really, I just wanted to quote MC Hawking :-)