Talk:Third law of thermodynamics

Rephrased quotes in introduction

I slightly rephrased some of these formulations of the third laws. I assume they are not exact original words, but crafted for pedagogical purposes.

The Nernst–Simon statement of the third law of thermodynamics concerns thermodynamic processes at a fixed, low temperature:

The entropy change associated with any condensed system undergoing a reversible isothermal process approaches zero as the temperature at which it is performed approaches 0 K.

Here I felt that it was important to emphasize that the reversible isothermal process actually occurs at a fixed temperature, which then takes on a sequence of values going to zero. Otherwise the non-thermodynamic reader imagines a process in which the temperature is gradually lowered, and wonders how this could be isothermal...maybe you just do it really slowly, so the temperature remains constant???

I moved the definition of condensed matter out of the statement of the law, which should be pithy.

I also wrote:

A classical formulation of the Nernst–Simon statement (not obviously equivalent to the above) is:

followed by the statement about a finite number of steps. This formulation is called "classical" because it is close to the Nernst quote that occurs later in the article. I don't think of it as "simpler" because it's not the same thing; it's merely qualitative and you can't actually derive the whole third law from it, as far as I can tell. So, strictly speaking, it shouldn't even be called a formulation of the third law, but rather a consequence of it. I think of it as a lagniappe. Or is there something I've missed?

178.38.125.245 (talk) 00:04, 23 April 2015 (UTC)

I noticed all the comments above about the "finite number of steps" statement. The upshot is that it's just a consequence. So I changed the article to reflect this. 178.38.125.245 (talk) 00:26, 23 April 2015 (UTC)

Nernst-Simon statement

I was wondering who refers to it as the Nernst-Simon statement? Simon doesn't get mentioned anywhere else in the article and neither the German nor the French wikis mention anything even resembling Simon.

And which Simon would that be? This guy https://en.wikipedia.org/wiki/Francis_Simon ? 195.75.72.179 (talk) 13:31, 6 July 2015 (UTC)

3rd law of TD was "proven"...?

Generally it's bad form to say a physical law has been "proven mathematically". More correctly it would be said that it has been restated, or shown as deriving from a more fundamental principle. However, there's nothing technically wrong with that statement, if one keeps in mind what being "proven" means in the context of physics. But it is misleading in context of popular science. Opinions? 93.103.25.142 (talk) 09:52, 30 March 2017 (UTC)

Combinations

If the system is composed of one-billion atoms, all alike, and lie within the matrix of a perfect crystal, the number of combinations of one-billion identical things taken one-billion at a time is Ω = 1.

Is this really a helpful way of explaining why the entropy of a crystal at T = 0 is zero? What do combinations have to do it with? Why are we considering a combination of a billion things taken a billion at a time here?

In physics more relevant is whether the crystal is in a pure state, i.e. a state that cannot be expressed as a nontrivial convex linear combination of other states. Pure states have entropy zero. John Baez (talk) 16:48, 31 July 2022 (UTC)