Tuesday, January 21, 2014

The Second Law of Thermodynamics: A "Lie To Children"?

link to Reddit...see the top comment.

Does anybody have anything to say about this stuff? Readings to point to that might be accessible to a layperson? I've heard it said before that the second law isn't, strictly speaking, true...  Of course, sometimes that's said of all scientific laws...

This book, I'm guessing, is not accessible to the layperson...but I'll let you know...

5 Comments:

Blogger Pete Mack said...

The second law of thermodynamics isn't "true" in the sense that there's a finite (1/1e100) chance that it's violated in a 1-litre volume (somewhere in the galaxy) over a period of 1 nanosecond. Which is to say, there's no fking chance at all.

Shorter 2nd law: perpetual motion is a sucker's bet.
In Feinman's terms, arguments violating the second law are not even wrong.
-mac

3:27 AM  
Blogger Pete Mack said...

PS: thermodynamics has to do with entropy, not energy, and all laws of thermo have to do with the properties of probability with exceedingly large numbers. (1e100 is a "small" number for most thermo situations.) Anyone betting against thermo would do better betting on sales of the Brooklyn Bridge. (Or on UNC making the final 4 this year, neener neener!)

The (extremely dubious) Reddit thread has to do with conservation of energy. It has nothing to do with the second law, and everything to do with the 0-energy level of interstellar vacuum...

-mac

3:36 AM  
Blogger Winston Smith said...

> Or on UNC making the final 4 this year.

Now that hurts.

Thanks for the rest tho

7:18 AM  
Anonymous jimbales said...

WS,

I agree with all above that the issue is the 1st law of thermo (energy is conserved. I had lunch today with a colleague on the Physics faculty here, whose research is in quantum field theory/string theory/black holes.

His comment was that:
1) Classically, energy is conserved.
2) In a flat universe (i.e., no general relativity), energy is conserved in an expanding universe (with classical physics or quantum mechanics).
2) Conservation gets tricky when dealing with both generally relativity and the expansion of the universe.

Expanding on 3), he says that Noether's theorem holds, and (because the equations of physics are invariant under translation in time) this means there is a conserved quantity that converges, in the classical limit, to our classical notion of energy. If you want to call that quantity "energy", then energy is conserved. But, there are other quantities that also converge in the classical limit to classical notion of energy, yet are not conserved in general relativity.

So, you can't talk about energy conservation in general relativity without first deciding on what you mean by energy,

Don't know that this is of help …
Jim

3:17 PM  
Blogger Winston Smith said...

Thanks Jim, that's very helpful, actually.

5:23 PM  

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