## Monday, February 20, 2012

### The Meaning of Life

The neat thing about thinking about science is that you get to believe you understand stuff, and sometimes you do. Of course, the deeper the thought the more ephemeral the understanding. As the bunnies say quantum mechanics is not only harder than you think, it's harder than you can think, but the back and forth about heat has lead Eli to an entrancing idea which starts by remembering that work is the product of a force aligned in a direction multiplied by the displacement in that direction. This ain't Lucia's so don't bother blathering on about definitions.

As the above video clearly states, heat and work are both energy, so what differentiates heat and work? Eli's Ansatz is that heat is the isotropic component of any flow of energy from any system. The directional component of the energy flow is work. To extract work from heat you have to dump the part of the energy flow that ain't moving in the direction you want to do work in. Entropy increase is the scattering of energy out of the direction of motion. (OK, that needs a bit of work). Some bunny brighter than Eli has got to have thought about this before. Fermi comes to mind as a possibility.

Arthur said...

Huh. If you restrict yourself to mechanical forms of energy then I think this is roughly correct.

But the way I like to think about it relates to entropy - though maybe you need a firm grasp on entropy first perhaps to understand. That is, given a body with total energy E at some temperature T, the portion of E which can be regarded as "heat" is that internal energy that corresponds to the maximum entropy condition (thermal equilibrium) of all the degrees of freedom of the body at temperature T. What's left over, in whatever form, is free energy (exergy is the trendy name I hear) and available to do work.

EliRabett said...

Arthur, consider the microscopic motion of the atoms in the body. Eli's definition works. If the body is at rest, all of that motion is isotropic and the body does not move, e.g. it's heat.

David B. Benson said...

The Meaning of Life is 42.

KAP said...

I believe the source of that quote is originally J.B.S. Haldane: The universe is not only stranger than we imagine, it is stranger than we can imagine.

Anonymous said...

The heat death of universe happens when everything stops.

David B. Benson said...

KAP --- Haldane used queerer, not stranger.

Recovering in the Florida Keys said...

That is interesting. A perfect explosion would be maximum entropy, which would be 100 work if your plan was creating a perfect explosion. A Carnot engine would be a perfect shaped charge, exploding in only one direction. So half work and half explosion would be the normal in nature we are trying to control for our purposes.

If you applied that to an object in space, an ideal black body would be the perfect explosion and an ideal gray body would be 50% explosion, emissivity, and 50% contained, energy retained in the atmosphere.

That would put a realistic range on atmospheric effect. Seems I have seen that somewhere before?

Lionel A said...

I am fairly sure that Feynman covered this in his Lectures on Physics, now a huge three volume work as a Millenium Edition.

Arthur said...

Dallas - explosions create a local high temperature - they can do work through Carnot-like processes on their surroundings at lower temperature - which *increases* the entropy associated with the energy as it's temperature goes down.

Somewhat unintuitively, high temperature = low entropy. Maximum entropy for a given quantity of energy comes when temperatures are as low as possible. Like I said, thinking entropically takes a bunch of experience, it's not always obvious. A lot depends on what you hold fixed and what you allow to vary - all those partial derivatives a typical student discovers early on in the field.

Anonymous said...

I agree with Lionel A ... I am taking down the Feymann Lectures, the old soft-cover red ones. I only have two ... someone told not to bother with the 3rd one on quantum theory.

Anonymous said...

The good doctor will wear his golden horshoe with pride. He has earned it. I saw Wamsley and googled it and immediately figured it was the teacher.

@Eli

I think you totally baited me on that one, not intentionally but the fact that there was another Wamsley who is a teacher was in your favor. Wamsley isn't exactly a common name. Either way, you got me, and the good doctor always admits when he has been bested.

Suffrin Succotash! You wily wabbit!

Anonymous said...

I'd also like to take the time to distance myself from this John O Sullivan guys' hypothesis that there is no temperature in space..or..I can't even tell what the hell he is trying to say.

So I have to ask the dumb question, has an astronaut been out next to a space station or on the moon with a thermometer? Wouldn't that be all it takes to prove this goof wrong?

EliRabett said...

The third volume is the best one.

Anonymous said...

I think you totally baited me on that one, not intentionally but the fact that there was another Wamsley who is a teacher was in your favor. Wamsley isn't exactly a common name. Either way, you got me,

No, Eli didn't get you. You got yourself because of your tendency to selection bias in the seeking, collection and analysis of evidence/data and your erroneous preconceived notions on certain issues. It's a form of confirmation bias and leads to poor decision making.

It's a salutary lesson which I fear you will not learn from, judging from past issues in the Rabett Run.

You do deserve some merit for addressing the issue of being wrong, though. Well done.

Cymraeg llygoden

Anonymous said...

@Cymraeg Ilygoden

Yeah sure, and you're decision to ignore billions of years of temperature and atmospheric data and instead focus on 150 years of data is also evidence of your confirmation bias, dude.

Anonymous said...

The chocolate teapot strikes (out) again!

Cymraeg llygoden

Anonymous said...

This whole conversation is quite TdS.

~@:>

Anonymous said...

Snow Bunny says:

Eli, I knew what heat is until you completely confused me. Since I don't like being confused, I will return to my chief job of keeping my skis dry.

Robert P. said...

Eli's ansatz works pretty well on the macroscopic level, for things like mechanical work (lifting a piston against gravity) or electrical work (using chemical reactions to drive an electric current, viz. the Nernst equation.) Not so well on the mesoscopic level - cell biology or biochemistry. On both levels, the distinction between "heat" and "work" is essentially expressed by delta-H vs. delta-G. When coupling reactions together so that one reaction can drive another that would not be spontaneous on its own, you look at their delta-G's, since delta-G is the maximum available work from a process that takes place at constant T and P. But this delta-G isn't necessarily related to some directional process.

I rather like McQuarrie's ansatz: "heat" corresponds to changing the energy of the system by changing the *populations* of its energy levels, "work" corresponds to changing the energy by changing the energies of the energy levels themselves. It has the nice property that it unifies the quantum mechanical and thermodynamic definitions of "adiabatic." In quantum mechanics, an adiabatic process changes the energies of the energy level without inducing transitions among them, which corresponds to changing the energy by doing work without any heat flow.

EliRabett said...

McQuarrie fails on stimulated vs spontaneous emission and similar. What it is good at is mechanical work because changing the volume in pressure volume work changes the energy levels.