🚀 go-pugleaf

[Looks like the line-eater is back, or something.  This msg
 arrived starting in mid-sentence.  --JoSH

thermodynamic cylinder with gas in it.  The        H =========== H
gas molecules bang around randomly inside the      H<> /^ /\ ^_/\H
cylinder, exerting some pressure on the plunger    H >< /  x_/ ><H   
(so that, for example, the plunger will slide      H<  |  X \L/ /H        
upwards if you increase the temperature) [see      H \/ \/\ / \/ H   
fig 1 -- and your imagination -- to the right].    H_V\ /__v__/\_H   
                                                   ---------------
                                          
                                                         {T}                 
...From a statistical mechanics point of view,     H      |      H   
there's a hypothetical condition where *all* of    H =========== H
the gas molecules could just happen to travel      H ^  ^  ^^  ^ H
in a parallel direction against the plunger.       H |  |  ||  | H
Ideally, they could be repeatedly reflected        H |  |  ||  | H
back and forth.  But if that happened, the         H |  |  ||  | H   
pressure on the plunger would oscillate...         H_V__V__VV__V_H   
And then you could put a transducer on the end
(a piezo?) to convert some of this motion into a useful form of
energy, like an AC current, and in the process "cool" the gas.

Which means you've got something like a device that totally converts
heat into energy, which is supposed to be impossible.  I think that
the orthodox objection is that this just shows that the laws of 
thermo are probabilistic: the hypothetical condition above is wildly
improbable, hence in all real world cases this 
will never happen.
                                                           {T}                 
But...  what if you make the cylinder really         H      |      H   
small?  What if it had only one molecule bouncing    H =========== H   
around in it?  And what if you could construct       H /\       /> H   
billions of them, all ganged together?               H<  \     //  H   
                                                     H \  \    /   H   
The you get a nano-mechanical perpetual motion       H     \  /    H   
machine of the second type...                        H______\/_____H   
                     
So, what am I doing wrong?  Is there a cold sink I'm missing somewhere?

(J.JBRENNER@MACBETH.STANFORD.EDU  Materials Science Dept/Stanford, CA 94305)

[Ok.  As well as I'm able to tell, the problem comes in when you 
 assume that you will be able to convert a periodic motion of the 
 piston at the molecular level to useful work.  Remember that, 
 assuming that everything is at the same temperature, each molecule
 in the whole structure is undergoing vibration, presumeably with
 lots of nice periodic modes, with the same kinetic energy as the
 molecule in the cylinder.  

 When you assume that you can build any mechanism that can be built
 at a macroscopic scale, such as a ratchet crank, to take useful 
 energy off the piston's motion, you tend to think in terms of 
 solid, continuous objects, which can be made to stand still at
 the appropriate times.  Now the hidden source of energy becomes
 more obvious: such parts would be an absolute zero heat sink.

 In reality, such parts don't exist.  You must try to design the 
 ratchet crank from parts made of balls strung together with springs--
 and each ball is vibrating with the same kinetic energy as the
 molecule in the cylinder.  Now only a fraction of that energy 
 would be imparted to the piston each collision-- so each molecule
 of each component of the mechanism is vibrating with much more
 energy as that you're trying to capture from the piston's motion.

 The same sort of thing happens when you try to design a spring trap
 door or the like to be a nano-mechanical Maxwell's Demon.

 --JoSH]