From: schinder@leprss.gsfc.nasa.gov (Paul J. Schinder)
Subject: Re: Closed vs. Isolated systems
Reply-To: schinder@leprss.gsfc.nasa.gov
Organization: Goddard Space Flight Center
Date: Thu, 30 Jul 1992 17:42:06 GMT

In <henley.920730113210@wilbur.eng.auburn.edu> henley@eng.auburn.edu (James Paul Henley) writes:

>In article <schinder.712457467@leprss.gsfc.nasa.gov> schinder@leprss.gsfc.nasa.gov writes:
>>
>>doing.  If it's not isolated, and I'm asked to compute the change in
>>entropy, I have to work to find out, and the answer may be either that
>>it increases or decreases.  In this sense, the definition of "closed"
>>that chemists use is not fundamentally useful, since I have to be
>>given specifics to find out what the entropy does.  It has *practical*
>>use in given problems.  But for example, if the "container" is
>>transparent and I send radiation into the container, I can change the
>>equilibrium state of the contents. I can't do that with an isolated
>>system; once it's contents are in equilibrium, they remain there.

>Herein lies the gist.  If a container is closed, but not isolated, then
>it can recieve and lose energy but not matter.  Heat is unique in that
>it depends on an external heat sink to leave, whereas work, be it chemical,
>electrical, mechanical, or otherwise can leave without a heat sink.  The

Pointless distinction, that's what you mean by heat.  Random kinetic
energy of molecules that flows from "hot" to "cold" (what else could
it do once you understand the microphysics?).  There's no
*fundamental* difference between heat and work, they're both just
forms of energy.

>problem is, that you have to have a heat sink that is cooler than some
>part of the system to get the heat to flow out.  Or, you have to have some
>point in a cycle in which the heat sink is cooler that system in order
>for heat transfer out (following the expansion in a Carnot Cycle).  The
>earth definitely has a heat sink.  Since the energy transfer out is
>primarily by radiation, you do not have to have any matter in contact
>with the system.  Radiation is special in that it "transcends" matter.
>At the microscopic level, it is not so special, because it can be viewed
>as matter - photons, etc.  At the macroscopic level it can't because you
>can't contain it in a flask.  You can't measure volume, temperature or
>pressure, not with a ruler, thermometer and pressure guage anyhow.

Yes you can.  With an appropriate setup, I can measure the temperature
of the sun's blackbody radiation with a thermometer.  You can measure
the pressure of a photon gas in a box (make the walls reflective, and
you *can* contain them in a flask), and you *have* to include the
radiation pressure in many stellar structure computations.  Like any
gas, a photon gas will fill the volume available to it; you can't
measure the volume of oxygen with a ruler, either (you measure the
volume of the box it's in).  You're making pointless distinctions
again.

>That is what engineers usually think in terms of - Physical measurements.

That's what photons are, physical particles.  They carry physical energy.
Ensembles of them have temperature and pressure, which you can measure in
the usual way.

>Nothing mystical, just that it does not depend on matter for the transfer.
>The side of the earth opposite the Sun has a 3 K heat sink, so heat can
>flow out by radiation.  There is a form of the second law especially for
>this kind of situation - heat transfer but no mass transfer.  Historically
>that law has been expressed in terms of what you *can't* do with a heat
>engine.  Namely, you can't have a PMM2 - Perpetual Motion Machine of the
>Second Kind.  This deals exclusively with cyclical apparati.  The apparati
>are closed systems overall, but may have subsystems that are open - just
>like the earth.  And what can't you do?  That's what it's all about.

Nothing that I know of that has to do with life or origins.  That's
what Chris Colby just asked you: what's the point of all this?  For
life, (being no biophysicist this is all speculation), everything
of interest occurs (on timescales of interest) in a constant
temperature heat bath except photosynthesis, so if it's energetically
allowed, it happens.  Photosynthesis relies on the availability of a
high temperature photon distribution, so effectively it's a heat
engine.  You've already computed the maximum efficiency of a heat
engine operating between 6000 K and 3 K, and it's near unity.  Unless
photosynthesis is doing better than that maximum efficiency (and it's
not very efficient from what I've read), it's not violating the second
law.  If you want to do a better job than this simple analysis, then
you must look into the microphysics.  I don't feel the need;
photosynthesis occurs and therefore does not violate the second law.
Life exists and therefore does not violate the second law.  Boeing
747's get built and therefore do not violate the second law.

So now I suppose we follow Jim Acker and look at abiogenisis, which
isn't well understood and isn't part of the theory of evolution.
Again it's a subject that's not very interesting to me, but unless you
can come up with a *physical* bottleneck, I see no reason to worry.
I'll let the biologists figure out the chemistry.


> 
>>
>>
>>>-- 
>>>Henry Shaw, Earth Sciences Dept., LLNL |    All opinions are my own.
>>>Internet: shaw4@llnl.gov               |  
>>>CIS: 76347,2523                        |
>>>Fidonet: Henry Shaw at 1:161/55        |
>>--
>>--------
>>Paul J. Schinder
>>NASA Goddard Space Flight Center
>>schinder@leprss.gsfc.nasa.gov

>James P. Henley Jr.
>Chemical Engineering Dept.
>Auburn University

--
--------
Paul J. Schinder
NASA Goddard Space Flight Center
schinder@leprss.gsfc.nasa.gov
Newsgroups: talk.origins