Re: Policy asked to investigate entropy-claim in website of Turku University in Finland


"Friar Broccoli" <EliasRK@xxxxxxxxx> wrote in message news:1176310384.515198.76450@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 3, 3:13 pm, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx>
wrote:
"Friar Broccoli" <Elia...@xxxxxxxxx> wrote in messagenews:1175620430.093442.8780@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Apr 2, 9:00 pm, "Perplexed in Peoria" <jimmene...@xxxxxxxxxxxxx> wrote:
[snippage]
What gravitation does to a cloud of gas is to condense it - Ok, that is
a decrease in entropy if you don't consider the increase in the temperature
of the gas and the resulting radiation of heat. And, of course, if you
do consider these things, then 2LOT is upheld.

But this is quite analogous to what happens when a supersaturated solution
crystalizes, or when cement or epoxy cures, or in any number of other
spontaneous exothermic processes.

But let us look again at what you originally wrote:
"In my view the fundamental source of negative entropy in our
universe is gravity."

Hmmm. We notice clumps of relatively low entropy. Things like planets
and crystals and solidified glasses. How did this happen? Aha! There
was an exothermic reaction, and then the heat was radiated away. There
are lots of exothermic reactions available, but the one which created the
biggest clumps of relatively low entropy is the reaction called gravitational
collapse.

So, if that is what you meant, then I agree with you.

I cannot say that I meant this, because until you explained
them I didn't know the balancing mechanisms that cause overall
entropy to be maintained.

Going a bit further, it seems to me that this paradox (for me)
has another layer ready to be peeled away. When quoting my
original comment, I note that you removed my comments
suggesting that gravity defines entropy differently than the
electromagnetic (EM) force.

Because, to my way of thinking, (Newtonian) gravitation doesn't do anything
special regarding the 2LOT. The 2LOT arises from more basic aspects of
mechanics (the conservation laws, maybe) and basic probability theory. It
should apply regardless of the shape of the force laws between particles.

I do not (or at least do not think I need to - for present
purposes) disagree with this. I am only trying to address the
question of how the back-eddies arise: ie. How is it that we
find a lot of order concentrated here, and an excess of entropy
off over there somewhere.

For this the varying shapes of the force laws between the
particles is critical. Electro-magnetism seems happiest
(entropically) when ordinary electron coated particles are
spread out as an ideal gas, but is over-ruled by gravity which
is entropically happiest when everything is clumped together.

It seems to me that this is simple, obvious and uncontroversial.
I am puzzled about why I cannot convey this to others, or
alternatively come to see the error of my ways.

All I can do is to repeat what I have already said. Perhaps saying it in
different words will create some resonance for you.

Electro-magnetism is not 'happiest' with neutral atoms spread out as an
ideal gas. Whether you get a high-entropy gas or a lower-entropy liquid
or a low-entropy solid is going to depend upon details of density and
temperature. Entropy and enthalpy are, in a sense, competing 'forces'
trying to shape reality in a closed (exchange of energy, but not matter)
system.

In an isolated system (no exchange of either matter or energy), you might say
that entropy always wins. Entropy is maximized. Period. But in a closed
system, things are more complicated. Entropy can be radiated away as heat,
or it can be retained in the system. Entropy *within* the closed system is
no longer maximized. Instead, Gibbs (or Helmholtz) free energy is minimized.
(The difference between the two has to do with whether the closed system
under consideration has constant volume. I'm not going to get into these
technicalities).

Free energy can be defined by
delta_G == delta_H - T * delta_S

Entropy (delta_S) and enthalpy (delta_H) are in opposition in determining
what happens (delta_G). Enthalpy wants to turn gasses into liquids and
liquids into solids. This is true whether we are talking about gravitation,
electromagnetism, or nuclear forces of adhesion. Entropy wants everything
to spread out.

Now, it is true that the way this plays out usually involves what you have
called 'back-eddies'. And it is also true that the different forces of
nature create back-eddies of different scales. The nuclear enthalpy forces
create back-eddies on the scale of atomic nuclei, in which nuclear attraction
overwhelms both entropy and electromagnetism. The electromagnetic enthalpy
forces were able to put together small globules of iron and nickel in the
solar nebula. If they had not succeeded in overcoming entropy to this extent,
the planets would never have formed. Both electromagnetism and nuclear forces
are quite capable of creating back-eddies, but on a fairly small scale. And
of course, gravitation has created back-eddies on a larger scale.

I'll leave it to people better at physics to penetrate to the heart of the
question of why the inverse-square force of gravity is the only true long-range
force, and why electromagnetism, in practice, is short-range even though it
too is nominally inverse-square. And I don't even understand the ultra-short
range of the nuclear forces. But I am pretty confident of the thermodynamics
of the situation. All three forces contribute to the delta_H term - all in
essentially the same way. There is nothing special about gravitation in this
regard. In closed (not isolated) systems, entropy and enthalpy are in opposition.
On fairly small spatial scales, enthalpy wins (with the relevant scale depending
on the nature of the forces generating the enthalpy). But on large scales,
entropy wins against nuclear and electromagnetism, and seems to have achieved
at least a draw with gravitation. And it may be that on the very largest scale
entropy wins even against gravitation. The universe is still expanding, after
all.

.

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