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entropy and gravitation



 
 
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  #1  
Old May 30th 17, 05:55 AM posted to sci.physics.research,sci.astro.research
Phillip Helbig
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Posts: 38
Default entropy and gravitation

A smooth distribution corresponds to high entropy and a lumpy one to low
entropy if gravity is not involved. For example, air in a room has high
entropy, but all the oxygen in one part and all the nitrogen in another
part would correspond to low entropy.

If gravity is involved, however, things are reversed: a lumpy
distribution (e.g. everything in black holes) has a high entropy and a
smooth distribution (e.g. the early universe) has a low entropy.

Let's imagine the early universe---a smooth, low-entropy
distribution---and imagine gravity becoming weaker and weaker (by
changing the gravitational constant). Can we make G arbitrarily small
and the smooth distribution will still have low entropy? This seems
strange: an ARBITRARILY SMALL G makes a smooth distribution have a low
entropy. On the other hand, it seems strange that the entropy should
change at some value of G.

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  #2  
Old May 30th 17, 12:30 PM posted to sci.physics.research,sci.astro.research
Eric Flesch
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Posts: 321
Default entropy and gravitation

On 30 May 2017 Phillip Helbig wrote:
it seems strange that the entropy should change at some value of G.


For a while I thought thermodynamics was the most marvellous science,
but now I think that "entropy" is just a fudge to fill in the gap
after the enthalpy is measured. So who ever proved that "disorder" is
a full explanation of so-called entropy? I had the same thoughts as
Phil about the effects of scale on that interpretation (as well as how
it is different in space than on a planet), but casting it in the
light of the value of G is a new one.




  #3  
Old May 30th 17, 01:47 PM posted to sci.physics.research,sci.astro.research
Jos Bergervoet
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Posts: 126
Default entropy and gravitation

On 5/30/2017 6:55 AM, Phillip Helbig (undress to reply) wrote:
A smooth distribution corresponds to high entropy and a lumpy one to low
entropy if gravity is not involved. For example, air in a room has high
entropy, but all the oxygen in one part and all the nitrogen in another
part would correspond to low entropy.

If gravity is involved, however, things are reversed: a lumpy
distribution (e.g. everything in black holes) has a high entropy


But if everything is in one big black hole, and the black hole
would need only mass and angular momentum and charge to describe
it, then that would be extremely low entropy (and essentially we
would have back the "ordinary" behavior you described first).

So the difference is only in the entropy that is in the "soft
supertranslation hair" (if that is the correct theory..)

If the oxygen in one corner of the room would also have this
extra entropy that black holes seem to have (for whatever reason),
then the cases would be the same.

Provided of course that before black hole formation occurs
the normal behavior (lumpy distribution has lower entropy) is
respected by gravity as it is by other forces. So the question
is: would there still be a reason, in cases without black holes,
to expect that gravity is different?

--
Jos


  #4  
Old May 30th 17, 06:55 PM posted to sci.physics.research,sci.astro.research
Phillip Helbig
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Posts: 38
Default entropy and gravitation

In article , Jos Bergervoet
writes:

But if everything is in one big black hole, and the black hole
would need only mass and angular momentum and charge to describe
it, then that would be extremely low entropy (and essentially we
would have back the "ordinary" behavior you described first).


The first clause doesn't really make sense, since if "everything"
(presumably meaning all matter in the universe) were "in one big black
hole", this would have to be something different than what is normally
thought of as a black hole, e.g. a static solution in a background of
Minkowski space.

  #5  
Old June 1st 17, 09:24 PM posted to sci.physics.research,sci.astro.research
Gerry Quinn[_3_]
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Posts: 3
Default entropy and gravitation

In article ,
says...

A smooth distribution corresponds to high entropy and a lumpy one to low
entropy if gravity is not involved. For example, air in a room has high
entropy, but all the oxygen in one part and all the nitrogen in another
part would correspond to low entropy.

If gravity is involved, however, things are reversed: a lumpy
distribution (e.g. everything in black holes) has a high entropy and a
smooth distribution (e.g. the early universe) has a low entropy.

Let's imagine the early universe---a smooth, low-entropy
distribution---and imagine gravity becoming weaker and weaker (by
changing the gravitational constant). Can we make G arbitrarily small
and the smooth distribution will still have low entropy? This seems
strange: an ARBITRARILY SMALL G makes a smooth distribution have a low
entropy. On the other hand, it seems strange that the entropy should
change at some value of G.


The smooth distribution always has the same entropy. Start with the
smooth distribution and no gravity, and increase the gravitational
constant. Now high entropy states start to become available that were
not available withouy gravity.

To put it another way, the 'clumpy' states in the non-gravitational
universe have lower entropy than the smooth state, but the clumpy states
in the gravitational universe have higher entropy than the smooth state.

The clumpiness versus dispersion 'paradox' isn't such a paradox either.
When gravitational clumping takes place, energy is released which will
eventually become widely dispersed as low-grade thermal energy. This
ultimately applies even if black holes are formed, although the thermal
energy will for a long time be locked up in black holes.

- Gerry Quinn

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  #6  
Old June 1st 17, 09:36 PM posted to sci.physics.research,sci.astro.research
Phillip Helbig
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Posts: 38
Default entropy and gravitation

In article ,
Gerry Quinn writes:

The smooth distribution always has the same entropy. Start with the
smooth distribution and no gravity, and increase the gravitational
constant. Now high entropy states start to become available that were
not available withouy gravity.


Sounds plausible.

To put it another way, the 'clumpy' states in the non-gravitational
universe have lower entropy than the smooth state, but the clumpy states
in the gravitational universe have higher entropy than the smooth state.


Imagine a clumpy universe with no gravity. It has low entropy (lower
than the smooth universe). Now G starts increasing from zero to, say,
its current value (at which point the clumpy universe has a higher
entropy than the smooth universe). At some value of G, the clumpy
universe must have the same entropy as the smooth universe (which you
say has the same entropy with or without gravity). So for this value of
G, the entropy is independent of the clumpiness.

Someone has made an error somewhere.

  #7  
Old June 2nd 17, 06:20 AM posted to sci.physics.research,sci.astro.research
Gerry Quinn[_3_]
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Posts: 3
Default entropy and gravitation

In article ,
says...

In article ,
Gerry Quinn writes:

The smooth distribution always has the same entropy. Start with the
smooth distribution and no gravity, and increase the gravitational
constant. Now high entropy states start to become available that were
not available withouy gravity.


Sounds plausible.

To put it another way, the 'clumpy' states in the non-gravitational
universe have lower entropy than the smooth state, but the clumpy states
in the gravitational universe have higher entropy than the smooth state.


Imagine a clumpy universe with no gravity. It has low entropy (lower
than the smooth universe). Now G starts increasing from zero to, say,
its current value (at which point the clumpy universe has a higher
entropy than the smooth universe). At some value of G, the clumpy
universe must have the same entropy as the smooth universe (which you
say has the same entropy with or without gravity). So for this value of
G, the entropy is independent of the clumpiness.

Someone has made an error somewhere.


Why should it not be independent of the clumpiness?

Consider a smooth universe full of hydrogen, with non-zero density and
no gravity. This universe is clumpy too, it's just that the clumps are
mostly H2.

You could make the same paradox by imagining a universe full of H atoms,
and slowly turning on atomic interactions.

- Gerry Quinn

---
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  #8  
Old June 2nd 17, 08:04 AM posted to sci.physics.research,sci.astro.research
jacobnavia
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Posts: 105
Default entropy and gravitation

Le 30/05/2017 √* 06:55, Phillip Helbig (undress to reply) a √©crit :
Let's imagine the early universe---a smooth, low-entropy
distribution---and imagine gravity becoming weaker and weaker (by
changing the gravitational constant). Can we make G arbitrarily small
and the smooth distribution will still have low entropy? This seems
strange: an ARBITRARILY SMALL G makes a smooth distribution have a low
entropy. On the other hand, it seems strange that the entropy should
change at some value of G.


What about time?

An aribtrarily small G will take an almost infinite time to manifest
itself. Weaker gravity will EVENTUALLY get matter clumpy but if gravity
is weak, it will take MUCH more time for gravity effects to manifest
themselves.

An arbitrarily small gravity will take arbitrarily long time to have any
effect.

Does the contradiction disappear if we take time into the picture?


  #9  
Old June 2nd 17, 08:16 AM posted to sci.physics.research,sci.astro.research
Poutnik[_5_]
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Posts: 68
Default entropy and gravitation

Dne 02/06/2017 v 09:04 jacobnavia napsal(a):


What about time?

An aribtrarily small G will take an almost infinite time to manifest
itself. Weaker gravity will EVENTUALLY get matter clumpy but if gravity
is weak, it will take MUCH more time for gravity effects to manifest
themselves.

An arbitrarily small gravity will take arbitrarily long time to have any
effect.

Does the contradiction disappear if we take time into the picture?


Thermodynamics generally does not care,
what time it takes for a system
to get into the preferred final state.

--
Poutnik ( The Pilgrim, Der Wanderer )

A wise man guards words he says,
as they say about him more,
than he says about the subject.


  #10  
Old June 2nd 17, 11:07 AM posted to sci.physics.research,sci.astro.research
Phillip Helbig
external usenet poster
 
Posts: 38
Default entropy and gravitation

In article ,
Gerry Quinn writes:

To put it another way, the 'clumpy' states in the non-gravitational
universe have lower entropy than the smooth state, but the clumpy states
in the gravitational universe have higher entropy than the smooth state.


Imagine a clumpy universe with no gravity. It has low entropy (lower
than the smooth universe). Now G starts increasing from zero to, say,
its current value (at which point the clumpy universe has a higher
entropy than the smooth universe). At some value of G, the clumpy
universe must have the same entropy as the smooth universe (which you
say has the same entropy with or without gravity). So for this value of
G, the entropy is independent of the clumpiness.

Someone has made an error somewhere.


Why should it not be independent of the clumpiness?


Because it's not. A room full of air with the same density everywhere
has higher entropy than a room with all of the air squeezed into one
corner. (In the case where gravity can be neglected. When gravity
plays a role, then the clumpier distribution has higher entropy.)

 




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