Question on entropy

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Question on entropy

#1  Postby Blip » Feb 01, 2019 9:44 am

I'm hoping for some help from one or more of the physicists here.

Some of you know that I'm doing a course on astrophysics with Oxford ContEd. I don't have a maths or physics background, but the course is designed to be accessible to a wide range of people, and so it is. Mostly.

However, I've come across something which I don't understand and with which our tutor's answer hasn't really helped me. Looking at results from Hubble, it seems that the most distant, i.e. oldest galaxies 'look strange – smaller, irregular, lacking clearly defined shapes.'

Nearer, i.e. more recent galactic views show more ordered galaxies; as that site explains '[c]loser in, we see numerous galaxy interactions and collisions as galaxies come together and merge, growing in the process. And nearer still, we see versions of the large, stately galaxies we know today. '

Help! How does this square with the entropy of the universe increasing?
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Re: Question on entropy

#2  Postby Animavore » Feb 01, 2019 9:58 am

Though the usual layman description involves coffee and milk*, I like to think of the universe like a pint of Guinness. When you first pour it it's a brown mess of low entropy, high-energy bubbles with little order or form. Then after a few seconds you see forming out of the mess a more orderly arrangement of brown and black waves heading toward the top of the pint as it tends toward higher entropy. After a while it becomes an inert amorphous, low-energy mass of black and cream in a state of high entropy.

The early universe is like that early Guinness with low entropy and high energy. Our current universe is in the middle, like our pint forming - this is where all the interesting stuff happens. Our universe will end in an inert, cold state where not much of anything happens, just like our pint.


*The problem I have with the coffee and milk analogy is that it requires the intervention of q coffee/milk stirrer. Which I can see being abused by theists of the type who take analogies too literally. The Guinness acts by itself.
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Re: Question on entropy

#3  Postby newolder » Feb 01, 2019 10:13 am

At early time, the radiation was in thermal equilibrium (maximum entropy) but the paradox is that entropy has increased since then. The resolution of the paradox is that gravitational clumping of matter allows the entropy to continue to increase. Most of the universe's entropy is found in black holes that will continue to grow until the remote future when the background temperature falls below that of the largest black holes and Hawking radiation evaporates them.

Sir Roger Penrose explains some of this in this clip:
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Re: Question on entropy

#4  Postby Blip » Feb 01, 2019 11:02 am

Thank you both; those are two very helpful posts.
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Re: Question on entropy

#5  Postby Cito di Pense » Feb 01, 2019 11:13 am

Pint well taken.
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Re: Question on entropy

#6  Postby socratus » Jun 15, 2019 10:49 pm

1.
Henry Poincare named the conception of "entropy " as a " surprising abstract ".
2.
Lev Landau (Dau) wrote:
" A question about the physical basis of the
entropy monotonous increasing law remains open ".
3
W. Ostwald said :" The entropy is only a shadow of energy.''
4.
The famous mathematician John von Neumann said to
"the father of information theory" Claude Shannon:
" Name it "entropy" then in discussions
you will receive solid advantage, because
nobody knows, what "entropy" basically is ".
#
It seems, scientists tackle problem of ''entropy'' in terms they exactly don't know.
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Re: Question on entropy

#7  Postby laklak » Jun 16, 2019 2:21 am

I tried to read all of that last post but I ran out of steam.
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Re: Question on entropy

#8  Postby Spearthrower » Jun 16, 2019 3:39 am

It was interesting right up until the moment socratus started typing.
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Re: Question on entropy

#9  Postby romansh » Jun 16, 2019 4:05 am

If you ask a chemist you might get a different answer.

It's got nothing to do with order or disorder.

http://secondlaw.oxy.edu/

I think it is a really good entry level explanation
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Re: Question on entropy

#10  Postby Blip » Jun 16, 2019 6:24 am

romansh wrote:If you ask a chemist you might get a different answer.

It's got nothing to do with order or disorder.

http://secondlaw.oxy.edu/

I think it is a really good entry level explanation


Thanks for that too, romansh; it was very useful.
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Re: Question on entropy

#11  Postby Blackadder » Jun 16, 2019 6:26 am

socratus wrote:1.
Henry Poincare named the conception of "entropy " as a " surprising abstract ".
2.
Lev Landau (Dau) wrote:
" A question about the physical basis of the
entropy monotonous increasing law remains open ".
3
W. Ostwald said :" The entropy is only a shadow of energy.''
4.
The famous mathematician John von Neumann said to
"the father of information theory" Claude Shannon:
" Name it "entropy" then in discussions
you will receive solid advantage, because
nobody knows, what "entropy" basically is ".
#
It seems, scientists tackle problem of ''entropy'' in terms they exactly don't know.
============================


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Re: Question on entropy

#12  Postby Cito di Pense » Jun 16, 2019 8:10 am

romansh wrote:It's got nothing to do with order or disorder.


Irreversibility has to do with order, and so, with probabilities. Entropy is defined in terms of probabilities, and that's why we have crank postings about entropy by socratus, who is probably some kind of determinist. But only probably.

Animavore wrote:
The early universe is like that early Guinness with low entropy and high energy.


And disequilibrium. Don't forget disequilibrium.

Blip wrote:Help! How does this square with the entropy of the universe increasing?


And also don't forget, the farther away we look, the farther back in time we see. Order is local. A lot of potential creativity has been lost along the way. The second law tells us that much more has been lost than has been gained by the work of gravitation.
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Re: Question on entropy

#13  Postby romansh » Jun 16, 2019 2:09 pm

Cito di Pense wrote:
romansh wrote:It's got nothing to do with order or disorder.

Irreversibility has to do with order, and so, with probabilities. Entropy is defined in terms of probabilities, and that's why we have crank postings about entropy by socratus, who is probably some kind of determinist. But only probably.

So what is the probability of having a particular order of a shuffled set of cards? Is not entropy a reflection of the number of ways a system can be shuffled rather than what is the probability of any order of that system?

Do you disagree with Lambert (my attachment) pages six and seven?
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Re: Question on entropy

#14  Postby Cito di Pense » Jun 16, 2019 3:24 pm

romansh wrote:
Cito di Pense wrote:
romansh wrote:It's got nothing to do with order or disorder.

Irreversibility has to do with order, and so, with probabilities. Entropy is defined in terms of probabilities, and that's why we have crank postings about entropy by socratus, who is probably some kind of determinist. But only probably.

So what is the probability of having a particular order of a shuffled set of cards? Is not entropy a reflection of the number of ways a system can be shuffled rather than what is the probability of any order of that system?

Do you disagree with Lambert (my attachment) pages six and seven?


What particular statement are you asking me to agree or disagree with? I don't have the desire to read a verbose non-technical treatment of people's non-technical misunderstandings of entropy.

Lambert is presenting entropy by skirting any discussion of the partition function. He discusses entropy in terms of dispersal of energy rather than partitioning. Relative to the audience he's trying to reach, his treatment isn't wrong, but he spends a lot of pages to say very little, and what he writes has a great deal to do with his own idiosyncrasies, i.e. his presumed orientation toward kinetics, his "Why don't things go wrong more often?" I think he needs to update his treatment in light of new data.

Lambert spends a lot of words to say whatever it is he's saying. What do you think he's saying? As usual, you cite a web page and seem to think you're done.
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Re: Question on entropy

#15  Postby newolder » Jun 16, 2019 3:29 pm

The cards can be ordered 52! ways. The probability of any individual ordering is 1/52! One is the reciprocal of the other and depends in no way on any chemistry at page 6 of that link. :scratch:
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Re: Question on entropy

#16  Postby Cito di Pense » Jun 16, 2019 3:51 pm

Lambert writes:

Entropy is no mystery or complicated idea. Entropy is merely the way to measure the energy that disperses or spreads out in a process (at a specific temperature). What's complicated about that?


http://2ndlaw.oxy.edu/entropy.html

There's nothing complicated about it. The other side of that coin, of course, is that it's some feeble hand-waving that doesn't permit anyone to compute or predict or analyze anything.
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Re: Question on entropy

#17  Postby romansh » Jun 16, 2019 4:24 pm

newolder wrote:The cards can be ordered 52! ways. The probability of any individual ordering is 1/52! One is the reciprocal of the other and depends in no way on any chemistry at page 6 of that link. :scratch:

from Cito's Link

The energy in a cube of ice is constantly being redistributed - in any one of a humanly incomprehensible large numbers of ways, microstates. From the above calculation via the Boltzmann equation, there are 10^1,300,000,000,000,000,000,000,000 microstates for "orderly" crystalline ice, with the energy of the ice in only in one microstate at one instant. Do you see now why it is not wise to talk about "order" and entropy in ice compared to "disorderly" water? What could be more disorderly than that incredible mess for ice of not just trillions times trillions times trillions times trillions of microstates (i.e., which would be only 10^48 !) but 10^1,300,000,000,000,000,000,000,000 ? (There are only about 10^70 particles in the entire universe!)


So water is 2.0/1.3 times more disorderly than ice? Lambert's point at the bottom of the page.
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Re: Question on entropy

#18  Postby romansh » Jun 16, 2019 4:31 pm

Cito di Pense wrote:
http://2ndlaw.oxy.edu/entropy.html

There's nothing complicated about it. The other side of that coin, of course, is that it's some feeble hand-waving that doesn't permit anyone to compute or predict or analyze anything.


Who's claiming it does not permit anyone to predict anything?
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Re: Question on entropy

#19  Postby newolder » Jun 16, 2019 4:41 pm

romansh wrote:
newolder wrote:The cards can be ordered 52! ways. The probability of any individual ordering is 1/52! One is the reciprocal of the other and depends in no way on any chemistry at page 6 of that link. :scratch:

from Cito's Link

The energy in a cube of ice is constantly being redistributed - in any one of a humanly incomprehensible large numbers of ways, microstates. From the above calculation via the Boltzmann equation, there are 10^1,300,000,000,000,000,000,000,000 microstates for "orderly" crystalline ice, with the energy of the ice in only in one microstate at one instant. Do you see now why it is not wise to talk about "order" and entropy in ice compared to "disorderly" water? What could be more disorderly than that incredible mess for ice of not just trillions times trillions times trillions times trillions of microstates (i.e., which would be only 10^48 !) but 10^1,300,000,000,000,000,000,000,000 ? (There are only about 10^70 particles in the entire universe!)


So water is 2.0/1.3 times more disorderly than ice? Lambert's point at the bottom of the page.

Interesting, but how is it connected to a shuffled deck of 52 playing cards?
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Re: Question on entropy

#20  Postby romansh » Jun 16, 2019 5:01 pm

newolder wrote:
Interesting, but how is it connected to a shuffled deck of 52 playing cards?

Which has a higher entropy a pack arranged by suit and order or a shuffled pack?
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