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(quote):  "Place 20 coins, heads up, on a tray and film it as you give it a shake.  Then play the film backwards.  From a jumbled mess, the coins all jump and come to rest with the same side up - an unreal, slightly creepy sequence.  ("How to think about Entropy", New Scientist 30 June 2018, p. 37)

 

The article seems to say this is due to thermodynamics, the science of heat, energy and, most crucially, entropy.  I am sure there is something I do not know but it seems to me that the reason they all end up with the same side up is that the film was run backward.  At its beginning, the coins were all placed heads up.  Of course, the article says they all ended "with the same side up".  It doesn't say "with heads up".

 

Maybe somebody has a copy of this magazine and can read further.  What is it I am missing?  Thank you.

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I do not get what your issue is. I mean what would you expect to happen?

My fault.  I did not make my question clear.  The article seems to say this is due to thermodynamics, the science of heat, energy and, most crucially, entropy.   That is what I was questioning but maybe not so much "is this true?" as "isn't the answer much simpler?"  Didn't the coins ending up all with the same side up happen simply because the film was shown backward?  The coins started out all heads up.  Wouldn't a backward-running film finish with them that way?

 

Is that more clear?  I hope.

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I guess it is a case of make simple things complicated just like "when the air cools there is a phase transition of the water molecules from gaseous to liquid, which then become too heavy to be supported in air by wind and air and they then fall due to gravitational laws to earth, but due to friction and heat thereby generated there can be another phase transition back to gaseous state and then cooling again back to liquid till eventually the molecules drop to the ground" vs. "when humid air cools down it rains". It is not that one is wrong but just that one explains it in the laws of physics and the other in common sense.

Same in your example, as I understand it, either you say "due second principle of thermodynamics entropy stays constant or increases with time, hence it follows that moving backwards in time it stays constant or decreases" vs " just the opposite happens".
If you interpret entropy as the number of possible states of a system (which is right in some ensemble/ in some micro-level) and then extrapolate it to coins initial state is 1= 20 coins tower, final states are all possible ways the tower can increase-->entropy increased-->agrees with thermodynamics. If the tower can fall in only 1 way -->constant entropy-->agrees too.

Now say that entropy can decrease in this closed system. And for the sake of the argument say the tower has 2 possible states, last coin flipped up or flipped down. So decreasing entropy would mean that the tower can fall into only 1 state (eg. all heads up), which just does not make sense :-)
 

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I guess it is a case of make simple things complicated just like "when the air cools there is a phase transition of the water molecules from gaseous to liquid, which then become too heavy to be supported in air by wind and air and they then fall due to gravitational laws to earth, but due to friction and heat thereby generated there can be another phase transition back to gaseous state and then cooling again back to liquid till eventually the molecules drop to the ground" vs. "when humid air cools down it rains". It is not that one is wrong but just that one explains it in the laws of physics and the other in common sense.

 

Same in your example, as I understand it, either you say "due second principle of thermodynamics entropy stays constant or increases with time, hence it follows that moving backwards in time it stays constant or decreases" vs " just the opposite happens".

If you interpret entropy as the number of possible states of a system (which is right in some ensemble/ in some micro-level) and then extrapolate it to coins initial state is 1= 20 coins tower, final states are all possible ways the tower can increase-->entropy increased-->agrees with thermodynamics. If the tower can fall in only 1 way -->constant entropy-->agrees too.

 

Now say that entropy can decrease in this closed system. And for the sake of the argument say the tower has 2 possible states, last coin flipped up or flipped down. So decreasing entropy would mean that the tower can fall into only 1 state (eg. all heads up), which just does not make sense :-)

 

(quote)  Same in your example, as I understand it, either you say "due second principle of thermodynamics entropy stays constant or increases with time, hence it follows that moving backwards in time it stays constant or decreases" vs " just the opposite happens".   (unquote)  :-)

 

Trying to make it sound like hard work.  Or magic?  Thank you.  "moving  back in time".  I posted something this morning about quantum computers which sounded like they would let us move back in time.  Not that I have any desire to do so but it gets interesting.  Anyway, that isn't exactly what they were saying.  Just a thought.

 

Thank you for clarifying and reassuring my thinking skills.  Calm my entropy.  :-)

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That is what I was questioning but maybe not so much "is this true?" as "isn't the answer much simpler?"  Didn't the coins ending up all with the same side up happen simply because the film was shown backward?  The coins started out all heads up.  Wouldn't a backward-running film finish with them that way?

 

Is that more clear?  I hope.

 

It seems obvious that the statement about the coins is designed merely to illustrate (by analogy) some OTHER point, which you're not including.  What is the context here?

Edited by Moronium
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The coin flip is probably to reflect the following.

 

"the entropy of a system will never decrease in thermodyanmic systems it will either remain the same or increase."

 

the reversing of the film is to illustrate that under reversible processes the entropy will remain the same. The film highlights a reversible process the coin flips simply help illustrate entropy as disorder. More formally greater entropy will require greater information to describe the exact physical state.

 

the film example does not describe irreversible processes those always increase in entropy

Edited by Shustaire
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The coin flip is probably to reflect the following.

 

"the entropy of a system will never decrease in thermodyanmic systems it will either remain the same or increase."

 

the reversing of the film is to illustrate that under reversible processes the entropy will remain the same. The film highlights a reversible process the coin flips simply help illustrate entropy as disorder. More formally greater entropy will require greater information to describe the exact physical state.

 

the film example does not describe irreversible processes those always increase in entropy

Shustaire,  I am  not ignoring your post.  I am concentrating on this:  "the entropy of a system will never decrease in thermodyanmic systems".    Since I know (or think) entropy can decrease in some situations, maybe I'd better go back to thermodynamic systems and see what is different here.  Is it the heating from the action? 

 

Leave it to me.  I'll find it.  Thanks.

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 "Place 20 coins, heads up, on a tray and film it as you give it a shake.  Then play the film backwards.  From a jumbled mess, the coins all jump and come to rest with the same side up - an unreal, slightly creepy sequence.

 

 

--
You are confusing 2 different things. A process of 'shaking a set of coins', and the process of  filming that process. The 1st involves 2^20 outcomes. The 2nd involves 1 outcome, a certainty,  predetermined as a history on film.
Edited by sluggo
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  • 3 weeks later...

"the entropy of a system will never decrease in thermodyanmic systems".    Since I know (or think) entropy can decrease in some situations,

Not in a closed system. It can increase in an open system (for example, sunlight added to Earth => complex life)

 

But if you extend the boundaries of the system to include the sun, then the overall entropy is actually increasing.

 

Another way to say this is that entropy can temporarily decrease locally in a system, but not globally.

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(quoting myself)

 

I did not make my question clear.  The article seems to say this is due to thermodynamics, the science of heat, energy and, most crucially, entropy.   That is what I was questioning but maybe not so much "is this true?" as "isn't the answer much simpler?"  Didn't the coins ending up all with the same side up happen simply because the film was shown backward?  The coins started out all heads up.  Wouldn't a backward-running film finish with them that way?

 

I think my confusion is how did thermodynamics and entropy get mixed up in it?  Why can't we simply say the coins all ended up with the same side up because that is how they started out and running the film backward would naturally make them end up that way.

 

That is, of course, assuming we are watching the process on film, not in reality.  Seeing it happen as a "real 'live'  happening" is a whole other story which requires another kind of understanding.

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(quoting myself)

 

I did not make my question clear.  The article seems to say this is due to thermodynamics, the science of heat, energy and, most crucially, entropy.   That is what I was questioning but maybe not so much "is this true?" as "isn't the answer much simpler?"  Didn't the coins ending up all with the same side up happen simply because the film was shown backward?  The coins started out all heads up.  Wouldn't a backward-running film finish with them that way?

 

I think my confusion is how did thermodynamics and entropy get mixed up in it?  Why can't we simply say the coins all ended up with the same side up because that is how they started out and running the film backward would naturally make them end up that way.

 

That is, of course, assuming we are watching the process on film, not in reality.  Seeing it happen as a "real 'live'  happening" is a whole other story which requires another kind of understanding.

 

Yes. I'd say mentioning playing the film backwards is merely to give an image of : "This is what it would look like, if it happened in reality".

 

Playing the film backwards is not literally part of the concept of thermodynamics they're trying to communicate to the reader.

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(quoting myself)

 

I did not make my question clear.  The article seems to say this is due to thermodynamics, the science of heat, energy and, most crucially, entropy.   That is what I was questioning but maybe not so much "is this true?" as "isn't the answer much simpler?"  Didn't the coins ending up all with the same side up happen simply because the film was shown backward?  The coins started out all heads up.  Wouldn't a backward-running film finish with them that way?

 

I think my confusion is how did thermodynamics and entropy get mixed up in it?  Why can't we simply say the coins all ended up with the same side up because that is how they started out and running the film backward would naturally make them end up that way.

 

That is, of course, assuming we are watching the process on film, not in reality.  Seeing it happen as a "real 'live'  happening" is a whole other story which requires another kind of understanding.

It sounds to me as if what they are trying to illustrate by way of the coins is the concept of entropy and its unidirectional nature (in a closed system).

 

In mechanics, (the part of physics concerned with forces and motion of objects), every process is in principle reversible. However many thermodynamic processes are irreversible, because of the operation of random statistics on the component molecules, like the random outcome of coin tossing. Such irreversible thermodynamic processes proceed with an increase of entropy, which means the arrangement of the molecules is less ordered at the end of the process than it was at the start. 

 

Running the film backwards, to get the coins all back to being aligned the same way, is exactly what is not possible in real life, illustrating the concept of irreversibility.

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(quote):  "Place 20 coins, heads up, on a tray and film it as you give it a shake.  Then play the film backwards.  From a jumbled mess, the coins all jump and come to rest with the same side up - an unreal, slightly creepy sequence.  ("How to think about Entropy", New Scientist 30 June 2018, p. 37)

 

(quote Dave C):  Yes. I'd say mentioning playing the film backwards is merely to give an image of : "This is what it would look like, if it happened in reality".

 

(quote ExChemist):  Running the film backwards, to get the coins all back to being aligned the same way, is exactly what is not possible in real life, illustrating the concept of irreversibility.

 

(quote hazel m):  I think my confusion is how did thermodynamics and entropy get mixed up in it?

 

Well, the title was "How to think about entropy".  There is the problem.   I must get out that article again.  I do not remember the title being worked into the short article.

 

Thanks Dave and ExChemist.

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(quote):  "Place 20 coins, heads up, on a tray and film it as you give it a shake.  Then play the film backwards.  From a jumbled mess, the coins all jump and come to rest with the same side up - an unreal, slightly creepy sequence.  ("How to think about Entropy", New Scientist 30 June 2018, p. 37)

 

(quote Dave C):  Yes. I'd say mentioning playing the film backwards is merely to give an image of : "This is what it would look like, if it happened in reality".

 

(quote ExChemist):  Running the film backwards, to get the coins all back to being aligned the same way, is exactly what is not possible in real life, illustrating the concept of irreversibility.

 

(quote hazel m):  I think my confusion is how did thermodynamics and entropy get mixed up in it?

 

Well, the title was "How to think about entropy".  There is the problem.   I must get out that article again.  I do not remember the title being worked into the short article.

 

Thanks Dave and ExChemist.

The idea is that, due to the intrinsic tendency for molecular-scale order to dissipate into less ordered states (like the coins), the availability of heat (which is the energy due to molecules in motion) for doing mechanical work tends to decrease.  

 

Entropy is the thermodynamic entity that quantifies this "unavailability-to-do-work" of heat energy.  It is not an easy concept, admittedly. One learns about entropy only in 6th form science.  

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