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Old Jun 23rd 2016, 02:14 AM   #1
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Question Why is Maxwell's demon a significant argument?

I was watching this youtube video (about 13 minutes long):
https://www.youtube.com/watch?v=gKRzXMZEug0

Why is the ability to have information about a system of particles so significant in thermodynamics? Wouldn't the demon have to expend energy opening and shutting the trap door or am I missing the point of the argument somewhere?
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Old Jun 25th 2016, 04:58 AM   #2
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The possession of information about a system is important in any branch of the physical sciences.

In thermodynamics we often consider a barrier 'that is suddenly removed or added', frictionless pistons and so on in ideal systems.

The daemon's doorway is such a device, so expends no system energy.
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Old Jun 30th 2016, 06:14 PM   #3
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It is becoming clear that information is a fundamental, arguably the fundamental, feature of physics.
Maxwell's demon is celebrated because it was one of the earliest indicators of this.
You might be interested in this site:
http://www.informationphilosopher.com/.../physics/interpretation/
I'm not sure I can properly understand all the arguments put forward here, and I'm not sure I agree with all the arguments I can understand.
However it does provide many intriguing avenues for consideration.

Last edited by Woody; Jun 30th 2016 at 06:18 PM.
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Old Jul 5th 2016, 06:46 PM   #4
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I think the key issue against the arguments expressed on the link in my last post would be the creation and destruction of information.
Would I be correct that the standard argument in physics states that information cannot be created or destroyed (just rearranged)?
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Old Jul 5th 2016, 09:37 PM   #5
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Originally Posted by Woody View Post
I think the key issue against the arguments expressed on the link in my last post would be the creation and destruction of information.
Would I be correct that the standard argument in physics states that information cannot be created or destroyed (just rearranged)?
I'm going to step lightly here as I don't know much about information theory.

There is a question in my mind about "destruction" of information. I have heard of this in two different ways. The first is that information cannot be destroyed at all. That is to say no information is ever lost in any way shape or form. The second is that information has more of a conservation law. Information can possibly change it's form in some way or another. It is this that I think is more on peoples' minds as you can apply it to an extension of Thermodynamics.

I don't know if there is yet a theoretical preference between the two viewpoints.

-Dan
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Old Jul 14th 2016, 12:33 AM   #6
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Originally Posted by Woody View Post
It is becoming clear that information is a fundamental, arguably the fundamental, feature of physics.
Maxwell's demon is celebrated because it was one of the earliest indicators of this.
You might be interested in this site:
http://www.informationphilosopher.com/.../physics/interpretation/
I'm not sure I can properly understand all the arguments put forward here, and I'm not sure I agree with all the arguments I can understand.
However it does provide many intriguing avenues for consideration.
It might take a while for me to digest all of that and to understand how the arguments put forth have a bearing on irreversible entropy but is potentially interesting. Not sure at this point how the collapse of a QM wave function
is an example of the conservation of information and if it is is that the basis of derivation for the Landau limit.

Speaking of which, if there is a landau limit, a minimum energy required for deletion of information from the universe doesn't that negate conservation of information? What is perhaps more interesting for me is that it implies that there is a difference between throwing a rock into a black hole and an encyclopedia but I don't know yet how that difference would be manifested.
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Old Jul 14th 2016, 02:20 AM   #7
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Those who study analysis in maths soon come to face the consequences of the fact that infinity is not a real number and infinities obey different rules of arithmetic from real numbers.

Thus conservation laws in an infinite system have a different meaning from those in a finite one.

It is not known if the universe is a finite or infinite system and the laws of thermodynamics have been developed for finite systems.

The relationship between 'information' and classical thermodynamics is one of the triumphs of physics, but is a consequence of the mathematical fact that any 'arrangement', physical or non physical, contains a particular amount of information. The same arrangement presented in different realisations contains the same amount of information.

The thermodynamic realisation is about energy states.
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