Maxwell's Demon question: What if the demon is not a "finite being"?

[Blue_Blistering_Barnacle]

Am I wrong to think of the Maxwell’s Demon experiment as follows?

A) simple version by Maxwell- the demon lowers the entropy of the connected bottles.

B) more complete version- the demon is interacting with the bottles, and while the entropy of the bottles decreases, the entropy of the the whole system (bottles and demon) increases

C) OP proposal- the demon has access to separate “infinite” energy source (maybe 11th dimension), and entropy of demon-bottle system decreases

D) more complete version- the proper system to consider is demon-bottle-11th dimension; perhaps for this system, the entropy increases (if you can math out an “infinite” energy supply). Certainly the entropy would increase if you replace “infinite” with “arbitrarily large”?

[CalMeacham]

@DPRK

You are reading too much into the name of this thought experiment (one of several, like Feynman’s ratchet, showing how the second law of thermodynamics works at a statistical mechanical level, the relationship between thermodynamic and information-theoretical entropy, and physical constraints on micro and macroscopic mechanisms and devices). Maxwell’s Demon is not a real guy. If you accidentally summon a real demon, sure they can generate infinite energy and violate entropy constraints, but IME initially you’ll have your hands full just keeping it from ripping your head off. Eventually, if you have a good relationship, it might oblige you by occasionally materializing a round of drinks out of thin air and inviting you to the best Walpurgis parties, but make sure you have a good handle on your soul; most people don’t.

Larry Niven had his demon act as an air conditioner in "Unfinished Story #1, printed in his collection All the Myriad Way. (If you’re a sorceror, you already have a tamed demon you can use).

His accountant’s name was Maxwell…

[k9bfriender]

@PlaceboTarget

The speed of each particle must constantly change due to the innumerable collisions, but the total energy of all the particles within the two chambers must remain constant. Does that mean the average speed stay the same as well?

If the box is closed system, and there is not transfer in or out, then yes, average speed will stay the same.

Average speed of particles is also known as temperature.

@PlaceboTarget

Also, we know an omnipotent being cannot create a stone it cannot lift. Similarly, there may be logical or objective impediments that could prevent the demon from violating the second law of thermodynamics, despite his supernatural abilities.

Nothing natural can violate the second law of thermodynamics. By definition, anything that did would be supernatural.

Easy analogy, take a pool table, and make it frictionless. shove some balls around, they collide with others, and things tend to move towards the average speed.

Now, put a wall up across the table, with a door in it. When you see a ball moving fast towards one side, or a slow ball heading to the other, you open the door, else wise you close it.

You will end up with fast balls on one side, and slow on the other. But, you then have to realize that you put work into the system, so it is no longer a closed system.

[Chronos]

Eh, you can do that with an arbitrarily small amount of work. It’s not the work you put in that matters; it’s the information you took out.

[DPRK]

@k9bfriender

You will end up with fast balls on one side, and slow on the other. But, you then have to realize that you put work into the system, so it is no longer a closed system.

More precisely, you have decreased the entropy of the system without (apparently) doing any work. (The system does not heat up, as you point out.) You will heat up/consume energy/increase in entropy, though.

[Quercus]

@PlaceboTarget

But the spontaneous entropy reversal you mention seems to refer exactly to this natural “demon”, whose existence we have just agreed would violate the laws of physics. :eek:

The difference is that the demon does it predictably (the right side will always get hotter) Whereas the spontaneous entropy reversal is random and unpredictable.

So, for instance, you could use the demon to get free energy, run a perpetual motion machines, etc. You can’t use spontaneous energy reversal for anything useful.

[k9bfriender]

@Quercus

The difference is that the demon does it predictably (the right side will always get hotter) Whereas the spontaneous entropy reversal is random and unpredictable.

So, for instance, you could use the demon to get free energy, run a perpetual motion machines, etc. You can’t use spontaneous energy reversal for anything useful.

The second law of thermodynamics is, as best we know, only statistical in nature. To say that a closed system can never decrease entropy is not exactly correct, it is just not very likely to.

And that probability has enough zeros behind it that it is effectively zero for any purpose in the macroscopic world. You will never find a system with more than a few dozen particles violating it.

On an individual particle level, though, entropy almost never comes into play. All interactions are reversible.

Why that is, is a very good question.

[markn_1]

As Chronos mentioned in #24, the problem is not that the demon is doing work by opening and closing the door, since that is a reversible process that can be done without an increase in entropy. And measuring the speed of the molecules can also be done reversibly, without increasing entropy. What increases the demon’s entropy, perhaps surprisingly, is the process of discarding or erasing the information it obtained about the speed of the molecules. Erasing information is a non-reversible process that increases entropy (known as Landauer’s Principle). The demon could just try to keep all the information it gathers, but eventually it will run out of storage space and will need to start erasing something.

[Blue_Blistering_Barnacle]

@markn_1

As Chronos mentioned in #24, the problem is not that the demon is doing work by opening and closing the door, since that is a reversible process that can be done without an increase in entropy. And measuring the speed of the molecules can also be done reversibly, without increasing entropy. What increases the demon’s entropy, perhaps surprisingly, is the process of discarding or erasing the information it obtained about the speed of the molecules. Erasing information is a non-reversible process that increases entropy (known as Landauer’s Principle). The demon could just try to keep all the information it gathers, but eventually it will run out of storage space and will need to start erasing something.

So, instead of an infinite 11th dimensional energy source, our super demon really needs an infinite 11th dimensional database?

What happens if our demon merely has a vast database (in its head)? After a hundred years of refrigeration duty, it wipes its memory and disappears in a huge fireball?

[Chronos]

Or it finds some other way of transferring its entropy elsewhere. But yeah, a fireball would probably be one way to do it.

[Blue_Blistering_Barnacle]

So you get a “free” refrigerator for 100 years plus a fireball in the bargain? I could put the memory core inside a power plant before wiping it. Sounds kind of anti-entropic.

There must be a catch that I’m not accounting, such as the entropy required to build a memory core or some limit on the quality of heat released…

[DPRK]

The entropy does not disappear, though.
It is accounted for when you cool down the demon.

ETA the limit you refer to, is the Second Law of Thermodynamics… (which puts a limit to how much useful work you can extract from hot objects)

[Chronos]

It’s no different, in principle, from having a really big block of ice, instead of a demon. Once you have that big block of ice, it’ll give you “free” refrigeration, until it’s used up. Get a big enough block of ice to start with (analogous to a demon with a large enough memory), and it might even last you for 100 years.

[Enola_Straight]

Here’s a video of liquid nitrogen boiling/freezing in a vacuum chamber.

By letting fast moving, warmer molecules escape, slow moving, colder molecules remain and solidify.

A little demonic?

[DPRK]

@Enola_Straight

Here’s a video of liquid nitrogen boiling/freezing in a vacuum chamber.

By letting fast moving, warmer molecules escape, slow moving, colder molecules remain and solidify.

A little demonic?

The demon would reverse whatever process would otherwise spontaneously happen, so in this case catch hot nitrogen molecules from the thin atmosphere and use them to heat the liquid even more, or something. Boiling in reverse.