We've had more than a century of technological progress since Maxwell's thought experiment, so where are our perpetual motion machines? As you might have guessed, there are some problems with Maxwell's Demon. The biggest objection is this one: If the "demon" were a real device and not some magical being, then it would use energy to detect the individual molecules and to trigger the opening between the chambers.
Specifically, the demon would actually use more energy to identify and move the molecules than you could get out of the final product. Of course, this thought experiment wouldn't keep popping up in scientific journals if it were that easily debunked. Scientists continue to debate and test the nitty-gritty details of Maxwell's Demon and there has been some progress , especially in the realm of quantum physics. Maybe one day, we'll be as smart as Maxwell's little creature. You'd never have to charge your phone again! Get stories like this one in your inbox or your headphones: sign up for our daily email and subscribe to the Curiosity Daily podcast.
Pay the Troll Toll. A schematic representation of Maxwell's demon. The Demon Is in the Details. Written by Ashley Hamer July 25, Wake up with the smartest email in your inbox. Our Best Articles Daily.
Viewpoint: Exorcising Maxwell’s Demon
So you could say, look, my average temperature is here, but I have a whole distribution of particles. So let's say this is number of particles. And I won't put a scale there.
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You'll get the idea. So I have a bunch of particles that are at T1, but I have some particles that could be really close to absolute 0. I mean, it'd be very few, but. And then you have a bunch that are maybe at T1, and then you have a bunch of particles that could have actually kinetic energy higher than T1. Higher than the average kinetic energy. Maybe that's this one here. Maybe the guy down here is this guy with barely any kinetic energy.
It means there's some guy who's almost completely stationary, who's, you know, sitting right around there someplace. So there's a whole distribution of particles. Likewise, this T2 system right here, on average, these molecules have a lower kinetic energy.
But you know, there might be one particle here that has a really high kinetic energy. But most of them on average are lower. So if I were to draw the distribution of T2, my average kinetic energy is lower, but my distribution might look something like this.
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It can't go backwards like that. It might look something like this. Oh, I don't know, maybe it looks something like that. Let me try it a little different. I'll make it go just as high. Maybe it looks something like that. So notice, there are some molecules in T1 that are below the average kinetic energy of T2.
There are these molecules here. These are these slow guys right there. And notice, there are some guys in T2 that have a higher kinetic energy than the average in T1. So these are these guys right here. And so the fast guys in T so even though T2 is, quote unquote, colder, it has lower average kinetic energy, there's some molecules, if you look at the micro state, that are actually moving around quite rapidly, and there are some molecules here that are moving around quite slowly.
So what Maxwell said is, hey, what if I had my-- and he actually didn't use the word demon, but we'll use the word demon, because it makes it seem very interesting and metaphysical on some level, but it really isn't-- what if I had some dude, let's call him the demon, with a little trapdoor here? Let me draw a little bit neater. So between those two systems, let's say that they're insulated. Let's say that they're separated from each other. So this is T1 where I have a bunch of particles, you know, with their different kinetic energies.
And then, here is T2.
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And I'm making them separated, and maybe they're connected only by this little connection right here. These guys have a slower kinetic energy. And what Maxwell, his little thought experiment was, hey, let me say that I have some dude in charge of a door-- maybe the door is right here-- and he has control over this door. And whenever a really fast particle in T2, one of these particles over here, come near the door-- so let's say this guy is flying-- let's say that guy right there.
He's going super fast.
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He has super high kinetic energy, and he's just going perfectly for the door. So the demon says, hey. I see that guy. He's coming for the door. He's going to lift his hatch, and he's going to allow this particle to get into T1. So after he lifts the hatch, that particle will just keep going, and it'll be in T1. And then he closes the hatch again, because he just wants the fast particles to go from T2 to T1. And then when he sees a little slow, you know, pokey little particle coming here, one of these guys down here, he opens the trapdoor again, and he allows that one to go.
So then that guy shows up in here. So if he just kept doing that, what's it going to look like at the end? Well, at the end, you're going to segregate-- and it could take a while. But you're going to segregate all the slow particles on-- let me draw it. I'll make the boundary in brown, because now it's not clear which one is-- well. We'll talk about it a little bit. So that's the boundary. That's his door.
What's going to happen at the end? All the fast particles-- some of them are going to be the original fast particles that are in T1, right?
There are some original fast particles in T1 are going to be still on the side of the barrier. Let me draw-- make sure you don't get these two confused. This is a separate picture. Now all of the fast particles from T2 are also going to be stuck there. Because eventually they're all going to get close to that door, if you wait long enough. So then this guy's also going to have a bunch of the, what would originally, in the T2 side of the barrier, they're also going to be there. So you're going to have a bunch of fast particles. Likewise, all the slow T2 particles are going to be remaining on the side of the barrier.
So these are the slow guys. And he would have let all the slow T I shouldn't even call them T1 anymore. I'll call them side 1. Side 1 particles here. Slow side 1 particles. So what just happened here? This was the hot body, this was the cold body.
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The second law of thermodynamics would have told us that heat would have gone from here to here. That their temperatures should have equalized to a certain degree. So the hot bodies should get colder, the cold bodies should get hotter. They should kind of average out a little bit. But using this little demonic figure, what did he do? He made the hot body hotter, right? Now the average kinetic energy here is even higher. He transferred all of these high kinetic energy particles to that distribution, so now that distribution is going to look-- the way you could think about it, if you transferred all of these guys to this guy over here, the distribution will now look something like-- let me see if I can do it.
It will look something like that for T1, instead of the old one. And T and he took all the hot ones away, all the cold ones away, from T1. So these guys are going to disappear. They're not going to be there anymore. And he added them to T2. So the distribution of T2 is going to look like that, and he erased, of course, these from T2. He took all of these guys out of T2. Let me erase this right here. That was the old distribution of T1. So the T2 distribution now looks something like this.
So T2, the new average might be something like here.