Maxwell's demon | Thermodynamics | Physics

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Maxwell's demon | Thermodynamics | Physics | Khan Academy

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15 жыл бұрын

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Maxwell's Demon: A thought experiment that seems to defy the 2nd Law of Thermodynamics. Created by Sal Khan.
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Пікірлер: 150

@edabakb 4 жыл бұрын

Watching this now so I can understand Christopher Nolan's new movie Tenet better when it comes out.

@ShambhavAviral 4 жыл бұрын

I also watched this for tenet only

@felipebulac 4 жыл бұрын

Same here!

@xxX_420BlazeIt_Xxx 8 жыл бұрын

Even magic requires work.

@Takeru9292 5 жыл бұрын

Lol

@bijoydeori4469 3 жыл бұрын

says clausius

@DimitriosDenton 7 жыл бұрын

But how about an Incredibly Lucky Maxwell's demon? So he wouldn't waste any energy on sensing the particles. He would just open the door at random, but because he was super lucky, every time he opened the door, there would be a hot particle flowing from the cool side and vice versa.

@upandatom 7 жыл бұрын

An incredibly Lucky Maxwell's demon is fantastically unlikely. There is nothing saying that the second law of thermodynamics isn't physically possibly, only extremely extremely unlikely. So much so that a violation of the law has never been observed in the history of the universe.

@fragstja3231 6 жыл бұрын

Up and Atom Yes you are right you can think entropy as a particular order in a card deck and what you are talking about is that when you mix the cards randomly they generate the same particular order.It is possible but very very hard.

@petrus94 6 жыл бұрын

D. Tong says : "The phrase 'highly unlikely' is used only because the English language does not contain enough superlatives to stress how ridiculously improbable a violation of the second law would be. The silly number of possible states in a macroscopic systems means that violations happen only on silly time scales: exponentials of exponentials. This is a good operational definition of the word 'never'", which i find a quite satisfying view on the unlikely term ;)

@bouipozz 3 жыл бұрын

Im glad you asked this as I was thinking the same thing. Assuming the door was only opened and closed randomly, sooner or later (however unlikely) the second law would surely be violated. Of course this would be completely impractical, but are we discussing what is practical or what is fundamentally possible? Supposing that you weren't concerned with measuring individual particles but simply the average of all the particles let through during any opening it somehow seems more practical. Perhaps in a system based purely on chance we must consider all possibilities and take the average entropy of all of them rather than simply focusing on the one that produces the desired result? I am nowhere near qualified enough to say, but would be very interested to hear an explanation from someome who is. It seems at the very least that Maxwell has drawn attention to a very curious possibility, or maybe the second law was only ever meant to describe the average state of macroscopic systems, or does the stipulation that the second law applies only to closed systems mean that the opening and closing of some door is not allowed? Certainly food for thought...

@steveaustin5344 2 жыл бұрын

@@upandatom You can break the 2nd law of thermodynamics. It has been demonstrated several times. Search "Tuning Up Maxwell's Demon" (2021 article) in the Proceedings of the National Academy of Sciences (PNAS), a peer reviewed journal of the National Academy of Sciences. Plenty of solid evidence. Fascinating how science can accidently be like a religion. Let's be good scientists and not get too fanatical, especially as you are likely emotional now I challenged your belief.

@hsleff 15 жыл бұрын

You missed a key point, namely, that in principle, measurement can be done with arbitrarily little dissipation. However, the demon must periodically erase its memory, which forces a definite non-negligible entropy increase. It is this that "saves" the second law. See the book Maxwell's Demon 2: Entropy, Classical and Quantum Information, Computing by Leff and Rex. This tells the whole story. So does Maxwell's Demon: Why Warmth Disperses and Time Passes by von Baeyer.

@hsleff 15 жыл бұрын

I have read that Einstein said that one should make a theory as simple as possible, "but no simpler." Omitting the key reason that the second law is "saved" to make things easier also makes them incorrect. The explanation has been made simpler than possible.

@neveda2e3e 8 жыл бұрын

I was also wondering that wouldn't knowing the location of all the particles and their speed violate Heisenberg's Uncertainty Principle

@pauldcunha488 8 жыл бұрын

+neveda2e3e HEisenberg's Principle talks about certian subatomic particles like electrons. Molecules are too big for quantum mechanics.

@neveda2e3e 8 жыл бұрын

+Paul D'C fair enough. Where do u draw the line between quantum mechanics and classical mechanics

@Mikeontube 7 жыл бұрын

Paul D'C you are absolutely WRONG! www.nature.com/nature/journal/v401/n6754/abs/401680a0.html

@ProfessorWaltherKotz 6 жыл бұрын

Yes. Heisenberg's uncertainty principle wouldn't allow us to measure the momentum (speed * mass) of ANY particle with maximum precision without blurring the particle's position.

@Saptarshi.Sarkar 6 жыл бұрын

I was thinking about the same thing and I read your comment

@nobodyimportant2494 9 жыл бұрын

I believe they chose a demon because it is a magical entity that knows when to perform an action without having to directly observe any thing.

@awesomebearaudiobooks 5 ай бұрын

Well, a demon doesn't just appear from the thin air. It would then also come from some other source, probably from a parallel universe, or maybe from a parallel 3d space inside some 4d space that would be common to the both of us, so the entropy would increase either way. I mean, imagine that we're in a multi-level building, and we have our particles in two rooms on the first floor, and we're also on the first floor, and the ceiling is only transparent on one side, so that we don't see the demon, while the demon can clearly see us, and the demon can see all the particles, and it would open the door at will, with all the entropy created at the second floor (because the demon's thought processes and all the censors and the combustion motor for opening the door would be on the second floor), but we won't be able to feel it since we're on the first floor.

@ChrissyoSpace 15 жыл бұрын

"is there a chance that the Demon could interfere without adding to the system" Well, no, that's the point. In order to know when to open the door, he has to observe the particles in some way which requires him to do work. Even opening the door requires the demon to do work which will increase entropy. If you have the demon not interferring with the system in any way, you won't be able to have the door opened and you won't get the apparent paradox.

@Mac40581 8 жыл бұрын

Don't forget to carry the 2.

@johnywhy4679 4 жыл бұрын

10:48 Why does the demon have to keep track of ALL the particles, all the time? Doesn't he only have to sense the particles which approach the trap-door?

@jerrylewison8654 3 жыл бұрын

Fast particles from the higher temperatures (T1) could approach the door, slower particles from the lower tempreture (T2) could also approach the door. There are multiple collisions in many possible directions that are happening at the same time, that might have the particles heading in immensely various direction with a wide assortment of kinetic energy. It is a seemingly random motion, we could only make sense of it or predict outcomes as to where the particle might go after a collision or at what place it is at a particular time and what its velocity or kinetic energy is (could be both slow or fast,and in any direction) by utilizing an immense amount of computing power,so that's why we need to keep track because we could know what kind of particle we might be getting near the door at any given time, fast or slow from either sides of the door.

@tetekofa 11 жыл бұрын

Dr Samuel Collins of MIT built a cryrogenic helium liguefaction apparatus at the beginning of WWII. It is still running today in his Lab at MIT, apparently with no input power...how do I know this you ask?? He's my great uncle.

@maplebayou1 14 жыл бұрын

What Maxwell's demon does illustrate, which is in a sense revolutionary, is the equivalence of thermodynamic and informational entropy, and therefore the equivalence of energy and information. A variation of Maxwell's demon is Szilard's engine, which is actually much simpler. Just last month a paper was published using this principle to convert information into energy.

@orbsandtea 15 жыл бұрын

He didn't miss it, he just didn't include it, in order to make things easier. The same reason he didn't include the mathematics that proved it... ;)

@rentatrip1videos 13 жыл бұрын

much more simple stated - Maxwell's Demon , is the Fact - That when any attempt is made to seperate fast (hot) from Slow (cold) - there will never be complete seperation-there will always be a per cent of the total that are half way inbetween and are mixture of both slow & fast or YPORTNE !- which is the study of the random order which will never quite fit in either fast or slow but linger somewhere in between Accentuate the Positive Eliminate the Negative- don't mess with Mr. In Between

@pineapplepenumbra 9 жыл бұрын

This is daft; do you know what even a cheap demon's hourly rate is? It's way too expensive for humans to afford!

@muhendisChe 5 жыл бұрын

There is a paradox in this theory.. information cannot be generated without energy .. Can Maxwell demon produce information without energy ? The question to be asked here is, is it possible to produce information without energy input? Such a claim is a violation of entropy law.

@fyescas777 9 жыл бұрын

Google a vortex tube, you introduce pressurized air at 5 atm at 0°C and you can split it at lower pressure into two streams of -20°C and 175°C and 1 atm. All that without doing any work to the system.

@Erik_g33k 14 жыл бұрын

Simplicity is the aesthetics of mathematics. Not just Einstein who said that. Besides, this is KZfaq, it's not the world's physics tribunal...

@mybluemars 9 жыл бұрын

Opening that door takes some energy, so work is done.

@aaronmorgan1879 8 жыл бұрын

+Severan Mal excuse me but wouldn't energy be absorbed by the diode upon contact?

@MisterTutor2010 11 жыл бұрын

"Maxwell's Dude" :)

@YtubeUserr 4 жыл бұрын

Why not Maxwell's Genie? Or Maxwell's Angel? I would have preferred to use "Genie"

@ross259 14 жыл бұрын

Yes, Heat IS being transferred from cold body to hot body in this example clearly explained at 6:00. The hot body has many high kinetic molecules and few low kinetic molecules. The cold body has many low kinetic m's and few high kinetic m's. If you take all the "fast" molecules from the cold body and add them to the hot body and all the "slow" m's from the hot body and add them to the cold body, the avg temp of the hot body will increase and the avg temp of the cold body will decrease.

@ritokazoriv 6 жыл бұрын

Taking heisenberg's uncertainty principle into account the demon can't know the kinetic energy and if its about to go through the trapdoor at the same time, so the 2nd law isnt violated

@pafloxyq 5 жыл бұрын

but sir, in Maxwell's own interpretation the did some work on the door whenever he opened it and as the same the same amount of work was returned to the demon when he closed the door , the door considered here frictonless obviously. i think it is rather more definite to say that information simply costs entropy .

@JGS2295 6 жыл бұрын

The 2nd law of Thermodynamics is somewhat of a misnomer. Calling it a "law" implies it is universally applicable for ALL possible systems, scenarios and times. However, all the "law" states is that it is overwhelmingly more likely for the entropy to increase than decrease - particularly for systems of n particles where n is incredible large. This does not mean it's impossible for entropy to decrease. A closed system of air COULD evolve such that there was a build up of air on one side compared with the other - hence decreasing the entropy. But that is unbelievably unlikely.

@seanbullis3364 2 жыл бұрын

I believe the law is the entropy of the universe is always increasing. But in smaller subsets of the universe it could decrease but the increase somewhere else occurs outside of the measured subset but still within the bounds of the universe.

@CvikliHaMar 6 жыл бұрын

And what if we just simply place a sensor before the door, so we don't have to track every single molecule, only those that are in front of the doors? It sounds less hassle.

@Takeru9292 5 жыл бұрын

And how does the sensor operate? Batteries? Will eventually run out

@SlavaVB 14 жыл бұрын

The second law of thermodynamics isnt a multitier system in regards to scale.

@SingHouse 11 жыл бұрын

i thought it was the irreversible erasure of information that the demon would eventually have to do, which increased entropy, not what you described?

@amolmishra7406 8 жыл бұрын

sir , can't we give an approach to heisenberg's uncertainity principle ? I mean if he measures the velocity , would e able to measure the accurate position hence giving this demon a huge conflict ? #FoodForThought

@SlavaVB 14 жыл бұрын

One thing I find discouraging is that this effect isn't found in nature and life forms. All living things prefer eating and digestion over this process.

@edgararreola7370 4 жыл бұрын

All I have for you is a word TENET

@Matice21 15 жыл бұрын

This is far above my head!!!

@ambientvirtual 3 жыл бұрын

not for me. haha

@blackhole672 7 жыл бұрын

What if there was just some kind of net at the microlevel that would let pass thru high energy particles in one direction and low energy particles in the other direction? No computation, just a selectivity in the structure of my net that acts thru dissecting energy states in specific directions. The only question would be if such a structure could exist...if yes, second law would be violated.

@upandatom 7 жыл бұрын

The mechanisms in the net would probably be using energy and therefore be increasing the net entropy of the system.

@FranklyLate 12 жыл бұрын

The key thing is that the demon must have information on exactly what molecules are moving in which direction and at what speed. Information costs energy from the system. This nullifies it.

@gc1979o Жыл бұрын

What about vortex tube cooling it doesn’t need any extra energy just geometry of the tube used to generate the vortex needed to separate hot and cold streams ?

@thirajwegala8030 5 жыл бұрын

Sal. You're amazing; thank you. Please please can you make a couple of videos on the thermodynamic cycles; Brayton, Rankine, Sterling, Otto, etc, maybe an example of each? Will appreciate it greatly!

@discosqueakyfly 14 жыл бұрын

Okay, question. I have been pondering Maxwell's Demon for about three days, and what I cannot understand is based on several definitions I have found that state that Maxwell's Demon expends NO energy in doing the job described. Well, everyone argues the energy expended would offset the entropy decreased in the system, but if it expended no energy then that would be a moot point. Therefore, it seems a rather inconsequential thought experiment because no such being is found to exist in nature.

@MrNiki2015 6 жыл бұрын

Hello Sir, I'm currently working on my Thermodynamics class and was wondering about this Maxwell Dude. In this Video, which is well explained, you say that the measuring process will rise the level of Entropie. But in my Script, this point was refuted a couple of centuries ago. Theoratically it should somehow be possible to measure all that informations without rising the amaount of Entopie. The Answer that was given to me by my Script is: The Demon needs to delete the Information from one Microstate, to take the next measurment. This process of deleting is irreversible and does not contridict the second law of Thermodynamics. I'm not sure abot allthis stuff but maybe that's some kind of flaw in ur video. Greetings, Niklas

@Takeru9292 5 жыл бұрын

Youre right. This maxwell demon thought experiment was debunked years ago but it is profound in that it took 100 years to finally solve and also that it gave rise to information theory and statistical mechanics

@wideyxyz2271 7 жыл бұрын

as always it throws up more questions to answer.... gotta love sciences....

@chocolateboy10 6 жыл бұрын

8:25 A balance!

@atriagotler 2 жыл бұрын

The demon should be using two doors. Neither of them would be open simultaneously. When transferring particles from cold to hot, the opening times of the doors would be set as such that only the fast particles would be able to bounce through the 2-door system. Slower particles would be bounced back to the coldness. (The door on the side of the heat should be able to register when a bounce occurs which might or might not add to the entropy of the system...)

@rene12393 13 жыл бұрын

Maxwell's Demon may now be hard at work turning some corner of hell into a refrigerated room using the principles of the second law, wouldn't you say so?

@bharattandon4768 Жыл бұрын

If the demon needs to track which particles have which velocity and where they are exactly present at any given time to that he can demonstrate his "demoness", won't that violate the Hiesenberg Uncertainity principle where the demon won't be able to tell how fast an atom is moving and where it is simultaneously, for the entire system on a microscopic level. This is a microsystem so I guess it would still apply.

@jod125 11 жыл бұрын

I've always wondered: how many atoms in a molecule?

@ambientvirtual 3 жыл бұрын

@SlavaVB 14 жыл бұрын

This also explains sort of that intelligence itself causes a decrease in entropy of information and material

@idster7 14 жыл бұрын

maybe i don't understand entropy, but i don't get this explanation. i mean, even in this example, heat is NOT being transferred from cold to hot because the particles going to the hot system are ALREADY hot. heat is still being transferred from hot to cold, just on a microstate.

@MaxxG94 12 жыл бұрын

I like how you combined stats in to this concept

@johnywhy4679 4 жыл бұрын

8:21 Before segregation, what would cause the temperatures to equalize, if the chambers are insulated?

@Cardgames4children 6 жыл бұрын

The way I think i see it is this: In such a world like ours, the logical world,, to be able to implement and actually accomplish Maxwell's Demon, the overall entropy would actually increase, as you say. Computation power, moving the door, etc. But what if, hypothetically, this is a magical world now, and the situation (i.e. door) "knows" via its magic that a fast/slow particle is approaching it and thus disappears/reappears? In a magical world like this, I don't think nothing would stop such things from occurring, but then the catch is that I guess in such a world the second law wouldn't hold also. Among pretty much anything else, I guess. hmmm

@sunitatopno1333 4 жыл бұрын

Nice

@sciencenerd7639 2 жыл бұрын

this is neat

@badbuners 13 жыл бұрын

the process of evolution defy the the second law of thermodynamics. true story or at leased to an extent

@Takeru9292 5 жыл бұрын

Doesnt. Complexity can exist because of entropy

@catklyst 11 жыл бұрын

Ahh physics always brings a smile to my face, but the prospects for a truly unlimited source of energy seems impossible. Perhaps one day we will figure out how to harness the wiggle of atoms.

@ChiChithePygo 14 жыл бұрын

Wonderfully lucid explanation. Thanks very much!

@gabeanderson8501 11 жыл бұрын

Very well articulated!

@chakradharsp_0369 Жыл бұрын

The demon itself generation a more entropy than the system XD

@rku840 8 жыл бұрын

You don't need a demon but a normal door like our room door without latch, the door can be open one way only, from one side the momentum of a molecule can open the door and passes, but from the other side the door is blocked. This is better than the demon because eventually all moving molecules will end up on one side of the wall leaving behind all molecules with zero speed on the other side!

@upandatom 7 жыл бұрын

What about the fast moving molecules on the side to which the door opens?

@jonnythebutcher 14 жыл бұрын

what is the relation between entropy in thermodynamics and entropy in information theory? In the physical world, can the level of organization of a system always be reduced to something proportional to temperature? And don't living evolving systems contradict the second law of thermodynamics?

@kaushiksaic 4 жыл бұрын

Doing my prep for Tenet

@thedarksecrets-official 4 жыл бұрын

Now I understand Tenet

@rupeshtashildar Жыл бұрын

The diagrams are more chaotic than traffic in India

@ws_zilch 4 жыл бұрын

Next do a video about Laplace's demon :D

@Nomoreidsleft 14 жыл бұрын

@Mal1234567 It's not a mathematical question. It's philosophical. The answer is zero, since angels would not waste their time to dance on the head of pins.

@shru5151 11 жыл бұрын

hey ! can u cover maxwell's corkscrew rule ? and tangents .

@hickswasright 15 жыл бұрын

This is all very logical and left-brained, considering the quantum physics stuff to do with the observer, is there a chance that the Demon(using his right sided brain..??) could interfere without adding to the system, without the use of computers, thus disproving the 2nd "law".. ?? reason i ask is because Georg Cantor's infinity question couldn't be solved using maths. Love Entropy, cheers, but don't enjoy 'laws', Hehe :-) just thought i'd ask..

@thisismyname007 11 жыл бұрын

Nice. Now tell me about quantum tunneling from one compartment to the other. There's no "demon" needed for particles to quantum tunnel. The "gotcha" is that it's not a one way process.

@NLarsen1989 13 жыл бұрын

@badbuners Living organisms on this planet aren't in a closed system, we receive energy from the sun.

@jod125 11 жыл бұрын

Well, on programs and things of the sort they always say molecules and in other things they say atom. are they two different ways of explaining something or...

@seanalire-moynihan9142 8 жыл бұрын

So... Maxwell thought of thermodynamics in quantum superposition? We cannot have perfect information of a particle due to the Uncertainty principle. Even using one dimensional system is uncertain to a degree. Is thermodynamics more fundamental tgan quantum mechanics? More fundamental than randomness?

@Nautilus1972 11 жыл бұрын

A molecule of what?

@ambientvirtual 3 жыл бұрын

beer

@drumttocs8 15 жыл бұрын

That's the first step :) Now go figure it out!

@MrMcdagy 13 жыл бұрын

thats the same analogy trying to create perpetum mobile , its funny people are still trying to make such a device . The heat generated opening the door is going to destroy the whole theory.

@Iamatheist1234 12 жыл бұрын

@Crillak1 Yes and I guess Leó Szilárd's respond suggested that such hypothetical "demon" cannot exist in reality due to the reason above. btw can you send me more info about the vortex tube?

@kreeslak 14 жыл бұрын

@kreeslak excuse my english, gets worse with tehcnicism.

@MunchVids 14 жыл бұрын

Yes, the demon would increase entropy by opening the door.

@Amanwithbones 11 жыл бұрын

I mainly came here cause of the Don't starve wiki

@AChocolateOrange 11 жыл бұрын

If there was something in between T1 and T2, wouldn't it transfer heat?

@testatikamethernitha1157 12 жыл бұрын

Osmotic pressure!!!!

@heroncortizo1993 4 жыл бұрын

Very interesting this “demon”! 😈 But sometimes I like to Read a subject to understand it better. 😉

@Nautilus1972 11 жыл бұрын

What does that mean in English?

@kreeslak 14 жыл бұрын

Sounds a bit like just a stadistic fail, You know maybe median temperature it's jsut taken too far as a total parto of such random particle bodies. Or maybe the error its to place that boundary between bodies like a country alike. Would in fact if those molecules don't colide between different bodies ones maybe this bodys are just mixing not exchanging kinetic energy but material then no thermo but mass dynamic rules and new bodies difinition are needed. Macroballsdymanimcs

@SolacePiano 12 жыл бұрын

Maxwells demon disliked this..

@RumoredAtmos 6 жыл бұрын

What if in a molecular level you create a self-sustaining system you wouldn't be able to get energy out of it until you create this demon to do the work and allow this to happen

@arety33 14 жыл бұрын

You are awesome!

@jjwtj95 6 жыл бұрын

I'm a 10/10 T1, slide into my D(e)M(on)s

@SoniaLata 6 жыл бұрын

Flirting in physics be like..

@Takeru9292 5 жыл бұрын

You dont have the potential energy to keep up with the amount of entropy(disorder) i would do to your body lol

@amaryllisw1686 5 жыл бұрын

this voice sounds soooo familiar.

@Nautilus1972 10 жыл бұрын

E.g. a molecule of water has two hydrogen atoms and one oxygen. H20

@vlovskiy 4 жыл бұрын

There are so many unproven assumptions in this "proof" that you start to wonder if this is even remotely describes the reality. Let alone the question why the faster particles in each individual section did not transfer part of their kinetic energy to the slower particles in the same section to begin with. Why do you unquestionably assume that slower particles from the left side and the faster particles from the right side would even "attempt" to cross the open door? What if they wouldn't behave like particles at all?