# Thread: Can we reverse the second law of thermodynamics?

1. First of all, I'm actually kind of surprised that the second law of thermodynamics made it into a law. the law is based on chance, basically. in a closed system, entropy always TENDS to go up, but there are fluctuations, and sometimes, entropy will go down, just by pure chance (http://www.ted.com/talks/sean_carrol...w_of_time.html).

Now since this law is not absolute, isn't it possible, that because we are intelligent, we can create the conditions so, that entropy will decrease?

Maybe i dont understand the concept of entropy fully. entropy i learned is dissorder, but i presume this only means that energy in the form of heat is equally distributed within the system if the entropy is high, and unequally distributed if low, right?
So this would have nothing to do with the structure of matter, but with the heat energy that matter has?

So can we turn the tide against the second law?

2.

3. Carroll does NOT say that entropy can go down without adding energy to the system. The law applies to closed systems, is a law, and entropy always increases unless energy is added.

More on Sean Carroll's comments here:

http://www.wired.com/wiredscience/2010/02/what-is-time/

4. i already watched his presentation. what he said was that entropy always increases, but with fluctuations. so sometimes the entropy actually decreases, but it just increases alot more often.
you know the example of the glass with cream on the top and coffee on the bottom?
if you wait, the cream and coffee will mix together, but they will never go back apart.
but if you actually wait long enough, (longer than the age of the universe) it will actually turn back apart, that's what he said.

He also said that the second law is not absolute. im not making this up.

5. Originally Posted by questioner1
He also said that the second law is not absolute. im not making this up.
It's a bit like saying the laws of probability are not absolute, so you can win at roulette in Las Vegas. Well, sometimes you can win a little but in the long run, you lose.

6. Originally Posted by questioner1
First of all, I'm actually kind of surprised that the second law of thermodynamics made it into a law. the law is based on chance, basically. in a closed system, entropy always TENDS to go up, but there are fluctuations, and sometimes, entropy will go down, just by pure chance (http://www.ted.com/talks/sean_carrol...w_of_time.html).

Now since this law is not absolute, isn't it possible, that because we are intelligent, we can create the conditions so, that entropy will decrease?

Maybe i dont understand the concept of entropy fully. entropy i learned is dissorder, but i presume this only means that energy in the form of heat is equally distributed within the system if the entropy is high, and unequally distributed if low, right?
So this would have nothing to do with the structure of matter, but with the heat energy that matter has?

So can we turn the tide against the second law?
It is quite true that thermodynamcis in general and the second law in particular are statistical in nature. So they are not absolute laws.

On the other hand, they are valid statistical laws, and the law of large numbers is a valid theorem in the theory of probability.

So, no you cannot reverse the second law of thermodynamics.

7. from experience , thanks

8. "It's a bit like saying the laws of probability are not absolute, so you can win at roulette in Las Vegas. Well, sometimes you can win a little but in the long run, you lose."

Well you could grab the ball and throw it where you want to. i know that's cheating, but why is this similar thing not possible in thermodynamics?

"It is quite true that thermodynamcis in general and the second law in particular are statistical in nature. So they are not absolute laws.

On the other hand, they are valid statistical laws, and the law of large numbers is a valid theorem in the theory of probability.

So, no you cannot reverse the second law of thermodynamics."

I know the statistical laws are valid, but do they always apply?

I think you misunderstood my question.
I'm not trying to disprove the second law, i just want to understand why you can't reverse it.

9. Originally Posted by questioner1
Well you could grab the ball and throw it where you want to. i know that's cheating, but why is this similar thing not possible in thermodynamics?.
Isn't that Maxwell's demon?

10. Originally Posted by questioner1
"
I know the statistical laws are valid, but do they always apply?
Yes

11. Originally Posted by Ophiolite
Originally Posted by questioner1
Well you could grab the ball and throw it where you want to. i know that's cheating, but why is this similar thing not possible in thermodynamics?.
Isn't that Maxwell's demon?
Precisely

12. .

13. I don't understand why maxwell's demon doesn't work.

i know that his intervening in the system makes him part of the system, and that his 'intelligence' required to let all the warm molecules to the warm part of the system, increases entropy itself.

but i do not understand why his intelligence necessarily requires increasing entrop, and how we can theoretically say that this increase HAS to be higher than the entropy he decreases in the rest of the system.

14. wat about hot water boiler ? the hot get on top . thanks

15. yeah. i don't understand that either.

and what about this: you have a one sided mirror (the ones they use in interrogation, so that the police can see the criminal but not vice versa)
You put two substances on both sides of the mirror, won't one side eventually get colder than the other, because more light energy is emitted from one to the other?

16. Originally Posted by questioner1
Well you could grab the ball and throw it where you want to.
LOL You rock. You live. Well put.

17. One sided mirrors only work when one of the two rooms is darker than the other. The mirror actually transmits and reflects about 50% both ways, but one room is darker so has less to transmit.

Basically, Maxwell's demon would violate conservation of energy as a passive way of creating a temperature differential. (Heat rising doesn't create a significant differential, and it mostly exists during the process of evening out a temperature differential.)

18. fluctation man ?

19. Originally Posted by MagiMaster
One sided mirrors only work when one of the two rooms is darker than the other. The mirror actually transmits and reflects about 50% both ways, but one room is darker so has less to transmit.

Basically, Maxwell's demon would violate conservation of energy as a passive way of creating a temperature differential. (Heat rising doesn't create a significant differential, and it mostly exists during the process of evening out a temperature differential.)
Maxwell's demon violates the second law of thermodynamics, but not the first law (energy conservation).

20. Couldn't you use Maxwell's demon to create a temperature differential for free, then a heat engine to extract work from that differential?

21. Originally Posted by questioner1
You put two substances on both sides of the mirror, won't one side eventually get colder than the other, because more light energy is emitted from one to the other?
So you think visible light accounts for the entire balance of electromagnetic radiation passing between the two zones?

22. Originally Posted by Ophiolite
Originally Posted by questioner1
You put two substances on both sides of the mirror, won't one side eventually get colder than the other, because more light energy is emitted from one to the other?
So you think visible light accounts for the entire balance of electromagnetic radiation passing between the two zones?
No.

23. So I guess the second law of thermodynamics is a bit like Vegas...you can win a few bucks in the short-term, but over the long run you will lose. And if you try to cheat the system (Maxwell's demon) you will still lose.

24. Originally Posted by gc
So I guess the second law of thermodynamics is a bit like Vegas...you can win a few bucks in the short-term, but over the long run you will lose. And if you try to cheat the system (Maxwell's demon) you will still lose.
Yep.

An there are so many molecules in any macroscopic system that there is no appreciable short run.

25. Originally Posted by questioner1
Originally Posted by Ophiolite
Originally Posted by questioner1
You put two substances on both sides of the mirror, won't one side eventually get colder than the other, because more light energy is emitted from one to the other?
So you think visible light accounts for the entire balance of electromagnetic radiation passing between the two zones?
No.
In that case, why did you ask the question? Do you not see that the potential for nergy to pass through the mirror in a form other than visible light ensures that eventually equilibrium will be reached (assuming no other external inputs).

26. so you're saying that as soon as one room is warmer than the other it will emit a higher frequency light that will pass through the mirror? in that case, what if you use multiple one sided mirrors for different frequencies?

27. Originally Posted by gc
So I guess the second law of thermodynamics is a bit like Vegas...you can win a few bucks in the short-term, but over the long run you will lose. And if you try to cheat the system (Maxwell's demon) you will still lose.
The rules of thermodynamics (Vegas Style):

1. You can't win
2. You can't break even
3. You can't get out of the game.

28. Originally Posted by questioner1
so you're saying that as soon as one room is warmer than the other it will emit a higher frequency light that will pass through the mirror? in that case, what if you use multiple one sided mirrors for different frequencies?
You have the physics all screwed up.

A warmer body emits more electromagnetic energy than a cold one Therefore energy will flow from a warmer body to a colder one.

If you use mirrors, it will slow the process, but the direction of heat flow will be the same.

If you evacuate the region between the two bodies, it will eliminate conduction and convection, but radiant heat transfer will still go from the warmer body to the colder one. Mirrors can slow the process further, but not stop it. No mirror is 100% reflective. This is the prinicple of the thermos bottle.

29. Originally Posted by DrRocket
Originally Posted by questioner1
so you're saying that as soon as one room is warmer than the other it will emit a higher frequency light that will pass through the mirror? in that case, what if you use multiple one sided mirrors for different frequencies?
You have the physics all screwed up.

A warmer body emits more electromagnetic energy than a cold one Therefore energy will flow from a warmer body to a colder one.

If you use mirrors, it will slow the process, but the direction of heat flow will be the same.

If you evacuate the region between the two bodies, it will eliminate conduction and convection, but radiant heat transfer will still go from the warmer body to the colder one. Mirrors can slow the process further, but not stop it. No mirror is 100% reflective. This is the prinicple of the thermos bottle.
but for sort time and sort place, fluctation , man ?

30. Originally Posted by Water Nosfim
but for sort time and sort place, fluctation , man ?
and you can go ferther

31. Originally Posted by Water Nosfim

but for sort time and sort place, fluctation , man ?
Huh? man

32. Originally Posted by DrRocket
Originally Posted by Water Nosfim

but for sort time and sort place, fluctation , man ?
Huh? man
For a spontaneous process, the second law says that the entropy of the universe (Suniv) must be greater than zero, but it does not place a restriction on either the entropy of the system (Ssys) or surroundings (Ssys). Thus it is possible for either Ssys, or Ssurr to be negative, as long as the sum of these two quantities are greater than zero.

33. What is practical sense in creating of Maxwell's demon?
Theoretically you could create infinite motion in
closed system in easier way.You just need to eliminate
friction.For example it could be a flywheel on magnetic
bearings moving in absolute vacuum.Or electron "moving around" nucleus if you want to have any physical example.If you want "eternal engine" in open system there is no way without overcoming First Law of
thermodynamics.For example you have "eternal engine" installed on your car.When car is moving it creates friction of air and by its wheels.When wheels heated they produce infrared waves which leave the Earth and flee in the Space.You can't turn them back.
So you will need to break First Law and create energy from nothing for you car to run eternally.I don't see a
way how Maxwell demon could produce any usable work.

34. Originally Posted by Stanley514
What is practical sense in creating of Maxwell's demon?
Theoretically you could create infinite motion in
closed system in easier way.You just need to eliminate
friction.For example it could be a flywheel on magnetic
bearings moving in absolute vacuum.Or electron "moving around" nucleus if you want to have any physical example.If you want "eternal engine" in open system there is no way without overcoming First Law of
thermodynamics.For example you have "eternal engine" installed on your car.When car is moving it creates friction of air and by its wheels.When wheels heated they produce infrared waves which leave the Earth and flee in the Space.You can't turn them back.
So you will need to break First Law and create energy from nothing for you car to run eternally.I don't see a
way how Maxwell demon could produce any usable work.
If you had a Maxwel demon (of course this is impossible), then from, say a room temperature sample of air, you could isolate the hot molecules and obtain a bottle of hot air. Then you could take that hot gas, expand it through a turbine, and do work.

So a Maxwell demon could indeed allow you to extract more work from a fluid than is otherwise thermodynamically possible.

This does not violate conservation of energy (first law). It does violate the second law.

35. So a Maxwell demon could indeed allow you to extract more work from a fluid than is otherwise thermodynamically possible.
If I no make mistake you wanna say something that different molecules in air have different energy and room temperature of air is just average of their kinetic energy.But first of all number of really hot molecules in
air should be very tiny because average temperature is
very low (in comparison to what we need to run a car).
And therefore you will need to reprocess giant amount
of air to extract sufficient number of really hot molecules.I think that with the same or even grater efficiency you could use heat pump.But amount of processed air should be giant in any case and doesn't
seem to be practical.If I understood you right average
temperature of air should fall after use of hot molecules in demon of Maxwell?

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