Temperature, Colder than Absolute Zero

[MuellerNick]

Nick, you don't see a way around that problem and I don't.

It might sound contradicting:
The researcher found distinct atoms with a negative temperature. Considering that atoms interact with each other with all the quantum stuff (I don't understand at all), it might be possible for some atoms to have negative temperature. As soon as you have a bunch of them, in sum, they are at or above absolute zero.
This is just my explanation, I'm not a physics professor at all, nor do I claim to be one or try to pretend to be one.

The wiki-link repeatedly excluded quantum-effects (that's what I understood).

Edit:

more of an average of energy states of the atoms.

That's what you wrote, and I think the same. And that's what the Boltzman distribution says.
And that's what would explain the observation (within my very limited knowledge on that matter).

Nick

 

[tups]

OrangeAlpine and MuellerNick are on the right path -

Classically, there is no way to get past the "infinite energy asymptote" - but you can, for a small group of atoms (temperature is in any case a collective phenomenon) by employing quantum effects.

Whereas Entropy455's implication that it is "all hogwash" is correct where it concerns perpetual motion and negative energy, the mathematics does not forbid negative temperatures - they are just not what you would intuitively expect.
The equation Entropy455 quotes, 3/2kT = E is true for an ideal gas, or any mass of non-interacting volume-less particles, but it cannot be used to generally define temperature. The Boltzmann equation is a much more general - whereever there is an energy difference it can be used to define a temperature. The E = 3/2kT follows from the Boltzmann distribution by applying the postulates of the kinetic gas theory to it. Reaching a negative temperature is quite impossible under the conditions where the postulates retain their validity, so in that sense, you are right, it is nonsense.

But calling negative temperatures hogwash is throwing out the baby with the bathwater. Of course the scientists will speculate about what it mathematically means. And of course the most sensational quotes will get used and distorted in an article that is pointed towards the general public. Do the authors of the research genuinely believe that they will be able to decrease entropy in the universe by creating negative temperatures, or be able to create a perpetual motion engine ? I would be genuinely surprised. The bottom line is you cannot use mathematics where it suits you, and then disregard its conclusions if and when you do not like them. Either you discard the entire model and build a better one, or you accept its quirks where they apply to states of the universe that do not generally occur. And very occasionally the model will predict an anomaly that leads to actual new and surprising knowledge. Read up about the kinetic gas theory and the viscosity of gases - it led to the realisation that atoms actually do exist.

The "negative temperature and what we could do with it" discussion is somewhat comparable with that about "Boltzmann's demon" - if you could construct a very small machine that would be a one-way valve for high energy gas atoms, you could create "free energy". But the energy needed to make the machine work makes the whole of the system obey the second law of thermodynamics anyway. There is no free lunch, and it is exactly the same here - you need a prodigious amount of energy to set up the boundary conditons for making a very small sample of matter with a negative temperature, and you can never win. And the scientists who did it know that very well too.

 

[Omnimill]

This is interesting.
Link

Now look what you've done Peter! You've got some of these guys fit to bust a blood vessel! You won't do that again will you! Rof}

 

[Entropy455]

If you could construct a very small machine that would be a one-way valve for high energy gas atoms, you could create "free energy".

It’s time for a sanity check. If this check-valve device were possible, you could install it on the intake manifold of a piston engine, then proceed to extract massive amounts of mechanical power. The machine would ingest atmospheric air, output usable mechanical work, and exhaust nothing but cold air.

In the engineering profession, we call this idea a Clausius Violator of the Second Kind – in that it’s impossible to construct a device that extracts work from a single thermal reservoir (see the Second Law of thermodynamics). Not only would the device demand that heat flow from cold-to-hot, it would also require system entropy to decrease - both of which are not possible.

I took gas dynamics in college. It was one of my favorite classes. I really liked the topic of supersonic nozzle design, and also determining shock-angles from various object geometries within super-sonic flight. FWIW, if an engineering student proposed a free-energy check-valve device within a gas-dynamics class - the Dean of Engineering would probably kick the student out of the engineering program for life. Does this seem extreme? Ask yourself the following question: would you want the engineer who designed the wing of the airplane you’re riding in, to (A) believe in imaginary machinery and impossible technology? Or (B), have a firm understanding of the laws of physics, and capable of differentiating between achievable and impossible machine designs?

Heat flows from hot to cold. Entropy always increases. Absolute zero is “absolute”. There is no such thing as free energy - as perpetual motion is not possible.

 

[Entropy455]

There is no free lunch, and it is exactly the same here - you need a prodigious amount of energy to set up the boundary conditons for making a very small sample of matter with a negative temperature, and you can never win. And the scientists who did it know that very well too.

Apparently not. “The experiments may shed light on the nature of dark energy, and indicate that a 100 percent energy-efficient internal combustion engine, which had previously been considered impossible, might in fact be achievable.” Source: Braun, S.; Ronzheimer, J. P.; Schreiber, M.; Hodgman, S. S.; Rom, T.; Bloch, I.; Schneider, U. (2013). "Negative Absolute Temperature for Motional Degrees of Freedom". Science 339 (6115): 52–55.:fan:

 

[tups]

It’s time for a sanity check. If this check-valve device were possible, you could install it on the intake manifold of a piston engine, then proceed to extract massive amounts of mechanical power. The machine would ingest atmospheric air, output usable mechanical work, and exhaust nothing but cold air.

In the engineering profession, we call this idea a Clausius Violator of the Second Kind – in that it’s impossible to construct a device that extracts work from a single thermal reservoir (see the Second Law of thermodynamics). Not only would the device demand that heat flow from cold-to-hot, it would also require system entropy to decrease - both of which are not possible.

I took gas dynamics in college. It was one of my favorite classes. I really liked the topic of supersonic nozzle design, and also determining shock-angles from various object geometries within super-sonic flight. FWIW, if an engineering student proposed a free-energy check-valve device within a gas-dynamics class - the Dean of Engineering would probably kick the student out of the engineering program for life. Does this seem extreme? Ask yourself the following question: would you want the engineer who designed the wing of the airplane you’re riding in, to (A) believe in imaginary machinery and impossible technology? Or (B), have a firm understanding of the laws of physics, and capable of differentiating between achievable and impossible machine designs?

Heat flows from hot to cold. Entropy always increases. Absolute zero is “absolute”. There is no such thing as free energy - as perpetual motion is not possible.

I will make one more post on this topic, Entropy455, and then I will simply stop.
1st point.
The entire post above summarizes succinctly our knowledge about thermodynamics acquired in the last two centuries. My argument about "Boltzmann's demon" is a *thought experiment* (are you familiar with those ?) used by Peter Atkins in his famous book "The Second Law" to lead to the conclusion that all you write above is exactly true. We are disagreeing on exactly nothing in this discussion, except on your calling negative temperatures "hogwash". You know, thought experiment in the sense of "if you could construct a one-way valve - but you can't, because if you could, x, y and z would follow, and we know that that is impossible". This book by Peter Atkins (which I heartily recommend) also derives the existence of negative temperatures if I remember correctly, and this was in 1984. It follows from the mathematics employed, you can do the calculations yourself on the back of an envelope, but instead of opening your eyes and seeing, you rather choose to parrot what you have heard in a thermodynamics class I don't know how many years ago. Use your imagination, for heaven's sake!

2nd point.
Please understand there is a difference between the interpretation of a scientific article by journalists and what the authors actually wrote. The sentence you quoted in your other post right after the one above is nowhere to be found in that article. I'll PM you a copy if you like to see for yourself. If it would have been in there, perhaps because all the authors would have been delusional nutcases, the peer review process to which all scientific articles are subjected prior to publication would have very quickly weeded it out. And incidentally, the authors do a pretty good job at explaining the basics behind it too, so perhaps you should at least read the introduction of the article for yourself.
Whatever interpretation journalists give to it is mainly meant to be thought-provoking - or perhaps provocative, especially to people like yourself I suppose. They do not mean at any time that this could be a practical way to a free energy machine. Because those don't and can't exist. Yes, we know you know that. And I know it too. And so do these authors. The journalist who wrote that sentence - well perhaps. I do hope so.

3rd point.
I especially take offense at the mention of me being kicked out of an engineering curriculum for life by the Dean on mentioning "Boltzmann's demon" - which, once more, is a very instructive thought experiment to demonstrate the validity of the second law of thermodynamics - it says you cannot win, even if you try to cheat. You really should read that Atkins book, and get rid of this "It cannot be done because it's the (second) Law" attitude, and instead try to breed a little understanding of the reasoning, process and mathematics behind it.

And that is where my contribution to this shouting match will end. I think I'll go do some model engineering to "cool down" (hee hee).

 

[Entropy455]

The negative temperatures in the article are a way of cheating - they will never provide a way to break the second law of thermodynamics (except locally - to be compensated in the surroundings, as in so many other processes that do exist), and the authors never stated otherwise. Because they are serious scientists, not driveling journalists.

So, if you were following my thermodynamics class, which I teach in an engineering curriculum with the express purpose of making my students realize which machines can and cannot be built, and which chemical reactions are or are not spontaneous, based on a firm understanding of the laws of thermodynamics and their correct application, I think I'd personally kick you out, for (a) sustained and stubborn demonstration of lack of ability or willingness to understand and (b) not being able to process new information efficiently and place it in its proper context.

http://arxiv.org/pdf/1211.0545v1.pdf

There’s no need to send me private messages. This is an important part of the discussion. I hope you don’t mind me posting a portion of the private message you sent me.

Why didn’t you say you were a thermodynamics professor?

Before you kick me out of class, perhaps you can clearly answer one very specific question for me - in the link you provided to the actual article (thank you for finding that by the way) – the author makes reference to the Carnot cycle being able to exceed an efficiency of one. He does so not once, but twice.

How can this be anything but an acknowledgement by the author(s), that the Second Law of Thermodynamics can be violated – clearly implying that perpetual motion heat engines are feasible?

 

[terrywerm]

The only way to get negative temperatures, is with negative energy.

Doggone! My wife says I'm FULL of negative energy, and it's worst first thing in the morning before I've had my coffee! stickpoke

 

[MuellerNick]

I think, this is a discussion between an engineer and a physics.
The engineer says, that you can't go below absolute zero, and he is right.
The physics says, that you can go below absolute zero, and he is right.
The contradition is in the scale both look at the problem. The engineer looks at it as a whole, practical thing. The physics looks at it at a atomic level.

How can this work out?
It is statistics! If you take a sample big enough (engineer), you can't go below absolute zero. If you take a sample small enough and pick out only what you want (physics), you can observe below zero.

This explanation might well be wrong (I'd like to be corrected) and a bit "popular science".


Nick

 

[lensman57]

It’s time for a sanity check. If this check-valve device were possible, you could install it on the intake manifold of a piston engine, then proceed to extract massive amounts of mechanical power. The machine would ingest atmospheric air, output usable mechanical work, and exhaust nothing but cold air.

In the engineering profession, we call this idea a Clausius Violator of the Second Kind – in that it’s impossible to construct a device that extracts work from a single thermal reservoir (see the Second Law of thermodynamics). Not only would the device demand that heat flow from cold-to-hot, it would also require system entropy to decrease - both of which are not possible.

I took gas dynamics in college. It was one of my favorite classes. I really liked the topic of supersonic nozzle design, and also determining shock-angles from various object geometries within super-sonic flight. FWIW, if an engineering student proposed a free-energy check-valve device within a gas-dynamics class - the Dean of Engineering would probably kick the student out of the engineering program for life. Does this seem extreme? Ask yourself the following question: would you want the engineer who designed the wing of the airplane you’re riding in, to (A) believe in imaginary machinery and impossible technology? Or (B), have a firm understanding of the laws of physics, and capable of differentiating between achievable and impossible machine designs?

Heat flows from hot to cold. Entropy always increases. Absolute zero is “absolute”. There is no such thing as free energy - as perpetual motion is not possible.

Hi,

I am with you there, all my training as an ex student of engineering tellls me that this negative energy is not feasible to either muster or utilise. Theoretical physics will have you believe that impossible things could happen and the next decade someone else comes along and says that no it can not happen. I guess the example of an elephant being able to fly under its own power in theory would be too tacky to mention. For decades they have us believe that the universe started with a big bang, now they are saying that it couldn't have happened that way and there must have been another mechanism at work. All this might be theoretically correct or achievable but we do not trust our machines to do a job based on unproven abstract physics. We do not create energy, we are not capable of doing so, all we can do is convert one type to another with questionable degrees of efficency much the same as that we can not create wealth, we move it around from one place to another and from one type of people to another yet day in day out people go around talking about creating wealth.

I for one would leave the theories to the people that research these and untill there is soild proof that it exists and can work, would leave the engineers alone to deal with reality.

Regards,

A.G

 

[Entropy455]

This is not an issue of cup-half-full, verses cup-half-empty. The issue here is the clearly stated implications made by the scientists - specifically with being able to exceed a Carnot efficiency of 1.

Please read this link: http://en.wikipedia.org/wiki/Carnot_heat_engine

Key equation:

Where:
n is efficiency
W is the energy exiting the system as work
Qh is the heat energy entering the system
Tc is the absolute temperature of the cold reservoir
Th is the absolute temperature of the hot reservoir

Here's why negative temperatures are hogwash: per the right-side Carnot equation, if the cold reservoir (Tc) is negative, then the Carnot Efficiency is capable of exceeding 1 (which is 100% engine efficiency). This also means (using the left side equation) that it’s possible to get more work out of the engine (W), than heat energy going into it (Qh). That's like getting 5 crankshaft horsepower out of an engine, with only a 3 horsepower thermal input. . . It's an indisputable perpetual motion claim, as exceeding a Carnot Efficiency of one IS the textbook definition of perpetual motion.

Read this link: http://en.wikipedia.org/wiki/Perpetual_motion

Key quote: “No heat engine (an engine which produces work while moving heat from a high temperature to a low temperature) can be more efficient than a Carnot heat engine.”

They also claimed to be able to destroy entropy, which is just as absurd as their claim of exceeding a Carnot efficiency of one.

 

[Herbiev]

This is a model engine building forum not a site for plucking bits of info from Wikipedia so let's just wait for those in the know to supply a nice little PDF on building a machine that converts 1Kw input to 2Kw output. Then the horrendous power bill funds can be used to buy more toys ;D

 

[Philjoe5]

OK, I think we have covered this topic pretty well. Considering all the negative energy expended in this discussion consider it locked.

However, anyone who has built a model engine with 100% efficiency is encouraged to start a new thread. A video would be mandatory, of course.

Cheers,
Phil