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# What 'Negative Temperature' Really Means

#### Soulskill posted about a year ago

204

On Friday we discussed news of researchers getting a quantum gas to go below absolute zero. There was confusion about exactly what that meant, and several commenters pointed out that negative temperatures have been achieved before. Now, Rutgers physics grad student Aatish Bhatia has written a comprehensible post for the layman about how negative temperatures work, and why they're not actually "colder" than absolute zero. Quoting: "...you first need to engineer a system that has an upper limit to its energy. This is a very rare thing – normal, everyday stuff that we interact with has kinetic energy of motion, and there is no upper bound to how much kinetic energy it can have. Systems with an upper bound in energy don’t want to be in that highest energy state. ...these systems have low entropy in (i.e. low probability of being in) their high energy state. You have to experimentally ‘trick’ the system into getting here. This was first done in an ingenious experiment by Purcell and Pound in 1951, where they managed to trick the spins of nuclei in a crystal of Lithium Fluoride into entering just such an unlikely high energy state. In that experiment, they maintained a negative temperature for a few minutes. Since then, negative temperatures have been realized in many experiments, and most recently established in a completely different realm, of ultracold atoms of a quantum gas trapped in a laser."

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#### Anonymous Coward 1 minute ago

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### Seeing as this is Slashdot... (-1)

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#### Anonymous Coward | about a year ago

...It'll have something to do with Australia.

Everything on Slashdot has something to do with Australia, now.

### Re:Seeing as this is Slashdot... (1)

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#### jamesh | about a year ago

...It'll have something to do with Australia.

Everything on Slashdot has something to do with Australia, now.

Of course it will. Australia is the centre of the universe. Even the name "Aatish Bhatia" is obviously Australian in origin, and Rutgers is a suburb of Sydney I think.

### Re:Seeing as this is Slashdot... (1)

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#### DavidClarkeHR | about a year ago

...It'll have something to do with Australia.

Everything on Slashdot has something to do with Australia, now.

Of course it will. Australia is the centre of the universe. Even the name "Aatish Bhatia" is obviously Australian in origin, and Rutgers is a suburb of Sydney I think.

Considering how "new" australia is as a country, it's not surprising that these things may appear to belong to other parts of the world. It's called intertexuality, and it's a natural process of borrowing ideas from established works.

### Laws against intertextuality (1)

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#### tepples | about a year ago

It's called intertexuality, and it's a natural process of borrowing ideas from established works.

Until people start using copyrights and patents to suppress this process.

### Re:Seeing as this is Slashdot... (0)

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#### RKBA | about a year ago

Australia was after all, the last nation to survive a global nuclear war On the Beach in 1959.

### -1 post (-1)

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#### Nyder | about a year ago

Very very cold here.

### Re:-1 post (-1, Redundant)

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#### Nationless | about a year ago

I've spent all my mod points, please down-vote parent to -1 to prove a pun.

### Re:-1 post (1, Funny)

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#### Anonymous Coward | about a year ago

It's called 'mod down' not 'downvote' you idiot. Go back to fucking Reddit where you belong.

### Re:-1 post (-1)

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#### Anonymous Coward | about a year ago

y le u so le mean? LEL! y u no play nice? *downvotes* LEEEEEEEEEEEEL

(fictive story)

### Layman (4, Insightful)

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#### Anonymous Coward | about a year ago

I do not think this word means what you think it means.

### Re:Layman (5, Funny)

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#### Biff Stu | about a year ago

layman
n.
A man who gets laid. Also known as a non-Slashdotter.

### Re:Layman (1)

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#### mrops | about a year ago

or maybe it does

you will never know until you look inside the box... errr RTFA

### Re:Layman (1)

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inconcievable!

### now this IS news for nerds (1)

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kudos souskill

### Less uncommon than the name suggests (1)

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#### Anonymous Coward | about a year ago

At least nowadays. Plenty of lasers around.

### Re:Less uncommon than the name suggests (1)

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#### c0lo | about a year ago

Plenty of lasers around.

No, lasers are not an example of negative temperature.

For a thermodynamic system, zero temperature is when you can't vary (as in... decrease it) the internal energy of the system, the order of system is maximum.
For a "negative temperature system" (no longer a thermodynamic one), this translates into "after a point, one can no longer pump energy into the system, the order has reach the maximum". This does not happen into a laser.

### so doesn't this mean (0)

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#### Anonymous Coward | about a year ago

that absolute zero isn't absolute anymore? don't we just move the bar of absolute zero downward?!?

### Re:so doesn't this mean (1)

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We're going to need James Cameron.

### Re:so doesn't this mean (1)

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#### DavidClarkeHR | about a year ago

We're going to need James Cameron.

Just because we're talking about below-zero temperatures doesn't mean we need to involve ice.

### Re:so doesn't this mean (1)

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#### SternisheFan | about a year ago

A few days back I put in for submission one of the many stories just out in the news about this. Headlines like, "Scientists go a few degrees below absolute zero!", etc. To Slashdot's credit, that and other submissions weren't accepted, because they were wrong. So yes, kudos Soulskill.

Slashdot. Not always perfect, but they do try to be.

### Re:so doesn't this mean (2)

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#### jcoy42 | about a year ago

I think you meant François Petit.

### Re:so doesn't this mean (1)

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#### marcosdumay | about a year ago

To make it short, everything with more energy (should I say hotter?) than the most likely state has a negative temperature.

We down't move downward from zero, we get into the negative by moving upward.

### Uhhhh (4, Interesting)

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#### Anonymous Coward | about a year ago

This doesn't really help. I pondered this for a while the other day when I read that first and gave up trying to wrap my head around it. I was always under the impression that 0 kelvin (absolute 0) meant a state at which there was no movement at the atomic/subatomic level. It would seem as though to reach a negative temperature, one would have to slow a substances particles to less than 0 movement. Then I realized they were talking about a quantum state and I pretty much gave up trying to understand it at that point, because anything which has the word 'quantum' in it suddenly defies all the rules I'd ever been taught about anything at all. :o)

### Re:Uhhhh (1)

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#### alphatel | about a year ago

Did you know also that light cannot escape a black hole?

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

so if there is a black hole in the universe then all light must be sucked into it, right?

so why is there light if it can not escape?

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

Light cannot escape once it has crossed the event horizon.

### Re:Uhhhh (1)

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#### Anonymous Coward | about a year ago

oh so light can escape a black hole given its not exceeded a condition, but that doesn't sound as scary

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

To escape something, you have to be imprisoned there in the first place. Light cannot escape once imprisoned.

### Re:Uhhhh (-1)

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#### Anonymous Coward | about a year ago

My cock entered and escaped many of those.

### Re:Uhhhh (1)

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#### chronokitsune3233 | about a year ago

Whatever you say, Chuck. I bet your tears cure cancer, too.

### Re:Uhhhh (1)

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#### Anonymous Coward | about a year ago

So, you never got it past the event horizon, eh?

### Re:Uhhhh (5, Insightful)

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#### cwebster | about a year ago

All quantum means is that energy can only have specific values. Imagine a stereo with a volume knob that clicks between values, ie it can be 1, 2, 3, n, but cannot be anything inbetween those numbers. Now you have a quantum volume knob.

Temperature is a statistical property of matter that only exists once we consider things as a continuum. At scales where we consider quantum mechanics, a molecule has energies (kinetic, rotational, vibrational, electrical, etc) which can only take on specific values (quantized) and these values are specific to the atom/molecule to some degree (atom makeup, radiative properties, etc).

That probably doesnt help wtih the sub-0 part of the article, but perhaps it will help with the quantum part.

### Re:Uhhhh (5, Funny)

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#### binarylarry | about a year ago

awesome, im totally buying that \$2500 quantum volume knob from Monster Audio now. I bet it sounds amazing!

### Re:Uhhhh (3, Funny)

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#### ColdWetDog | about a year ago

Hah, already got one. It goes to 11.

### Re:Uhhhh (5, Funny)

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#### PlusFiveTroll | about a year ago

Mine's even better, it goes to -1...

I don't use it anymore after I damaged physical reality on its first use.

### Re:Uhhhh (1)

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"It's very special, because as you can see, the numbers all go to -1, right across the board".

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#### Anonymous Coward | about a year ago

Wish you would have been my physics teacher, all I remember about quantum stuff is that it can't really be defined with a particular value. Or rather it can be, but you can't know *when* it was that value. Or something like that....isn't that the whole Heisenberg Principle/Schrodingers Cat thing? Or am I getting my high school physics stuff completely screwed up?

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

No! Quantum is not the same as discrete. The Schrodinger equation for a free particle has continuous allowable positions, energies etc.

It can be the case that quantization LEADS to discreteness in some cases (eg energy eigenvalues for atoms etc) but it is certainly NOT a given.

### Re:Uhhhh (4, Insightful)

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#### hairyfeet | about a year ago

That still doesn't explain how in the fuck you get below zero movement, how can you move less than none? For those that haven't seen it I suggest the excellent PBS documentary "The search for absolute zero" which is easy enough to find on the web where the second half deals with nothing but the attempts to reach absolute zero. in that video the scientists explain quite plainly that the reason its so damned hard to get those last couple of degrees out of the system is because you ALL movement from the medium has to be removed, not a single atom can move because movement is energy and absolute zero is the absolute absence of ALL energy.

So sorry, still don't get it, its not like you can magically remove something from nothing. Absolute zero is absolute nothing, no energy left it the system at all, so how in the fuck are you gonna get less than nothing?

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

That probably doesnt help wtih the sub-0 part of the article, but perhaps it will help with the quantum part.

That still doesn't explain how in the fuck you get below zero movement,

Wow, we have a smart one here!

### Re:Uhhhh (4, Informative)

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#### martin-boundary | about a year ago

That still doesn't explain how in the fuck you get below zero movement, how can you move less than none?

The short answer is that physicists throw out the "temperature describes amount of molecular movement" definition and replace it with something more abstract.

The abstract definition of temperature allows negative values, and that's ok because nobody cares anymore about molecular movements in that case.

### Re:Uhhhh (1)

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#### RespekMyAthorati | about a year ago

Which is unfortunate, since the word "temperature" predates modern physics by centuries.
The original meaning was the average speed of the molecules in a sample of matter - not atoms or subatomcs particles. Since speed is the length of a velocity vector, it cannot be negative, and hence there is no such thing as a negative temperature. It's a shame that physicists were too lazy to invent a new word for "slope of the entropy vs. energy curve" and decided, instead, to recycle - and corrupt - the meaning of a common English word.

### Re:Uhhhh (2)

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#### mysidia | about a year ago

That still doesn't explain how in the fuck you get below zero movement, how can you move less than none?

Read the article for explanation. You indeed cannot have below zero "movement" or "jiggling". Negative temperature, says nothing about movement. That is the definition of temperature does not involve the amount of movement.

That is, Temperature is not exactly equivalent to a measure of movement; there are things stated to have temperature where no notion of movement occurs; things like the magnetic spins and other quantum systems can have temperature, even if there is no kinetic energy. Temperature is defined as: 1/T = dS/dE

\frac{1}{T} = \frac{dS}{dE} which says, in words, that the temperature is inversely proportional to the slope of the entropy vs. energy curve.

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

If you were paying any attention....

The negative temperature does NOT correspond to "less than zero" movement. It actually corresponds to MORE movement than something with an infinitely high temperature. TFA and associated links within it explain this (and why it makes some kind of sense) a lot better than I can.

To put it another way, consider the graph of 1/x. Any negative and positive values are allowed, but not zero. Similarly temperature can be positive or negative but not absolute zero, bearing in mind that negative temperatures are rare and behave differently to what is expected. (1/x has no relevence to the temperature stuff, I'm just illustrating a point. One article said something along the lines of "negative temperature entities approach absolute zero from below", rathern than normal objects which approach it from above.)

### Re:Uhhhh (4, Informative)

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It's just a quirk in our temperature scale. What we define as infinite K is not the highest-energy state that can be reached. It's the highest state that can be reached through heating, but higher states can be reached through other mechanisms. Once we realized that, we needed another scale for the higher-energy states at the other side of infinity, so we started using negative numbers for them. So negative temperatures are not at the cold side of 0K, but at the hot side of inifinity K. More complete explanations here and here.

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

I never thought of explaining it to people with the volume knob analogy, that's very clever, thank you.

### Re:Uhhhh (1)

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#### kaws | about a year ago

Don't worry, just skim the article again because the claim isn't making temperatures go below absolute 0. Negative temperatures mean something completely different. My understanding is with negative temps, reverse what happens to water when you add energy. In other words, it's like heating up water but then the water starts to freeze. As you add energy to a negative energy system, it becomes more organized.

### Re:Uhhhh (1)

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#### Anonymous Coward | about a year ago

Think of temp behaving as if it worked based on an absolute value (you know the whole |x| notation). As you add energy to a negative system (i.e. |-x+2|), it behaves as if you subracted energy from a positive one (|x-2|) because in absolute terms it is the same.

### Not Helpful at all! (1)

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#### DavidClarkeHR | about a year ago

This doesn't really help. I pondered this for a while the other day when I read that first and gave up trying to wrap my head around it. I was always under the impression that 0 kelvin (absolute 0) meant a state at which there was no movement at the atomic/subatomic level. It would seem as though to reach a negative temperature, one would have to slow a substances particles to less than 0 movement. Then I realized they were talking about a quantum state and I pretty much gave up trying to understand it at that point, because anything which has the word 'quantum' in it suddenly defies all the rules I'd ever been taught about anything at all. :o)

That was my first reaction when I learned about quantum mechanics - nothing fundamentally works the way I was taught it works, it only appears to work that way under certain conditions.

Though, for this article, my first reaction was And the relevance of this discovery (again) is what, exactly? I didn't understand it before, I don't understand it now, and I don't see how it makes any difference what-so-ever.

### Re:Uhhhh (1)

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#### Runaway1956 | about a year ago

Sounds to me like absolute zero means absolute zero temperature. But objects at absolute zero still retain energy, other than kinetic energy. One you reach absolute zero, those objects dig deep to find energy to give away, somehow converting that energy into heat, or kinetic energy.

Maybe what we need here is a new form of measurement, something like "absolute energy" rather than "absolute temperature". If/when an object reaches absolute zero energy, what happens? I guess all the matter has been converted to energy, and the object no longer exists?

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

The most important thing to understand is that motion is *not* the only component of energy in a real system and that the concept of absolute zero was obtained from a consideration of particles (in an *ideal* gas) that have nothing *but* kinetic energy (the energy associated with motion).

Thus, real systems that have potential energy (strongish inter-particle interactions) can exhibit behaviors that ideal gases cannot (such as negative temperatures).

### Re:Uhhhh (4, Informative)

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#### Livius | about a year ago

The point they're making is that temperature can refer to energy and entropy other than just the kinetic motion kinds.

Unfortunately understanding the definition still doesn't get us very far for those of us without intuitive models of those other kinds of situations, so we're no farther ahead.

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#### Anonymous Coward | about a year ago

Stop thinking of temperature as the energy of a system, but think of it as the Maxwell–Boltzmann distribution of energy of the system. Certain temperature - certain shaped distribution. Bung in a temperature value, get out a distribution shape. Now, muck with the energy distribution such that the number input to the Maxwell–Boltzmann function to get that shape is negative. There you go, negative "temperature" while there's still energy in the system.

### MOD PARENT UP (1)

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nt.

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

It depends on how you define temperature. In this case, Temperature can be defined as the likelihood of a system to give up energy to an external system it makes contact with. For example, light is a form of contact, and the sun emits light. The sun is very likely to give up energy to systems it is in contact with through light, so the sun has a negative temperature. The more energy you give the sun the more light it emits, and the more energy it gives up to external systems it is in contact with.

You also have to remember that "contact" is any process by which two amalgamations of matter can exchange energy.

Of course this is a gross oversimplification.

### Re:Uhhhh (2)

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#### LordCrank | about a year ago

This doesn't really help. I pondered this for a while the other day when I read that first and gave up trying to wrap my head around it. I was always under the impression that 0 kelvin (absolute 0) meant a state at which there was no movement at the atomic/subatomic level. It would seem as though to reach a negative temperature, one would have to slow a substances particles to less than 0 movement. Then I realized they were talking about a quantum state and I pretty much gave up trying to understand it at that point, because anything which has the word 'quantum' in it suddenly defies all the rules I'd ever been taught about anything at all. :o)

As far as 'quantum' goes, if you're okay with the idea that a particle can have either a positive spin or a negative spin, even though spinning would always seem to imply a positive amount of spin, that's halfway to understanding what's going on here.

The way that temperature is defined, (1 / Temperature) = (Change in Entropy) / (Change in Energy). By this definition, absolute zero would mean that there is an infinite decrease in entropy for any decrease in energy, i.e. going to absolutely no movement of particles as energy decreases.

What happened here is that scientists developed a system where increasing energy decreased entropy, so (Change in Entropy) / (Change in Energy) had a negative value. This naturally involved a vacuum and a lattice of lasers and anything else a Bond villain could ask for, with the end result being that the particles could continue to take energy while decreasing the entropy in the system.

As far as this particular article being easy enough for a layman to understand, if it were I wouldn't expect to read "researchers getting a quantum gas to go below absolute zero" in the summary, because:

tl;dr: A quirk in the definition of temperature allows for it to be negative without having to remove energy from a system that is at absolute zero, meaning the temperature never 'goes below' absolute zero.

### Re:Uhhhh (2)

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#### c0lo | about a year ago

This doesn't really help. I pondered this for a while the other day when I read that first and gave up trying to wrap my head around it. I was always under the impression that 0 kelvin (absolute 0) meant a state at which there was no movement at the atomic/subatomic level. It would seem as though to reach a negative temperature, one would have to slow a substances particles to less than 0 movement)

My understanding on negative temperature without requiring QM:

1. in the classical thermodynamics and forcing the terms, the temperature is defined as "the measure of willingness of a system to un-aided transfer energy to another system". If, when set in contact, two system do not exchange energy, they have the same temperature. If one system spontaneously (i.e. not aided, without intervention) transfer energy to a second, then the temperature of the first one is higher than the second one

2. you need to adjust your view on what "absolute 0 temperature" means: it is not that the total energy of the system is zero (thus no movement), but the system tends towards a constant energy. For thermodynamic systems (most of the systems in the nature), this constant energy is the minimum the system can reach. Also, in this state, the order of the system is maximum (the entropy, as a measure of disorder, is minimum)
Bottom line: to reach absolute zero temperature, one needs to extract energy from a thermodynamic system; for a thermodynamic system, a zero temperature means a point where no energy can be extracted any more because the order of the system is maximum (entropy is minimum)

3. special arrangements can be made so that some system will have a higher order at higher energies (the system is not a thermodynamic one any more). For such systems, to reach a point where the order is maximum (and the energy of the system becomes constant), one needs to pump energy into the system. Reaching this maximum will make the system "unwilling" to absorb any more energy - and this is a mandatory condition for the current definition of "systems with negative temperature" (this is why lasers are not good examples of such systems).

Now, as such a system the notion of "temperature" does not apply sensu stricto any more, because the system is no longer a thermodynamic one. If set in contact with another system, the "negative temperature" one will gladly transfer energy at the cost of increasing the disorder of the system. It is the third law of thermodynamics such a system violates (thus, no longer being a thermodynamic system).

But, like the mathematicians, one may try to expand the definition of a function domain and force the definition of the temperature as a relation to the entropy (thus enforce the validity of the third law).
One can do that only when sacrificing at least one of other principles of thermodynamics or arrange for some strange meanings of the temperature scale, in which "negative temperatures" a actually higher than +infinity K .
Trying to think of negative temperatures as "below 0K" is invalid, in fact "negative absolute temperatures" are hotter than anybody can imagine.

### Re:Uhhhh (0)

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#### Anonymous Coward | about a year ago

Well, at absolute zero, helium will still be a liquid, so not all movement is halted.

### Re:Uhhhh (1)

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#### blueg3 | about a year ago

You're thinking of "temperature" as only being a measure of the (average) kinetic energy of a collection of particles. However, in physics, it has a more general definition.

So, the short answer to "it doesn't make sense to have less than zero motion" is that that's not what's happening at all. So no worries.

### Re:Uhhhh (1)

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Try this; it's a bit shorter and the quantum mechanics is masked as binary logic.

### Anthropomorphism (0, Troll)

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#### mfwitten | about a year ago

Systems with an upper bound in energy don’t want to be in that highest energy state.

Sigh...

### Re:Anthropomorphism (3, Insightful)

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#### Iamthecheese | about a year ago

Give up a little precision and rigor for ease of understanding you snob.

### Re:Anthropomorphism (2, Funny)

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#### Anonymous Coward | about a year ago

Yeah. Systems hate snobs and their feelings get hurt.

### Re:Anthropomorphism (0)

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#### Anonymous Coward | about a year ago

Don't be stupid. Shorthand is very useful, and everyone knows what it means.

### Re:Anthropomorphism (5, Insightful)

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#### dispersionrelation | about a year ago

I majored in Physics and am currently in grad school and I have no problem with that wording. In fact we Physicist often anthropomorphize when talking amongst ourselves, so what the hell is your problem? Grow up and realize that language is simply a tool used to convey ideas, no one with half a brain reads that statement and actually thinks the particles in the system have needs or desires. Instead they will realize by the wording and context that the particle(s) are simply less likely to be in the higher energy states for reasons that the author doesn't want to go into. If you disagree you're wrong.

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#### mfwitten | about a year ago

In fact we Physicist often anthropomorphize when talking amongst ourselves

Yes. It's a great shame.

### Furry hater (0)

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#### Anonymous Coward | about a year ago

Anthropocentric Neoteny will kill us all!

### Re:Anthropomorphism (1)

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#### Charliemopps | about a year ago

Yes, but over the past 50 years or so, physicists have started using a lot of wording like that. The problem is there are a lot more crackpots out there than their are reasoned intelligent individuals. You, being a physicist don't generally run into these people. I, on the other hand, have to deal with them daily. They know I have an interest in such things so they like to bounce their insane ideas off of me, and it's hard to argue logic with them when you use shitty wording like that. What that sentence implys to many laymen is intelligent design. And I'd never steer someone away from such a belief, it's theirs to have. But they need to argue their point rationally and with real data. Not some nonsense they cooked up because scientists can't explain things properly.

### Re:Anthropomorphism (3, Insightful)

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#### sydneyfong | about a year ago

You, being a physicist don't generally run into these people. I, on the other hand, have to deal with them daily.

You blame a wording used to more conveniently convey a meaning, because you surround yourself with idiots.

It's not a physicists problem that you end up with uncool friends. Give it up, no amount of "correct" wording is going to make sane people out of crackpots. Your attempts to teach them logic are going to be futile no matter what (hey, you called them crackpots, and you're _still_ arguing with them). Just give it up dude.

### Re:Anthropomorphism (-1)

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#### Anonymous Coward | about a year ago

If you disagree you're wrong.

Screw you, you fucking Buddy Bear.

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#### Anonymous Coward | about a year ago

...., no one with half a brain reads that statement and actually thinks the particles in the system have needs or desires.

I have it on good authority that electrons are ninja-like xenaphobic whores. My apologies to other, ninja-like xenaphobic whores.

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#### DMUTPeregrine | about a year ago

Systems with an upper bound in energy have fewer possible configurations at or near the highest energy state, so the probability of remaining in one of those few configurations as opposed to the many, many more lower-energy configurations is low.

### Re:Anthropomorphism (3, Funny)

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#### c0lo | about a year ago

Systems with an upper bound in energy don’t want to be in that highest energy state.

Sigh...

Well, I concur, anthropomorphising these systems is a big problem.

You see: the matter and energy (no matter their colour - dark/white, orientation - up/down, flavour/charm/strangeness, etc) are freer and have more self-determination than any human being will ever have. They only obey the laws of physics, while the human beings need to obey heaps of others (e.g. did you ever see an electron being groped by TSA agents when passing through a semiconductor gate?).

Anthropomorphizing is degrading for physical entities and, for their sake, need to stop. Join the movement for upholding the inalienable rights of energy and matter before is too late!

### Proof by definition (0)

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#### Anonymous Coward | about a year ago

So essentially they changed the definition of temperature to one which allows for negative values. Interesting but not quite as radical as achieving negative motion.

### Re:Proof by definition (1)

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#### kaws | about a year ago

I think actually it's more of a problem with our current definition of temperature.

### News For Nerds? (0)

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#### Anonymous Coward | about a year ago

If 'nerds' had paid any attention to their thermodynamics/statistical mechanics class they would have already know all this and we would have been spared two frivolous posts in the front page.

### Re:News For Nerds? (4, Funny)

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#### ColdWetDog | about a year ago

If 'nerds' had paid any attention to their thermodynamics/statistical mechanics class they would have already know all this and we would have been spared two frivolous posts in the front page.

Why are you being so negative?

### Re:News For Nerds? (0)

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#### Anonymous Coward | about a year ago

Maybe he has rust on his penis.

### Re:News For Nerds? (1)

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#### c0lo | about a year ago

If 'nerds' had paid any attention to their thermodynamics/statistical mechanics class they would have already know all this and we would have been spared two frivolous posts in the front page.

Why are you being so negative?

Actually, s/he's beyond infinitely positive.

(as in: correctly stating the problem is, most of the time, a necessary step to solve it. As in: yes, there is a possibility to solve a problem without knowing about it, but what's the probability?)

### Sounds like a semantics thing (0)

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#### Anonymous Coward | about a year ago

Just change the definition and you have negative kelvin, even though it really isn't.

### this is what it really means: (0)

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#### Anonymous Coward | about a year ago

temperature = change in entropy /total system energy

This graph of a system with finite energy will look like the graph of y=-(x-2)^2 + 4 (go google it for visual). obviously the dimensions will be different, but energy is on x and entropy is on y. my p.chem professor told me that negative temperatures were achievable in our schools research lab. this was 2 years ago and at a very good research school.

### It wants to get colder (1)

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#### Iamthecheese | about a year ago

I'm still not getting the definition of "temperature" here. As I read this it says "some matter in some states will get colder without giving it energy." How does this not go directly against the laws of physics by reversing entropy?

### Re:It wants to get colder (3, Informative)

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If you increase the average energy in certain types of quantum systems beyond a certain point, the entropy starts to go down again. Take a large number of ordinary binary bits and define the average energy as the number of 1s and the entropy as (the logarithm of) the number of combinations/binary numbers that have that many 1s. You'll see that there's only one combination for "all 0s" (entropy=0), the entropy peaks at "50% 1s", and then goes down again to reach 0 at "all 1s". I tried to explain that here.

### What 'Negative Temperature' Really Means (5, Funny)

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#### rossdee | about a year ago

In the USA, it means its really, really cold, you'll have to dress well, including good gloves and hat. If there is any wind you'll wand to cover your face too.
and the air is very dry, inside, getting a humidifier is a good idea.. If your car or truck has been parked outside for a while you would need to start it and have it warm up for 10 minutes before driving off.

In the rest of the world its cold but bearable, since its just below freezing sidewalks may be slippery.

### You mean, Canadian temperatures ... (1)

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#### DavidClarkeHR | about a year ago

In the USA, it means its really, really cold, you'll have to dress well, including good gloves and hat. If there is any wind you'll wand to cover your face too. and the air is very dry, inside, getting a humidifier is a good idea.. If your car or truck has been parked outside for a while you would need to start it and have it warm up for 10 minutes before driving off.

In the rest of the world its cold but bearable, since its just below freezing sidewalks may be slippery.

So, what you're saying is that the canadian climate has below 0 temperatures for two reasons: The system of measurement is fundamentally flawed, and it's colder than we get in this area, normally.

### The rest of the world calls them (0)

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footpaths

### Re:What 'Negative Temperature' Really Means (0)

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#### Anonymous Coward | about a year ago

At absolute zero motion stops. That doesn't mean it can't get any colder. It only means we can't measure temperature below absolute zero due to lack of motion.

### Purcell and Pound (4, Informative)

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#### calidoscope | about a year ago

It would have been nice for Aatish to go a bit into what Purcell and Pound did in their 1951 experiment, namely "inverting" the orientation of the fluorine nuclei in the presence of an applied magnetic field by application of a radio frequency magnetic pulse, where the frequency is the Larmor frequency of fluorine and the pulse amplitude and length was sufficient to cause a 180 degree nutation. The result is that the nuclei have the same order (entropy) as the rest state, but have higher energy. In NMR, this is referred to as applying a 180 degree or pi pulse.

Aatish's comment about reality being liberal is unconvincing.

### Re:Purcell and Pound (2)

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#### DavidClarkeHR | about a year ago

Aatish's comment about reality being liberal is unconvincing.

Only to the part of the population that isn't the 47%.

### Re:Purcell and Pound (0)

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#### TubeSteak | about a year ago

Now, I know there are some polls out there saying this man [President George Bush] has a 32 percent approval rating. But guys like us, we don't pay attention to the polls. We know that polls are just a collection of statistics that reflect what people are thinking in reality. And reality has a well-known liberal bias.

Stephen Colbert said this to President Bush's face at the 2006 White House Correspondents' Association Dinner.
The joke that "reality has a well-known liberal bias" has since taken on larger meanings about Republican/Conservative ideas and ideology being divorced from reality and reality being biased towards liberal ideas because liberal ideas are more in tune with facts. See Also: Truthiness

So why am I inventing this socialist utopia with rampant income redistribution? Itâ(TM)s because this is closely analogous to the physics of heat (as Steven Colbert put it, reality has a well know liberal bias).

Socialist utopia with rampant income redistribution = his physics analogy = reality
Does the joke make sense now?

### blah (1)

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#### Anonymous Coward | about a year ago

It just means the pressure pulls inwards rather than pushes outwards. Given given P=nRT, that would correspond to a negative temperature (since it means the pressure is negative (like a vacuum) and since n and R must be positive (being a count and a constant respectively), thus you can only get the negative sign from T (temperature). Never mind that baked into R (Rydberg Constant) there are assumptions that would exclude the current application and thus the "Negative Temperature" assertion, it's marketing, and marketing ignores the facts if they get in the way.

### Oh, for fuck's sake. (2, Insightful)

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#### VortexCortex | about a year ago

a system with a truly negative temperature in absolute terms on the Kelvin scale is hotter than any system with a positive temperature. If a negative-temperature system and a positive-temperature system come in contact, heat will flow from the negative- to the positive-temperature system.

That a system at negative temperature is hotter than any system at positive temperature is paradoxical if absolute temperature is interpreted as an average internal energy of the system. The paradox is resolved by understanding temperature through its more rigorous definition as the tradeoff between energy and entropy, with the reciprocal of the temperature, thermodynamic beta, as the more fundamental quantity. Systems with positive temperature increase in entropy as one adds energy to the system. Systems with negative temperature decrease in entropy as one adds energy to the system.

You add more energy, but the entropy doesn't increase. Gods damn that moronic blogger and his useless "tricks" metaphor. You don't "trick" shit you stupid fuck. You wouldn't say gunpowder "tricks" a lead projectile to scurry from the gun barrel if you were explaining a gun. We're not idiots, we just need to have the terms defined because some of us hadn't heard the term before in relation to absolute zero.

Protip: Next time you want to submit or vote up a "follow-up" fucking read the damn thing, and compare it to the wiki. Unless it's significantly more useful than the damn wikipedia article, don't fucking submit or vote it up.

### Re:Oh, for fuck's sake. (0)

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:D

### This is explained in textbooks (0)

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#### Anonymous Coward | about a year ago

Literally 50 years old textbooks. This isn't news at all.

### Oblig (1)

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### Basic math (0)

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#### Anonymous Coward | about a year ago

Inverse temperature is proportional to the rate of change of entropy with energy. So if you can make entropy drop with increasing energy in a system you get negative temperature. Entropy is a measure of the likelihood of a system state so you need unlikely high energy states.

### Is it a mathematical artefact (0)

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#### Anonymous Coward | about a year ago

Like negative frequencies in some calculations of electronic filters and such?

### come again? (0)

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#### Anonymous Coward | about a year ago

I suppose you should call me a semi layman... er... mostly layman. I have a lot of physics knowledge that I've gotten 2nd hand if you will over the years. Huge gaps in my knowledge, so bear with me....

Isn't the article talking about a different way of thinking about temperature? It's not "negative" in terms of it being "less than zero", it's negative in terms of its ability to absorb energy. I find the comparison and the use of the word "temperature" kind of inappropriate.

negative temperature implies by adding energy, you could get back to zero and then keep adding and be positive again, but all of his example actually are entirely different processes...
He cites black holes, which of course is increasing the mass/gravitational force, not "getting colder". Those particles ( particle if you are going to call it a singularity I suppose )
He cites "cooling the sun" which similarly is adding mass and thereby gravitational force, which you might say is "cooling" but I would say is more akin to just adding matter to a "battery"... would the surface temperature of the sun actually go down if you added a meaningful amount of hydrogen or helium to it? I suppose. In the same way, adding logs to a fire, brings the average temperature down on the fire.

And he goes on to say that as the star loses energy its temperature rises... and of course this might be observationally true, but only to a point... once it has lost enough energy ( after a Nova ) , it will undoubtably cool. So that behavior is not simply by the definition of loss of energy. There's more to it.

I have a feeling this is mostly a clash of terminology rather than a misunderstanding. Sort of like classical gravity vs general gravity maybe?

I would like someone to explain to me if negative temperature is indeed possible outside of intense gravitational situations, does this mean that Randall Mill's Hydrino theory on sub-ground state Hydrogen is right?
To get below zero K, y

### So... (2)

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#### slashmydots | about a year ago

So you give more energy to it to force it into a high energy state and that lowers its temperature even though it's more energy? Or you force the material to act like it's in a high energy state without giving it the energy so its amount of transmittable heat results in a math glitch? Either way, that's stupid and all it means is temperature isn't measured correctly. I'm in the minority who considers temperature to be total average speed that a group of atoms are moving at. Since that type of system can't drop below zero, I'd say it's superior.

### Re:So... (1)

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You're welcome to introduce your own temperature scale. It won't be a linear function of the existing temperature scales and will be very inconventient for practical purposes, though.
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