Quantum Gas Goes Below Absolute Zero

First time accepted submitter mromanuk writes in with a story about scientists at Ludwig Maximilian University of Munich who have created an atomic gas that goes below absolute zero. "It may sound less likely than hell freezing over, but physicists have created an atomic gas with a sub-absolute-zero temperature for the first time. Their technique opens the door to generating negative-Kelvin materials and new quantum devices, and it could even help to solve a cosmological mystery."

Comments

Not as new as it seems

[Grantbridge]

Lasers have had negative temperature for decades!

Re:Not as new as it seems

[140Mandak262Jamuna]

Epic fail. Every Jedi knight builds his own light sabre. What the galaxy is coming to now a days, aspiring jedi knights nonchalantly ordering their light sabre by mail order... What next? Subject verb object order Yoda learns?

Re:Not as new as it seems

[Noughmad]

What the hell want you from 900 year old man? English perfect?

The Doctor seems to be doing quite well for his age.

Re:Not as new as it seems

[Talderas]

Just start teaching a "Defense Against the Dark Side" course. I'm sure that will turn out well.

Re:Not as new as it seems

[da007]

The Doctor seems to be doing quite well for his age.

Doctor Who?

better explanation

[ssam]

wikipedia has quite a good explanation of negative temperature.
http://en.wikipedia.org/wiki/Negative_temperature

Re:better explanation

[hydrofix]

An interesting quotation from that article:

A substance with a negative temperature is not colder than absolute zero, but rather it is hotter than infinite temperature.

It seems this is a very specific quantum mechanical perversion, and no classical systems can reach the state quantum physicists call "negative temperature".

Re:better explanation

[Rhaban]

So, temperature uses unsigned floats?

Re:better explanation

[Anonymous Coward]

Is this proof of a simulated universe?

Re:better explanation

[Anonymous Coward]

Temperature isn't defined in physics as anything to do with heat, but the derivative of energy with respect to entropy. Absolute zero is the temperature at which there is no energy left in the system. At normal temperatures, it is positive. At absolute zero, it's zero. If you can create a system with dU/dS as negative, it's technically negative temperature, even though the system still has energy.
It's hard to explain due to how things like temperature and energy are defined, not because physicists are being smug. There isn't a proper name for it because it doesn't happen very much. That's why it's news.

Re:better explanation

[Rogerborg]

"Technically correct" is the best kind of correct.

Re:better explanation

[locofungus]

It's a quirk of the way the temperature scale was defined.

One possible definition of temperature:

Put lots of little magnets in a magnetic field. They will line up with the field. At absolute zero there will be no (technically minimal[1]) deviation from them all being perfectly aligned. As you warm them up they will start to be less and less well aligned until at what we call infinite temperature, there is no alignment with the field at all and the alignment is completely random.

But, if instead of warming them up, you flip the magnetic field they will then "cool" through "infinite" temperature.

If we use this definition of temperature then it would make more sense to have absolute zero as negative infinite temperature, infinite as zero and still hotter temperatures as greater than zero.

This makes the unreachability of absolute zero make more sense. "Infinite" temperatures (and greater than infinite) are only unreachable via trying to add more heat.

Lasers utilize population inversion - which is a state that is impossible via naive thermodynamics and also does not have a sensible temperature as a result.

[1] Zero point energy.

Tim.

Re:better explanation

[mrbester]

It's the previously unquantifiable temperature of a McDonald's Apple Pie.

Re:better explanation

[cgaertner]

It seems this is a very specific quantum mechanical perversion, and no classical systems can reach the state quantum physicists call "negative temperature".

This is by no means a quantum perversion, just a natural consequence of the definition of temperature as 1/T = dS/dE. There's nothing mysterious about negative temperatures from a thermodynamical point of view, it just happens that calssical systems don't exhibit this property because they do not come with an upper limit on energy, whereas there are quantum ones that do.

The common interpretation of temperature as average energy per degree of freedom comes in via the equipartition theorem, but breaks down in various edge cases, eg when the energy levels cannot be approximated by continuity (eg heat capacity of diatomic gases) or for non-ergodic systems (some plasmas, I believe).

As to the problem of infinite temperature: In a sense, thermodynamic \beta = 1/kT is the more natural measure of hotness and coldness and has a pole at T = 0. Coming from T > 0, this corresponds to infinite coldness, whereas coming from T < 0, this corresponds to infinite hotness.

Re:better explanation

[Savage-Rabbit]

There cannot be any proof, it is obviously impossible to distinguish between "simulated" and "real" reality

Not that obvious to me. You're assuming the simulators have made a perfect simulation, which they may not have done. Or they could leave deliberate clues, if they so wished, which would help us distinguish simulation and reality. Of course, on a broader philisophical point, you could argue there would still be no difference - reality could be a simulation and still be real.

http://www.technologyreview.com/view/429561/the-measurement-that-would-reveal-the-universe-as-a-computer-simulation/

Hi there,
You can stop philosophizing, I just deleted that guy from the simulation, he was getting annoying. Incidentally, if you subscribe to the specific flavor of mass delusion you guys call 'Christianity' and are wondering when the rapture will happen, it'll come the day I finally slip up while combining wild-cards and the 'rm' command on my Simulatron 6000 (TM).

Sincerely,
Your lord and cereator.

Re:better explanation

[Anonymous Coward]

Sure, don't bother trying to learn why this is; just blame it on someone else and think yourself the better man for being ignorant.

Richard Feynman: "If you can't explain something to a first year student, then you haven't really understood it."

I'll take Feynman's attitude towards obtuse, confusing jargon over your smug shit any day.

Re:better explanation

[serviscope_minor]

This is one of the things I love about slashdot. People with no knowledge of a subject call professionals "retarded" and get modded insightful.

It seems to me to be a retarded description, like calling infinity + 1 a negative number.

Think about reciprocals.

They need to use a proper name for it,

How about "nagative temperature". That's a proper name for it.

Temperature is defined by energy and entropy. Add energy and the entropy increases. That means the temperature is positive. How positive is how big that change is. Nice, straightforward, works well. Does whay you expect.

Then some quantum physicists discovered that adding energy makes the entropy go down. Well, plug that into the definition of temperature and the number comes out negative.

So basically, what you are claiming is that physicists are retarded because you don't like how the maths work out and you would rather they change the perfectly good classical definition of temperature to fit your sensibilities.

Deal with it. Quantum physics is very strange and many ideas you bring with you from the classical world simply don't work.

That doesn't make the professional physicists retarded, by the way.

Re:better explanation

[ArsenneLupin]

Temperature isn't a property of individual atoms. It is a property of a huge set of atoms, describing their energy distribution.

In a body with positive temperature, there are more atoms in the low energy states (moving slowly) than in the high energy states.

In a body with negative temperature, there are more atoms in the high energy states than in the low energy states. Normally that can only happen if there is an upper bound to the energy. Kinda like a speed limit, or, more realistically, if the states being talked about are not related to speed at all, but to some other physical property of the atom (such as orientation of spin within an external magnetic field...)

Re:better explanation

[OneAhead]

Actually, since this is predominantly a computer science crowd, let's try to explain it in purely binary terms (or a simplified pure quantum mechanical model if you wish). Every particle in your system is a binary bit; 0 is ground state (low energy) and 1 is excited state (high energy). Now, our kelvin scale is defined so that 0K is all 0s (there's only one state that satisfies this criterion) and +infinity is a 50/50 mix of 0s and 1s (which has the largest number of possible combinations/states := highest entropy). That worked pretty well for a long time since one never can go higher than 50/50 through ordinary heating. The problems started when people figured out clever tricks to have more 1s than 0s. This is called a population inversion, and LASER and NMR/MRI rely on it. The temperature of such an inverted population would be "beyond infinity", in other words, not representable in the kelvin scale. The solution was to use negative temperatures for these inverted populations: all 1s would be -0K (the fact that -0 is not the same as +0 is not a problem because neither of these states can ever be reached), and the temperature would go down (-1, -2,...) as 0s are introduced, to ultimately reach -infinity at the same 50/50 mix as +infinity (so basically + and - infinity are the same state). This weird system turns out to have mathematically convenient properties. Just to get an idea, if one inverts this temperature scale (ie. define a new new (K^-1) scale that goes with 1/T), the 50/50 state would be 0(K^-1), all 1s is -infinity (K^-1) and all 0s is +infinity (K^-1), so the problems at 0 and infinity are solved.

Remarks: - given the above, I feel it's more correct to state that inverting a population is going through infinity (as opposed to going through zero).
- inverted populations are not stable; when perturbed, they always equilibrate to positive temperature states (and they cannot be maintained through ordinary heating as another reply incorrectly stated, though they can through pumping, as in continuous-wave lasers). This equilibration can, however, take several seconds (in NMR applications) - long enough for practically useful applications.

TL:DR; version: negative temperature matter doesn't contain less energy than 0K; a good deal more in fact.

Dark Energy

[metamarmoset]

Observtions during the experiment could point to new research on dark energy.

From TFA:

Another peculiarity of the sub-absolute-zero gas is that it mimics 'dark energy', the mysterious force that pushes the Universe to expand at an ever-faster rate against the inward pull of gravity. Schneider notes that the attractive atoms in the gas produced by the team also want to collapse inwards, but do not because the negative absolute temperature stabilises them. “It’s interesting that this weird feature pops up in the Universe and also in the lab,” he says. “This may be something that cosmologists should look at more closely.”

Older hardware

[alendit]

Sadly, our universe runs on a quite old hardware, which allowed the scientists to overflow the temperature variable. Why the Great Programmer didn't use unsigned longs ist beyond me, rookie mistake, really!

Simple

[famebait]

Heat is just atoms moving around, after all, so negative temperatures are easy:
just make the atoms move backwards.

man pages

[jabberw0k]

You mean -- The serpent offered Eve a Perl script to parse /etc/passwd, and Adam's punishment was crypt (3) ...?

Re:The real question...

[jellomizer]

Proving/Disproving God isn't a Scientific Mission. Understanding how the Universe works is.
If we ever figure it all out we can go.
Well that is how the Universe Works and that is it.
or we can go.
Wow so that is how God did it.

You are confusing the Idea of a God with Religious interpretations of God. Science has more or less disproven that the Stories in the Bible are often not Factual or at least exaggerations. But it doesn't disprove God.

God and Science do not Mix. The God idea exists outside of Science as God is defined as a SuperNatural entity or more plainly God exists out of the rules of Observable Nature, Science is the study of Observing Nature.
This come with a two edge sword.

1. Any Science that states that God did it, is faulty because God is unobservable thus you cannot equate it as an observed fact. At best if there is a God Influence it would probably be considered a seemingly Random Element that will need further study.

2. The counter to this, is Science can't disprove God, because he is out of Observable Ability. Thus any work to Disprove God will be trying to apply God as a factor to disprove it.

Keep God out of Science, Also Keep Atheism out of Science as well.