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Quantum Gas Goes Below Absolute Zero 264

Posted by samzenpus
from the stop-moving dept.
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."
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Quantum Gas Goes Below Absolute Zero

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  • by Grantbridge (1377621) on Friday January 04, 2013 @06:23AM (#42473449)
    Lasers have had negative temperature for decades!
  • better explanation (Score:5, Informative)

    by ssam (2723487) on Friday January 04, 2013 @06:28AM (#42473469)

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

    • by hydrofix (1253498) on Friday January 04, 2013 @06:49AM (#42473527)
      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".

      • by Rhaban (987410) on Friday January 04, 2013 @06:56AM (#42473557)

        So, temperature uses unsigned floats?

        • by Anonymous Coward on Friday January 04, 2013 @07:09AM (#42473611)

          Is this proof of a simulated universe?

          • by mrbluze (1034940)
            Maybe it's an imaginary temperature?
          • Re: (Score:3, Insightful)

            There cannot be any proof, it is obviously impossible to distinguish between "simulated" and "real" reality
            • Bingo. Not from the inside of it anyway.

              Anyway there is no wrap-around in temperature, as I read the explanations, and without wrap-around it is difficult to go on and say "it smells like" a simulation.

              OTOH genesis 3:22 speaks about obtaining root privileges so Eden appears as a simulation with bad security, ain't that interesting.

            • 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/ [technologyreview.com]

              • by Savage-Rabbit (308260) on Friday January 04, 2013 @09:08AM (#42474119)

                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/ [technologyreview.com]

                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.

              • 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. ...

                Why do you assume reality is "perfect"? Perhaps inconsistent results is part of the built-in quantum randomness of the Universe.

        • Re: (Score:3, Funny)

          by Anonymous Coward

          No, the temp was calculated with the original Pentium!

      • by locofungus (179280) on Friday January 04, 2013 @07:35AM (#42473687)

        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.

        • If you flip the magnetic field they will be in an unstable state and therefore all flip, perhaps completely randomly, so as to produce the infinite temperature you speak of.

          The entire point of this experiment was to keep the unstable state, stable, which they call negative temperature.

        • by OneAhead (1495535) on Friday January 04, 2013 @05:07PM (#42480115)

          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 [wikipedia.org] (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 [wikipedia.org]). 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.

      • by cgaertner (1004238) on Friday January 04, 2013 @08:21AM (#42473881)

        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: (Score:2, Funny)

          by Anonymous Coward

          Hotness frequently dances around a pole.

      • How about you instead explain in normal people terms (or at least computer specialist terms) how atoms can have less motion than not moving at all, because that sounds completely made up and impossible.
      • It's actually not quantum mechanical, at least not explicitly, but it requires that the system in question have an ordered state that is at a high-energy bound.

        A classical system that does this is an array of magnetic dipoles in a magnetic field. When all the dipoles are aligned against the field, the system is fully ordered, and is in its highest-energy state. If you look at deviations from this state, what you find is that all of them increase the entropy (because the state is fully ordered), and decrease

        • Isn't this an unstable state, it wouldn't last for long? The experiment in the article claimed to have made an unstable state, similar to the one you describe, stable.

      • by Dunbal (464142) *
        Pretty much by definition you can't reach absolute zero because the moment you go "below" it, all you managed to do is redefine "absolute zero" as meaning a new temperature.
  • Dark Energy (Score:5, Interesting)

    by metamarmoset (2728667) on Friday January 04, 2013 @07:29AM (#42473671)
    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.”

  • by alendit (1454311) on Friday January 04, 2013 @07:49AM (#42473761)

    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 (Score:5, Funny)

    by famebait (450028) on Friday January 04, 2013 @08:16AM (#42473861)

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

  • by mjr167 (2477430) on Friday January 04, 2013 @08:48AM (#42474029)
    HAH! When I was a freshman in college a long long time ago, I lost points in a computer science assignment because I did not perform error checking to ensure the user enter temperatures were above absolute 0. Prof didn't believe me when I told her that wasn't a hard limit, so there!
    • by ledow (319597)

      And your prof was right - the user can still be stupid and you, as a programmer in this instance, should have worked to ensure that the user COULDN'T do anything bad by being (deliberately or not) stupid.

      Take, for instance, things like this were a result from an experiment erroneously kicks out -0.000001 K and you allow it into your program to wreak havoc with your assumption (e.g. if you were storing it in unsigned at any point, or dividing by it assuming it was always >0 K).

      Or the user hits the minus k

  • Sub Means below? (Score:3, Interesting)

    by NSN A392-99-964-5927 (1559367) on Friday January 04, 2013 @08:54AM (#42474049) Homepage

    So is this story misleading to say that absolute zero was achieved. Wikipedia The Celsius and Fahrenheit scales are defined so that absolute zero is 273.15 C or 459.67 F. https://simple.wikipedia.org/wiki/Absolute_zero [wikipedia.org]

    But in the news story it says SUB and SUB means below, yet there is no mention of the temperature whatsoever in the article and going beyond absolute zero is not possible even out in space! You can get close, but not to absolute zero otherwise you would have created the ultimate weapon!

    Enough said.

    • by Twinbee (767046)
      Ultimate weapon?
    • by Sockatume (732728)

      Sometimes you take an idea with a perfectly normal, intuitive meaning - "temperature is a measure of how fast the atoms are going" - and formalise it. In this case that formalism is something along the lines of "temperature is a measure of the population distribution of the kinetic energy of the particles in an ensemble". Well, sometimes when you make a definition like that, and you invent something that doesn't exist in nature - a laser, say - then you try to apply that definition to the new object, and yo

  • by Anonymous Coward

    These researchers had to give it 110% to achieve this less than nothing.

  • These physicists should hang their heads in shame.

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