How to create temperatures below absolute zero

[n2doc]

01 December 2010 by David Shiga

ABSOLUTE zero sounds like an unbreachable limit beyond which it is impossible to explore. In fact there is a weird realm of negative temperatures that not only exists in theory, but has also proved accessible in practice. An improved way of getting there, outlined last week, could reveal new states of matter.

Temperature is defined by how the addition or removal of energy affects the amount of disorder, or entropy, in a system. For systems at familiar, positive temperatures, adding energy increases disorder: heating up an ice crystal makes it melt into a more disordered liquid, for example. Keep removing energy, and you will get closer and closer to zero on the absolute or kelvin scale (-273.15 °C), where the system's energy and entropy are at a minimum.

Negative-temperature systems have the opposite behaviour. Adding energy reduces their disorder. But they are not cold in the conventional sense that heat will flow into them from systems at positive temperatures. In fact, systems with negative absolute temperatures contain more atoms in high-energy states than is possible even at the hottest positive temperatures, so heat should always flow from them to systems above zero kelvin.

Creating negative-temperature systems to see what other "bizarro world" properties they might have is tricky. It is certainly not done by cooling an object down to absolute zero. It is, however, possible to leap straight from positive to negative absolute temperatures.

more

http://www.newscientist.com/article/mg20827893.500-how-to-create-temperatures-below-absolute-zero.html

[derby378]

1. So anything colder than absolute zero is unbelievably hot?

I've hear this theory bantered around before, the idea that heat and cold are basically two sides of the same coin. All you need to do is "call it, friendo."

[laconicsax]

2. Wouldn't this result in full knowledge of both position and velocity?

Even at absolute zero atoms aren't stationary but jiggle a bit. Wouldn't having even less entropy result in a violation of uncertainty--we'd be able to know both position and velocity?

[derby378]

3. I think atoms only jiggle because of the electron orbits

I would think you'd have to cause the electrons to come to a complete stop, as they possess a tiny amount of rest mass despite no known actual structure. If you have jiggling, can you really call their temperature abolute zero?

[laconicsax]

4. I had to look it up. You're right about it being the electrons.

You can't cause the electrons to come to a complete stop without violating uncertainty. Here's what Feynman says:

...Remember that when a crystal is cooled to absolute zero, we said that the atoms do not stop moving, they still jiggle. Why? If they stopped moving, we would know where they were an that they had zero motion, and thatis against the uncertainty principle. We cannot know where they are and how fast they are moving, so they must be continually wiggling in there!

Absolute zero, as I understand it, is a minimum entropy state. Presumably, going 'below' absolute zero in terms of entropy would require a violation of uncertainty.

It's also entirely possible that New Scientist, in their intermittent quest to be a sensationalist rag, got the explanation wrong or left something important out.

[jberryhill]

5. If you have jiggling...

Then you might consider support appropriate to being, shall we say, full figured.

[Thor_MN]

7. Jiggling went out of style in the late '70s

I blame the Neocons...

[thereismore]

6. Sensationalist nonsense. Negative temperatures have been known in physics

for a long time. The thing is, invariably, such a system exists inside another system whose temperature is positive, and the whole system is unstable. You can, for examlpe, get electrons in a state of "negative" temperature, but the electrons are inside the atomic matrix. After a short time, the two systems equilibrate and they end up at positive temperature. So, in summary: negative temps exist only formally for a brief moment in an unstable subsystem.

[TheMadMonk]

8. But it's on the "edges" that the fun stuff happens.

I actually derived a piece of this in a limited and mostly erroneous sense by playing with tachyonic solutions to Maxwell's, Lorentz's and the big A's equations about 30 years ago as a kid.

Though my thoughts were more along the lines of getting below 0K could result in transfinite/superluminal velocities.

[somone]

9. Purcell and Pound demonstrated negative temp in 1951

A graph of their experiment can be found in some graduate textbooks.