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[Scood]

http://www.newscientist.com/article/mg20827893.500-how-to-create-temperatures-below-absolute-zero.html?DCMP=OTC-rss&nsref=online-news

physics, you surprise me sometimes

[Argembarger]

This sounds incredibly silly!

So let me see if I understand this correctly. We screw with atoms with a bunch of lasers, holding them in some kind of "optical lattice", and get them in a state where, uh... where we can add energy... to the atoms... but they don't move because they are trapped...

And um...

And then when they are released from the lattice, they have a higher energy than corresponding "positive" temperature particles...

I don't understand where the "negative" part comes in, though... If they have energy, don't they have a positive temperature? I was always under the impression that absolute zero temperature is the complete absence of kinetic energy in the particles... But it sounds like these particles DO have energy, so what makes them negative? If you combine equal amounts of -50 degrees kelvin gas with 50 degrees kelvin gas, do they cancel each other out?

Bluh bluh crazyscience bluh.

[Sowelu]

"Temperatures" below absolute zero.

If you've got a thousand switches, and exactly ten of them are flipped 'up', how many ways can you arrange them?  Lots of ways.  How many ways can you arrange them if only two are flipped 'up'?  Less ways.  That's their definition of temperature in this case.

But if you get a LOT of switches, things change.  Maximum entropy is when you have 500 switches.  But if you need to have 990 switches flipped 'up', you have a lot less entropy, even though more of them are up.  That's negative temperature:  when over 50% of the states are high-energy.

This definition of temperature is kind of weird compared to everyday experiences; it only applies to entropy, and not the ability to melt your face off.  Also, I strongly object to calling it negative, even though that probably makes more sense for their equations somehow.  It's just weird.  >:|  I mean they don't even cross an asymptote!

[Argembarger]

That... actually was a really good visual, and this makes some degree of sense now.

It seems really unconventional. Is our temperature system built more out of practicality and convenience than it is to form an actual model of what's going on then?

[Tellemurius]

the Fahrenheit system works as a norm for people.

[Eagle_eye]

It seems to me as if its more of a completely different scale of temperatures than the current one's negative continuation...

[Tellemurius]

It seems to me as if its more of a completely different scale of temperatures than the current one's negative continuation...

What the Kelvin system? the kelvin measures the activity of a atom moving around, most accurate temp reading from hot as stars to absolute zero and apparently now lower. reminds me of high energy microwaves moving faster than light in a void medium.

[Eagleon]

To be honest I don't see the point. This is a little like accelerating something upwards and saying you've created negative gravity. From my understanding the atoms are perched in unlikely energy states, and kept there by a lattice of light beams. But I have an easier way to perform this experiment.

Matter is composed of energy. By creating a box, like such

Spoiler: Box device (click to show/hide)

and adding very hot pudding within, the puddings are being confined by energy on all sides, "perched" on top of the bottom of the box. By increasing the height of the box, and thus the energy, the puddings are less likely to "boil over". This is the very definition of negative entropy in systems of puddings. Remove the sides, decreasing the energy, and the puddings will slump away chaotically, having gotten their order wrong and being very upset with the service.

Problem, physics?

[Virex]

The reason they call it negative energy is because that's how it behaves, if you take the formal thermodynamic definition of temperature. They could've called it pseudotemperature or something, but that doesn't really tell you how to treat it when doing calculations.

[Leafsnail]

Hmm... well, it's actually meant to be impossible to even get something down to absolute zero.  Afterall, where's the last bit of heat gonna go?

[Sowelu]

Still, it's worth noting that the coldest place (ever?) in the observed universe is in our laboratories.  We do things to matter that just don't occur naturally, much colder than space.

[Virex]

(Whoa I just realized you wrote "it's worth noting". I've grown so accustomed to seeing "it's worth nothing" that it's a relief to see some proper English)

Hmm... well, it's actually meant to be impossible to even get something down to absolute zero.  Afterall, where's the last bit of heat gonna go?

We move heat from a low temperature area to a high temperature area all the time. Ever heard of a refrigerator?

[Leafsnail]

The thing is, a refrigerator's efficiency reduces as your temperature goes down.

At absolute zero, the efficiency is 0%.