Scientists go below Absolute Zero - Page 11

On January 09 2013 08:57 Luepert wrote:
Doesnt volume vary with temperature? 0 temperature= zero volume.
And now negative temperature, I feel like negative volume is a good way to make a black hole or something lol.

On January 09 2013 08:57 Luepert wrote:
Doesnt volume vary with temperature? 0 temperature= zero volume.
And now negative temperature, I feel like negative volume is a good way to make a black hole or something lol.

On January 09 2013 23:15 adiga wrote:


Yeah but they are locking the atoms at their spots so volume doesn't change. And that's why the temperature drops bellow zero.

On January 06 2013 00:41 micronesia wrote:

We have been able to get negative temperatures since before this paper.... it is just the first time it was done with a gas, I believe.

The common understanding of temperature that it is a measure of the speed of the motion of molecules in a system, while useful, is not accurate. You can actually define temperature using this formula:

1/T = dS/dU where S is entropy and U is internal energy. Temperature therefore has to do with how a change in internal energy relates to a change in entropy. For normal systems (positive Kelvin temperatures) increasing energy of a system will increase entropy (this is very important for studying the Carnot Cycle). For systems where the opposite happens (negative temperature), the object will give off heat to any system it comes into thermal equilibrium with. A few cases:

System A      System B                        Result
Warm            Hot                               Heat flows from hot to warm; temperatures equalize
Negative      Warm                               Heat flows from negative temperature system to warm system
Negative      Very Hot                        Heat flows from negative temperature system to hot system

Another example where you can get negative temperature: Place a 2-state paramagnet into a magnetic field such that the dipoles align. Then, reverse the magnetic field polarity.

If de approaches 0, and dE approaches Infinity

On January 10 2013 02:28 gyth wrote:

For this material adding energy decreases the entropy, that is why de/dE is negative.

On January 10 2013 02:15 Setev wrote:


OK, from an equation perspective, T = temperature, de = change in Entropy, dE = change in Internal Energy.

So from micronesia's passage, 1/T = de/dE.

If de approaches 0, and dE approaches Infinity (as stated in a negative T system), how is T negative? 1/T will be approaching zero Kelvin, because 0/Infinity = 0. T will then be near infinity Kelvin. How come the temperature derived from this equation can be below 0 K?

It'd be great if someone can elaborate...

If I touched something that was the coldest we've "achieved" previously, which I understand is slightly above absolute zero,

It would feel very cold.

If I touched something that was actually absolute zero,

It would feel slightly colder.

If I touched this new "negative temperature"...

It would feel even colder still?

On January 18 2013 00:37 Fenris420 wrote:
Have I understood this correctly by saying it is not hacking, but clever use of game mechanics? As in we abuse the definition of temperature rather than actually making something colder.