12 ms·
I did not read the article (shame on me), but the story goes like this: Normally, energy of a system is bounded from below (there's a lowest energy). Adding en
by cygx 14y ago
I did not read the article (shame on me), but the story goes like this:
Normally, energy of a system is bounded from below (there's a lowest energy). Adding energy to the system increases the number of accessible microstates (individual particles may occupy energy levels from lowest to highest accessible one) and thus the entropy. Such a system is characterized by positive temperature.
Now, quantum systems may come with an energy bounded from above, and adding energy to the system will decrease the number of accessible microstates (individual particles are forced into the highest energy level and have nowhere else to go). Such a system is characterized by negative temperature.
A system with negative temperature is hotter than one with positive temperature in the sense that heat will flow from the system with negative temperature to the one with positive temperature.
- JshWright 14y agoWhy was this something that needed to be 'created' then? Isn't it just a different way of thinking about the same thing?
- cygx 14y agoNegative temperature is a quantum effect than can be tricky to produce experimentally. There's nothing mysterious about negative temperature from the thermodynamical point of view, but there are no classical systems that exhibit this property.
- JshWright 14y agoBut isn't the property, as described, simply a different way of reasoning about the same physical phenomenon? (Clearly it's not, I'm just not sure where the gap in my understanding is)
- raverbashing 14y agoThis is eq 7 here (scroll down) if I'm not mistaken: http://en.wikipedia.org/wiki/Temperature#Second_law_of_thermodynamics http://en.wikipedia.org/wiki/Temperature#Second_law_of_therm... That is, temperature relates to the change of entropy in relation to the energy that enters the system
- cygx 14y agoCorrect. Equation (8) can be used as definition for thermodynamical Temperature whereas equation (7) tells us about the direction of heat flow.