



I. It's a Very, Very Mad World





Potassium atoms

Here is where the special behavior takes hold.



II. Negative Absolute Temperatures?  That's Really Cold, Right?


Lord Kelvin
[Image Source: Unknown]







Sources: Science, Nature

Comments     Threshold


RE: huh?
By PaFromFL on 1/9/2013 11:47:03 PM , Rating: 2
After the quantum mechanical and statistical processes underlying thermodynamics were discovered, temperature was redefined as a factor relating the increase of energy of an isolated system to an increase in entropy (randomness). This definition allows negative temperatures.

For an ideal gas, added heat increases the average speed of the molecules, spreading the energy over a wider range of speeds. The wider range of speeds corresponds to an increase in entropy (or randomness). The temperature is positive because added heat increases entropy.

For very cold gases, quantum mechanical effects limit the speeds (or other energy-related quantities) to discrete values. For some gases, a small amount of added energy is not enough to jump the speed beyond a certain limit, so that added energy tends to produce speed values at or below the limit. This actually decreases the entropy because high speeds occur more frequently than low speeds (maximum entropy occurs when all speeds are equally likely). When an increase in energy reduces entropy, the modern definition of temperature is negative.

