Another metaphor for temperature: there are two basic "currencies" in
physics, entropy and energy. If you have an ordered state, you can
usually easily trade it for a less-ordered state, and if you have an
energetic state, you can usually easily trade it for a less-energetic
state. Temperature is the "exchange rate" between these two
currencies. At low temperatures, energy is dear and order cheap, so
we wind up with systems whose parts are predictably in one of their
lowest energy states. At high temperatures, order is dear and energy
is cheap, so we wind up with systems whose parts are unpredictable,
as likely to be in arbitrarily high-energy states as lower ones.
A negative temperature is then the equivalent of a negative exchange
rate -- which is why it takes some effort to set up*, as the universe
usually conspires to quickly arbitrage such situations away.
-Dave
* if you find localized negative energy states, there's probably some
biology somewhere meddling with your physics; a related slogan is
that "life is fire, slowed down, with an attitude".
- [silk] temperature as forex Dave Long
-