[silk] temperature as forex

[Dave Long]

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".