# What Does “Negative Temperature” Mean, Anyway?

The most talked-about physics paper last week was probably Negative Absolute Temperature for Motional Degrees of Freedom (that link goes to the paywalled journal; there’s also a free arxiv preprint from which the above figure is taken). It’s a catchy but easily misinterpreted title– Negative absolute temperature! Below Absolute Zero! Thermodynamics is wrong!– that obscures…

# Final Notes on a Toy Model of the Arrow of Time

We’re in the home stretch of this term, and it has become clear that I won’t actually be using the toy model of the arrow of time I’ve talked about in the past in my timekeeping class this term. These things happen. Having spent a not-insignificant amount of time playing with the thing, though, I…

# Notes Toward a Toy Model of the Arrow of Time

I’m fairly certain somebody has already done this, because it’s such an obvious idea. It’s a little beyond my cargo-cult VPython skills right at the moment, though (I can probably learn to do it, but not right now), and I none of the applets I Googled up seemed to be doing this, so I’m posting…

# Difficult Problems in Automotive Thermodynamics

While clearing the cars of frost Thursday morning, I was reminded of a difference of opinion Kate and I have about the best approach to a cold car. I tend to start the car up, and immediately turn the defrost on full blast; she prefers to let the car warm up for a while first,…

# The Advent Calendar of Physics: Science Works

Moving along in our countdown to Newton’s birthday, we come to 1900, and one of the most revolutionary moment in the history of physics, represented in today’s equation: This is Max Planck’s formula for the spectrum of the “black-body” radiation emitted by a hot object at temperature T. It’s also the equation highlighted on what…

# The Advent Calendar of Physics: Entropy

As I said yesterday, I’m going to blow through another entire subfield of physics in a single equation, as our march toward Newton’s Birthday continues. Today, it’s statistical mechanics, a very rich field of study that we’re boiling down to a single equation: This is Boltzmann’s formula for the entropy of a macroscopic system of…

# The Advent Calendar of Physics: Ideal Gas

Once again, the advent calendar is delayed until late at night by a busy day with SteelyKid– soccer in the morning, playing with a trebuchet after lunch, then Arthur Christmas at the Colonie mall. We’re running low on days to honor great milestones in physics, though, so I don’t want to skip a day entirely.…

# Greenhouse Physics and Car Shades

I got a new comment on an old post asking an interesting question about thermodynamics: I have a question that bears somewhat on this issue of keeping cars parked in the sun, cooler. You all know those accordion folded/aluminized shades you can put up inside the windshield and back window. Seems to me putting them…

# The Physics of Frustration: “Quantum Simulation of Frustrated Classical Magnetism in Triangular Optical Lattices”

One of the benefits of having joined AAAS in order to get a reduced registration fee at their meeting is that I now have online access to Science at home. Including the Science Express advance online papers, which I don’t usually get on campus. Which means that I get the chance to talk about the…

# Beat the Heat with SCIENCE!

It’s really frickin’ hot in much of the US. Fortunately, we have central air at home, A/C in the car, and convenient local businesses with air conditioning and free wi-fi. The inadequate HVAC systems in the Science and Engineering building on campus aren’t anywhere near being able to cope with this, so I’m working from…