# Advent

# Category archives for **Advent**

As we started the last week of the advent calendar, I was trying to map out the final days, and was coming up one equation short. I was running through various possibilities– the Dirac equation, Feynman’s path integrals, the Standard Model Lagrangian, when I realized that the answer was staring me right in the face:…

A week and a half ago, when the advent calendar reached Newton’s Law of Universal Gravitation, I said that it was the first equation we had seen that wasn’t completely correct. Having done our quick swing through quantum physics, the time has come to correct that equation: If you say “Einstein equation” to a random…

Newton’s birthday (in the Julian calendar) is Sunday, so we’re in the final days of the advent calendar. Which means it’s time for the equations that are least like anything Newton did, such as today’s: This is the Schrödinger equation from non-relativistic quantum mechanics. If you want to determine the quantum state of an object…

Today’s equation in our march to Newton’s birthday is actually a tiny bit out of order, historically speaking: This is the Rydberg formula for the wavelengths of the spectral lines in hydrogen (and hydrogen-like ions), with R a constant having the appropriate units, and the two n‘s being two dimensionless integers. This equation was developed…

Yesterday’s equation was the first real result of quantum theory, Max Planck’s formula for the black-body spectrum. Planck never really liked the quantum basis of it, though, and preferred to think of it as just a calculational trick. It wasn’t until 1905 that anybody took the idea really seriously, leading to today’s equation: From the…

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…

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…

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.…

Moving along through our countdown to Newton’s birthday, we have an equation that combines two other titans of British science: This is the third of Maxwell’s equations (named after the great Scottish physicist James Clerk Maxwell), but it originates with Michael Faraday, one of the greatest experimentalists of the day. Faraday was a fascinating guy,…

As we march on toward Newton’s birthday, we come to the second of Maxwell’s famous equations, which is Gauss’s Law applied to magnetic fields: For once, this is pretty much as simple as it looks. The divergence of the magnetic field is zero, full stop. As I said yesterday (albeit using the wrong terminology), the…