2018 was a fun year to teach thermal physics. At Drew, this course is offered every other year, using a textbook by the late Dr. Ashley Carter. The Chapter 18 in the textbook is about blackbody radiation, and students (and I) enjoy wrapping up the course with some reviews of Bose-Einstein statistics (i.e., counting the number of microstates for photons), optimization of entropy with Lagrange multiplier, calculation of degeneracy, etc.

Using some modern physics (e.g., E = hv = hc/lamda), students then are able to derive the formula for the blackbody radiation in the same form as appears in Planck’s 1901 paper. In the class, I distribute English-translation of this classic paper, and go over the broad outline. I point out interesting terminologies like “complexion” that Planck used. Also, Planck’s N and P correspond to w and N in our textbook’s notation, respectively. Planck’s paper ends with experimental estimates for h and k.

One of the big science news in 2018 was the re-definition of SI units, by fixing the values of the fundamental constants, including h and k. After ~100 years since the beginning of quantum mechanics and modern statistical mechanics by Planck and Boltzmann, the constants that are named after them have been deemed so fundamental that the units of mass (kg) and temperature (K) have now been defined in terms of their values. What a big paradigm shift! See nist.gov for more details.