Ludwig BoltzmannThere Are More Ways To Be A Mess.

The sticker says There Are More Ways To Be A Mess. That sentence is most of the second law of thermodynamics.

Sweep a room's worth of gas into one corner and it will not stay there. In the 1870s Ludwig Boltzmann explained why, and the explanation is counting. A macrostate, such as 'the gas fills the room', can be built from an enormous number W of microscopic arrangements. 'The gas sits in the corner' can be built from far fewer. In 1877 he tied entropy to the logarithm of that count.

So nothing forbids the molecules from tidying themselves into a corner. For anything the size of a room it is just so overwhelmingly improbable that nobody will ever see it happen. The second law is statistics, not prohibition, and that is why entropy goes up.

The equation on the sampler, S = k log W, is carved on his tombstone in Vienna's Zentralfriedhof. Boltzmann never wrote it in that form. Max Planck did, around 1900–1901, and Planck introduced the constant k. In his Nobel lecture Planck remarked that it is often called Boltzmann's constant although, to his knowledge, Boltzmann himself never introduced it. The idea is Boltzmann's and the compact notation is Planck's, so the epitaph is a joint effort.

Since 2019 the constant has had an exact value, 1.380649×10⁻²³ joules per kelvin, and it now defines the kelvin. The log on the tomb is the natural logarithm.

His broom is not part of the theory. The mess is.