37 Quantum Mechanics

37.1 Entropy

Ludwig Boltzmann’s grave in Vienna bears his famous entropy formula, S = k log W, which relates the entropy of a system to the number of possible microscopic states. Ludwig Boltzmann was an Austrian physicist and philosopher who made significant contributions to the fields of statistical mechanics and thermodynamics including the formulation of the H-theorem- which explains the behavior of gases in terms of statistical mechanics, the concept of the Boltzmann constant (k)- a fundamental constant in physics that relates temperature to the average kinetic energy of particles in a gas, the Boltzmann equation- which describes the behavior of a gas by incorporating statistical probabilities. The concept of a “Boltzmann Brain” was introduced by cosmologists, inspired by Boltzmann’s work. It suggests that there is a minuscule possibility of a conscious entity, like a human brain, spontaneously fluctuating into existence in an otherwise empty and chaotic universe. This idea sparked debates and discussions about the nature of reality and the interpretation of probabilities in cosmology.

An under appreciated fact of history is that quantum physics implicitly started with Boltzmann.

Entropy, energy per degree kelvin, is essential quantized because the number of possible micro states is an integer.

Planck, in his 1901 paper, “On the distribution of energy in the normal spectrum” — in what Planck called “an act of desperation” — derived his quantized equation for black body radiation directly from Boltzmann’s equation for entropy.

It is arguable that the father of quantum mechanics is truly Boltzmann, not Planck.

Physics in History (Twitter Thread)

37.2 Many-World Interpretation

Ball

The idea that the universe splits into multiple realities with every measurement has become an increasingly popular proposed solution to the mysteries of quantum mechanics. But this “many-worlds interpretation” is incoherent, Philip Ball argues in this adapted excerpt from his new book Beyond Weird.

Phillip Ball (2018) Why the Many-Worlds Interpretation Has Many Problems