2021 Axel Memorial Lecture - "Amor Caloris: Why does nature love heat so much?"

Two seemingly unrelated phenomena - high-energy collisions of atomic nuclei and black hole formation in gravitational collapse - have motivated theoretical physicists in recent years to revisit the question how thermal equilibrium is attained in situations where the classical Boltzmann picture of thermalization via two-body collisions of particles does not apply. In both instances, one encounters hot regions of space that are essentially “hot vacuum”, or space that has the quantum numbers of the vacuum but is filled with thermal energy. In my lecture I will discuss some of the concepts that have been developed to understand how thermal equilibrium in such unusual situations can be established.