The Physics of Superheroes

James Kakalios

2 annotations • data

First annotation on Nov 26th, 2025.

Introduction

There is nothing in the principle of conservation of energy, which underlies the First Law of Thermodynamics, that prevents or forbids the construction of a 100 percent efficient machine, where the work created by the device exactly equals the heat energy put into it. In fact, if all we had to go on was the First Law of Thermodynamics, we would reasonably expect that machines must be 100 percent efficient, for we know that energy can never be gained or lost, but only transformed from one form to another. In order to understand what limits the conversion of heat into work, we must introduce a new concept, complementary to, but as important as, energy. This concept, called "entropy," is intimately connected to heat flow, and will give the Atom a very bumpy ride, even when he isn't floating along thermal drafts.
What determines the exact temperature and pressure at which a phase transition takes place depends on the details of how the individual atoms link up when their electronic clouds overlap. To determine the temperature at which a phase transition such as melting or boiling occurs, we must do more than simply count up the energy needed to break each chemical bond that holds a solid or liquid together. We also have to take into account the large change in the randomness of the atoms—that is, their entropy. For a given internal energy, systems tend to increase their entropy, because all other things being equal in general there are more ways to be in disordered configurations than in neat, ordered piles. The competition between lowering energy and increasing entropy leads to a fascinating collective phenomenon in which all of the atoms in a solid decide to melt at the same temperature.