Until the End of Time: Mind, Matter, and Our Search for Meaning in an Evolving Universe

by Brian Greene

The chain of events, highly idealized and simplified to be sure, shows how a star—a pocket of low entropy, a pocket of order—can be produced spontaneously even though no engineer directs the action and even though the second law of thermodynamics, with its dictum that total entropy increases, remains in full force. Compared with a steam engine, the cosmic setting is more exotic, but what we’ve found is another instance of the entropic two-step. Much as a steam engine and its surrounding environment engage in a thermodynamic dance—the steam engine releases waste heat, causing its entropy to decrease, while the environment soaks up the heat, causing its entropy to increase—a gas cloud that’s large enough for gravity to matter engages in an analogous pas de deux. As the core of such a gas cloud contracts under the pull of gravity, its entropy decreases, but in the process it releases heat that causes the entropy of the surroundings to increase. A local region of order is created within an environment that undergoes a more than compensating surge in disorder. The new feature of the gravitational version of the entropic two-step is that it’s self-sustaining. As the gas cloud contracts and emits heat, its temperature rises, causing yet more heat to flow outward and driving the two-step to continue stepping. By contrast, when the steam engine performs work and emits heat, its temperature drops. Without burning more fuel to heat the steam back up, the engine peters out. That’s why...