The heat death of the universe

Lore & Background

The idea of heat death stems from the second law of thermodynamics, which states that entropy tends to increase in an isolated system. From this, the hypothesis implies that if the universe lasts for a sufficient time, it will asymptotically approach a state where all energy is evenly distributed. In Bailly's view, all planets have an internal heat and are now at some particular stage of cooling, with the final state described as one of 'equilibrium' in which all motion ceases. Thomson's views were elaborated over the next decade by Hermann von Helmholtz and William Rankine. Thomson introduced the heat death paradox, which challenged the classical concept of an infinitely old universe, since the universe has not achieved its thermodynamic equilibrium.

Reader's Guide

The heat death hypothesis is significant because it represents one of the earliest scientific attempts to apply the laws of thermodynamics to the entire universe, shaping modern cosmology's understanding of the universe's ultimate fate. The theory, originating with Lord Kelvin in the 1850s, extrapolated the second law of thermodynamics—that entropy tends to increase—to a universal scale, leading to the prediction that the universe will eventually reach a state of maximum entropy where no thermodynamic free energy remains. This idea has persisted and evolved, with current proposals depending on assumptions about the universe's curvature and dark energy. In a theorized 'open' or 'flat' universe that continues expanding indefinitely, either a heat death or a Big Rip is expected. The concept has been extended to quantum physics, where even after thermodynamic entropy reaches its maximum, other quantities such as quantum circuit complexity continue to increase. The heat death paradox, introduced by Kelvin, also provided an argument against an infinitely old universe, as the existence of stars and temperature differences can be considered empirical proof that the universe is not infinitely old. The legacy of this hypothesis lies in its foundational role in discussions of cosmic entropy and the eventual fate of all matter and energy.

Did You Know?

• The heat death of the universe is also known as the Big Chill or the Big Freeze.
• Lord Kelvin introduced the heat death paradox, which challenges the concept of an infinitely old universe.
• If the cosmological constant is positive, the temperature will asymptote to a non-zero positive value, and the universe will approach a state of maximum entropy.