Heat death held a morbid fascination for Victorian-era physicists. It was an early example of how everyday physics connects to the grandest themes in cosmology. Drop ice cubes into a glass of water, and you create a situation that is out of equilibrium. The ice melts, the liquid chills, and the system reaches a common temperature. Although motion does not cease ?" water molecules continue to reshuffle themselves ?" it loses any sense of progress, and the overall distribution of molecular speeds doesn't change. The 19th-century founders of thermodynamics realized that the same goes for the universe as a whole. Once the stars all burn out, whatever is left ?" gas, dust, stellar corpses, radiation ?" will come to equilibrium. "The universe from that time forward would be condemned to a state of eternal rest," Hermann von Helmholtz wrote in 1854. Modern cosmology has not altered this basic picture.