Nothing can take place in this universe without a gradient - a difference in some property between one part of the universe and another. All the heat in the world is incapable of conversion to work if the temperature everywhere is uniform; a steam engine requires both a hot box and cold water for a condenser.

Mechanical work requires a potential energy gradient; the heaviest weight imaginable can do no work if there is no place for it to fall. Chemical work requires the presence of high-free-energy compounds that can be broken down into low-free-energy molecules such as CO₂ and water, or else high concentrations of a substance in one location and a scarcity of that substance somewhere else. This structure to the universe - different properties in different places - is a form of order. Every time a real process takes place, some of this order is whittled away. The "mixed-upness," or entropy, of the universe increases.

The universe therefore carries the seeds of its own death. From a free energy standpoint, it continually is running down. The only way for nothing to run down is for nothing to happen. Every time something real does take place, it makes the universe just a little bit less able to cause more things to happen.

When a boulder rolls downhill it can be harnessed to a device for saving some of its energy; but the energy saved, if used to hoist the boulder, will not be quite enough to get it to the top of the hill again. These losses are tied up with the inevitable rise of entropy in any real process.

When the last star has burned out and has either shrunk to a white dwarf or exploded into a supernova, when the last heat source has been dissipated, the last energy-rich organic compound has broken down, and the universe is a uniform dispersion of cold dust, then everything will be over. If the laws of thermodynamics as we see them are universally valid, then there appears to be no way of escaping this "entropy death" of the universe. It will be a long time in coming, but is inevitable.