Heat death of the universe

The heat death of the universe is a historically suggested ultimate fate of the universe in which the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain processes that consume energy (includingcomputation and life). Heat death does not imply any particular absolute temperature; it only requires that temperature differences or other processes may no longer be exploited to perform work. In the language of physics, this is when the universe reachesthermodynamic equilibrium (maximum entropy). The hypothesis of heat death stems from the ideas of William Thomson, 1st Baron Kelvin, who in the 1850s took the theory of heat as mechanical energy loss in nature (as embodied in the first two laws of thermodynamics) and extrapolated it to larger processes on a universal scale.

Since Kelvin's day, it has been recognized by a respected authority on thermodynamics, Max Planck, that the phrase 'entropy of the universe' has no meaning because it admits of no accurate definition. Kelvin's speculation falls with this recognition.

from Wikipedia