The notion of irreversibility

"The entropy of the universe tends toward a maximum"

"Within a finite period of time past, the earth must have been, and within a finite period of time to come the earth must again be, unfit for the habitation of man ..."
　

... Rudolf Clausius  (1822-88), German physicist and mathematician, one of the central founders of Thermodynamics. In 1865 he introduced the concept of entropy.