erial world is for motion to become diffused, and that as a whole the reverse of concentration is gradually going on – I believe that no physical action can ever restore the heat emitted from the Sun, and that this source is not inexhaustible; also that the motions of the Earth and other planets are losing vis viva which is converted into heat; and that although some vis viva may be restored for instance to the earth by heat received from the sun, or by other means, that the loss cannot be precisely compensated and I think it probable that it is under-compensated. Compensation would require a creative act or an act possessing similar power, resulting in a rejuvenating universe (as Thomson had previously compared universal heat death to a clock running slower and slower, although he was unsure whether it would eventually reach thermodynamic equilibrium and stop for ever). Thomson also formulated the heat death paradox (Kelvin's paradox) in 1862, which uses the second law of thermodynamics to disprove the possibility of an infinitely old universe; this paradox was later extended by William Rankine. In final publication, Thomson retreated from a radical departure and declared "the whole theory of the motive power of heat is founded on ... two ... propositions, due respecti