Description: Since the universe is not infinitely old, it cannot be infinite in extent. Formulated in 1862 by Lord Kelvin, Hermann von Helmholtz and William John Macquorn Rankine,[1] the heat death paradox, also known as Clausius' paradox and thermodynamic paradox,[2] is a reductio ad absurdum argument that uses thermodynamics to show the impossibility of an infinitely old universe.