Editing Heat death paradox (section)

==Kelvin's solution==
In February 1862, Lord Kelvin used the existence of the [[Sun]] and the [[star]]s as an empirical proof that the universe has not achieved [[thermodynamic equilibrium]], as entropy production and free work are still possible, and there are temperature differences between objects. [[Helmholtz]] and [[Rankine]] expanded Kelvin's work soon after.<ref name="On the Age of the Sun's Heat"/>
Since there are stars and colder objects, the universe is not in thermodynamic equilibrium, so it cannot be infinitely old.

===Modern cosmology===
The paradox does not arise in the [[Big Bang]] or its successful [[Lambda-CDM]] refinement, which posit that the universe began roughly 13.8 billion years ago, not long enough ago for the universe to have approached thermodynamic equilibrium. Some proposed further refinements, termed [[eternal inflation]], restore Kelvin's idea of unending time in the more complicated form of an eternal, exponentially-expanding multiverse in which mutually-inaccessible baby universes, some of which resemble the universe we inhabit, are continually being born.