Cosmic heat death

MSUSpartans_Logo.svgWhen I was at Michigan State University, Lou Anna Simon, the President was fond of talking about constructive tension as a source of innovation and progress. In other words, creative or productive work arises out of differences, for instance between aspirations and reality, or between supply and demand.  Rudolf Clausius in the 1850’s identified the irreversibility of heat flow across a temperature difference from hot to cold [see last week’s post on ‘Why is thermodynamics so hard?].  Sadi Carnot worked out the productivity of this difference in terms of the maximum efficiency with which work could be extracted from it [see my post ‘Impossible perfection‘ on June 5th, 2013].

William Thomson [1827-1907] followed a much more sinister line of thought and concluded that if all heat flows from hot to cold then eventually everything must end up at a uniform temperature, i.e. no differences.  He argued that no temperature differences implies no work could be extracted.  And nothing at all happens.  This is known as ‘cosmic heat death’.

A fellow Scotsman, James Clerk Maxwell [1831-1879] believed that this challenged human free will.  He proposed a loophole in the second law of thermodynamics to demonstrate its falsity and invalidate the cosmic heat death argument.  Imagine Maxwell’s demon, as it became known, controlling a trapdoor separating two clouds of gas initially at the same temperature, which means the gas molecules in the two clouds have the same average internal energy.  The demon allows ‘hot’ molecules (i.e. those with higher than average internal energy) to one pass way through the trapdoor and ‘cold’ molecules (i.e. those with lower than average internal energy) to move the other way. After a period of time, all the ‘hot’ molecules will be on one side of the trapdoor and all the ‘cold’ molecules will be on the other side.  Heat has moved from colder (initial average temperature) to hotter (on one side of the trapdoor) and the second law has been contravened.

Maxwell created hope for the inventors of perpetual motion machines! [see my post entitled ‘Dream machine‘ on February 4th , 2015]  But then along came Leó Szilárd in 1929, who pointed out that the demon would have to expend energy [do work] to identify the internal energy of the molecules and to open the trap-door.  The second law was saved and cosmic heat death became a prospect once again although a very, very distant one.  Some modern physicists, though not Professor Brian Cox, reject the possibility of cosmic heat death by suggesting that the universe is too complex and our understanding too incomplete to allow Thomson’s simple reasoning to be applied.  John Updike protested against the idea in his poem ‘Ode to Entropy‘.  And on a human timescale, it is hard to believe that all tensions will ever be resolved.


Ball, P., A demon-haunted theory, Physics World, April, 2013, p.36-9

Updike, J., ‘Ode to Entropy‘ available in the Faber Book of Science edited by John Carey 2005

Cox, B., Death of the Universe, World Space Week Special BBC Wonders of the Universe, 2013

6 thoughts on “Cosmic heat death

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