Tag Archives: perpetual motion

Cosmic heat death

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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.

Sources:

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

Dream machine

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Painting by Katy Gibson

Painting by Katy Gibson

A machine that can do work indefinitely without any external input of energy.  It would solve the world’s energy problems, eliminate global warming and make the inventor very rich.  There have been so many attempts to design such a machine that a classification system has been established.  My machine, that does work indefinitely with no energy input, would be a perpetual motion machine of the first type because energy is not conserved – a contradiction of the first law of thermodynamics.  The second type contravene the second law of thermodynamics, usually by spontaneously converting heat into work, and the third type eliminates friction and, or other dissipative forces.

I said ‘my machine’ in the sense that I have an on-going sporadic correspondence with the inventor of a machine that is claimed to produce ‘power above the primary power that drives it’.  It is an epistemic impossibility, which means that it cannot exist within our current understanding of the real world.  In other words, if a perpetual motion machine was to be proven to exist then the laws of thermodynamics would have to be rewritten.  This would probably lead to an invitation to Stockholm to collect a Nobel prize.

Such arguments make no difference to inventors of perpetual motion machines.  Many appear to start from the premise that the laws of thermodynamics have not been proven and hence they must not be universally applicable, i.e. there is space for their invention.  Whereas the laws of thermodynamics form part of our current understanding of the world because no one has demonstrated their falsity despite many attempts over the last two hundred years.  This is consistent with the philosophical ideas introduced by Karl Popper in the middle of the last century.  He proposed that a hypothesis cannot be proven to be correct using observational evidence but its falsity can be demonstrated.

So, inventors need to build and demonstrate their perpetual motion machines in order to falsify the relevant law of science.  At this stage money as an input usually becomes an issue rather than energy!

 

The painting by Katy Gibson is from a series made as part from an art and engine collaboration between Okemos High School Art Program and the Department of Mechanical Engineering at Michigan State University.