Friday, January 13, 2017

Humphrey Potter and the Ghost in the Machine

Humphrey Potter adds strings to Mr Newcomen's engine so that he can go play.
The first steam engines were slow-working beasts that needed constant human tending. To work its minutes-long cycle, the first Newcomen steam engine needed a human hand to open and close valves for cold water and steam. The machine provided great power, but someone had to control it.

At some point, however, some brilliant mechanical mind noticed that the machine was, after all, creating its own motion. Why not connect the moving piston to the valves, and let the engine run itself?

Some sources even claim to identify the person who first made this brainstorm work: a young boy named Humphrey Potter, who was paid to operate a Newcomen engine by hand. Young Potter hooked up a system of “strings and latches” that made the machine itself do his work for him. Then he ran off to play.

Apparently the sources for this story are not considered reliable. I can’t find any of them myself, and the modern texts that mention Humphrey Potter refer to his story as a legend. That’s a shame, because I’d like to think I could put a name to the person who first made a useful engine run all by itself. 

Apart from the practical advantages of getting a machine to run itself, the scientific point of lazy Potter’s clever trick is that it took any form of intelligence out of the loop of doing work. The entire engine process, from fuel combustion to pumping water, was now a purely mechanical operation. Humphrey Potter banished the ghost from the machine. He made it clear that everything that was occurring, in the marvelous process that turned lumps of coal into useful work, was occurring strictly under the basic laws of physics. It all ran all by itself.

In one way we take this insight for granted now, and may even extend it to processes more complex than lifting weight by burning coal, processes like life and consciousness. Yet in a very practical sense science still has not fully taken the point that engines can run as closed systems, without external power or control, and without any ingredients beyond basic physics. Engineers invoke higher level concepts like pressure and temperature, and while these are clearly valid, they leave a lot of details hidden under the hood. Theoretical physicists analyze parts of the whole process, like how gas particles adapt their motion when a piston moves in a predetermined way, but they do not simultaneously consider how the piston motion is itself determined by the gas particles bouncing off it. We don’t really believe there is any ghost in the machine, but when we have to explain how the machine works, somehow we keep sneaking the ghost back in, in some form or other.

If there's something strange
in your phase space neighborhood ...
At least, until now. Quite recently we have discovered a very simple mathematical model for a minimal kind of combustion engine, that runs as a closed system under basic physics. So we now have a bare-metal, first-principles model for an engine. Its operation is in some ways very reminiscent of a steam engine, but in other ways it is radically different. We are hoping that it may teach us about the microscopic roots of thermodynamics, but someday, perhaps, it might be the basis of a whole new class of power nanotechnology.

Readers who know Hamiltonian mechanics may enjoy our first paper on this subject. "Hamiltonian analogs of combustion engines: A systematic exception to adiabatic decoupling" is published in Physical Review E 94, 042127 (2016), and is also available in e-print form at