Day 11: Laplace's Demon

In 1814, Pierre-Simon Laplace wrote this, in "A Philosophical Essay on Probabilities":

We may regard the present state of the universe as the effect of its past and the cause of its future. An intellect which at a certain moment would know all forces that set nature in motion, and all positions of all items of which nature is composed, if this intellect were also vast enough to submit these data to analysis, it would embrace in a single formula the movements of the greatest bodies of the universe and those of the tiniest atom; for such an intellect nothing would be uncertain and the future just like the past would be present before its eyes.


For reasons I've not yet fathomed, these sentences, or at least the encompassing intelligence so described, have come to be known as "Laplace's Demon." This reaching for the most profound certainty, for "a single formula" that would collapse time—"future just like the past would be present before its eyes"—and reveal the universe's first causes, could not be informed in 1814 by what physicists now understand, at least those who adhere to the Copenhagen interpretation of quantum physics—that when you ascertain "all forces" of "the tiniest atom," you render yourself unable to know "all positions of all items." And the converse: ascertain the positions and the forces become unknowable.

How's that for a demon?

For the second time in three days, I find myself back to James Gleick and The Information. Gleick notes Laplace and his demon of a thought experiment, and draws in Alan Turing. Turing saw the possibility of creating Laplace's supreme intelligence within the deterministic confines of a computational machine, but not in the universe. Why? In 1950, Turing wrote:

The system of the "universe as a whole" is such that quite small events in initial conditions can have an overwhelming effect at a later time. The displacement of a single electron by a billionth of a centimeter at one moment might make the difference between a man being killed by an avalanche a year later, or escaping.

The impossibility of Laplace's deterministic demon that can know all and understand all and plot the course of all, is the crack in the vessel that lets the artist in. It is the microspace in which the poet or the singer or the painter can say well, perhaps this, and a new universe is born.