The Demon of Laplace

South African author Joan De La Haye offers Demon Friday. Surprisingly, it's each Friday and it involves a demon from one grimoire or another. She also greets us as 'freaky darlings', similar to Vampira. Top class!

This is my own take on Demon Friday, except it's not always on Fridays and it doesn't feature real demons or pictures of real demons. Sorry.

These are all my posts on demons:

1. The demon of Laplace, regarding probability.


2. The demon of Maxwell, regarding thermodynamics.


3. The demon of Descartes, designed to invoke skepticism.


4. The demon of Morton, designed to make one aware of confirmation bias.

Inspired by this medieval motley crew, I decided to offer a grimoire of demons closer to my heart. Or perhaps closer to my head.



Pierre-Simon Laplace as captured by the Wikipedia paparazzi.

Laplace's Demon

Pierre-Simon Laplace is famous for being both French and smart simultaneously. In this rare combination, he managed to contribute to the development of mathematics and statistics. His contributions to statistics include an early version of Bayesian analysis.

Laplace was so impressed with the success of statistics and probability to determine guesstimates of the occurrences of events that he proposed the notion of Laplace's demon.

What is Laplace's Demon?

Laplace's demon is a hypothetical creature that - instead of hiding in your broom closet or underneath your bed - knows the exact location and momentum of each atom of the universe. Armed with this knowledge, Laplace claimed that his friendly demon would be able to predict the exact future location and momentum of each atom of the universe. In effect, Laplace's demon would know the past, the present and the future from analysis.



Pierre-Simon Laplace's demon as captured by the Wikipedia paparazzi.

Should we believe in Laplace's Demon?

Heisenberg's uncertainty principle states that there are difficulties with knowing both position and momentum of a body simultaneously. This means that we're stuck with at best half a demon at any given time. Perhaps Laplace's demon may give us the odds, but it can't give us certainty as to the causal outcome of a given event. Laplace's demon may fail due to interpretations of quantum mechanics. A more accurate description of Laplace's demon may then perhaps be Laplace's bookmaker of the universe.