What is Pascal's demon?

Answer 1

You may have confused Laplace and Pascal - both French mathematicians and philosophers, although Pascal came about a century earlier.

Laplace's Demon is a thought experiment concerning order and chaos in the universe. When I burn a log, I am converting the chemical energy of the log into thermal energy in the smoke. This is a relatively ordered model, because I can predict the change in energy. However, the smoke will never be burnt or reform into a log, and I will have a harder time predicting where the energy will go. Eventually, all of the forms of fuel in the universe, from fossil fuels to the nuclear cores of stars to the sugar burning up inside of you and me will be burnt up, and we won't know how energy will move. This is a chaotic model.

Pierre-Simon Laplace proposed the following question: What if there was a demon (or angel or god or scientist or pastry chef, it doesn't really matter) who knew the position of every atom in the universe? If he knew where the carbon atom was in a log that was burning, he'd be able to predict that it would form carbon dioxide in the smoke, because it's an ordered model. If he knew where an oxygen atom was getting closer and closer to two hydrogen atoms, he'd be able to predict that it was about to form water. Conversely, if he knew the speed a water molecule was traveling, he'd be able to use kinematics (study of motion) to figure out how the atoms were moving before they bonded. He would know where everything was, where everything was going to be, and where everything had been, right?

But because the universe is chaotic and getting more and more chaotic all of the time, thanks to entropy - which is a whole other issue, but in this case it can be simplified and thought of as the tendency for fuel to burn up - Laplace's Demon doesn't always know. He might be able to make a reasonable guess, sure, he wouldn't be able to tell you how smoke moves. The smoke molecules have kinetic energy, and so they have to be moving, but the universe doesn't care which way, and so Laplace's Demon can't help.

That said, our understanding of physics is changing all the time, and many scholars have come forward with a possible pattern in the way smoke moves and so forth. Laplace's Demon will remain relevant as we explore Quantum Mechanics and the movements of the very small and very fast pieces of the universe.

Answer 2

Pascal's demon is a thought experiment by Blaise Pascal that explores the concept of an all-knowing demon that could violate the second law of thermodynamics by sorting molecules in a way that decreases entropy. This hypothetical demon led to discussions on free will, determinism, and the limits of scientific knowledge. It highlights the tension between the deterministic laws of physics and the idea of human agency.