Wait, Probabilities can be Negative?! – A Peek at Quantum Foundations #SoME1

A video for 3Blue1Brown’s Summer of Math Exposition 1. See how thinking about negative probabilities can lead us to deep ideas in quantum theory. 00:00 Introduction 01:27 Example with negative probability 09:09 The Double Slit 13:01 Closing thoughts Corrections: At 2:04, I messed up the conventional notation for conditional probability. It should read “P(1|S),” which means “The probability of event 1 happening given that S happened.” At 5:16, 0.6*0.3=, not . So the final answer should have been instead of . Similarly, at 5:36, the number on the farthest right branch should be , not . Basically, I accidentally switched the numbers coming out of B when I made the slides. This does not affect the main points of the video.