Overview

Quantum theories are a better approximation to reality than classical physics.

“I’m not happy with all the analyses that go with just classical theory, because nature isn’t classical, dammit”

Richard Feynman

In quantum theories, we no longer describe the trajectories of individual particles but only talk about probabilities that certain events can happen.

So instead of describing the path between some points $A$ and $B$, we ask instead: "What's the probability that a particle which started at $A$ ends up at $B$?".

This idea is rooted in the observation that the only things that are actually important are those that we observe. Whatever happens between two measurements is not important, since we do not measure it. So when we do not measure the position of the particle between $A$ and $B$ it could have taken any path.

While this sounds strange for everyday objects, this is the natural point of view for much tinier particles. We measure the position of a ball whenever we look at it. Such a measurement has no significant effect on the ball.

In contrast, for tiny particles like an electron every measurement has a huge effect on it and hence is important. In addition, we do not measure the electron position permanently but only at certain times.

• Gamifying Quantum Theory by Matthew S. Leifer

History

• Jim Baggott; The Quantum Story
• Robert P. Crease and Charles C. Mann, The Second Creation: Makers of the Revolution in Twentieth-Century Physics
• Abraham Pais, Inward Bound: of Matter and Forces in the Physical World