So, the semester is over, which means I have a little more time to turn to issues that keep me awake at night. One thing I am trying to do this summer is relearn some facets of quantum mechanics I may have forgotten over the years. In the process I am getting hit over the head, yet again, with how weird the world is at the micro-level. I was thinking that it would be fun to share these little tidbits with the 13.7 community. So today I begin an ongoing series of little posts on what makes quantum mechanics so strange.
Let's start with the most basic fact. On small enough scales, the world, which seems like a seamless whole to us, resolves itself into sand. What I mean is that, ultimately, reality is granular. That is what "quantum" in physics means: "package." To paraphrase Oliver Morsch:
"The photon... is the the quantum of light and as such indivisible: it is the smallest denomination of the currency of nature representing electromagnetic radiation. With a real currency such as the dollar you can, in principle, speak meaningfully of a fraction of a cent (when quoting for instance, stock market prices) although as a physical object it doesn't exist. No so in physics. A photon cannot be divided into anything smaller, period."
What is true of a photon is also true for something like spin. The spin of a particle is quantized. There are only certain values it takes and nothing else. Everything in nature, including energy, motion and space and time comes in discreet chunks. It's as if when, walking from one side of the room to another, you could only appear and disappear from discreet locations as you cross. That is weird.
And it only gets stranger from there.