Yesterday was Erwin Schrödinger’s birthday, as those of you who actually visit the Google home page would have noticed.
This auspicious event nudged me (a day late, admittedly) to do something I’ve been contemplating for a while now — explain the basic ideas of quantum mechanics the best way I know how, at an accessible level (no equations) but without any frustrating length limitations. Sure, you can do pretty well in just five words, but sometimes you need to be a little more expansive.
Fortunately, very little work was required, since I’ve already done it! This is what happens when you write popular books on physics. Depending on the subject, one of the early chapters is guaranteed to be an overview of either quantum mechanics or general relativity. When I wrote From Eternity to Here, I fooled everybody with an unprecedented step: I put my intro to QM late in the book, in Chapter 11. (The intro to GR was, admittedly, Chapter 5.)
I tried hard in that chapter to do justice to the important ideas of quantum mechanics — superpositions, entanglement, measurement, decoherence, probabilities — without getting bogged down in technical details. I glossed over the fact that amplitudes are complex numbers, although I certainly emphasized that they can be negative as well as positive. It laid some groundwork for the rest of the book, but that chapter itself didn’t really talk about (or rely on previous discussion of) entropy, cosmology, or the arrow of time.
So I’ve simply made it into its own web page, here freely available to all:
It’s about 13,000 words — there’s a lot to explain. But now I have somewhere to point to if someone wants to know the basics.
Of course, physicists famously don’t quite agree about what quantum mechanics actually says. Naturally, I’m giving the version I think is right. At the end I try to distinguish what everyone agrees on from what is still conjectural, but this is certainly not the place to go for an overview of all the different interpretations. It’s just the particular view of one cheerful psi-ontologist.