Recommended by a friend of a friend who’s a working physicist. One experiment, two hundred years. Shine light through two slits and it makes an interference pattern, like waves. Fire it one particle at a time and the pattern still builds up, which means each particle went through both. Watch to see which slit it used and the pattern disappears. Ananthaswamy builds the whole book on that, running from Young in 1801 to labs firing molecules of eight hundred atoms and getting the same result. Around it, he lays out what people think it means — Copenhagen, many worlds, pilot waves, collapse — without picking a winner, because nobody has. Almost no math, which means even I can understand it. Mostly.
Through Two Doors at Once