Which Universe Are We In Again?
When considering the many worlds of the multiverse the picture that probably springs to mind, born of a thousand popular physics documentaries, YouTube videos or books, is of the universes like a sheaf of A4 paper or the pages of a book, all stacked neatly on top of one another, running in parallel, minding their own business until the science communicator sticks a sharp pencil through the stack for some reason. It's not that though. Another common mental model is of a constant bifurcation and splitting so that whenever a decision is made a new universe is created (which seems a bit of a waste if the decision is just about which pair of socks you're going to wear that day). It's not quite that either though. The multiverse is much more like a dark smoke-filled room, a continuum of possibility, probability and particles that simultaneous contains all conceivable universes and sock choices. What you decide doesn't create a universe, it just moves you into that part of the...