And that the space of all possible wave functions is called the Hilbert Space which may or may not have an infinite number of dimensions (I apologise in advance to any physicists reading this if I have butchered above brief summaries). That this is called decoherence and, according to Everett, means the wave function branches into multiple worlds, representing all the different ways in which such interactions could have played out. Or the fact that parts of the universe interacting (two particles for example) lead to them becoming entangled. Or about Everett’s assertion that the universe can be described by a single wave function, evolving according to the Schrödinger equation. I could write about quantum entanglement and whether or not, depending on which theorem you follow, particles interacting at a distance means that information is travelling faster than light. This was empirically shown by the famous double-slit experiment.

(Actually, that bit I did understand.) I could write of Werner Heisenberg’s uncertainty principle and Niels Bohr’s concept of complementarity: particles have a wave function and you can describe either a particle’s position or its momentum (its velocity), but not both simultaneously. quantum wave functions appear particle-like when observed. Here, particles exist in a superposition of all possible locations and velocities that only take on a single value when we observe them, i.e. I could write about the contrast between classical mechanics where particles have a location and a velocity, and quantum mechanics where these are replaced by a cloud of probability. “Carroll’s opening salvo, and one of the main reasons to write this book, is that physicists do not understand quantum mechanics. I could go ahead and try and summarize the ideas put forward in this book, leaving you with the impression that I understood everything he is talking about. This is where we reach a fork in the road. What is worse, Carroll writes, is that many physicists scoff at the idea of spending time and effort on understanding its foundations.Ĭarroll thinks we have made good progress with this, though, and throughout this book, he champions the Everett or Many-Worlds formulation of quantum mechanics that was developed in 1957 by Hugh Everett. And for a theory that was pretty much formulated by 1927 that is more than a bit embarrassing. They know how to use it to design new technology or predict the outcomes of experiments, but they do not truly understand it.

Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime, written by Sean Carroll, published in Europe by Oneworld Publications in September 2019 (hardback, 368 pages)Ĭarroll’s opening salvo, and one of the main reasons to write this book, is that physicists do not understand quantum mechanics.

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