This book works at more than one level, and is for popular science readers and physicists alike. It's about the puzzle of quantum mechanics: is it the mind of the experimenter that causes the change from waves to particles, or could it be something else? For ninety years observations have been thought to do it, but now physicists are starting to think it's something else. In the accompanying 2019 documentary for TV ('The Interactions Avenue'), the author of the book, Jonathan Kerr, talks to two of the world's best known physicists, Carlo Rovelli and Neil Turok. They both belong to the fast growing minority who take the new approach, known as "interactions, not measurements". To measure something, you have to make light or matter collide with it. Experiment has strongly supported the idea that somehow, interactions are what causes the change from waves to particles. The book looks at the different views on these fascinating questions. (Neil Turok was for ten years Director of the Perimeter Institute in Canada, the main hub of theoretical physics.) When people realised that interactions could replace measurements in quantum mechanics, they saw what may be the beginnings of the next paradigm. Now we have a way to leave the mind of the experimenter, and consciousness in general, out of the process completely. So it removes what's known as 'the measurement problem' - it also removes what some would see as the unscientific side of quantum mechanics. Some very good physicists nowadays take the view that measurements were a red herring, and are irrelevant. It's just that until now, no-one has been able to say why interactions should do that. In the later part of the book Jonathan Kerr explains his own theory (which he discusses with Carlo Rovelli and Neil Turok in the film). It's an unexpected, lateral solution to the puzzle, coming out of the interactions approach. It provides a new way of completing what has been, until now, an unfinished picture.