We all know that quantum physics is wacky. Yet, our equations are able to make extremely precise predictions. The Higgs boson is a perfect example. We should be proud of that. Although, there is one major problem. Do we understand what quantum mechanics are fundamentally? This is the question that Carroll attempts to answer in his book. He argues that this slightly philosophical area of research is drastically under-appreciated and lacks funding. He also argues that we live in many universes at once…
Let me explain. Our common understanding of quantum mechanics is the Copenhagen interpretation. It was devised mainly by Heisenberg and Born in the 1920s. Its main postulates are that everything is probabilistic and that there is an arbitrary boundary between the ‘classical’ and ‘quantum’ realms. Sean Carroll writes that this is quite a shaky set of ideas. Even Einstein would agree with his famous “God doesn’t play dice”.
The author proposes that the Everettian interpretation of quantum mechanics is the right way to look at the world. The only postulate of this theory is that everything is a smoothly evolving wave function with solutions given by the Schrodinger equation. Particles arise from collapses of the wave function in fields. I won’t get into the details too much because Carroll does a way better job at that.
You might be wondering: how does this theory interpret uncertainty in measurements? A random electron in space has a 50/50 chance to be either spin-up or spin-down. When the system interacts with an observer, the wave function collapses and we observe either outcome. Here is the cool part. The Everettian interpretation states that when we observe a quantum event, we create two copies of the universe. In one of them the electron is measured to be spin-up, in the other it is spin-down. The world can’t interact with one another, so we never see them manifested in “our” universe. This seems unfalsifiable, but Carroll tries to convince the reader that this is a straightforward prediction arising from a simple postulate. Although, it’s tremendously difficult to grasp it philosophically. This is called the many-worlds interpretation of quantum mechanics.
This book is fantastic. It solely revolves around the argument I just presented, but it goes in depth into other theories such as hidden variables, and gives a great background. The Socratic dialogue between father and daughter is an awesome narrative device for addressing a lot of the concerns with the theory. Although, I have to mention that this shouldn’t be your first book about quantum mechanics. Sometimes Carroll commits huge conceptual leaps, which can be hard to follow. Overall, it’s a phenomenal read on the boundary of philosophy and physics.