Quantum mechanics is weird. Probably the weirdest part is that it only makes predictions about the probability of what can happen. Newton’s laws say that, with a give force, an object will move this way. Quantum mechanics says that it is probable that it will move a given way, but there is a probability it will move another way. So, with quantum mechanics, we are always dealing with probability. When we measure something, one of the many choices is actually realized. But, this is at the heart of the weirdness: which one?

There are several interpretations of quantum mechanics that try to address this, but they are all, essentially, non-testable hypotheses. One is that all possibilities happen and we are living in one of those potential worlds. That is, whenever a quantum measurement is made, reality splits into different worlds, where each possibility has happened. This is the many-worlds interpretation of quantum mechanics. This splitting occurs whenever there is a measurement of a quantum system. Going even further, the many-minds interpretation says that any time a mind makes a decision, reality splits. It is this interpretation that is at the heart of Blake Crouch’s Dark Matter.

Really, the many-minds view of quantum mechanics is just the backdrop, a vehicle to let Crouch explore ideas about the road not taken. We all have wondered “what if,” what if I had asked that girl out, what if I had gotten that other job, what if that special someone was still alive? We only get one chance at life and we make the best of it. But, what if there was a chance to redo it, to take that untaken road? Crouch’s main character, Jason, had promise as a brilliant physicist. His wife, Dani, was an up and coming star artist. However, they both put those plans aside when Dani becomes pregnant, to raise their son. While both are happy, both also have regrets. What if they had made different choices?

I won’t give away the plot, as there is a lot of daring-do and action to go along with the exploration of these themes. I’ll just say that, in the end, Jason learns a few important lessons:

• And maybe I can let go of the sting and resentment of the path not taken, because the path not taken isn’t just the inverse of who I am. It’s an infinitely branching system that represents all the permutations of my life…
• I thought I appreciated every moment, but sitting here in the cold, I know I took it all for granted. And how could I not? Until everything topples, we have no idea what we actually have, how precariously and perfectly it all hangs together.

Dark Matter uses some out-there physics to explore some fundamental questions of existence, doing so while telling an action packed story that has some really interesting plot twists. Crouch’s approach to writing took inspiration from Michael Crichton: “I realized that he wasn’t just coming up with cool plots. He was writing books that allowed him to explore topics that interested him. Writing a thriller as self-education.” And, by educating himself, Crouch provides a yarn that is both thought-provoking and full of action.