The author is a former academic physicist with a leaning toward the experimental side of physics, as opposed to the theoretical side. From the preamble:

I know why you’re here.

You know that quantum mechanics is an extraordinarily successful scientific theory, on which much of out modern, tech-obsessed lifestyles depend. . . .You also know that it is completely mad. Its discovery forced open the window on all those comfortable notions we had gathered about physical reality . . . and shoved them out. Although quantum mechanics quite obviously works, it appears to leave us chasing ghosts and phantoms, particles that are waves and waves that are particles, cats that are at once both alive and dead, lots of seemingly spooky goings-on, and a desperate desire to lie down quietly in a darkened room.

But, hold on, if we’re prepared to be a little more specific about what we mean when we talk about “reality” and a little more circumspect about how we think a scientific theory might represent such a reality, then all the mystery goes away [Note: not really] . . . 

But . . . a book that says, “Honestly, there is no mystery” would . . . be completely untrue. For sure we can rid ourselves of all the mystery in quantum mechanics, but only by abandoning any hope of deepening our understanding of nature. We must become content to use the quantum representation simply as a way to perform calculations and make predictions, and we must resist the temptation to ask: But how does nature actually do that? And there lies the rub: for what is the purpose of a scientific theory if not to aid our understanding of the physical world.

. . . The choice we face is a philosophical one. There is absolutely nothing scientifically wrong with a depressingly sane interpretation of quantum mechanics in which there is no mystery. If we choose instead to pull on the loose thread, we are inevitably obliged to take the quantum representation at face value, and interpret its concepts rather more literally. Surprise, surprise, The fabric unravels to give us all those things about the quantum world that we find utterly baffling, and we’re right back where we started.

My purpose in this book is (hopefully) . . . to try to explain what it is about quantum mechanics that forces us to confront this kind of choice, and why this is entirely philosophical in nature. Making different choices leads to different interpretations or even modifications of the quantum representation and its concepts, in what I call . . . the game of theories.

Mr. Baggott follows the usual path that includes the work of Einstein and Niels Bohr and Erwin Schrödinger and ends with various theories of the multiverse. He lost me around page 160 in chapter 7. Up until then, I felt like I was understanding almost everything. Given the nature of quantum mechanics, that probably meant I was deeply confused. After that, my confusion was obvious.

He does make clear how anyone trying to understand the reality behind quantum mechanics, or to “interpret” it, ends up veering into philosophical speculation. His strong preference is for interpretations that can be tested empirically. That’s one reason he’s skeptical about multiverse theories, which don’t seem to be testable at all.

I’m glad I read the book, but I could have jumped from chapter 7 to the Epilogue, which is entitled “I’ve Got a Very Bad Feeling About This”:

I hope I’ve done enough in this book to explain the nature of our dilemma. We can adopt an anti-realist interpretation in which all our conceptual problems vanish, but which obliges us to accept that we’ve reached the limit or our ability to access deeper truths about a reality of things-in-themselves. The anti-realist interpretations tell us that there’s nothing to see here. Of necessity, they offer no hints as to where we might look to gain some new insights of understanding. They are passive; mute witnesses to the inscrutability of nature.

In contrast, the simpler and more palatable realist interpretations based on local or crypto-local hidden variables offered plenty of hints and continue to motivate ever more exquisitely subtle experiments. Alas, the evidence is now quite overwhelming and all but the most stubborn of physicists accept that nature denies us this easy way our. If we prefer a realist interpretation, taking the wavefunction and the conceptual problems this implies at face value, then we’re left with what I can only call a choice between unpalatable evils. We can choose de Broglie-Bohm theory and accept non-local spooky action at a distance. We can choose to add a rather ad hoc spontaneous collapse mechanism and hope for the best. We can choose to involve consciousness in the mix, conflating one seemingly intractable problem with another. Or we can choose Everett, many worlds and the multiverse. . . . 

There may be another way out. I’m pretty confident that quantum mechanics is not the end. Despite its unparalleled success, we know it doesn’t incorporate space and time in the right way [it seems to presume absolute space and absolute simultaneity, not Einstein’s relative spacetime]. . . . It may well be that any theory that transcends quantum mechanics will still be rife with conceptual problems and philosophical conundrums. But it would be nice to discover that, despite appearances to the contrary, there was indeed something more to see here.

That’s the end of the book. 

I got a copy of Quantum Reality after reading a very positive review by another physicist, Sabine Hossenfelder. She said it’s “engagingly written” and requires “no background knowledge in physics”. Maybe not, but a background would help, especially when you get to chapter 7.

I did acquire one idea, which fits with an idea I already had. It seems that the famous two-slit experiment, in which a single photon appears to take multiple paths, has a simple solution. When the photon is sent on its way, it’s a wave. It passes through both slits at the same time. Then, when it hits the screen on the other side of the two slits, it becomes a particle. Maybe this is the de Broglie-Bohm theory referred to above, which implies “spooky action at a distance”. But it sounds plausible to me.

The wave instantaneously becoming a particle seems (to me) to fit with the way entangled particles simultaneously adopt opposing characteristics. One is measured and found to be “up”, which means the other instantly becomes “down”, no matter how far away the two particles are. This suggests that spacetime isn’t fundamental. The distance we perceive as being far too great for two particles to immediately affect each other isn’t the fundamental reality. There’s something going on that’s deeper than spacetime. So the way in which a wave that’s spread out simultaneously disappears, resulting in a single particle hitting a screen, reveals the same thing.

So I feel like I’m making a bit of progress in understanding physics. This is most likely incorrect, but it makes me feel better. Now all I have to do is figure out why physicists claim we couldn’t find the location of the Big Bang. Sure, space is expanding in all directions from the Big Bang, they say, but they deny the universe has a center, where the Big Bang occurred (it would make a great location for a museum and a gift shop). I don’t understand their reasons for saying there is no center.

But one small, confused step at a time.