The title is a slightly vague. By "Why does the world exist?", you might think he was looking for an is-there-a-God? type answer. Nope: more basic. Holt attempts to find out why there is something rather than nothing. But even that question is ripe for misinterpretation. Most people when confronted with that would interpret it as Why is there stuff rather than an empty universe? or What came before the Big Bang? You have to go deeper still. The question is really why is there existence? Empty space is "something". What Holt is talking about is really nothing, not even empty space or time itself. Why is there existence at all?
This question is so far removed from our lives, so abstract, and so impossible to answer that it really is about as purely an intellectual exercise as can be conceived. The practical value is pretty close to zero. In fact I would argue the question cannot be answered by the human mind since every path leads to something-from-nothing philosophical gymnastics and unavoidable logical conflicts. To me this indicates that if there is an answer it is simply beyond the capabilities provided to our minds by the parochial path of our evolution. Interestingly, one of Holt's interviewees, none other than the late novelist John Updike, had reached precisely the same conclusion.
Still, those minds have been bestowed with a healthy dose of intellectual curiosity -- for some of us anyway -- so we indulge. Holt takes us on a journey from Paris to Oxford to Manhattan to Texas and back, where he interviews some of the high-end philosophers and cosmologists who have struggled with this question, along the way pointing out how similar approaches and conclusions have been reached by historical figures, going all the way back to Plato. If nothing else, this book will demonstrate that while our knowledge of the functional features of the universe has expanded astronomically (pun not intended), our answers to the ultimate questions still boil down to the same logical concepts as they have for thousands of years, and they still run into the same problems. The fundamental problem is that either there is a brute fact or infinity, neither of which our minds can comprehend.
A brute fact is, essentially, a thing that just is. It can take many forms: God, the Singularity, Logic, Goodness -- whatever it is called, it is the thing that started it all. It was not caused to exist by anything else, it is just there and that's that. Philosophers call this a contingency problem: a Brute Fact simply is, it is not contingent on anything else for it to happen. Our minds rebel at this because everything we see in the course of our lives, and everything anyone has ever observed, has a cause. It makes no sense to us not to ask, "How did this happen?"
The problem with that is that you then open the door to infinity. If everything was caused by something there is no starting point. Infinity is beyond our comprehension. Everything in our experience, however big or small, reaches a limit. We use the concept of infinity colloquially, but it never actually means infinity. We use it in mathematical equations conceptually, but when we try to apply it to the real world things get unreal straight away. If infinity shows up in your theory in physics, you're dead.
And yet, all this is tangential to the question at hand. We think that if we could figure out the source of existence we could explain why existence exists. There may be a good deal of distance between those answers. So we are pretty far removed from being pretty far removed.
That is not to imply this book is a pointless exercise. (Really, if you purchased a book actually expecting it to tell you the reason for everything, you need to rethink your existence on a more personal level.) But should you read Why Does the World Exist? I give it a qualified Yes. It's blast for anyone who is given to seriously musing about such topics. Holt writes clearly, especially considering the often intricate complexity of the topic, and with just enough irreverence to give the impression he's doing it all with a sly grin. Then he ups his game in the final chapters when it all comes back to a personal level. Still, I'm not sure how it would work out going in totally cold. I've been a reader of pop-sci books for years and tend to spend a lot of time in my own head, which is the only place this topic has much value. Without a least a passing, casual understanding of fundamental ideas like quantum mechanics and a penchant for abstract musing, some of this may sail right by. If you are a very practical person, you can safely pass. But have no doubt, this is a very rewarding read. As Updike says, we may not be able to figure it out, "but who doesn't love the universe."