 The single most striking thing I've learned so far in my career as a scientist is that the ultimate nature of reality, whatever it is, is just much weirder than we thought. Much more different from what we thought it was than people in their wildest dreams would have imagined in the past. We used to think, well, there's this stuff, it moves in certain ways, certain properties, and this is solid, this is a bit squishy, this is red. And gradually, I think we've come to the conclusion that all of this is governed by these mathematical rules, which are very much like what you would experience if we were actually inside of a video game. If you were Pac-Man or something and started to study your Pac-Man world, you would discover not only his stuff moving around, it had certain properties, but the things that you first thought had some sort of philosophical, physical nature are all behaving according to simple mathematical rules. You'd be basically rediscovering the source code that the programmer had put in there. And that first sounds kind of nutty when you say it, and in my mathematical universe, the book, I even go as far as saying our universe isn't just described by math, it is mathematical in the sense of being a mathematical structure, by which I mean that our universe doesn't just have some mathematical properties, it has only mathematical properties, much like a computer game. That sounds very nutty, so let's break it down a little bit. If you take an object, this book for example, it seems like it has a lot of very non-mathematical properties, it's sort of bendable and has a paper smell and has different colors. Those don't seem like mathematical properties at all. My mom and many with her think of math basically as a sadistic form of torture that school teachers have invented to make us feel bad about ourselves, or maybe as a bag of tricks for manipulating numbers. But what properties of this book are numbers? Well, there's a three here, but that tells us nothing about the nature of reality. I decided to put it there. But if you look more closely, what you actually have here, seen through my physics eyes, is a big blob of electrons and quarks. And what properties does an electron have? Minus one, one half, one, and so on. And even though we physicists have given these properties nerdy names like the electric charge, the spin, and the lepton number, they're just numbers, right? The only difference between an electron and a quark, as far as we can tell, are what those corresponding numbers are. And in fact, all the particles that make us everything in the world here are described by just different sets of these, these numbers. And space itself, that all of this stuff is in, you know, what properties does space have? Three is the property of space. That's the largest number of fingers I can hold that are all perpendicular to each other. Again, you know, we came up with a nerdy name for this, the dimensionality of space, but it's a number. And Einstein discovered some more properties of space called curvature and topology, which are also things mathematicians study. And if ultimately everything in space, as well as space itself, has only mathematical properties, then it starts to sound a little bit less insane that actually we are just living in this gigantic mathematical object.