Reading books about cosmology, there's always that point where you feel a slight shiver going down the backbone. Suddenly you get a glimpse of the consequences of that infinity the author is talking about. Penning down the stuff in his or her most friendly voice reminds you that something can be without a start, without and end. It's all there is, and it's not embedded in something else.
That's the point when they most likely start to talk about the meaning of the word "real". By then it's time to get some coffee to feel a bit better. Unsettling, that's the right word.
Max Tegmark's voice is a pleasant one, and sounds far from unsettling. But his theory from Our Mathematical Universe: My Quest for the Ultimate Nature of Reality (2011) is unsettling all the same. He wants to know what "reality" really is.
His theory is fresh and new, and simultaneously old and very Plato. Tegmark, cosmologist and professor at MIT, thinks the ultimate reality is a mathematical structure. That is: all things fundamental are mathematical in nature. They are abstract without physical baggage, thus defining reality (as we perceive it) as the relation between these mathematical properties. If the mathematical construction is complex enough, things can become self-aware. Like us, Tegmark means. And being self-aware, you construct a picture of everything around you, making it physical in nature.
What's to like about this book? First of all Tegmark himself, mixing hard to grasp concepts with dollops of humor. Mixing ridicule of scientists stuck in the rut of conventionality with self-critic and reflection. After the standard fare, introducing the reader in the wonderful world of cosmology, Tegmark takes a sharp dip into the sea of the mathematical universe theory. During this journey, Tegmark touches on things like "what is consciousness" and "why will we destroy ourselves (maybe)". Not every step of the journey is equally interesting and sometimes a bit disjoint. But in the end, it's all fun to read.
I can talk on about Tegmark postulating his four levels of Multiverse, the blessings of string- and M-theory, the difference between a theory and that which a theory implies to be unavoidable, but the fun is in following his own words without too much prior knowledge. It will lead to moments where you're inclined to become a bit sceptical, but at the same time there are more than enough mild "aha"-moments.
Tegmark is not afraid of some controversy. He's always courteous to his opponents; and they are many. I've read what some staunch critics have said about his theories. Sometimes I wonder if they have read his papers at all. Most of the time I am personally too uninformed in math and cosmology to make any judgement at all. But one thing is important to me: the search for Simplicity Tegmark embarks on.
When physics started to discover the multitude of neutrinos, quarks and gluons, the outlines of the Standard Model of particles and everything that came with it, Richard Feynman once said that he was not convinced we were heading in the right direction. It only became more convoluted, not less. Complexity rose, it didn't disappear, thus a skeptical Feynman.
Tegmark tries to tackle this. He's looking for a theory of everything with unconventional means. What he wants is a bumper sticker, or a print on a T-shirt. He says it might not fit on that T-shirt, but the theory of everything - the Holy Grail his science community is looking for - should fit on a single piece of paper. I like that. No reduction ad absurdum, but a search for a basic structure that makes sense.
Deep inside, humans suspect reality is simplicity. They constantly suspect what the elements of this simplicity are. No wonder, because we're all made from the same simplicity.
Every period in time has its own crude way of trying to describe that simplicity. Tegmark doesn't claim to have the right description for our times. What he does claim (and here he's certainly not alone) is that we need a combination of philosophical and radical concepts combined with hard science to progress to the next description in the future. If we make it there - considering Tegmark's observations about the state of affairs in our world.
It would be a shame if we wouldn't. The sale of bumper stickers and T-shirts would make many of us rich.