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**I**s the Universe Made of Math?

In this excerpt from his new book, Our Mathematical Universe, M.I.T. professor Max Tegmark explores the possibility that math does not just describe the universe, but makes the universe

When we look at reality through the equations of physics, we find that they describe patterns and regularities

**.**But to me, mathematics is more than a window on the outside world: I argue that our physical world not only is

__described__by mathematics, but that it is mathematics: a mathematical structure, to be precise

**.**Image: Max Tegmark

*Excerpted with permission from*Our Mathematical Universe: My Quest for the Ultimate Nature of Reality ,

*by*Max Tegmark

**.**Available from Random House/Knopf. Copyright © 2014**.**
What's the answer to the ultimate question of life, the universe, and everything

**?**In Douglas Adams' science-fiction spoof “The Hitchhiker's Guide to the Galaxy”, the answer was found to be 42; the hardest part turned out to be finding the real question**.**I find it very appropriate that Douglas Adams joked about 42, because mathematics has played a striking role in our growing understanding of our Universe**.**
The Higgs Boson was predicted with the same tool as the planet Neptune and the radio wave: with mathematics

**.**Galileo famously stated that our Universe is a “grand book” written in the language of mathematics**.**So why does our universe seem so mathematical, and what does it mean**?**In my new book “Our Mathematical Universe”, I argue that it means that our universe isn’t just described by math, but that it is math in the sense that we’re all parts of a giant mathematical object, which in turn is part of a multiverse so huge that it makes the other multiverses debated in recent years seem puny in comparison**.****Math, math everywhere**

**!**But where's all this math that we're going on about

**?**Isn't math all about numbers

**?**If you look around right now, you can probably spot a few numbers here and there, for example the page numbers in your latest copy of Scientific American, but these are just symbols invented and printed by people, so they can hardly be said to reflect our Universe being mathematical in any deep way

**.**

Because of our education system, many people equate mathematics with arithmetic

**.**Yet mathematicians study abstract structures far more diverse than numbers, including geometric shapes**.**Do you see any geometric patterns or shapes around you**?**Here again, human-made designs like the rectangular shape of this book don't count**.**But try throwing a pebble and watch the beautiful shape that nature makes for its trajectory**!**The trajectories of anything you throw have the same shape, called an upside-down parabola**.**When we observe how things move around in orbits in space, we discover another recurring shape: the ellipse**.**Moreover, these two shapes are related: the tip of a very elongated ellipse is shaped almost exactly like a parabola, so in fact, all of these trajectories are simply parts of ellipses**.**
We humans have gradually discovered many additional recurring shapes and patterns in nature, involving not only motion and gravity, but also areas as disparate as electricity, magnetism, light, heat, chemistry, radioactivity, and subatomic particles

**.**These patterns are summarized by what we call our laws of physics**.**Just as the shape of an ellipse, all these laws can be described using mathematical equations**.**
Equations aren't the only hints of mathematics that are built into nature: there are also numbers

As opposed to human creations like the page numbers in this book, I'm now talking about numbers that are basic properties of our physical reality

**.**As opposed to human creations like the page numbers in this book, I'm now talking about numbers that are basic properties of our physical reality

**.**For example, how many pencils can you arrange so that they're all perpendicular (at 90 degrees) to each other**?**3 – by placing them along the 3 edges emanating from a corner of your room, say**.**Where did that number 3 come sailing in from? We call this number the dimensionality of our space, but why are there 3 dimensions rather than 4 or 2 or 42**?**And why are there, as far as we can tell, exactly 6 kinds of quarks in our Universe**?**There are also numbers encoded in nature that require decimals to write out – for example, the proton about 1836**.**15267 times heavier than the electron. From just 32 such numbers, we physicists can in principle compute every other physical constant ever measured**.****In this excerpt from his new book, Our Mathematical Universe, M.I.T. professor Max Tegmark explores the possibility that math does not just describe the universe, but makes the universe**

There's something very mathematical about our Universe, and that the more carefully we look, the more math we seem to find

**.**So what do we make of all these hints of mathematics in our physical world**?**Most of my physics colleagues take them to mean that nature is for some reason described by mathematics, at least approximately, and leave it at that**.**But I'm convinced that there's more to it, and let's see if it makes more sense to you than to that professor who said it would ruin my career**.****The mathematical universe hypothesis**

I was quite fascinated by all these mathematical clues back in grad school

**.**One Berkeley evening in 1990, while my friend Bill Poirier and I were sitting around speculating about the ultimate nature of reality, I suddenly had an idea for what it all meant: that our reality isn't just described by mathematics – it is mathematics, in a very specific sense

**.**Not just aspects of it, but all of it, including you

**.**

My starting assumption, the external reality hypothesis, states that there exists an external physical reality completely independent of us humans

**.**When we derive the consequences of a theory, we introduce new concepts and words for them, such as “protons”, “atoms”, “molecules”, “cells” and “stars”, because they're convenient**.**It's important to remember, however, that it's we humans who create these concepts; in principle, everything could be calculated without this baggage**.**
But if we assume that reality exists independently of humans, then for a description to be complete, it must also be well-defined according to non-human entities – aliens or supercomputers, say – that lack any understanding of human concepts

**.**That brings us to the Mathematical Universe Hypothesis, which states that our external physical reality is a mathematical structure**.**
For example, suppose a basketball trajectory is that of a beautiful buzzer-beater that wins you the game, and that you later want to describe what it looked like to a friend

**.**Since the ball is made of elementary particles (quarks and electrons), you could in principle describe its motion without making any reference to basketballs:
Particle 1 moves in a parabola

Particle 2 moves in a parabola

…

Particle 138,314,159,265,358,979,323,846,264 moves in a parabola

**.**Particle 2 moves in a parabola

**.**…

Particle 138,314,159,265,358,979,323,846,264 moves in a parabola

**.**
That would be slightly inconvenient, however, because it would take you longer than the age of our Universe to say it

The ball was designed by humans, but it's quite analogous for composite objects that aren't man-made, such as molecules, rocks and stars: inventing words for them is convenient both for saving time, and for providing concepts in terms of which to understand the world more intuitively

**.**It would also be redundant, since all the particles are stuck together and move as a single unit**.**That's why we humans have invented a word “ball” to refer to the entire unit, enabling us to save time by simply describing the motion of the whole unit once and for all**.**The ball was designed by humans, but it's quite analogous for composite objects that aren't man-made, such as molecules, rocks and stars: inventing words for them is convenient both for saving time, and for providing concepts in terms of which to understand the world more intuitively

**.**Although useful, such words are all optional baggage**.**
All of this begs the question: is it actually possible to find such a description of the external reality that involves no baggage

**?**If so, such a description of objects in this external reality and the relations between them would have to be completely abstract, forcing any words or symbols to be mere labels with no preconceived meanings whatsoever**.**Instead, the only properties of these entities would be those embodied by the relations between them**.**
To answer this question, we need to take a closer look at mathematics

**.**To a modern logician, a mathematical structure is precisely this: a set of abstract entities with relations between them**.**This is in stark contrast to the way most of us first perceive mathematics – either as a sadistic form of punishment, or as a bag of tricks for manipulating numbers**.**
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