I’ve been running simulations of our universe, according to Stephen Wolfram’s computational theory of physics.
Where’s the computer that runs these simulations?
Well, it’s right here:
This low-powered laptop is literally the computer that runs these universes.
It’s natural to ask a follow-up question.
If Wolfram’s right and the real universe evolves computationally in the same way as these simulated universes, where’s the computer that runs the universe?
It sounds like a simple question, but it’s deceptive.
It’s going to take several articles to dig deeply enough into physics and philosophy to explore possible answers.
I’m going to begin, in this article, with the striking similarities between the question: “Where’s the computer that runs the universe?” and a question that has been asked since the earliest days of physics: “Where’s the mover?”
Before numbers
These days, we’re so used to thinking of physics as being all about the numbers that we forget that the wedding of physics to mathematics is a relatively recent innovation.
Go back more than a few hundred years, and physics wasn’t about the numbers at all.
Just ask Aristotle.
If I’d dropped a stone in Aristotle’s presence, he’d have explained its falling by saying that earth-like things seek their natural place at the centre of the universe, below all water-like, air-like and fire-like things.
Aristotle’s contemporaries wouldn’t have remarked on the lack of numbers in his explanation.
They wouldn’t have countered: “OK, but... How long does the stone take to fall? How fast does it fall?”
Time wasn’t as precise back then. The Ancient Greeks didn’t have stopwatches. Without precision instruments, it didn’t make much sense to ask about the time it takes for the stone to fall, let alone its speed. Try timing the fall of a stone with a sundial.
Instead, Aristotle’s contemporaries might have asked: “OK, but... Who’s making the stone fall? If I move a stone from one place to another, I know who’s making the stone move, I know who the mover is: it’s me! But when I drop a stone, who’s making it move downwards, towards its natural place at the centre of the universe? Who’s the mover?”
It’s a natural question to ask.
Except...
It implies that there’s a whole other universe beyond the one we observe.
It imagines an invisible universe inhabited by a God-like mover of stones, beyond the visible universe in which stones fall.
Why would the Ancient Greeks dream into existence a whole other universe that can’t be observed?
Well, because of an analogy with their world.
In their world, a stone didn’t move unless someone or something moved it.
If a stone’s on the ground, you can sit and watch it all day, and it isn’t going to move, unless someone or something moves it.
By analogy, if you drop a stone, it moves downwards, so there must be someone or something moving it.
By analogy with their world, the Ancient Greeks might have imagined someone – God, or a pantheon of gods – or something – a force, or a purpose – moving the stone downwards.
Because of this analogy with their world, the Ancient Greeks might have dreamt into existence a whole other universe of gods and goals that can’t be observed.
And the reason it can’t be observed might just be that it doesn’t exist.
Do the math
A few hundred years ago, Galileo brought numbers into physics.
It wasn’t enough, for Galileo, to say that the stone falls. He wanted to know how long it takes to fall and how fast it falls.
Kepler, Leibniz and Newton went further. They invented calculus to describe not only the fall of the stone but the orbits of the planets.
Suddenly, physics was wedded to mathematics. The marriage has lasted, for better or for worse, to the present day.
Galileo found, by rolling a bronze ball down a wooden ramp, that the ball’s speed increased by equal amounts in equal time intervals.
(Rolling a ball down a ramp is the same, mathematically, as dropping a stone; the ramp just slows down the motion. And since Galileo didn’t have a stopwatch, either, it was important to slow down the motion to make it easier measure with his water clocks.)
So if the ball, released from at the top of the ramp, increased its speed to 2 feet per second after 1 second, it would increase its speed by another 2 feet per second after another 1 second, giving a total speed of 4 feet per second after 2 seconds.
I know, I know, that’s way too many numbers in a single sentence.
Here’s the point.
Galileo’s contemporaries wouldn’t have remarked on the lack of executable code in his explanation.
They wouldn’t have countered: “OK, but... How would you simulate that motion in C++?”
Computation wasn’t a thing back then. Renaissance scholars didn’t have computers. Without them, it made no sense to ask about writing an algorithm to model acceleration on an inclined plane. Try executing C++ code with a quill, a pot of ink and a piece of paper.
Instead, Galileo’s contemporaries might have asked: “OK, but... Who’s doing the calculation? Who’s adding the 2 feet per second to 2 feet per second to find the total speed of 4 feet per second? If I do arithmetic – in my head, or with tables, or using an abacus – I know who the calculator is: it’s me! But when I drop a stone, or roll a ball down a ramp, who’s doing the arithmetic? Who’s the calculator?”
Put another way: “Where’s the abacus that does the arithmetic for the universe?”
Come calculus, in the age of Kepler, Leibniz and Newton, the question becomes even more complex: “Who’s solving the differential equations? Who’s performing the indefinite integrals? Who’s doing the calculus?”
It’s a natural question to ask.
Except...
It implies that there’s a whole other universe beyond the one we observe.
It imagines an invisible universe inhabited by a God-like solver of equations, beyond the visible universe in which stones fall and balls roll down ramps.
Why would Renaissance scholars dream into existence a whole other universe that can’t be observed?
Well, because of an analogy with their world.
In their world, numbers didn’t get added unless someone added them, in their head, or with tables, or using an abacus.
By analogy, if you drop a stone, or roll a ball down a ramp, it accelerates according to precise arithmetic, so there must be someone or something adding the numbers.
By analogy with their world, Renaissance scholars might have imagined someone – God, or a cloister of monks – or something – an abacus, or a book of logarithmic tables – doing the arithmetic.
Because of this analogy with their world, Renaissance scholars might have dreamt into existence a whole other universe of celestial monks with abacuses that can’t be observed.
And the reason it can’t be observed might just be that it doesn’t exist.
The computer
You know where I’m going with this.
A few years ago, Stephen Wolfram wedded physics to computation.
His theories are computational.
According to Wolfram, the universe is a graph of nodes and edges. The rules that determine what happens to the universe are simple. You can apply them by drawing a graph with a pencil, erasing the nodes and edges deleted by the rule and drawing in the nodes and edges created by the rule.
But if you want to see how the universe evolves over any appreciable time scale, you’re going to need a computer.
Wolfram’s contemporaries might ask: “OK, but... Who’s doing the computation? Who wrote the C++ code that applies the rule to the graph? Where’s the computer that runs the universe?
It’s a natural question to ask.
Except...
Once again, it implies that there’s a whole other universe beyond the one we observe.
It imagines an invisible universe inhabited by a God-like executor of algorithms, beyond the visible universe in which stones fall, balls roll down ramps and spacecraft visit distant planets.
Why would we dream into existence a whole other universe that can’t be observed?
Well, because of an analogy with our world.
In our world, algorithms don’t get executed unless someone writes the C++ code and runs it on a computer.
By analogy, if, as Stephen Wolfram proposes, our universe evolves according to precise algorithms, there must be someone or something running the code.
By analogy with our world, we might imagine someone – God, or a shared workspace of software developers – or something – a computer, or a server farm – executing the algorithms.
Because of this analogy with our world, we might dream into existence a whole other universe of celestial programmers and computers that can’t be observed.
And the reason it can’t be observed might just be that it doesn’t exist.
Analogize at your own risk
Where’s the computer that runs the universe?
I’m not saying that it doesn’t exist. Indeed, in future articles, I’m going to explore the possibility that it does exist.
I’m just saying that it’s a natural question to ask, and that it’s natural to answer it by analogy with our world.
Maybe there is a pantheon of gods, each with their own goals, who move stones.
Maybe there is a cloister of celestial monks, each with their own abacus, who add numbers and solve equations.
And maybe there is a shared workspace of celestial software developers, each with their own laptop, executing algorithms to apply rules to graphs.
Or maybe we humans are just a little too quick to answer questions about our universe by analogy with our world.