Elon Musk thinks it's almost certain that we are living in a computer simulation.

In short, we are characters in an advanced version of The Sims — so advanced that it creates, well, us.

I understand the instinct to treat the idea as absurd, and to ignore people who suggest these things. It’s what happens when you challenge the common beliefs about reality, kind of like Aristarchus of Samos, who first thought the Earth wasn't at the center of the universe — almost 2,000 years before Galileo.

But these ideas push us to think more rigorously about what we accept as reality. We are reminded, time and again, that what we see and what we know are quite limited. And we have to devise increasingly clever experiments to see more of the unseen.

This cartoon is about laying down the logic of the simulation argument.

Understand it first, and then dismiss it — or, better yet, don't. It doesn't argue that we are necessarily in a simulation. It just says it's one of three possibilities for the future of humanity.

Oxford University philosopher Nick Bostrom wrote the definitive paper on this, so we're essentially walking through his piece.

Let's go back 40 years!

In the early 1970s, the most advanced game was Pong — two rectangles and a circle, bouncing around.

Fast-forward to 2000, and we have The Sims — animated characters that interact with each other, with objects, and with their own feelings.

Now we have 3D headsets, like the HTC Vive and the Oculus Rift. You are the character, and your body can interact with the simulated world. We've tricked our minds into thinking that pixels are real.

With modern computing, we're also able to forecast weather and simulate how chemicals in our body work, among many other complex things. We’ve come a long way in a short time.

So let's fast-forward 10,000 years!

We went from Pong to headsets that transport our minds into fantasy worlds — in just 40 years. So even if our speed of technological advancement slows down, in 10,000 years we should be able to run simulations of ourselves. (That is, if we're alive, of course. But more on that later.)

It's not just that the graphics will be better or the mechanics will be better. No, it's that we'll be able to simulate the individual synapses in the human brain, much like The Sims kept track of how hungry your character was.

We can simulate these things because, according to scientific evidence, everything that makes us human is physical processes. Presumably we will understand all of it in 10,000 years and then recreate these processes in a computer simulation, much like how we can recreate the way a ball bounces.

So in 10,000 years, computers could simulate the entire world.

(This dome is only a representation of these simulations, which would occur computationally — not inside domes. But it’s a great visual, right?)

And how do we get the computing power for this? Bostrom says we can send tiny robots to other planets, which will self-duplicate and turn the planet into a huge computer.

So if we can build world simulators, we’ll probably simulate our past selves

If we can simulate human worlds, then presumably future humans will run simulations of their ancestors — us!

And because simulating the entire mental history of humans would cost a tiny fraction of future humans' resources, they'll run it again and again — maybe millions or billions of times:

But what if the people in the simulations create their own simulation?

If we've run billions of ancestor simulations, surely a lot of them would reach the stage when they can create their own simulations.

But if we are creating billions of simulated, conscious humans inside a computer — and they have the same capabilities as us — then that means our consciousness is no different from that of our simulated humans.

That means we could be characters in a simulation

In fact, if there are zillions of conscious humans, and far fewer humans living in "base" reality, it's almost likely we are in a simulation right now, as you read this story.

But another possibility: We kill each other before then

The other possibility is that humans go extinct before we reach that stage.

Maybe it's global warming. Maybe it's killer pandas. But Bostrom says the most "natural" interpretation is that we develop a technology that is misused — like self-replicating nanobots that are essentially a mechanical bacteria, which end up killing all life on the planet.

And another possibility: Future humans just don't want to run ancestor simulations

This could be because they find it unethical, since they would have to make conscious simulated humans go through the suffering of, well, life — especially life before their innovations.

Or it’s possible that future humans don't have any desire to run ancestor simulations, because they're more concerned with advancing for pleasure.

So the simulation argument is: One of these things must be true

That means we’ll end up using technology for pleasure and we don't even care about simulating ancestors, we’ll end up killing ourselves, or we’re living in a simulation.

Musk thinks it's almost certain we're in a simulation. Bostrom believes there is about a 20 percent chance that we're in a simulation, but thinks it is subjective.

But both believe one of these three possibilities will happen.

The coolest part of all of this: It helps us ground fascinating conversations, even about the metaphysical

There's a reason Elon Musk and his brother talked about this so much that they had to ban it from the hot tub.

Bostrom, in the introduction to his paper, wrote something beautiful about this argument:

Apart from the interest this thesis may hold for those who are engaged in futuristic speculation, there are also more purely theoretical rewards. The argument provides a stimulus for formulating some methodological and metaphysical questions, and it suggests naturalistic analogies to certain traditional religious conceptions, which some may find amusing or thought-provoking.

If we are in a simulation, then there exists some higher-level being — albeit very different from an all-powerful, benevolent one. But that being is us, or a future version of us.

And that brings up the fascinating question of where base-reality humans come from — the ones not in a simulation.

Perhaps our overlords are still asking the same thing. Perhaps they’re running these ancestor simulations, hoping one of us finds out first.