An exploration of the thought experiment that seeks to determine whether we're living in a computer simulation.

by Brian Dunning

Filed under Logic & Persuasion

Skeptoid Podcast #622

May 8, 2018

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https://skeptoid.com/audio/skeptoid-4622.mp3

Unless you've been hiding under a rock, you've heard at some point in the past few years that some very smart people believe that we are — or at least, that we are almost certainly — living inside a computer simulation. That your life, as you know it, is not a reality in the physical world, but a fantasy of bits and subroutines and memory locations and semiconductive gates that open and close as electrons race to form your ghostly virtual universe. Today we're going to turn the skeptical eye on the pop-culture fad of belief in "the simulation hypothesis" — the claim that our entire universe is one of countless billions of simulations running somewhere in some transhumanist's godlike supercomputer.

For a long time, people have been requesting this question in a Skeptoid episode. It comes and goes in and out of the news, whenever some celebrity makes a statement asserting that we either do or do not live in a simulation. I've always rebuffed the request, because I found it was not a science question, but purely a philosophical matter, and thus outside of my Skeptoid wheelhouse. But the requests have never slowed, so I'm going to answer with my analysis of why the idea that we live in a simulation is not scientific. We're going to see what extraordinary evidence — if any — supports this extraordinary claim.

The most notable example of a celebrity promoting this idea is Elon Musk, who has gone on record asserting his belief that we almost certainly live in a simulation. His reasoning, which has been around for a long time, is that eventually computers will be able to simulate a realistic world complete with sentient characters; and once computers achieve that, thenceforth there will forever be a countless number of simulated universes. Thus, the chances that this universe you're experiencing right now is the original one, and not one of the countless simulations, is virtually nil. It's about the same likelihood that the lottery ticket you're holding happens to be the winning one.

Given that we're clearly on a trajectory to have games that are indistinguishable from reality... and there would probably be billions of such computers or set-top boxes, it would seem to follow that the odds that we're in base reality is one in billions.

A very different argument in favor of simulation was suggested thousands of years ago in Plato's allegory of the cave. In this thought experiment, prisoners were chained in a cave facing a wall such that all they knew of the world were shadows on the wall from a puppet show behind them. If our ability to perceive is limited by a set of rules, it's safe to assume that much goes on that we can't know about. Of course our perceptions are limited; none of us is omniscient, and much does go on that we can't know about. Thus, we have no reason to suspect that we're not players in a game observed and controlled by others who exist outside our limits. The limits of our perception prohibit us from knowing anything about the nature of this outside world.

Philosophers have debated the simulation hypothesis ever since, and it's been popular in fiction as well; most notably in the 1999 movie The Matrix (and don't forget the 1976 episode of Doctor Who, "The Deadly Assassin", which also featured a universe simulation called the Matrix. But it was Nick Bostrom's 2003 paper "Are You Living in a Computer Simulation?" published in the journal Philosophical Quarterly that broke into the academic mainstream and put the idea into the heads of guys like Elon Musk.

Bostrom's basic assertion was that we're either almost certainly living in a simulation right now, or else such simulations will never exist, because we'll either go extinct first or be interested in other things. He spoke of the human race as eventually reaching the "posthuman" stage, defined as:

...Where humankind has acquired most of the technological capabilities that one can currently show to be consistent with physical laws and with material and energy constraints.

...wherein we could do things like convert entire planets into gigantic computers more powerful than we can scarcely imagine today. In such a world, lives and even the mind would become "substrate independent" — a universe might just as well run on silicon computer chips as on the bricks and mortar and actual matter of the physical universe. Even simulated societies could become posthuman, resulting in an infinite number of levels of simulation: digital turtles all the way down. Astronomer Neil deGrasse Tyson neatly unified Bostrom's idea with Musk's on the Larry King Live show in 2017:

Now you're a character in that world and you think you have free will and you say "I want to invent a computer," so you do. "Hey, I want to create a world in my computer." And then that world creates a world in its computer. And then you have simulations all the way down. So now you lay out all these universes, and throw a dart. Which of these universes are you most likely to hit? The original one that started it, or the countless simulations — the daughter simulations — that unfolded thereafter? You're going to hit one of the simulations.

I am forced to recall Tom Hulce's description of the nature of the universe in the movie Animal House (1978) while sharing a fat spliff with Donald Sutherland:

That means that our whole solar system could be like one tiny atom in the fingernail of some other giant being. That means that one tiny atom in my fingernail could be... ...could be one little tiny universe.

The scene gives an accurate depiction of just how scientific the simulation hypothesis is. I will now give you three reasons why it's not.

1. It's not falsifiable.

Every scientific theory has to be falsifiable — if there's no way to test it in order to prove it wrong, it's not science. More than anything else, this characteristic of the simulated universe hypothesis is what persuaded me that it's pure philosophy and thus outside of Skeptoid's scope.

The idea that we're living in a simulation is what we call a special pleading, an idea that needs no proof because its nature puts it out of reach of our understanding. We can say that we're all living inside a computer simulation, and it is equally valid to say we're all living inside Bozo the Clown's dream. We've all been bonked on the head and are hallucinating our lives. A witch in Khanka, Uzbekistan has brewed a potion, and a big green cloud is steaming out of it, and a whole little civilization exists in that vapor, and we live in that. These are all special pleadings. By their nature, they cannot be disproven, because these civilizations been magicked into existence with the belief that they have always existed. A character in a dream or a magic spell or a hallucination or a simulation has no outside perspective, and so cannot know the limits of his existence. By the very rules of the universes in which these characters live, their universes' natures cannot be falsified.

2. It's not based on any observations.

At its basest level, any scientific theory is an effort to explain an observation — a consistent, replicable observation. An observation is what tells us that there is a phenomenon in need of an explanation for how and why it exists and functions.

Such an observation would be the fabled "glitch in the Matrix" — an error, or an inconsistency, or something suggesting that what we see is not what is. Nowhere do we find an observation that tells us the world as we know it is not the world we know.

On the holodecks in the Star Trek: The Next Generation series, you could live in a simulated universe, but you could always say "Freeze program" to stop the world, or you could say "Arch" to bring up a control panel. These are examples of observations in need of an explanation. In one such episode of the show, the simulated character Dr. Moriarty made these observations, learned their nature, and proved to himself that he was living in a simulation.

Hypotheses are provisional ideas to explain observations. We have never found a Star Trek "arch" to suggest an alternate nature of our world — thus the simulation hypothesis is not a hypothesis, but merely a philosophical thought experiment.

3. It makes no testable predictions.

Moriarty's experience brings us to the core of why the simulation hypothesis is not science. A fundamental requirement of every scientific theory is that it make testable predictions. The theory of gravity predicts how fast a hammer will accelerate when I drop it — and if that test fails, I need to revisit my theory. The simulation hypothesis — and granted, I am blurring the line a bit between hypothesis and theory — makes no such prediction. Moriarty's theory of the holodeck predicted that if he said the word "Arch" a control panel would appear, and also predicted the effects of using that control panel. His tests succeeded every time. The characters in The Matrix understood the workings of their virtual world, and understood the rules governing their interaction with it. The knew how to get in and out of it, and were able to do things (even specific things they had never done before) because they understood its rules. Their theory of the Matrix was nearly as complete as a video game developer's theory of his own game, who knows exactly what will happen given any particular set of inputs.

The simulation hypothesis gives us no testable predictions at all. There is not a single thing we can say like "If this world were a simulation, I could click my heels three times and exit out of the game." We cannot cross our arms, nod our head, and bring up a preferences screen allowing us to change the rules of the simulation. There isn't even anything like "The simulation will run out of power tomorrow at noon, and everything will freeze." And thus, because the theory makes no testable predictions at all, it is by definition not a science question. It is pure philosophy.

These three points make the simulation hypothesis as a science null and void, period, end of discussion. They don't invalidate its value as a philosophical construct, only as a science. You can have all the conversations you want to about consciousness and Descartes and the nature of existence and Transhumanism and the philosophy of mind, but you're not allowed to stray into saying the idea is backed up by science, because it's not. Bostrom's paper even took a deep dive into computer power and the required energy to run simulations, and also came up with equations (not too different from the famous Drake equation giving the probability of extraterrestrial civilizations); and all of this gave the appearance of being based on science. But by the definition of the scientific method, the simulation hypothesis simply does not make the cut. It's a fascinating philosophical question, but a philosophical question nonetheless.



By Brian Dunning

Follow @BrianDunning