Right at this very moment, scientists are working on realistic simulations of our universe. What if, at some point, a simulation gets so good that it gives rise to our solar system, our planet, and our species? Even more interesting, what if that’s already happened and we’re living in that very simulation? Many popular figures think this isn’t just possible, but likely, while others say it’s next to impossible. Who’s right?
Cosmos Ex Machina
The most popular argument for what’s known as the simulation hypothesis came from University of Oxford philosopher Nick Bostrom. In a 2003 paper, he put it this way: “If there were a substantial chance that our civilization will ever get to the posthuman stage and run many ancestor‐simulations, then how come you are not living in such a simulation?” He followed that up with a Fermi-paradox-esque formula laying out the likely number of all “observers with human-type experiences” — people like you and me — based on the number of civilizations that survive to reach a “posthuman” stage, the number of simulations those civilizations would run, and the number of actual people that lived in one of those civilizations.
Proponents say that it’s more than just a matter of probability. The laws of physics don’t seem that different from code in a program, according to some, and it’s likely that with enough time, a sufficiently advanced civilization could crunch the numbers and produce a simulation that mimics the existence and behavior of every particle in our universe.
MIT cosmologist Max Tegmark is one of those proponents. “If you look at how these quarks move around, the rules are entirely mathematical as far as we can tell,” he said at the 2016 Isaac Asimov Memorial Debate on the topic. “If I were a character in a computer game … I would also discover eventually that the rules seemed completely rigid and mathematical. I would just be discovering the computer program in which it was written. So, that kind of begs the question: How can I be sure that this mathematical reality isn’t actually some kind of game or simulation?”
But others are staunchly against the idea — theoretical physicist Sabine Hossenfelder, for one. In March of 2017, she published a post on her blog Backreaction plainly titled, “No, we probably don’t live in a computer simulation.”“Among physicists, the simulation hypothesis is not popular and that’s for a good reason — we know that it is difficult to find consistent explanations for our observations,” she wrote. “After all, finding consistent explanations is what we get paid to do.”
Once you start digging into the details, Hossenfelder says, the hypothesis falls apart. If the universe is a computer simulation, then it must be made of bits like any computer program. But what kind of bits? Classical physics (the physics of the big) and quantum mechanics (the physics of the small) don’t play well together in our universe. If you use bits that work on classical physics, they won’t produce quantum effects. You’d have to use quantum bits, or qubits. In fact, Perimeter Institute physicist Xiao-Gang Wen has tried doing that exact thing to model the universe, but his models don’t jibe with Einstein’s theory of relativity.
“Our presently best theories are the standard model and general relativity, and whatever other explanation you have for our observations must first be able to reproduce these theories’ achievements,” Hossenfelder concludes. “‘The programmer did it’ isn’t science. It’s not even pseudoscience. It’s just words.”
That might be the biggest problem with the simulation hypothesis: It’s not actually possible to prove it wrong, and that puts it outside of the realm of science. “We’re certainly not going to get conclusive experimental proof that you’re not in a simulation,” NYU philosophy professor David Chalmers said at the 2016 debate. “Because any evidence that we could ever get could be simulated.”
Even some who disagree with Hossenfelder agree on this point. “… I agree with Sabine insofar as she argues that the simulation hypothesis is lazy,” theoretical computer scientist Scott Aaronson wrote on his blog at the time. “… it doesn’t pay its rent by doing real explanatory work, doesn’t even engage much with any of the deep things we’ve learned about the physical world.” But Aaronson still thinks it’s possible. “Blame it for being unfalsifiable rather than for being falsified!” he wrote.
If this is all starting to sound a bit more like religion than science, you’re onto something. In that case, perhaps Tegmark’s simulated version of Pascal’s Wager will have some appeal. In the 1600s, French philosopher Blaise Pascal pointed out that it’s in our best interest to behave as if God exists since if he doesn’t exist and you behave as if he does, you don’t lose much — but you lose everything with the alternative. Tegmark said something similar in 2016: “My advice to you is go out there and live really interesting lives and do unexpected things so the simulators don’t shut you down.” There are certainly worse ways to live.
By Ashley Hamer