They could create a plethora of pet universes, vastly outnumbering the real cosmos. This thought led philosopher Nick Bostrom at the University of Oxford to conclude in 2003 that it makes more sense to bet that we’re delusional silicon-based artificial intelligences in one of these many forgeries, rather than carbon-based organisms in the genuine universe. Since there seemed no way to tell the difference between the two possibilities, however, bookmakers did not have to lose sleep working out the precise odds.

Learning the Truth

That changed in 2007 when John D. Barrow, professor of mathematical sciences at Cambridge University, suggested that an imperfect simulation of reality would contain detectable glitches. Just like your computer, the universe’s operating system would need updates to keep working. 

As the simulation degrades, Barrow suggested, we might see aspects of nature that are supposed to be static — such as the speed of light or the fine-structure constant that describes the strength of the electromagnetic force — inexplicably drift from their “constant” values. 

Last year, Beane and colleagues suggested a more concrete test of the simulation hypothesis. Most physicists assume that space is smooth and extends out infinitely. But physicists modeling the early universe cannot easily re-create a perfectly smooth background to house their atoms, stars and galaxies. Instead, they build up their simulated space from a lattice, or grid, just as television images are made up from multiple pixels. 

The team calculated that the motion of particles within their simulation, and thus their energy, is related to the distance between the points of the lattice: the smaller the grid size, the higher the energy particles can have. That means that if our universe is a simulation, we’ll observe a maximum energy amount for the fastest particles. And as it happens, astronomers have noticed that cosmic rays, high-speed particles that originate in far-flung galaxies, always arrive at Earth with a specific maximum energy of about 1020 electron volts.

The simulation’s lattice has another observable effect that astronomers could pick up. If space is continuous, then there is no underlying grid that guides the direction of cosmic rays — they should come in from every direction equally. If we live in a simulation based on a lattice, however, the team has calculated that we wouldn’t see this even distribution. If physicists do see an uneven distribution, it would be a tough result to explain if the cosmos were real.

Astronomers need much more cosmic ray data to answer this one way or another. For Beane, either outcome would be fine. “Learning we live in a simulation would make no more difference to my life than believing that the universe was seeded at the Big Bang,” he says. But that’s because Beane imagines the simulators as driven purely to understand the cosmos, with no desire to interfere with their simulations. 

Unfortunately, our almighty simulators may instead have programmed us into a universe-size reality show — and are capable of manipulating the rules of the game, purely for their entertainment. In that case, maybe our best strategy is to lead lives that amuse our audience, in the hope that our simulator-gods will resurrect us in the afterlife of next-generation simulations. 

The weird consequences would not end there. Our simulators may be simulations themselves — just one rabbit hole within a linked series, each with different fundamental physical laws. “If we’re indeed a simulation, then that would be a logical possibility, that what we’re measuring aren’t really the laws of nature, they’re some sort of attempt at some sort of artificial law that the simulators have come up with. That’s a depressing thought!” says Beane.

This cosmic ray test may help reveal whether we are just lines of code in an artificial Matrix, where the established rules of physics may be bent, or even broken. But if learning that truth means accepting that you may never know for sure what’s real — including yourself — would you want to know? 

There is no turning back, Neo: Do you take the blue pill, or the red pill?

The Matrix Revealed

Tantalizingly, just weeks before The Matrix came out in 1999, astronomers analyzing the light from distant galaxies published hints that the universe’s “constants” might not be so constant. Specifically, they found that the value of the fine-structure constant — which determines how the galaxies’ light should appear — is one thousandth of a percent bigger today than it was 10 billion years ago. 

Glitches caused by our simulation being patched up could also be at the root of truly bizarre results that defy the normal rules of physics. One such possible effect appeared in 2011, when physicists working on the OPERA experiment in Europe made headlines as they claimed to have measured subatomic particles called neutrinos traveling faster than the speed of light, considered the universal speed limit. 

Unfortunately, neither case proved a slam-dunk for a virtual universe. Independent tests could not back up the fine-structure constant data, and the speedy neutrinos turned out to be due to a faulty experimental setup. But there is a more fantastical explanation: These inconstant-constants may have instead been simulation glitches, glimpsed just before our programmers fixed them.

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