"If we are living in a simulation, then the cosmos that we are observing is just a tiny piece of the totality of physical existence."
What if everything around us — the people, the stars overhead, the ground beneath our feet, even our bodies and minds — were an elaborate illusion? What if our world were simply a hyper-realistic simulation, with all of us merely characters in some kind of sophisticated video game?
This, of course, is a familiar concept from science fiction books and films, including the 1999 blockbuster movie "The Matrix." But some physicists and philosophers say it's possible that we really do live in a simulation — even if that means casting aside what we know (or think we know) about the universe and our place in it.
"If we are living in a simulation, then the cosmos that we are observing is just a tiny piece of the totality of physical existence," Oxford philosopher Nick Bostrom said in a 2003 paper that jump-started the conversation about what has come to be known as the simulation hypothesis. "While the world we see is in some sense 'real,' it is not located at the fundamental level of reality."
Simulating worlds and beings
Rizwan Virk, founder of the Massachusetts Institute of Technology's PlayLabs program and author of "The Simulation Hypothesis," is among those who take the simulation hypothesis seriously. He recalls playing a virtual reality game so realistic that he forgot that he was in an empty room with a headset on. That led him to wonder: Are we sure we aren't embedded within a world created by beings more technologically savvy than ourselves?
That question makes sense to Rich Terrile, a computer scientist at NASA's Jet Propulsion Laboratory in Pasadena, California. Detailed as they are, today's best simulations don't involve artificial minds, but Terrile thinks the ability to model sentient beings could soon be within our grasp. "We are within a generation of being those gods who create those universes," he says.
Not everyone is convinced. During a 2016 debate at the American Museum of Natural History in New York City, Harvard University physicist Lisa Randall said the odds that the simulation hypothesis is correct are "effectively zero." For starters, there's no evidence that our world isn't the array of stars and galaxies that it appears to be. And she wonders why advanced beings would bother to simulate Homo sapiens. "Why simulate us? I mean, there are so many things to be simulating," she said. "I don't know why this higher species would want to bother with us."
Echoes of Genesis
Yet, there's a familiar ring to the idea that there's a simulator, or creator, who does care about us. Similarly, the idea of a superior being forging a simulated universe parallels the notion of a deity creating the world — for example, as described in the Book of Genesis.
Some thinkers, including Terrile, welcome the analogy to religion. If the simulation hypothesis is correct, he says, then "there's a creator, an architect — someone who designed the world." It's an ancient idea recast in terms of "mathematics and science rather than just faith."
But for other scholars, including University of Maryland physicist Sylvester James Gates, the similarity between the simulation hypothesis and religious belief should be taken as a warning that we're off track. Science, as he said in a recent radio interview, has taken us "away from this idea that we are puppets" controlled by an unseen entity. The simulation hypothesis, he said, "starts to look like a religion," with a programmer substituting for god.
Who, or what, is the godlike entity that may have created a simulated universe? One possibility, supporters of the simulation hypothesis say, is that it's a race of advanced beings — space aliens. Even more mind-bending is the possibility is that it's our own descendants — "our future selves," as Terrile puts it. That is, humans living hundreds or thousands of years in the future might develop the ability to simulate not only a world like ours but the bodies and minds of the beings within it.
"Just as you can simulate anything else, you can simulate brains," Bostrom says. True, we don't yet have the technology to pull it off, but he says there's no conceptual barrier to it. And once we create brain simulations "sufficiently detailed and accurate," he says, "it is possible that those simulations would generate conscious experiences."
The search for evidence
Will we ever learn whether the simulation hypothesis is correct? Bostrum says there's a remote chance that one day we might encounter a telltale glitch in the simulation. "You could certainly imagine a scenario where a window pops up in front of you, saying, 'You are in a simulation; click here for more information,'" he says. "That would be a knock-down proof."
More realistically, physicists have proposed experiments that could yield evidence that our world is simulated. For example, some have wondered if the world is inherently "smooth," or if, at the smallest scales, it might be made up of discrete "chunks" a bit like the pixels in a digital image. If we determine that the world is "pixelated" in this way, it could be evidence that it was created artificially. A team of American and German physicists have argued that careful measurements of cosmic rays could provide an answer.
What if we did confirm that we were living in a simulation? How would people react upon learning that our world and thoughts and emotions are nothing more than a programmer's zeroes and ones? Some imagine such knowledge would disrupt our lives by upending our sense of purpose and squashing our initiative. Harvard astronomer Abraham Loeb says the knowledge could even trigger social unrest. Knowing that our thoughts and deeds aren't our own could "relieve us from being accountable for our actions," he says. "There is nothing more damaging to our social order than this notion."
Others imagine evidence in support of the simulation hypothesis could engender a new fear — that the creators might grow tired of the simulation and switch it off. But not Bostrum. "You could similarly ask, 'shouldn't we be in perpetual fear of dying?' You could have a heart attack or a stroke at any given point in time, or the roof might fall down," he says.
Whatever we might think of the simulation hypothesis, Bostrom thinks the mere act of pondering it provides a welcome dose of humility. He cites Hamlet's cautionary remark to a friend in Shakespeare's "Hamlet": "There are more things in heaven and earth, Horatio, than are dreamt of in your philosophy."
And Botrum insists that he takes the simulation hypothesis seriously. "For me, it's not just an intellectual game," he says. "It's an attempt to orient myself in the world, as best I can understand it."
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