What Is Simulation Theory? Are We Living in a Computer Simulation?

What is reality? Simulation theory tackles some heavy questions.

Written by Mike Thomas
What Is Simulation Theory? Are We Living in a Computer Simulation?
Image: Shutterstock / Built In
Brennan Whitfield | Dec 06, 2023

What is reality? Countless brainiacs and psychedelia enthusiasts have pondered that question for centuries, formulating theories that run the gamut from scientific to mystical.

Some outside-the-box thinkers, including philosophers and physicists, posit the answer can be found in simulation theory, which contends it’s possible that reality is merely an ultra-high-tech computer simulation where we sim-work, sim-live, sim-laugh and sim-love.

Simulation Theory Definition

Simulation theory is a theoretical hypothesis that says what people perceive as reality is actually an advanced, hyper-realistic computer simulation, possibly overseen by a higher being.


What Is Simulation Theory?

Simulation theory says that we are all likely living in an extremely powerful computer program, directed by an entity outside of our physical comprehension. In this situation, humans are not necessarily “real” and tangible beings, but instead predetermined, coded constructs of the digital world we inhabit. Living in a simulation can be likened to living in a gigantic game of The Sims, except we ourselves are the characters inside the screen.

If we live in a computer simulation, then who is the programmer? Swedish philosopher Nick Bostrom contends in his 2003 paper that future generations might have mega-computers that can run numerous and detailed simulations of their forebears, in which simulated beings are imbued with a sort of artificial consciousness. Odds are, we are products of that simulation, and we may not be the original species of humans.

“It could be the case,” Bostrom writes, “that the vast majority of minds like ours do not belong to the original race but rather to people simulated by the advanced descendants of an original race. It is then possible to argue that, if this were the case, we would be rational to think that we are likely among the simulated minds rather than among the original biological ones.”

Other philosophers have expanded on Bostrom’s argument. New York University philosophy professor David Chalmers described the higher being responsible for this potential hyper-realistic simulation as a “programmer in the next universe up,” perhaps one we mortals might consider a god of some sort — though not necessarily in the traditional sense. 

“[They] may just be a teenager,” Chalmers said, “hacking on a computer and running five universes in the background … But it might be someone who is nonetheless omniscient, all-knowing and all-powerful about our world.”

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How Would Simulated Reality Work?

For a simulated reality to operate, this could be carried out through one of two notable scenarios.

1. Everything We Know Is Simulated

In the first scenario, this assumes that everything that exists — including every person, environment, object, occurrence and sensation — is a byproduct of code. This scenario would require hardware powerful enough to simulate all of these components and known physics on a highly detailed, intergalactic scale. Reality, in this sense, may be imagined as an elaborate, open-world program that is running on a supercomputer or quantum computer beyond our capable understanding. 


2. The World We Know Is Simulated

In the second scenario, this assumes humans themselves are real and organic, but that the world and a number of people that surround us are simulated. To carry this out, we would have to trick our consciousness into thinking that we are in true reality, in which all sensations feel lifelike and simulated characters mimicking humans are able to pass the Turing Test. Along with powerful computing hardware, this scenario would also require artificial intelligence complex enough to be perceived as real by the human mind.

Simulation theory in this scenario can be illustrated by the movie The Matrix. The film depicts a post-apocalyptic world in which a race of machines have captured most of humanity and imprisoned their minds within an artificial reality known as “the Matrix” in order to harvest humans’ body heat and electrochemical energy. In the film, humans going about their everyday lives didn’t realize they were actually living in a simulation because a cable plugged into their neocortices beamed signals into their brains and read their reactions.

Some ways to achieve that could be through advanced virtual reality (VR) or brain computer interface (BCI) technologies, where VR could display realistic imagery for users or where BCIs could send signals to the brain to stimulate realistic sensory inputs like sight. As for achieving other realistic human characters, we would need to gain a greater understanding of human consciousness and how it works so we can produce conscious AI, Rizwan Virk, a tech entrepreneur and author of The Simulation Hypothesis, told Built In. 

“This,” Virk said, “is coming.”

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Arguments For Simulation Theory

The Multiverse and Virtual Universes

Bostrom argued in his paper that if humans are able to survive thousands of years to reach a “posthuman state” — one in which we have “acquired most of the technological capabilities” consistent with physical laws and material and energy constraints — it’s likely they would have the capabilities to run ancestral simulations.

In a posthuman civilization, Bostrom proposes that machines running simulations could be stacked, in that a simulated machine could simulate another machine. This makes for a possibility of multiple levels of reality, where the number and likelihood of simulated realities would only increase over time.

“Mathematicians have proved that a universal computing machine can create an artificial world that is itself capable of simulating its own world, and so on ad infinitum. In other words, simulations nest inside simulations inside simulations,” wrote cosmologist Paul Davies in 2003. “Because fake worlds can outnumber real ones without restriction, the ‘real’ multiverse would inevitably spawn a vastly greater number of virtual multiverses.”


Technological Limits Have Yet to Be Discovered

“The real question is what are the limits of computing powers,” said astronomer Martin Rees in an interview with Space.com. He continued to explain that “we can have a virtual universe in our computer, and calculate what happens if you crash galaxies together. It’s not crazy to believe that some time in the far future there could be computers which could simulate a fairly large fraction of a world.” Judging by the types of real-world simulations scientists can now run on supercomputers, what might they be able to run in the future as processing power achieves levels we currently can’t fathom?

Even if we’re not at that technological level yet, Virk thinks we will be at some point. There are 10 checkpoints on the road to full-blown simulation, he said, and we’re nearly halfway to our destination. 

Martin Rees - Are We Living in a Simulation? | Video: Closer to Truth

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Arguments Against Simulation Theory 

Simulating Humans Would Be an Odd Choice

In 2016, during the 17th annual Isaac Asimov Panel Debate at New York’s American Museum of Natural History, simulation theory was discussed by a panel of scientific experts that included professor Chalmers, astronomer Neil deGrasse Tyson, University of Maryland physics professor Zohreh Davoudi and Harvard University physicist Lisa Randall.

Randall was the group’s most definitive doubter. Although she allowed for the possibility that nothing is what it seems, including the cognitive process of observation, she also wondered about the judgment of our supposed simulators in choosing humankind for their grand experiment.

“It’s just not based on well-defined probabilities,” Randall said. “The argument says you’d have lots of things that want to simulate us. I actually have a problem with that. We mostly are interested in ourselves. Why simulate us? I mean, there’s so many things to be simulating. … I don’t know why this higher species would want to bother with us.”


Simulating Reality Would Require Too Much Computing Power

With the idea of Bostrom’s “posthuman simulator,” he also wrote that it would need sufficient computing power to keep track of “the detailed believe-states in all human brains at all times.” This would be in order to sense observations (of birds, cars and so on) before they happened and provide simulated detail of whatever was about to be observed. In the event of a simulation breakdown, the director could simply “edit the states of any brains that have become aware of an anomaly before it spoils the simulation. Alternatively, the director could skip back a few seconds and rerun the simulation in a way that avoids the problem.” 

Many argue if we will ever have technology powerful enough to make that possible.

In 2017, physicists Zohar Ringel and Dmitry Kovrizhi published a Science Advances article titled “Quantized gravitational responses, the sign problem, and quantum complexity,” which was widely thought to disprove the simulation theory once and for all by addressing lack of technological capabilities. 

In their work, they proved that a classical computing technique called “quantum Monte Carlo,” used to simulate quantum particles — photons, electrons and other types of particles that comprise the universe — was insufficient to simulate a quantum computer itself, a breakthrough that would negate the need to physically build these next-level machines, which is no easy task. And if it’s impossible to simulate a quantum computer, forget about simulating the universe.

Nonetheless, Ringel appeared to leave the door ever so slightly cracked when he told Popular Mechanics “Who knows what are the computing capabilities of whatever simulates us.”

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The Consequences of Proving Life Is a Simulation

Preston Greene, a philosophy professor at Nanyang Technological University in Singapore, said he thinks we could be living in a simulation right now. But proving as much, he has warned, would be catastrophic.

Tampering With a Greater Experiment

“If our physicists use experiments to prove we live in a simulation, and they tell everyone about this and that has a large effect on how our civilization behaves,” Greene explained, “then our simulation would no longer be useful for answering questions about the basement [foundational] level of reality, which contains the computers doing the simulations.”

Greene continued: “This is because such experimental proofs could never happen on the basement level. So even though there are many possibilities for how our simulators would react to our using experiments to prove we live in a simulation, simulation shutdown is worth taking at least as seriously as anything else, since it is supported by observed trends in simulation science.”


The Simulation Could End

Just as present-day researchers use simulations to digitally create scenarios to aid scientific study — such as what would happen if we eliminated mosquitoes — our world and every moment of our past existence might be the simulated experiment of future humans. And just as scientists can terminate simulations (of earthquakes, weather, etc.) when they no longer provide useful data, so too can our hypothetical overlords pull the plug at any time, without warning. 

But rest assured, Greene said, “It would be a quick and painless death.”


Why Does Simulation Theory Matter?

If we do all live in a simulation, why does any of this matter? What is the purpose of proving or disproving that life as we know it is merely a digital construct and existence simply an immensely complex experiment in someone’s virtual terrarium?

The broad answer, Virk said, is that which all good science pursues: truth. More specifically, our truth. 

If we do in fact exist inside a video game that requires our characters to perform certain quests and achievements in order to progress, Virk posited, wouldn’t it be useful to know what kind of game we’re in to increase our chances of surviving and thriving? 

His answer, not surprisingly, is an unqualified yes.

“I think it would make all the difference in the world.”

Whatever type of world it is.  


Frequently Asked Questions

Simulation theory is a hypothesis proposing that our perceived reality is a powerful computer simulation, possibly created by a higher being.

The theory assumes that either everything we know and that exists is simulated, or that the world we know of is simulated.

A one in three probability that we are living in a simulation is implied by Nick Bostrom in his paper "Are You Living in a Computer Simulation?"

David Chalmers states that there is at least a 25 percent probability of living in a simulation, according to his book Reality+: Virtual Worlds and the Problems of Philosophy.

As simulation theory remains a hypothesis, the probability that we are living in a simulation will vary between professionals.

Rose Velazquez contributed reporting to this story.

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