If we were in a hyper-realistic simulation, à la The Matrix, would it be possible to find out? A team of physicists believes so, and they are trying to fund their experiment with a Kickstarter campaign to find out. Whether it's possible even test this, how, and what are the consequences of finding out are all big questions waiting to be explored.
Simulation Theory, in its most basic form, goes like this: if humans (or another species, for cuteness feel free to imagine it's puppies) continues to advance for hundreds, thousands, or even millions of years, it's a pretty safe bet that we will have a lot of computational power at our finger/paw tips. If we were to expand out into the galaxy (or even further) we may harness the power of stars, or possibly even black holes.
With all this energy and computational power, it's likely that at some point our descendants will be curious enough to run "ancestor simulations", using just a tiny fraction of the computing power available to us.
Ancestor simulations, as put forward by Swedish philosopher and Oxford University Professor Nick Bostrom in his 2003 paper "Are you living in a computer simulation?", is the idea that future generations might have the computing power to run simulations on our forebears, and imbue these simulations with a sort of artificial consciousness. If this has already happened, this would mean the vast majority of people are simulations by the advanced descendants of the original humankind, and if that's the case, it's more rational to assume you are one of the simulations rather than one of the original biological humans.
In his paper, Bostrom proposes three possible scenarios:
1) The fraction of human-level civilizations that reach a stage where they are able to run these simulations is very close to zero.
I.e. it's likely we'll get wiped out before we reach a point where we are able to perform such tests.
2) The fraction of posthuman civilizations that are interested in running ancestor simulations is very close to zero.
In other words, our species has changed so much by that point that we are no longer interested in running simulations, and no curious individuals have access to the power to create them, or else running these simulations is banned.
3) The fraction of all people with our kind of experiences that are living in a simulation is very close to one.
If the other two are false, then we are left with option number three: our species develops the required technology and starts creating an incomprehensible number of ancestor simulations (over time). This would mean that the vast majority of "people" with experience of living on Earth are... inside a simulation, they just don't know it.
So far, so philosophical, but can we test it? Well, if you make a few assumptions about the limits of potential simulations, then it might just be possible.
TESTING SIMULATION THEORY
In 2017, a group of physicists proposed a few methods of finding out in their paper "On Testing the Simulation Theory" with varying degrees of complexity. Their idea rests on the assumption that the simulation would have limited resources, and so isn't simulating everything in the universe all at the same time. As such, the simulation would act much like a computer game, only rendering the parts of the simulation that are being observed by a "player" at the time. Sort of like how in the background of Super Mario, the designers chose not to simulate the entire observable universe off-screen, to save on computer power (a wise move).
The key to finding out whether we are in a simulated universe or a real one is to find out when information becomes available to us, the observers.
"To save itself computing work, the system only calculates reality when information becomes available for observation by a player, and to avoid detection by players it maintains a consistent world, but occasionally, conflicts that are unresolvable lead to VR indicators and discontinuities (such as the wave/particle duality)," the authors wrote in the paper.
Should it only be at the time of observation by an observer (and not apparatus), the team suggests this would be evidence that it is only being "rendered" at the point of observation, meaning that we are living in a simulation.
Testing this, the team says in the paper, isn't as complicated as it sounds. Though, obviously, it's still very complicated and involves the double-slit experiment. It all revolves around forcing "the VR rendering engine to create discontinuities in its rendering or produce a measurable signature event within our reality that indicates that our reality must be simulated."
In the double-slit experiment, single photons are fired at a double-slit cut into a screen. If you do this and look at the buildup of impacts on the screen, you will see a pattern emerge, as shown below. This pattern is what you'd expect if the photons were acting as waves.
So far, so simple. Now, if you detect which slit the photons are going through (imagine a beep every time a photon goes through the top slit, if it pleases you) the pattern that we get is two lines, as if the photons were behaving as particles (see below video).
Turn off the detector, and we're back to seeing the interference pattern (the waves seen above). Having or not having access to the "which way" data (essentially knowing which slit the photon went through) determines whether the photon acts as a particle or a wave. Photons can behave as either particles or waves, but cannot be observed as both at the same time.
If your brain hurts, imagine how quantum physicists feel every moment of their waking lives. But, for the authors of the 2017 study it could give us an opportunity to find out if we're real, which would be nice to know, even if it isn't going to imbue you with the power of Neo from The Matrix.
"The following experiments are designed based on the hypothesis that the availability of which-way data to an observer is the key element that determines the pattern found on the result screen: the simulated content (the virtual reality) is computed and available to be rendered to an experimenter only at the moment that information becomes available for observation by an experimenter and not at the moment of detection by an apparatus," the authors wrote.
By using a series of abstractions, they propose that it might be possible to find (should we live in a simulation) that the information is only given to us at the point of observation. To do this, they try to create versions of the double-slit experiment that would create a paradox.
“Two strategies can be followed to test the simulation theory," they explain. "1: Test the moment of rendering. 2: Exploit conflicting requirement of logical consistency preservation and detection avoidance to force the VR rendering engine to create discontinuities in its rendering or produce a measurable signature event within our reality that indicates that our reality must be simulated."
In one of the simplest of their proposed experiments, the which-way data and screen data are collected on two separate USB drives, and not seen by an experimenter. Keep doing this, and you have a lot of flash drives that contain which-way data, and screen data. You then destroy the which-way data USBs based on a coin flip (heads you survive, tails you die — like Anton Chigurh from No Country For Old Men, but in a lab coat).
"Destruction must be such that the data is not recoverable and no trace of the data is left on the computer that held and transferred the data. For n even, one can replace the coin-flipping randomization by that of randomly selecting a subset composed of half of the pairs of USB flash drives containing which-way data for destruction (with uniform probability over such subsets)," they say in the paper.
"The test is successful if the USB flash drives storing impact patterns show an interference pattern only when the corresponding which-way data USB flash drive has been destroyed."
I.e. if you open up the screen data and see wave patterns when the corresponding which-way USB stick has been destroyed, that would mean that the simulation had rendered reality at the point of observation (you opening the file) and not when observed by the detector.
HOW YOU CAN HELP TEST IF THE SYSTEM EXISTS
Of course, the simulation could be clever enough that it knows of intent and will find tricksier ways of concealing this from you, so should this not work, the team propose a series of ever more complex ways that you could test the system (if it exists). They even started a Kickstarter in order to fund the tests, which has raised over $236,590 so far.
Of course, if we find out that we're not living in a simulation that has implications too. Going back to Bostrom's proposal, it would mean that we are looking at option 1 or 2: we either don't make it as a species, or become something virtually unimaginable. Both of which might be preferable to finding out that we are in a simulation. If that happened it could ruin whatever "they" were testing by running the simulation in the first place. They might simply turn us off.