Are we living in a simulation? This experiment could tell us

Thomas Anderson, also known as Neo, is walking up a flight of stairs when he sees a black cat shake himself out of a door. Then the moment seems to repeat itself before his eyes. Just a touch of déjà vu, he thinks. But no, his colleagues insist: he lives inside a computer program and has just witnessed a failure.

This is a scene of The matrixa film released in 1999, but we have been fascinated and disturbed by the possibility that we may be living inside a simulated reality for centuries. The idea is so profound in part because it is so difficult to disprove: if we are immersed in a false world, how could we know?

Some physicists take this notion seriously. “The entire universe can function like a giant computer,” says Melvin Vopson from the University of Portsmouth, UK, who has long been interested in the simulation hypothesis. He believes there are already important clues to suggest this is correct, and has even proposed how we might discover the truth with an experiment.

The idea of ​​living in a false reality dates back at least to the ancient Greek philosopher Plato. In his allegory of the cave, Plato imagined people locked in a cave so that they saw only the shadows of objects passing by outside. Plato thought that the prisoners would have no desire to escape: they could not conceive of anything beyond the cave and did not know that they were trapped.

In 2003, the philosopher Nick Bostrom published an article arguing that it isWe are more likely to live in a simulation than not.. The argument is backed by Elon Musk, among others. However, it is worth knowing who makes such claims. “Most of this comes from the world of technology; they are interested in saying that we can build something as rich as reality,” says the astrophysicist. franco vazza at the University of Bologna, Italy, who published a paper earlier this year suggesting that it is almost impossible we live in a simulation.

That said, there are reasons to reflect on the simulation hypothesis. Take quantum mechanics itself, which says that particles are in a superposition (a cloud of ill-defined possibilities) before we measure them. We have struggled over how to interpret this for a century. But if the universe was really a simulation, it would make sense. In a computer game, objects are not represented until the player finds them. Maybe the same thing happens with unobserved particles?

However, this amounts to circumstantial evidence at best. “It sounds a bit far-fetched,” says Vazza. But could we devise a suitable test?

Enter Vopson. It begins by assuming that if the universe is a simulation, it is fundamentally made of information. That has certain consequences. Take as an example the equivalence between mass and energy, enshrined in Albert Einstein’s equation. my = mc². In 2019, Vopson went a step further, positing that this equivalence extends to information. Based on that principle, then calculated the expected information content per elementary particle. This would be the amount of information needed to encode a particle in our simulated universe.

But how do you know how much information a particle contains? In 2022, Vopson proposed an experiment That involves taking a particle-antiparticle pair, like an electron and a positron, and letting them annihilate each other. This is a well-established process that produces energy in the form of photons. Vopson suspects that the process should also erase the information contained in the two original particles, and this missing information would leave a trail. If such collisions produced the exact range of frequencies he has predicted, he believes it would be evidence that the universe is indeed made up of bits of information.

Testing the simulation hypothesis

Vopson has attempted to crowdfund this experimentbut so far he has not managed to raise the money. But it doesn’t matter, because he has since developed another way to attack the simulation hypothesis. It revolves around the second law of thermodynamics, an iron law of physics that says that disorder, or entropy, always increases in a closed system. Explain why ice cubes melt and cups of tea get cold.

If the universe is just information contained on some strange hard drive, principles like this should extend to the information itself, Vopson says. So in 2022, he proposed what he calls the second law of infodynamics. This states that the average amount of information a system can contain must remain constant or decrease, balancing the increase in physical entropy. “Information can never be written on its own, but it can be erased,” Vopson says. “Over time, the files on a memory card will degrade and some files may disappear. But a document, book or image will never appear on its own on an empty memory card.”

Vopson claims that his law is true in nature, at least to some extent, based on his studies of the way information in viral genomes changes over time. But his key idea came when he applied his new law to the entire universe. Here, the law breaks down because, over time, the influence of gravity has organized matter into information-bearing patterns: stars, planets, galaxies, and the cosmic web.

What does this mean? Vopson says gravity must be a mechanism that prevents the information entropy of the cosmos from getting out of control. That, he believes, would be just the kind of thing anyone simulating a universe would want: a way to ensure the size of the program doesn’t grow too large. “Gravity is not a force but a compression mechanism, which reduces the entropy of information by bunching matter together,” he says.

“Applying information theory to have a different view of physics is something I value,” says Vazza. But ultimately, he doesn’t think Vopson’s work supports the simulation hypothesis. In fact, he has calculated that it would be necessary impossible amounts of energy to really simulate our universe.

Still, we may have other ways to detect glitches in the Matrix. In 2007, the late cosmologist John Barrow proposed that any simulation would generate minor computational errors that a programmer would have to correct. Would we notice such interventions? Barrow suggested that a subtle signal would be nature’s constant change. And interestingly, one of the fiercest debates in physics today revolves around evidence that the rate at which the universe is expanding has slowed over the past 3 billion years. Suspicious? Maybe. But the timeline is too long to be the result of fixing a problem, says computer scientist Roman Yampolskiy of the University of Louisville, Kentucky. “It has to be sudden,” he says.

If we live in a simulation, the question inevitably arises as to whether we can ever escape. Yampolskiy weighed our options in a document from 2023. One possibility, he suggests, would be to build our own simulation and then ask an AI to escape. Maybe then we could copy the AI’s strategy. Alternatively, we could try to draw attention beyond the program, perhaps by talking a lot about the simulation. “The best option is always an assisted escape, having someone from outside give us information,” he says.

Then again, whoever’s running the simulation might not want us to escape. We may not even be able to survive outside the confines of our computerized cosmos. All of which is enough to make us wonder: if we lived in a simulation, would we really want to know?