New Study Rules Out Popular Version Of The Simulation Hypothesis

A surprising number of people, if Internet forums are anything to go by, are of the belief that we are living inside a simulation.

The idea, made popular by films like The Matrix, is pretty simple to explain. Instead of being in "base reality", we are simulated beings living in a simulated world created by other life forms or perhaps advanced humans recreating their ancestors at some distant point in the future. 

One particularly influential paper by philosopher Nick Bostrom suggests that one of three things must be true: either humanity goes extinct before we are able to run "ancestor simulations", we lose any interest in running such simulations, or humanity will go on to produce many, many simulations of our ancestors. The simulation argument, as Bostrom terms it, argues that if the third option is correct, then any conscious being should assume they are simulated, as the simulated beings would far outnumber those in base reality. 

But how plausible is that idea? According to a new paper, not very. In fact, several types of simulation have been deemed impossible, or so implausible that we can basically rule them out.

In the paper, astrophysicist Franco Vazza, an associate professor in the Department of Physics at the University of Bologna, looked at several types of simulations that an advanced intelligence may look to create, and assessed whether those simulations would be possible in the universe we observe around us. 

"Our starting point is that 'Information is physical', and hence any numerical computation requires a certain amount of power, energy, computing time, and the laws of physics can clearly tell us what is possible to simulate, and under which conditions," Vazza writes in his paper. "We can use these simple concepts to assess the physical plausibility – or impossibility – of a simulation reproducing the Universe we live within, and even of some lower resolution version of it."

The first type explored is where the whole universe is a simulation. Unsurprisingly, he concludes that our observable universe could not be recreated in its entirety from within our observable universe, requiring energy "beyond imagination" to do so.

He then looked at whether the Earth could be simulated in its entirety, a far less computationally ambitious project for an advanced civilization to run. But again, he found that the energy required stretches plausibility.

"The initialization of a complete simulation of 'just' a planet like Earth requires either converting the entire stellar mass of a typical globular cluster into energy or using the equivalent energy necessary to unbind all stars and matter components in the Milky Way," Vazza explains in the paper.

"Elaborating on the implausibility of such a simulation, based on its energy cost, is straightforward: while this is indeed the requirement simply to begin the simulation, roughly the same amount of energy needs to be dissipated for each timestep of the simulation. This means that already after ∼ 10⁶ timesteps, the required energy is equivalent to the entire rest-mass energy of the Milky Way or roughly to the total potential energy of the most massive clusters of galaxies in the Universe."

He dismisses this possibility on the grounds that it would require whole galaxies to power this simulation down to the Planck level.

Next, he looked at whether an advanced intelligence could produce a "low-resolution" version of the Earth, where only scales explored by human experiments and observations are simulated, with a "subgrid" of physics for when we try to probe further down. Think of it like how the game Super Mario World does not put the effort in to simulate the atoms making up all the Goombas. 

Vazza looked at neutrino detections to work out the minimum scale that the simulators would have to simulate in order to line up with our observations. We detect neutrinos all the time, and so any simulation would have to simulate at least to that level of detail in order to create a consistent world.

At first, this looks more plausible, with the energy requirements to get the simulation started instead being around that produced by radiated energy from the Sun over the course of around two minutes. But in order to get information out of the simulation – presumably advanced civilizations would want to learn something from it – would again require immense amounts of computing power. 

In order to make it work, the simulators would have to be happy receiving information from the simulation on geological timescales, or attempt to speed it up. This would require the energy of "all stars in all galaxies within the visible Universe" and so is also ruled out by Vazza.

"All plausible approaches tested in this work (in order to reproduce at least a fraction of the reality we humans experience) require access to impossibly large amounts of energy or computing power," he concludes. 

"We are confident that this conclusively shows the impossibility of a 'Matrix' scenario for the [Simulation Hypothesis], in which our reality is a simulation produced by future descendants, machines, or any other intelligent being in a Universe that is exactly the one we (think we) live in – a scenario famously featured in the 'The Matrix' movie in 1999, among many others. We showed that this hypothesis is just incompatible with all we know about physics, down to scales that have already been robustly explored by telescopes, high-energy particle colliders, and other direct experiments on Earth."

Of course, what this really pushes against is the idea that a simulator could create a simulation of a universe/planet with laws of physics similar to its own. Perhaps there is a universe where the laws of physics are different and energy is cheap, and it is here where the simulation is taking place. But would such a universe, with different laws of physics, have beings similar to us? If this paper rules out anything, it is the ancestor simulation, where beings simulate worlds like or incredibly similar to their own.

For anyone hoping that the universe is simply a simulation run by humans of the future (we get it), Vazza leaves on a hopeful note.

"Luckily, even in the most probable scenario of all (the Universe is not a simulation), the number of mysteries for physics to investigate is still so immense that even dropping this fascinating topic cannot make science any less interesting."

The study is published in Frontiers in Physics.