Could our Universe be a simulation? How would we even tell?

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Ever since Oxford philosopher Nick Bostrom proposed his simulation argument in 2001, the nerdiverse has attempted to the assess the possibility that reality is not really real, that what we experience as our Universe is instead the product of a computer simulation. Popular figures such as Elon Musk and Neil deGrasse Tyson have offered their own conclusions, but taking a firm stance was not the point of Bostrom’s argument. Instead, Bostrom’s position is nuanced and careful, and it doesn’t arrive at fixed answers.

I’ll take it for granted that the Ars readership is more sophisticated than the average geek, so let’s take some time to dissect Bostrom’s simulation argument, exploring its construction, its implications, its strengths, and its weaknesses.

But I have to warn you: If you’re hoping for relief, one way or the other, from the existential crisis brought about by the possibility that we live in a simulation, you won’t find any comfort here. The firmest conclusion anyone can reach, after examining and re-examining the arguments for and against the simulation thesis, is a profound yet resigned “maybe.”

The Universe in a box

Bostrom’s argument relies on a simple observation. We continue to develop ever more powerful and capable computers, and our abilities to simulate the Universe, from cosmic to microscopic scales, are becoming more comprehensive with time. As a theoretical cosmologist who specializes in computation, I’ve witnessed this firsthand in my own field. Decades ago, we could only simulate small portions of the Universe, representing individual galaxies as tiny dots of gravitational attraction. Now, our most sophisticated universes-in-a-box include star formation, magnetic fields, cosmic rays, radiation, and more, and they trace the evolution of millions of galaxies simultaneously through billions of years of cosmic evolution.

At the other end of the scale, we apply the known forces of nature to simulate the behavior of nuclear matter, the interaction of elements and molecules, and even the complex relationship among synapses.

Presumably, simulations will eventually become sophisticated enough that we could re-create our entire experience of the Universe within a computer, with simulated conscious brains experiencing a simulated reality. Crucially, Bostrom’s argument doesn’t depend on when this turning point will happen, only that it does. It could be in the next decade, via some revolution in computing that’s right around the corner. It could be a hundred thousand years from now, where a post-human society wields a knowledge of physics currently unknown to us to build a planet-sized supercomputer that faithfully recreates our current experience of the Universe, complete with consciousness and exploding stars and the smell of a good camembert.

The second major piece of Bostrom’s argument relies on the nature of consciousness. Specifically, that consciousness is generic, whether it arises from wet, squishy biological synapses or clean, dry electronic hardware. For the simulation argument to work, consciousness has to arise within the simulated universes and be basically the same as the au natural version. It has to be aware and, well, act like we’re used to conscious human brains behaving: capable of self-awareness, independent action, and deep contemplation about the fundamental nature of reality.

Bostrom admits that this portion of his argument isn’t without controversy and is a matter of much debate within philosophical circles. But with these pieces in place, we can move on to Bostrom’s argument: Someday, our descendants, or some very eager alien civilization, will create simulated consciousness and place those digital brains in a simulated universe. Bostrom calls these “ancestor-simulations,” following the line that future cosmologists will want to recreate the entire history of their Universe down to the level of subatomic interactions. In our case, this would naturally include a simulated Solar System with a simulated Earth that evolves simulated people having simulated arguments on simulated Internet forums.

Once this starts, the number of simulated brains will vastly outnumber the organic brains. Think of all the digital creatures that have ever “lived” in all instances of all video games combined: how many NPCs, monsters, and avatars were born with the click of a button or the flip of a switch, followed their programming, and then were just as quickly shut off? With suitably powerful computers at their disposal, the simulation-builders wouldn’t just stop at one brain in one Universe; they would make a bunch of Universes, each containing a bunch of brains. At this point, the vast majority of conscious entities would be simulated rather than biologic.

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