At the most recent Isaac Asimov Memorial Debate, recently held at New York’s Hayden Planetarium, scientists gathered to address the question for the year: Is the universe a computer simulation? It’s an older question that you might imagine, and if we interpret it a bit more broadly then it’s really one of the oldest questions imaginable: How do we know that reality is reality? And, if our universe were a big, elaborate lie, could we ever devise some test to prove that fact? At the debate, host and celebrity astronomer Neil deGrasse Tyson argued that the probability is that we live in a computer simulation.
When you set yourself to proving, or disproving, the hypothesis that we live in a computer simulation, there are basically two modes of attack. One, you can try to collect evidence on the subject — a difficult and time-consuming approach that tends to leave you without much in the way of funding or public recognition. One approach to this is to look for glitches, things that have no place in any sensible physical universe. Another is to figure out some limitation of a simulation that ought not to exist in a real world, and to see whether our universe exhibits this limitation. Recent work examining cosmic rays in the upper atmosphere could one-day be expanded to provide such evidence, but it’s in no way assured.
The other, more popular strategy is to reason your way out of the box — the Descartes approach. This involves coming up with logical statements that cannot be locked to any particular reality in which we exist; classically, Descartes claimed that he could definitively prove he existed, simply by thinking. “I think therefore I am” is not a reference to self-awareness, and certainly not artificial intelligence, but the simple fact of existence: I can’t be having the thought I’m having now if I don’t exist somewhere, in some form. Descartes had a pre-digital understanding of a simulation, arguing that he could well be a “brain in a vat” being fed false experiences. But the basic form of the problem is the same as our computer interpretation, though less specific and testable.
Now, Descartes had to eventually abandon basic thought proofs in favor of some questionable further assumptions designed to make his quest for a sensible universe remotely possible. In particular, he had to fall back on ideas about God, and His unwillingness to viciously trick mankind. In other words, if our senses tell us a thing, we can trust in God’s fairness to assure that that thing is, at least roughly, the way we observe it to be. If it isn’t, then God has given us senses designed to trick us, and God would never do such a thing!
For modern physicists, this approach obviously won’t cut the mustard. Even highly religious scientists know they can’t reference God in their theories. To move past the problem of mere existence and on to more relevant questions, they and their atheist colleagues alike must lean on an equally convenient, and equally useless, argumentative crutch: infinite-time thought experiments.
This is the crux of Tyson’s point: if we take it as read that it is, in principle, possible to simulate a universe in some way, at some point in the future, then we have to assume that on an infinite timeline some species, somewhere, will simulate the universe. And if the universe will be perfectly, or near-perfectly, simulated at some point, then we have to examine the possibility that we live inside such a universe. And, on a truly infinite timeline, we might expect an almost infinite number of simulations to arise from an almost infinite number or civilizations — and indeed, a sophisticated-enough simulation might be able to let its simulated denizens themselves run universal simulations, and at that point all bets are officially off.
In such a reality, simulated universes might outnumber real ones by an infinity to one, and so to assume we live in the one and only real universe would be the height of arrogance.
It’s not so much that this thinking is “flawed” as it is “so useless it invalidates all of human thought and achievement from pre-history to today.” Think about it: If we are to be convinced by this sort of non-argument, then why not assume that every person around you is a time traveler? After all, if we imagine that time travel will one-day exist on an infinite time-line, then we must also assume that time travel has been used to visit every single time and place in our planet’s history — including this one. People will, in principle, want to have fun vacations in the past, putting on period-appropriate clothing and walking around using slang wrong; how could we be so arrogant as to assume that the people we meet are part of the real, finite population of our time, and not from the far more numerous ranks of temporal travelers from any time?
