Elon Musk likes to say pretty controversial things off the cuff, and so do I, but he inspired a number of threads by saying at Re:Code that there's a billion to one chance we're living in base reality. To use his word, this world is almost surely a "simulation."

While a lot of press attributed the idea to him, Musk is actually restating almost exactly the well known thesis of Nick Bostrom on this topic, which has spawned much debate (some of which can be seen at the site linked.) The short precis of the thesis is as follows:

If you accept that the eventual progression of our work in creating digital (or "simulated") worlds is to make ones that match our reality, then you probably accept that once we can do this, we will do it a whole lot, and that eventually there will be very large numbers of created digital worlds, many based on our own. If that's true, then the probability that any particular world (including this one, of course) is the original one is vanishingly small.

Like many, I find the argument interesting, though not quite so compelling, as it contains some logical fallacies. For one, even in the "root" universe, the argument is equally compelling, but also clearly false.

I also oppose the term "simulation." For far too many, "simulated" means "not real" or "less real." This world is clearly "real" even if it is synthetic and based on computation. If you accept the truth of "I think therefore I am," then you are thinking, not engaging in a simulation of thinking. (Just as AlphaGo doesn't simulate playing Go, it plays Go.)

Better terms include "Computational" and "Snythetic" or other synonyms like "digital," "emulated," or "artificial."

Leaving aside the debate over the merits of the argument, let's assume it's true for the moment. The biggest consequence of synthetic is that it means created. As in, "there is a creator/god" in the sense of a being who created this universe and who is in some limited way omnipotent over it and in another limited way omniscient about it. I say a limited way, because this "god" is perhaps a programmer named Martha who has a few hundred digital Earths running in her dorm room. A being perhaps (but not surely) exactly like us in her world, but with the potential ability to observe and change anything about this one.

That is a theistic view, though quite unlike typical theist doctrines. (It bears a small and bizarre similarity to Mormon theology which teaches that our god was once an ordinary being on another world who was rewarded with his own new world to be god of.)

From what we can observe, Martha doesn't interfere overtly with this world. As such, the first conclusion is that even if you believe in this, it should not change very much about how you live your life. If you have no shot at interaction with the "parent" universe, and there is always the chance this whole thesis is false, you should go about being you as though you felt you lived in the root or "first" universe -- what you might incorrectly call the "real" one.

There are some changes that are justified if you believe this, though. They are grand philosophical changes, but some apply to Elon Musk himself.

You see, Elon has made it his prime life goal to get humanity off the Earth. To stop us from being a "one planet species" which would be wiped out if something catastrophic happens here. History shows that bad things have happened naturally (like asteroid strikes) and more bad things could happen due to the works of humanity, like killer diseases or nuclear winters. As such, Elon's goal of getting a self-supporting colony on Mars is a grand one, well worthy of being a prime life-goal for a world-shaker.

But it's taken down a peg if you accept the synthetic world hypothesis. Now, you conclude it's very likely that this is very much not the only cradle of humanity. That there are probably millions or billions of them. That even this one quite probably has backups taken every so often, so that even if we wipe ourselves out, all can be preserved and even restarted, if Martha wants to.

We don't know anything about Martha's motives, other than she appears to not do any noticeable interference. Martha might not even be remotely human, though once again, the probability is (at least from our viewpoint) that beings would create more synthetic worlds like their own than entirely different experiments. But if you believe in Martha than you believe we are not alone and that alters goals about the future of humanity.

If you want to get more extreme, there is also an issue with Mars. While again, we have no information on Martha's goals for this project, it seems likely, unless resources are truly free, that most synthetic worlds will be just the surface of the Earth, just the interesting part in question. Running an entire galaxy or an entire universe is many orders of magnitude more costly. Sure, you might run some of them, but if you can run a trillion Earths for the cost of a couple of galaxies, that's gotta bend things a bit.

As such, the rest of the universe truly is "simulated" in that it's just being computed with barely enough resources to make the few photons which reach us be realistic. (Or it's just a playback of an earlier run.) Many fans of this theory like that it explains Fermi's famous paradox -- no aliens have visited because there are not any -- in this universe.

It's hard to imagine, unless computation is totally free, that there would not be any "optimization" of the computation. Now, at the extreme, this would mean the parts of your house that nobody is looking at would be computed at a lower resolution, and that indeed, if a tree fell in the forest and nobody was there to hear it, it truly would not make a sound in a full way. That's very philosophically spooky, but less spooky is the idea that until we went to it, Mars the planet would not even be "booted up" into our universe. When probes arrived, it might have been fully started, but more likely only where the probes went -- the rest would just be a recorded copy of the original Mars, presuming there is such a thing in Martha's world, as the whole sky would be.

As such, it would mean going to a place that only "fully exists" (which is to say is being computed at full resolution) because we went there. Somewhat less satisfying.

Still worth going?

People imagining the idea of a synthetic, computed Earth do like to speculate about the motives of its creation. If Martha is just like us, then they probably have rules and ethics about doing this. There are huge ethical questions about all the suffering and evil that comes with creating a universe. One rule I've imagined is that the creator really has some duties to the people inside. Those might include having a heaven of some sorts, or even letting people graduate up to the parent universe and gaining rights there. The most impressive might even get to chat with Martha, though she only has time for a few. Perhaps somebody who does something truly great, like taking humanity off-planet, gets some reward for it. We can suppose this because we might do something like that if we were making these computed places. But we really have no evidence for any of that. Some would argue there is almost nothing ethical about creating a world with so much misery and keeping the inhabitants in the dark about the reality to boot. At least by our standards -- not theirs.

Is there a root?

One popular theme is to suggest that Martha's universe is also synthetic, and there is another creator above her. I describe this by saying, "It's turtles all the way up." Nobody can truly be sure they are in the root of the tree.

This is particularly interesting if you speculate that the rules of our universe, when we finally learn them in depth, will show that computation lies at the bottom of everything. This has often been speculated, and most of the quests for a unified "theory-o'-everything" tend to try to express the rules in simpler and simpler mathematics. People care about that because for now, this theory is based on the idea that computation is being used to simulate the physics of a "real" universe, one made of particles and forces. We are only able to see the particles and forces, and so might conclude we aren't digital. Particularly when emulating the activity of subatomic particles is today very expensive computationally. It makes implementing a synthetic universe at the deep level seem impossible to us. If there are deeper rules that are computational, then you can also postulate that the "root" universe could also be computational. In fact, you sort of need that, because it's hard to figure out how to get the resources needed to have worlds within worlds if you have to implement particles based on computation done with particles which are based on computation and so on. You quickly run out. If, on the other hand, you are in a universe of computation and you create sub-worlds, you can just give those sub-worlds access to the computation substrate of your own, and it scales a lot better.

We like to believe our universe is made of particles which are physical and bounce off one another and follow analog rules. But we don't know that's true. The rules of our universe are a mystery to us. We don't know where they came from, and we can't even declare that whatever they are, any parent or root universe might not run on the same rules or a variant of them.

So should you believe this is a synthetic, computational universe -- or simulation if you insist? Well, you can, but unless you are leading a mission to Mars it is not greatly productive. When the time comes -- as it will -- that we make our own small digital worlds that match our own for reality, doubt will of course increase, but as long as Martha remains hands-off, live your life as you always would have. One of the more spooky ideas in this theory is Last Thursdayism -- the idea that there is no way to tell this world wasn't forked from a backup last Thursday, that all of your memories before then happened to a predecessor. Perhaps that's true, but again it doesn't alter how you should spend your days. Indeed, it is not my goal to convince Elon to abandon his quest for Mars at all; that's worthy even if it doesn't help save humanity.

Unless the creator wants to show up. Martha?