If we're in a sim...

There are only a few conditions under which it could possibly matter to me that I'm in a simulation. Among them:

1. The simulation is buggy. Under some conditions that are reachable from within the sim, it's possible to cheat at physics by overflowing some buffer or exploiting some other software bug.
2. The simulators are watching and interacting. There's someone watching me right now who has the power to change a few runtime variables and cause a kilo of gold coins, a kilo of Purple Kush, and a verthandi to appear next to me. (They are cordially invited to do so.)

Most of these questions seem extremely hard if not impossible to answer without something like talking to the makers of the sim or finding hacks to get at the source code. Some of these are however slightly testable. For example, if it turns out that BQP is comparatively large (to fix an example say it contains NP), then it would suggest that if we are in a simulation then the simulation is not being run on a classical computer.

One possible test to see if we are in a simulation, although a very weak one, is to collect a very large set of data about decaying particles and then analyze the data. If the data turns out to be much closer to a pseudorandom rather than truly random sequence then this would strongly suggest we are in a simulation. Note that if presently believed complexity conjectures are true, distinguishing actual pseudorandom data from genuinely random data should be extremely tough.

One serious issue about engaging in tests to try to see if we are in a simulation is that the most obvious tests are often tests which have some danger of potentially crashing the simulation or causing the programmers to stop it. Thus for example, one test that jimrandomh mentioned to me was bouncing laser beams off of farther and farther objects to expand the radius which we know is being accurately simulated (this mainly is usable for ruling out a simulation that only simulates our solar system in detail). This is however exactly the sort of thing which one could see as leading to the equivalent of a seg fault or other error. On the other hand, if the simulators are only running a simulation on our solar system then they are more likely to care about humans or life in general on Earth (at minimum, we're then a much larger and more significant part of the simulation) and so are more likely to have anticipated this sort of problem and made sure the code is somewhat resistant. That said, if all probes stopped transmitting back to Earth or showing any signs of existence a bit after our solar system (say 75 AU out) and all attempts to bounce lasers or radar off of distance objects failed, that would strongly suggest we are in a simulation that just includes our solar system.

The broad answer to those questions is "depends what the simulation is being run for".

To see why, consider why we run simulations. Answers include entertainment, e.g. SimCity; training, e.g. flight simulators; fundamental research, e.g. simulation of neural networks; engineering, e.g. simulation of a model building to determine whether its design withstands this or that catastrophic event, such as a quake. I'm probably forgetting many other areas.

A simulation is generally intended to answer a specific question or class of questions about some aspects of reality. The degree of fidelity, the "shortcuts" taken, the possibilities for intervention and so on are all determined by what questions are of interest to the people running the simulation.

If we decided to run a simulation to answer the question "can intelligent life arise out of deterministic physics", then we would build the simulation to have simplified but realistic physics, such that we could run the sim at a much faster rate than our baseline reality. Such a sim would likely not model anything at a higher level of abstraction than the laws of physics, since that would defeat the point.

If, on the other hand, we were running a simulation for the aesthetic purpose of recreating forgotten parts of our history, we would likely not bother with such minute details. For those who've read Permutation City, we would make something closer to Copies than to the Autoverse.

In fact, you could do worse than buy your dad a copy of Permutation City to stimulate his thinking about such questions.

If we are, I would place an extremely high credence in individuals not being modeled as objects.

• Doesn't look like it.
• Untestable, but it seems like it would be a lot of trouble.
• The laws of physics seem to go back all the way, so at the big bang or before.
• Doesn't look like it.
• If I imagine making something like the universe, it would be because I could - and a little scientific curiosity.
• Not sure. Our universe runs on pretty complicated and high-energy physics. If we're running inside a computer in a universe similar to ours, this computer would have to have a vastly higher maximum energy splitting than ours, or more generally work on physics that made computation really easy.

Actually, answering that last question led to an interesting thought. Ease of computation puts an ordering on the universes that can simulate each other. If our prior probability of the universe existing is can be thought of as a function of ease of computation in the universe (probably not, but simplifying), that puts an upper limit on the "tower o' universes." Then we can make assumptions about how rarely universes bother to simulate whole other universes and actually get finite numbers rather than pesky infinities! Thinking this has caused me to revise my probability of being in a simulation down.

If our universe was an artificial construct, then the potential scenarios spin out of control as we consider the possible motivations of the 'creators'. Although the assumption may not apply in universes with different physical laws, I'll operate on the premise that their computing power is finite.

In the first scenario, the one that normally shows up in popular science programmes referring to science fiction to entertain the audience, this is a game. If we were directly created by the 'creators', then we must be beings that they can conceive of, and reflect some side of their psyche. I don't think this planet is the most interesting setting for a game I could imagine, so assuming we can reflect our creators psyches with our own biases, the only data we'll ever get in this scenario, there are probably more perfect games for them to play. This implies they would only spend limited resources on this particular universe, and running a fully 'rendered' universe, minds and all, when a player isn't in the area would probably increase costs. I know I can think, feel, and, to a degree, comprehend the universe. You know you can think, feel, and, to a degree, comprehend the universe. Everyone reading this knows they can think, feel, and comprehend the universe, although none of us know for sure the others can, at least when we aren't interacting with them. If you're reading this while alone, we can probably say we do it even when another character isn't present, this implies we're more than just NPCs. If it's a game, then you, or someone you know, are probably one of the players. (Ask your dad straight out for a joke if he's playing a ridiculously complicated RPG.) An extension of this possibility is that this is simply a psychology experiment writ large, and I, or you, am actually a member of the creator species planted in this environment for the purposes of the experimenters. If you were the player, however, do you think you would be happy with the 'game' your playing now as pure recreation?

Therefore I think that if you, or me, are self-aware in a game, then we're either doing this as a psychology experiment, or we're side-characters for someone with a more engaging life. (Although the utility functions of any PC races are unknown.) They could be cleaners, sociopaths, or leaders, but we'd be looking primarily for people who show some degree of motivation.

The second possibility is that 'they' have the capabilities to generate an entire universe, or at least one solar system, down to the last atom, in cyber-space. If so, then we can only hope that we're very much a valued experiment, and won't be killed off like a lab rat once our immediate purpose if fulfilled.

Either way, if this is a simulation, we have no power over it, and won't be able to gain information on it. If it's a game, the servers could be reset, and if it's an experiment in such detail we all exist as we think we do, but in a simulation, we could likely be programmed to forget if it suited the programmers.

Besides, if this were a simulation, then we're presumably worthless or insane by the standards of the wider universe. Our actions have the greatest effect in a situation where our universe exists in full, and is a 'physical' universe, while they are all but worthless in a situation where the universe is a game. So to give the best chance of our actions mattering, we should operate under the assumption we, and everyone around us, exists.

Also, 'Well Done. Progress to Level 2!'

So what's your (simulated) gut feeling? Are you in a sim? If so, what's it for?

Any thoughts?

I just wanted to clarify that you are interested in undeveloped, naive thoughts as well? While I'm sure developed thoughts would be preferred, unless there are some science fiction writers out there who've had reason to think about this a lot, I think most people's thoughts would be undeveloped and naive, just because there's not much reason to dwell on such questions and, even if you do, not much entanglement with reality to train your thinking.

Personally, I enjoy this post because the hypotheticals are interesting and perhaps through discussion we can hone and develop our initially naive ideas into more mature ones. (Then, should I discover in a month we are in a simulation, I will be that much further advanced in my thinking compared to where I would have been...)

I assign a very high probability to this being wrong -- in other words, I wouldn't risk anything on this as a claim -- but if you ask what I would think, if I found out we were in a simulation created by conscious entities I would feel that these conscious entities were most interested in us, as other conscious entities. I would also feel that they were benevolent and cared about us.

My reasons are that I think consciousness is special. Even though it just comes out of the physics, it's something that gives the universe a point of view and thus a locus -- a point of origin and some reason to consider a particular time and place 'important'. I also think that consciousness is unifying. As soon as you have a sense of self, an entity begins categorizing things as 'self' or as 'other'. A sufficiently intelligent conscious being will recognize that other conscious entities are more like themselves than anything else.

It's hard to imagine the motives of a general intelligent being. But a being that simulates other beings is already a smaller group. They are curious and possibly lonely. I just think that loneliness is the fundamental condition of a self-aware being.

We were either simulated by conscious entities or simulated by non-conscious entities. If the former, I think we are the purpose of the simulation (or an initial step in the purpose). If we were not simulated by a conscious being, then we are being simulated by 'accident' and in that case I see no difference between that hypothetical simulation and the one we're in. Because I believe we are in a simulation, by how I define simulation, I just wonder if that simulation was created with intention or not.

My gut feeling is, that we are NOT inside a simulation. At least not in a one run by some anthropomorphic creatures. Or any creatures at all.

But suppose we are. Are our simulators also simulated? How far or high does it go? Why lose the raw computing power with some nested simulations?

Are intelligent entities modeled as objects? In other words, are they instantiated and managed as distinct tracked pieces in the simulation? Or is the universe just modeled as huge numbers of subatomic particles and energy?

We have no reason to believe that intelligent entities behave in a way that contradicts reductionism. This is a fact mostly independent of whether we're being simulated. So, intelligent beings may be tracked by the simulation, but they behave like collections of particles, so it seems simpler to suppose they are simulated the same way everything else is.

If intelligences aren't modeled as objects are they at least tracked or studied by whoever is running the sim? Or is the evolution of intelligence in the sim just seen as an uninteresting side effect and irrelevant to the sim's purposes?

Assuming we are simulated, we still know nothing about the simulators other than that they exist. To discuss the probability of propositions about them (are they studying us?), we have to make some limiting assumptions, and I know of no good prior for choosing these.

For instance, if there are infinitely many universes which may simulate each other, there are different ways of assigning probability mass to each of them: does a universe gain probability mass through being simulated multiple times, or in multiple other universes? Does this mass depend on the simulator's own mass? Can a universe have a nonzero probability mass at all if it's never simulated (that is, can there be an Unsimulated Simulator universe)? Does the whole concept even make sense when dealing with infinitely many "existing" universes?

Under some assumptions, every possible universe (every point in universe-history phase space) may have at least one other universe simulating it, or perhaps infinitely many. If you allow universes that have more physical computing power than our own appears to have (i.e. more than a Turing machine), then a single such universe may simulate all possible universes in finite time, and maybe for beings living in it that's an obvious first step before they start searching among the simulated universes for the one they want to study. And so on.

Gut feeling, no. I can give a reason for this: the Simulation Argument gives two other options, and I think each of the most credible assumptions that would reduce the likelihood of one No-Sim option would increase that of the other. But I've never devoted that much thought to it.

(I give fairly strong credence to the claim that reality acts more like a Turing machine than like any other model we could use. But I think this needs a different name, to discourage us from explaining the 'Turing machine' by one of our other 'models'.)