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I wrote a paper arguing that 'ancestor' simulations are effectively impossible. Part of that argument was that, in order for the simulations to be meaningful, t

I wrote a paper arguing that 'ancestor' simulations are effectively impossible. Part of that argument was that, in order for the simulations to be meaningful, the world had to work largely the same way as our own. (Otherwise, it's not an 'ancestor simulation'. Other types of simulations could work.) You could, for instance, just project a 'video' of the sky every night to save some energy costs. Until the simulated people gain the ability to, say, practice photometry. Then your have to spend a bit more energy simulating the actual physics. So, as time progresses in your simulation, energy costs rise. Eventually, your simulated beings develop the ability to compute. There are some things you'll be better at optimizing, but over time the simulated beings will get closer and closer to the optimal way of doing an operation; at which point any operation they do is an operation you are doing. Until they generate a simulation of their own. That's when it all falls apart. At the point they make their own simulations, now you're paying in energy for your simulations, plus all their simulations and their simulations' simulations in an infinite chain. Voila. Infinite energy requirement. (There's some caveats here... some simulations may result in a dead world, but presumably every successful simulation would run more than one successful simulation of its own.) So, your options are: 1. End the simulation when the simulation becomes capable of running its own simulation. Useful, perhaps, but not very for a very old civilization. It's not clear that humanity 1 million years will be that interested in simulating the first X00,000 years of humanity. 2. Dumb down the simulation. However, this would have to be done "just so" so that the energy use limit converges as the depth of simulations approaches infinity. This also provides a mechanism for a simulation to detect that it is a simulation (I forget why, it's been awhile), making the entire exercise not useful as an ancestor simulation. 3. Prevent simulations from running their own simulations. Like (2), this potentially allows the simulation to discover that it is a simulation. It also may make the results of that simulation less useful. If you, for instance, wanted to know what the world might be like if event X happened differently, you could change that event and let the simulation run, but as soon as you got to the point where they would have run their own simulations, you can't be sure of your results.

logfromblammo 8y ago
You don't add any energy from a simulation that is running a simulation. The higher-level simulation has to devote some portion of its own resources to running the lower-level simulation, and that cannot grow larger than all the resources available in the higher-sim universe. If the lower-level sim has more simulated resources, that just means a resource in the higher-level sim has to be multiplexed somehow. In terms of simulations like our own universe, if we simulate a universe twice as large as our own, using half the resources in our universe for the sim, and reserving the other half for us to continue to live in, then barring any shortcuts or optimizations and assuming multiplexing by time, the sim will advance one simulated second for every four real seconds. All that simulated energy is already tied up in the simulation hardware we built in our universe. If we are living in a simulation, then the parent universe won't ever have to spend more on our simulation than the maximums they set when starting it. Unless we break out of the simulation and hack our own simulator to allocate more resources, of course. We can't up the requirements from within, because the parent could just start multiplexing some resource without any simulated person ever noticing. Also we have no way to know whether the resources of a simulator-parent are infinite or not, or the aleph numbers of any infinite resources they may have. We think we might have an infinite universe, but the portion of it we can observe is finite (but very large, encompassing many galaxies), bounded by our light cone and the expansion of spacetime. If quantum effects are really just lazy evaluation in the simulator, the simulator should be able to prune everything we cannot observe.
- cgriswald 8y ago
  That’s really no different than (2). I’m specifically talking about ancestor simulations in which the world of the sim is largely identical to the real world. Changing from infinite resources to finite is a big change. And having the simulation run more slowly than real time probably defeats the point. Imagine waiting for 600+ years for the simulation to complete to find out what would have happened if Abraham Lincoln hadn’t been assasssinated.
  - logfromblammo 8y ago
    I argue that the distinction is effectively pointless, because human imagination can already simulate our reality. Have you ever had a particularly vivid dream? Ever daydreamed about punching that smug customer in the face, or launching a rocket at that ass in front of you in traffic? What would happen if you had a dream about having a particularly vivid dream? If you dream in that dream that you're having another dream, does your real brain cook itself from using too much processing power? If you dream that someone else is having a dream, does that matter at all to your simulation? It's entirely possible that you never have to simulate that at all, because the dreamer forgets all about their dream when they wake up, and that branch just gets pruned. By that standard, the (1) simulation would halt the instant some random animal ancestor fell asleep. The (3) simulation could not model anyone that made a decision based on a portentious dream--such as the dream about seven fat kine and seven lean kine found in a millennia-old book with some cultural significance. Only a (2) simulation has any chance of producing meaningful results. And given the predictability of events, you would need to run that Lincoln simulation hundreds of times to learn anything from it, and many times more if you want any reasonable degree of precision. Nobody wants to wait 1000 years just to find out with 95% confidence what Lincoln might have eaten for breakfast a month after not being assassinated. You could prune more extensively if you had a specific question you wanted answered. Even if you just want to wander around in a simulated Lincoln-unassassinated Earth, the sim could still prune based on what you decide to look at. The sim would probably have to simulate Lincoln's impact on journalism regardless of whether you read a newspaper or not, but if you never stop to smell the flowers, it could probably prune Lincoln's impact on gardening. An ancestor simulation has a great advantage over an alien simulation, because it can play back recordings of real observations rather than simulating or randomizing results from scratch.
JackFr 8y ago
Worm Ouroboros! Tail-recursive simulation FTW.

logfromblammo 8y ago

You don't add any energy from a simulation that is running a simulation. The higher-level simulation has to devote some portion of its own resources to running the lower-level simulation, and that cannot grow larger than all the resources available in the higher-sim universe. If the lower-level sim has more simulated resources, that just means a resource in the higher-level sim has to be multiplexed somehow. In terms of simulations like our own universe, if we simulate a universe twice as large as our own, using half the resources in our universe for the sim, and reserving the other half for us to continue to live in, then barring any shortcuts or optimizations and assuming multiplexing by time, the sim will advance one simulated second for every four real seconds. All that simulated energy is already tied up in the simulation hardware we built in our universe. If we are living in a simulation, then the parent universe won't ever have to spend more on our simulation than the maximums they set when starting it. Unless we break out of the simulation and hack our own simulator to allocate more resources, of course. We can't up the requirements from within, because the parent could just start multiplexing some resource without any simulated person ever noticing. Also we have no way to know whether the resources of a simulator-parent are infinite or not, or the aleph numbers of any infinite resources they may have. We think we might have an infinite universe, but the portion of it we can observe is finite (but very large, encompassing many galaxies), bounded by our light cone and the expansion of spacetime. If quantum effects are really just lazy evaluation in the simulator, the simulator should be able to prune everything we cannot observe.

cgriswald 8y ago
That’s really no different than (2). I’m specifically talking about ancestor simulations in which the world of the sim is largely identical to the real world. Changing from infinite resources to finite is a big change. And having the simulation run more slowly than real time probably defeats the point. Imagine waiting for 600+ years for the simulation to complete to find out what would have happened if Abraham Lincoln hadn’t been assasssinated.
- logfromblammo 8y ago
  I argue that the distinction is effectively pointless, because human imagination can already simulate our reality. Have you ever had a particularly vivid dream? Ever daydreamed about punching that smug customer in the face, or launching a rocket at that ass in front of you in traffic? What would happen if you had a dream about having a particularly vivid dream? If you dream in that dream that you're having another dream, does your real brain cook itself from using too much processing power? If you dream that someone else is having a dream, does that matter at all to your simulation? It's entirely possible that you never have to simulate that at all, because the dreamer forgets all about their dream when they wake up, and that branch just gets pruned. By that standard, the (1) simulation would halt the instant some random animal ancestor fell asleep. The (3) simulation could not model anyone that made a decision based on a portentious dream--such as the dream about seven fat kine and seven lean kine found in a millennia-old book with some cultural significance. Only a (2) simulation has any chance of producing meaningful results. And given the predictability of events, you would need to run that Lincoln simulation hundreds of times to learn anything from it, and many times more if you want any reasonable degree of precision. Nobody wants to wait 1000 years just to find out with 95% confidence what Lincoln might have eaten for breakfast a month after not being assassinated. You could prune more extensively if you had a specific question you wanted answered. Even if you just want to wander around in a simulated Lincoln-unassassinated Earth, the sim could still prune based on what you decide to look at. The sim would probably have to simulate Lincoln's impact on journalism regardless of whether you read a newspaper or not, but if you never stop to smell the flowers, it could probably prune Lincoln's impact on gardening. An ancestor simulation has a great advantage over an alien simulation, because it can play back recordings of real observations rather than simulating or randomizing results from scratch.

JackFr 8y ago

Worm Ouroboros! Tail-recursive simulation FTW.