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> Suppose we live in a computer simulation with the following x-xˆ property: for each memory-bit x in any computer in our world, there is a memory-bit ˆx in the

> Suppose we live in a computer simulation with the following x-xˆ property: for each memory-bit x in any computer in our world, there is a memory-bit ˆx in the simulating computer such that ˆx is used to store which value is stored in x. Then any such x is subject to two different types of soft errors: One thing I've never understood about the simulation theory is that if we live in a simulation, we have almost know basis for making any assumptions at all about the nature of the reality in which we're being simulated. If you assume it's like ours in every way, then it's also equally likely to be a simulation, and on to infinity.

sarah180 8y ago
The suggestion that we live in a simulation is really not a "theory" in any meaningful way at this time. It doesn't explain anything that we can't explain otherwise and it doesn't predict any behavior we haven't yet observed. It is, at present, effectively unfalsifiable and not much different from a claim that "God made all of this." It's just a different notion of God. This is not an argument that we shouldn't pursue this line of thinking, but we shouldn't call it a theory until it makes new predictions that we can confirm or disprove.
- tlb 8y ago
  It's really an umbrella term for a class of theories, some of which do make testable predictions (like anisotropy of space or, in this case, a minimum bound on memory error rate with zero radiation.) It's like the term "string theory". One thing that all simulation theories predict is that our universe is interesting. It's an alternative to anthropic theories to explain why our universe is one with life and not one that re-collapsed to a singularity or expanded out into a thin hydrogen plasma. See https://en.wikipedia.org/wiki/Fine-structure_constant#Anthropic_explanation https://en.wikipedia.org/wiki/Fine-structure_constant#Anthro... for one reason why it's only a small range of possible universes that are interesting.
cgriswald 8y ago
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.

sarah180 8y ago

The suggestion that we live in a simulation is really not a "theory" in any meaningful way at this time. It doesn't explain anything that we can't explain otherwise and it doesn't predict any behavior we haven't yet observed. It is, at present, effectively unfalsifiable and not much different from a claim that "God made all of this." It's just a different notion of God. This is not an argument that we shouldn't pursue this line of thinking, but we shouldn't call it a theory until it makes new predictions that we can confirm or disprove.

tlb 8y ago
It's really an umbrella term for a class of theories, some of which do make testable predictions (like anisotropy of space or, in this case, a minimum bound on memory error rate with zero radiation.) It's like the term "string theory". One thing that all simulation theories predict is that our universe is interesting. It's an alternative to anthropic theories to explain why our universe is one with life and not one that re-collapsed to a singularity or expanded out into a thin hydrogen plasma. See https://en.wikipedia.org/wiki/Fine-structure_constant#Anthropic_explanation https://en.wikipedia.org/wiki/Fine-structure_constant#Anthro... for one reason why it's only a small range of possible universes that are interesting.

cgriswald 8y ago

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.