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The questions aren't exactly the same. For example, we can imagine characterising our whole universe as a set of physical laws plus some initial conditions, and
by chriswarbo 13y ago
The questions aren't exactly the same. For example, we can imagine characterising our whole universe as a set of physical laws plus some initial conditions, and maybe a pseudo-random number generator. If we're given such a characterisation, we can write a simulation trivially. In fact, a simulation is probably the simplest form of such a characterisation. Hence, all we need is a computer (for example, SK calculus) and this relatively-simple simulation program (so simple that it could be a Boltzmann fluctuation). We don't necessarily need time to run the computation, since that would imply some kind of "outside universe", when it might be the case that computation can exist all by itself. From a pure reductionist point of view, we've removed unnecessary complexity and are left with just computation, which is nice and Platonic.
The brain in a vat idea, on the other hand, requires brains, vats and all manner of other support structures (eg. energy, entropy, etc.) to exist as well as the brain in a vat. In which case, we basically require an "outside universe" which is very similar to the "inside universe", so reductionism says that we're adding complexity with such an argument, so it's unnecessary.
- chriswarbo 13y agoAlso, note that specifying a brain simulation is much more difficult (takes more bits) than specifying a universe simulation. A brain simulation needs to have moods, emotions, headaches, sensory processing, etc. A universe simulation just needs a few equations (our best guess at the moment is general relativity plus the standard model). The chance that a universe simulation appears at random is much higher than the chance a brain simulation appears at random, even though a universe simulation may take vastly more resources to run.
- thaumasiotes 13y agoThe questions are exactly the same. All they do is point out that if all your information is routed through an intermediary, you'll never be able to prove that the intermediary is telling you the truth. Whether you describe that in terms of a meat brain being suspended in nutritive solution and hooked up to cables, or in terms of an electronic circuit receiving input from other electronic circuits, has no bearing on that.
- apw 13y agoBostrom's argument is a bit more sophisticated than the brain in a vat argument. Bostrom uses simple assumptions and basic probability to "prove" that it is overwhelmingly likely that you live in a simulation.
- chriswarbo 13y agoI wasn't proposing that a computer running our universe is based on electronic circuits; rather, I was proposing that computation itself is all that's needed to simulate our universe. Since an 'outside' universe doesn't need to bear any relation to our 'inside' universe, it can be vastly simpler. Maybe it's a rule 110 cellular automaton; maybe it's a 2,3 turing machine; maybe its an iota evaluator; it could even be just some abstract computational essence, distinct from implementation. That's enough to run a simulation. Now, the question is 'why simulate the universe when you could just simulate a brain'? This is basically the Boltzmann Brain argument. In terms of bits (see Kolmogorov complexity) the universe is simpler to describe (physics + initial conditions) than a whole brain (neurons, synapses, hormones, etc.). Basically, the universe can unfold from a tiny core (the big bang), whereas a single brain can't (it could unfold from a fertilised egg, but that's already huge, and requires all kinds of matter and physics to work which the big bang would have used anyway). In that case, a random program running on an 'outside' computer is much more likely to be a universe than a brain. By the anthropic principle, we could ask if our universe is the simplest which can support life, in terms of the number of bits required to encode the laws of physics as a program.