Bruno Marchal wrote a 10-point argument about determining whether or not we are simulated by some massive computer. Here is point 9 from that post:
9) Now, from computer science and logic, startlingly enough perhaps, we can isolate a measure on the 1-person comp histories, and this give us the laws of physics (this is too technical to be put here, and actually I have derived only the logical structure of the probability one, but I got something non trivial and very close to a quantum logic (which can be seen as the logic of the quantum probability one, as von Neumann has shown).
Bruno, I agree with everything in points 1-7 of the post I'm referring to.
Cool. (Kory is referring to my post http://www.escribe.com/science/theory/m5384.html )
I think I understand the main thrust of points 8 and 10, but they both depend on the truth of the quoted point 9.
Not at all. The point 8 follows only from the points 1-7. Actually the points 1 to 8 sum up the main result of my thesis, that is the reversal physics/machine's psychology (once we assume comp). This made the point 9 just a mathematical confirmation. I will try to explain, but actually it is me who does not understand why you don't see that the point 8 follows from the point 1-7. The proof really stop at 8. 9 is a mathematical confirmation with observer modelized (or even identify) with "equivalence class" of states of sound universal Turing machines.
I find this point  highly dubious, and I'm interested to hear more about why you believe it (or whether I'm actually interpreting it correctly).
OK. I promise I will try to make it clear, but that will be possible
only if you realize that 8 follows from 1-7. Keeping we assume comp all through.
I will first continue to comment your post, as a sort of preparation.
Is it your contention that if we start only with the idea of Platonia (which contains all possible computational structures and "events"), and we analyze the structure of all possible 1st-person histories weaving their way through this Platonia, we would see that a majority of them find themselves in universes like the one we currently inhabit, with stars, galaxies, relativity, quantum physics, etc.?
No. Such a contention is not mine. What you say here does not follow from neither 1-8, nor 9. Only the laws of physics follows, but the existence of the moon or of galaxies are not necessarily "laws of physics", but are quite possibly "geographical laws" (like being in Moscow instead of Washington). Now the stability of the appearance of matter is related to the laws of physics, and so, if (to talk like you) we analyze the structure of all possible 1st-person histories going trough your actual Kory-Heath state (including your memory of stars and galaxies) then the measure of your computational continuations in Platonia without stars and galaxies will (or should) be negligible. The disappearance of galaxies could be seen as a "talking white rabbit" event. So, only worlds with entities very similar to Kory Heath should contains galaxies. If this was false (in Platonia) then comp would be false (and refutable).
I find that extremely hard to believe; there are an infinite number of multi-dimensional cellular-automata worlds that contain nothing like stars, galaxies, or the familiar physics we know,
But then they don't contain entities sufficiently close to Kory Heath, (they don't go through Kory-Heath comp states) and those world/stories don't belong to your actual first person indeterminacy domain.
and I don't see any reason to believe that all the 1st-person histories weaving their way through these computational structures (which surely exist in Platonia) have less measure than those that weave through the structures more resembling our own universe.
You are right. No doubt there are worlds without stars and galaxies, but having srats and gilixas instead, and some Burno arguing to some Kyro about the geographical nature of those objects. Nothing in 1-8 prevents this.
I find it much easier to believe - in fact, it seems almost necessarily true - that, when we analyze the structure of all the 1st-person histories weaving their way through Platonia, we see that virtually all observers observe indeterminacy. This in itself seems like a non-trivial finding. It would be even more non-trivial if one could analyze the structure of the indeterminacy that virtually all 1st-person observers must observe, and find that it is very much like "quantum logic". This seems to be one of your claims, and it certainly seems possible (though I don't know enough yet to judge the issue for myself). However, it's a much further leap to conclude that we can go on to derive "the laws of physics" from the analysis of 1st-person histories weaving their way through Platonia. In the quote above, you acknowledge that you haven't actually done this - "actually I have derived only the logical structure of the probability one, but I got something non trivial and very close to a quantum logic" - but you seem to believe that it can be done. Why?
All right, you miss something. As I said, I feel *I* miss something because it seems to me that the point 8 follows directly from 1-7. (I suggest people print the post http://www.escribe.com/science/theory/m5384.html for having the 1-9 points in front of the eyes). Point 10 is not necessary because it concerns the particular question by Brett Hall. First let me copy the point 8, and let me rewrite it more carefully (if not less diplomatically!).
Point 8: (original version from post 5384)
8) So, if we are being simulated by a massive computer somewhere in a real universe, then to make any first person verifiable prediction we must take into account all the possible computations going through our actual state. So "the laws of physics", which we can temporarily define as the laws of whatever we can predict consistently, should be given by a measure on those 1-person computational histories.
Point 8bis: (Attempt toward a clearer ameliorated version. I have also make some emphases):
8bis) So, if we are being simulated by a massive computer somewhere in a real universe, then to make ANY first person verifiable prediction, we must take as domain of 1-person indeterminacy all the possible maximal consistent computational computations GOING THROUGH, AND FROM, OUR ACTUAL STATE, and existing in Platonia (more precisely in UD*, which is the complete infinite execution of the Universal Dovetailer). Let us (re)defined the laws of physics as the laws we can always predict and verify consistently (if any!). Now, having accepted the 1-7 points, the occurrence of such laws must have a measure 1, so the laws of physics must be derivable from what has measure 1 relatively to the measure on the computational histories. OK?
Let me illustrate a simple experiment in physics. Let us decide to let a chalk fallen. And let us compare some theories. A) The naive common sense theory: As far as I remember chalk always falls on the ground, so I infer that this will happen again. B) The first physicist: giving the laws F=ma, and Newton's gravitation law, I can predict with reasonable accuracy that the chalk will fall on the ground about here and about that time. C) The second physicist: the chalk is a many body quantum object in interaction with many bodies, so let us apply some gravitationnal form of Feynman summation on all quantum computational histories. After some phase randomization I can predict the chalk will fall here and at some time with more than 60 correct decimals. (He has been quick! I guess he used a quantum pocket calculator!) D) The computationalist: first let me bet on a comp level of substitution (which exists *hopefully*), and let me bet on my actual comp states, that is the one which describes my brain/body state in front of the chalk which I will let fallen. Now giving 1-7 (through comp) I "know" that my future first person experience is giving by a sum (average) on all computations (existing in Platonia) going from and through that state, and RELATIVE to that state. Obviously to compute that you need to run the complete UD in finite time and that's impossible, also you would be unable to recognize your own comp histories when described at other levels, so the computationalist will probably just answer "uncomputable".
But "platonistically" it remains that if comp is true the actual physical invariant must emerge as an average on ALL the maximal consistent extensions relative to our actual states (worlds, observer-moments, whatever ...). Although that can be proved useless for actually predicting the behavior of the chalk, it is enough for deriving physics. And that derivation goes in the reverse sense, that is, the more easy part will be the abstract logical structures, but that is enough for giving the geometry of the multiple histories.
Well I must go now, and if I hurry myself to much I will begin to be unclear ;-) Tell me if you have understand that keeping faith in comp through 1-7 leads necessarily to 8. Don't hesitate to give me an objection. The only difficulty in "8", I think, is to remember that we *assume* comp.
Then all what is needed for 9 (the mathematical confirmation) is to accept to "modelize" or better "identify" a platonistic observer by a sound modest (lobian) universal church-turing-post-markov-fortran-lisp- java-whatever machine (including quantum one). And to interview it about those relative consistent extensions and its inferable platonistic geometries and what is stable in their discourses. That has been made possible by the discovery of incompleteness (Godel 31) and its "axiomatizability" (Solovay 76).