>From: Marchal <[EMAIL PROTECTED]> >To: <[EMAIL PROTECTED]> >Subject: RE: Conditional probability & continuity of consciousness (was: >Date: Jeu, 6 Sep 01 10:53:17 +0100 > >Charles Goodwin wrote: > > > >I don't see how you can talk about the "probability of being a particular > >observer moment". The probability is 1 at that moment! We > >don't get dropped into observer moments from some metaphysical realm >(like > >Fred Hoyle's flashlight-and-pigeonholes analogy in > >"October the 1st is too late") - we ARE those observer moments. It's a >bit > >like the probability of me being born as me. The > >probability was 1, because otherwise I wouldn't be me! Similarly for this > >particular observer moment. > >So the question is "knowing that I am living (1-person view) this >observer-moment, what can I expect (immediately)? >The answer will be given by a measure on the 1- observer-moment >described in some 3-person view. >My feeling is that Charles and Jesse agree here. >Unlike Jacques Mallah, but like Charles, I cannot give meaning to an >absolute a priori probability on "observer-moment", but I can give, >like Jesse conditional or relative probabilities. This is because >the constraint of theoretical computer science are enough for >isolating natural nearness relations bearing on computational states >and histories. >I agree with Jesse that my actual observer-moment is not a matter >of definition. Nor will I appreciate, if I ask my doctor if there >is a high chance of surviving a delicate operation, that he answers >me that it is a matter of definition.
Hmm, I think we actually have a full spectrum of opinions here...Jacques believes only in absolute probability, Bruno believes only in conditional probabilities, and I believe in both. So, of course, I agree with what Bruno said about the importance of conditional probabilities--what happens to me after an operation is not a matter of definition--but I also think there should be an absolute distribution to tell me how likely it is that I will experience one type of observer-moment vs. another in the first place. I don't really think there's some "other metaphysical realm" where we get dropped from, but I do think that, as an analogy, the spotlight one is not actually so bad. After all, if you think that you just *are* your current observer-moment, how can you possibly become any other one? The observer-moment itself doesn't transform--it's just sitting there timelessly in Platonia among all other possible observer-moments. So, it's better to think of "continuity of consciousness" as a spotlight moving between different observer-moments, with the probability of going from one to another defined by the conditional probability distribution. Similarly, if you just *are* your current observer-moment with probability 1, nothing else can be said, so there doesn't seem to be any way to assign meaning to an absolute probability distribution on all observer-moments. I think it makes more sense to think of this distribution as the probability that a randomly-selected spotlight will be shining on a particular observer-moment, like in the Hoyle story. If we abandon the idea of an absolute probability distribution, we have no hope of explaining why I am this particular type of observer-moment experiencing this particular type of universe, and we can only explain why my future experience will have a certain amount in common with my current experience (assuming that's what the conditional probability distribution actually predicts). But plenty of observer-moments might find themselves experiencing universes with very different laws of physics--why am I experiencing these laws as opposed to some other set? Without a global probability distribution this can only be a brute fact, unexplained by the TOE. Likewise, why am I experiencing this particular era of the universe's history, or this unusual spatial region (the surface of a planet containing complex life), or this particular organism's point of view (a human vs. some other animal)? In all of these cases I think the intuitive explanation is something like the "anthropic principle" or the "self-sampling assumption" (this term is explained on http://www.anthropic-principle.com by Nick Bostrom, for anyone who's not familiar with it), and my hope is that the global probability distribution would incorporate a formalized version of something like this. But without such a global probability distribution, all this stuff becomes just more brute facts. Just because something has probability 1 from your current point of view, I don't think that means it should be treated as a brute fact. If so, all historical scientific theories would be pointless--cosmologists would be out of a job, for example. As long as we can imagine that things *could* have been different, we should try to explain why they are the way they are. Even though I know with probability 1 that I am Jesse Mazer sitting in front of a computer right now, I think I can imagine somehow that this could have been different--that my current experience could have been that of Blackbeard the pirate sailing the high seas, or that of a bat locating bugs through echolocation, or even that of a 12-dimensional alien living in a universe with very different laws of physics. The global probability distribution would hopefully tell me something about which types of observer-moments my "spotlight" is more likely to find itself shining on in the current moment. I wrote something about two different meanings of the "anthropic principle" in another post a while ago (at http://www.escribe.com/science/theory/m2445.html ) which might be relevant here. The idea was that the weak anthropic principle can be used in two slightly different ways--one version is just to say that I know with probability 1 that I am a particular type of intelligent organism, and that I use this to reason backwards and make deductions about what the universe must be like, given that fact. But the second version actually tries to go the other way and explain *why* I find myself to be an intelligent organism, by starting from a universe/multiverse large enough to contain at least a few intelligent organisms somewhere, no matter how rare, and then saying that in some sense I am guaranteed to find myself in one of those rare intelligence-containing regions since otherwise I wouldn't be an "I" at all. Here was the section of the post where I talked about the distinction: "I think we need to distinguish between two kinds of anthropic reasoning here. The first version just says "I observe that I exist, so I know with probability 1 that I must occupy a time and place where my existence is possible." Obviously this is completely uncontroversial. In this version, though, it's not really important that you say "I exist" or "intelligent observers capable of anthropic reasoning exist"--you could just as easily have made up the "star-thropic principle" which says that you know with probability 1 that stars exist, so you must be in a time and place where star formation is possible. As originally envisioned by Carter, both the "strong" and "weak" anthropic principles were versions of this idea. In "Modern Cosmology & Philosophy," John Leslie writes that "Carter's weak principle reminds us of the obvious but oft neglected truth that our place and time must, granted that we are in fact there, be a place and time where observers can exist: they are not, for example, fried immediately, as they would be shortly after the Big Bang. Carter's strong principle similarly reminds us that our universe must--as we do exist in it, don't we?--be a universe whose nature is not life-excluding...the 'must' is in both cases like that of 'The photo is marked WIFE, so *must* be of a woman.' No suggestion that the photo *had to be* of a woman or that it is somehow especially easy to be a woman!" But there's another version of "anthropic reasoning" which, although it perhaps deserves a different name, seems to me to be valid as well. This version says that, given that at least some observer-containing regions exist, "I" must find myself in one of these regions. In this case "I" is like the "I" in the Doomsday argument, which says "I" could have been born at any time in history, despite the fact that I wouldn't be the same person if I'd been born at some other time. In this version the fact that we're talking about "observers" is important--it wouldn't work with stars or anything else. If I win the lottery, I'm pretty "lucky"--I could just as easily have been one of the losers. On the other hand, despite the fact that physically realized genetic codes occupy only a tiny fraction of the space of all possible human DNA sequences, I wouldn't say I'm "lucky" to have an existing sequence rather than a nonexisting one--it isn't possible to "be" a nonexistent person, so of course I'm one of the existing ones (assuming for the moment that these other sequences aren't realized in a parallel universe or something). This is an application of the second version of anthropic reasoning. The distinction between these two versions still may not be entirely clear. Another way to put it is that the second version, when coupled with the assumption of multiple universes/regions, allows you to *explain* why you find yourself in what is possibly a quite unlikely set of circumstances. For instance, if we assume that many physical constants are indeed set randomly, then it seems the fact that our universe's constants are fine-tuned to allow life becomes less puzzling if we assume multiple universes (or multiple regions with different constants). In this case, the "explanation" for the apparent fine-tuning is that at least one correctly-tuned universe is likely to exist, and the second version of the anthropic principle says that's the universe that "I" must find myself in. In contrast, the first version can't explain anything at all--it's just a statement about your prior knowledge. An even clearer way to distinguish the two versions is that the second version allows you to make new inferences about reality, while the first only describes what you already know. For example, if we find that our universe is indeed fine-tuned, then by a version of Bayesian reasoning we can say we should be more inclined to believe in the existence of other universes with different constants, in order to explain the "coincidence" of observed fine-tuning (to make this more obvious, feel free to assume we know a priori that there's a 50% chance God created a single universe and a 50% chance he created a multiverse). This is similar to "copernican" reasoning, like the Doomsday argument, which also allows you to infer new things about reality just by observing your own position in it. In fact, I'd make a case for distinguishing the two anthropic principles by saying the second is identical to what's sometimes called the "copernican anthropic principle." For example, most people who say fine-tuning increases the probability of multiple universes would also say that we're more likely to find ourselves in a universe where observers (or observer-moments) are more common rather than one where they are rare, assuming the number of each kind of universe is about equal." Jesse _________________________________________________________________ Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp