Re: Is the universe computable?
John M wrote: George Q wrote (among many others, full post see below): A.the universe in which I live according to the current intuition I have of it and B: the possibility to simulate the universe at any level of accuracy. First I wanted to ask what is intuition, but let us stay with common sense (however divergent that may be). I don't have your intuition and you don't have mine. There is an assumption here which is that however divergent these intuition or common sense views of it might be, there exist (in some sense) something that we can refer to as the universe. By the way, this is not the first series of post with that title and though I am not sure I went through all of them this is the first time I see this issue discussed here. This is indeed a good question but why me ? And how do other participants define what the universe could be ? Now if A is true, I wonder upon WHAT can you simulate? I don't understand the question. Your reply points to first person processes. Yes but this is onky in one sense. There might exist a lot of other universes. Among all possible universes, I mean I am talking about the one I feel I live in. This is just a way to designate one specific universe (not to mean that I am not interested in the computability of others but I have a special interest in that one). I like better a 'mixed' way: MY 'interpretation' of something to which I have access only through such interpretation - but there must be a basis for the inter[retation both as my way of doing it, but more importantly the 'thing' to interpret. The (common sense) intuition comes into the 'my way'. Do we really disagree ont that ? C. (universe:)the smallest independent piece that does include myself First I object to independent which would lead to a multiple existence of parallel natures (all of them singularities for the others) and we cannot gain information from them - which would connect in some ways. Existence as we can reasonably speak about it, is interconnected - nothing independent. I think we agree here. I gave indication of what I meant by dependence (and therefore by independence) as: space-time continuity, particle interaction and this kind of things and I feel that everything in the universe is interconnected in that way (this makes my definition of universe a tautology but it can be linked in some way to the common sense) even when considering causally isolated regions of space-time (because these would be connected in some future and they cannot be considered as isolated from that future). If you make concessions to that and accept 'relative' independence, then the smallest 'unit' including you is you. I don't think you want to go solipsistic. I don't believe I can isolate something like 'me'. If you expand further - well, I did not find a limit. I am not sure of that. If many universes do exist, they might well be considered independent of each other (because of lack of spatio-temporal continuity or particle interaction or the like). This is why I concocted a narrative about a 'plenitude' (undefined, not Plato's concept) FROM which distinct 'universes' occur (in timeless and countless fulgurations, callable BigBangs) with some INTERNAL history - in 'ours' including space and time. So I have a 'universe to talk about' - within my intuition G. And many more 'universes', obscured by ignorance (no info) - not excluded. I don't restrict 'them' to our logic, math, system, not even causality. This sounds very speculative (not to say mystical) to me. I like your metaphor of the dominos. It pertains to a view we may have in our (exclusively possible) reductionist ways about the world: THIS ONE is the cause of an event (one side of the domino) while the rest of the system (all of it) is also influencing - whether we consider it in our limited model (within our chosen boundaries) or not. I have two views of causality. In the first one, causality is a local and macroscopic (and mesoscopic) emergent property linked to the fact that the universe would be more ordered on one side that on the other. In the second, events continuously trigger other events. The second view seems to be some kind of idealisation of the first one that will always be no more than a convenient simplification/approximation. Considering that everything occurs or must occur according to the second view sounds like an error to me. This error tends to make the universe viewed as somthing evolving through time while it should be viewed as a static (intemporal) object within which (the flow of) time emerges from its structure as a local property. This is also why views in which universes continously fork as events occur in one way or the other does not make much sense for me. This list goes many times beyond the reductionist ways of thinking. I don't think that the first view is beyond the reductionist ways of thinking. Both views are compatible with a completely mathematic
Why no white talking rabbits?
Jesse Mazer wrote: Why, out of all possible experiences compatible with my existence, do I only observe the ones that don't violate the assumption that the laws of physics work the same way in all places and at all times? Because a universe whose space-time was subject to different physical laws in different regions would not have been able to generate you and sustain you, or more precisely I suppose would only be able to generate and sustain you with infinitesimal probability. And it would be even more highly unlikely that should you have been magically conjured by this inconsistent-or-inconstant-physical-laws universe, that you would observe any other people (or rabbits, white or otherwise) because they themselves would have only infinitesimal probability of being magically, coincidentally conjured into that universe. It's better to find the all of the essential constraints (all the way back to 10^-43 seconds after the big bang) which made it highly probable that you (or something like you) would exist in the universe, and then explain how those constraints are all consistent with each other and with information theory, and then to realize that a set of constraints HAS TO BE consistent with (all of) each other and with information theory and with making your (or equivalent creature's) existence highly probable, in order for you to actually exist with any high probability. By the argument de facto, I think it's safe to say that things in the universe are such that people (or functional equivalents) are highly probable to exist on a small but significant set of planets (those with the right temperature ranges and proportions of different elements) in the galaxies in our observable portion of the universe. It is ONE HELL OF A DETAILED SET OF CONSTRAINTS that made all of this (us) highly probable, White talking rabbits with watches are inconsistent with those constraints, in ways too boring perhaps to get into. Ok, since we're way down here in the post, I'll get into it. General intelligence of human-like level (involving ability to hypothesize, abstract flexibly, construct a wide variety of functional, purposeful constructions out of raw materials, and plan actions and consequences in detail), only evolves by natural selection in critters that are physically equipped to DO SOMETHING with their intelligence. For a rabbit, it's pretty much limited to hopping about in more complex patterns to avoid being eaten, based on some kind of vastly intelligent psyching out of where its preditor is going to strike next, and to determining where to find the very best places to find the most nutritious and tasty grass. This is too limited a domain to require or select for a general, long-range constructing and planning mind-firmware to develop in a rabbit brain.. Another favorite of mine is why dolphins and whales are KIND OF intelligent (like a poodle or parrot is) but not extremely...So what, we're going to develop more complex tricky ways to bump things with our snouts? I don't think so. Group hunting (in a too-easy, too uniform, too acceleration-constrained-because viscous fluid habitat) is as complex as dolphin brains ever need to be. Cheers, Eric
Re: Is the universe computable?
Dear Jesse, A very good question, containing its own answer! You wrote: Why, out of all possible experiences compatible with my existence, do I only observe the ones that don't violate the assumption that the laws of physics work the same way in all places and at all times? Have you taken into account the idea that observers can communicate their finding to each other and that, maybe - just maybe - this plays into the wave function's behavior? David Deutsch has just posted a paper discussing a related subject (http://xxx.lanl.gov/abs/quant-ph/0401024). Let us take some time to read it and then pick this discussion back up. ;-) Kindest regards, Stephen - Original Message - From: Jesse Mazer [EMAIL PROTECTED] To: [EMAIL PROTECTED] Sent: Thursday, January 08, 2004 1:17 AM Subject: Re: Is the universe computable? Stephen Paul King wrote: Dear Jesse, Would it be sufficient to have some kind of finite or approximate measure even if it can not be taken to infinite limits (is degenerative?) in order to disallow for white rabbits? A very simple and very weak version of the anthropic principle works for me: Any observation by an observer must not contradict the existence of that observer. But there are plenty of observations that would not result in my destruction, like seeing a talking white rabbit run by me, anxiously checking its pocket watch. To pick a less fantastical example, it would also not be incompatible with my existence to observe a completely wrong distribution of photons hitting the screen in the double-slit experiment. Why, out of all possible experiences compatible with my existence, do I only observe the ones that don't violate the assumption that the laws of physics work the same way in all places and at all times? I disagree with David's claim that The universe doesn't depend on the rock for its existence... since the notion of quantum entanglement, even when considering decoherence, implies that the mere presense of a rock has contrapositive effects on the whole of the universe. The various discussions of null measurements by Penrose and others given a good elaboration on this. I think you're talking about a different issue than David was. You're talking about a rock that's a component of our physical universe, while I think David was responding to Chalmers' question about whether random thermal vibrations in a rock instantiate all possible computer simulations, including a complete simulation of the entire universe (complete with all the rocks inside it). To me the computational question boils down to the question of how does Nature solve NP-Hard (or even NP-Complete) problems, such as those involved with protein folding, in *what appears to be* polynomial time. What do you mean by the computational question? Are you addressing the same question I was, namely how to decide whether some computer simulation is instantiating a copy of some other program? If we imagine something like a detailed physical simulation of some computer circuits running program X, it seems intuitive that this simulation instantiates a copy of program X, but Chalmers' paper suggests we don't have a general rule for deciding whether one program is instantiating any other given program. And as I said, this is relevant to the question of measure, and a measure on observer-moments is probably key to solving the white rabbit problem. --Jesse _ Get reliable dial-up Internet access now with our limited-time introductory offer. http://join.msn.com/?page=dept/dialup
Re: Is the universe computable?
At 11:34 08/01/04 +0100, Georges Quenot wrote: I am very willing (maybe too much, that's part of the problem) to accept a Platonic existence for *the* integers. I am far from sure however that this does not involve a significant amount of faith. Indeed. It needs an infinite act of faith. But I have no problem with that ... There are some objections to it and I am not sure that none of them make sense. Also, as someone said (if anybody has the original reference, in am interested): the desire to believe is a reason to doubt. I think that, even if it is true, arithmetic realism needs to be postulated (or conjectured) since I can't figure how it could be established. All right. That's why I explicitly put the AR in the definition of computationalism. About your question is the universe computable? the problem depends on what you mean by universe. The definition you gave recently are based on some first person point of view, and even that answer does not makes things sufficiently less ambiguous to answer. Don't hesitate to try again. You can also read my thesis which bears on that subject (in french). You may be interested in learning that at least the *physical* universe cannot be computable once we postulate the comp hypothesis (that is mainly the thesis that I or You are computable; + Church thesis + AR). The reason is that with comp, as with Everett (and despite minor errors in Everett on that point), the traditional psycho-parallelism cannot be maintained. See my URL below for more. Why there is no FAQ? Because we are still discussing the meaning of a lot of terms I agree with you in your critics of Searle. I agree with most critics of Chalmers too, also. Welcome, Bruno http://iridia.ulb.ac.be/~marchal/
Re: Is the universe computable?
Possibly relevant to this thread: NYTimes: January 8, 2004 New-Found Old Galaxies Upsetting Astronomers' Long-Held Theories on the Big Bang By KENNETH CHANG ATLANTA, Jan. 7 Gazing deep into space and far into the past, astronomers have found that the early universe, a couple of billion years after the Big Bang, looks remarkably like the present-day universe. Astronomers said here on Monday at a meeting of the American Astronomical Society that they had found huge elliptical galaxies that formed within one billion to two billion years after the Big Bang, perhaps a couple of billion years earlier than expected. A few days earlier, researchers had announced that the Hubble Space Telescope had spotted a gathering cloud of perhaps 100 galaxies from the same epoch, an early appearance of such galactic clusters. On Wednesday, astronomers at the meeting said that three billion years after the Big Bang, one of the largest structures in the universe, a string of galaxies 300 million light-years long and 50 million light-years wide, had already formed. A light-year is the distance that light travels in one year, or almost six trillion miles. That means the string is nearly 2,000 billion billion miles long. Some astronomers said the discoveries could challenge a widely accepted picture of the evolution of the universe, that galaxies, clusters and the galactic strings formed in a bottom-up fashion, that the universe's small objects formed first and then clumped together into larger structures over time. The universe is growing up a little faster than we had thought, said Dr. Povilas Palunas of the University of Texas, one of the astronomers who found the string of galaxies. We're seeing a much larger structure than any of the models predict. So that's surprising. In the prevailing understanding of the universe, astronomers believe that slight clumpiness in the distribution of dark matter, the 90 percent of matter that pervades the universe but still has not been identified, drew in clumps of hydrogen gas that then collapsed into stars and galaxies, the first stars forming about a half billion years after the Big Bang. The galaxies then gathered in clusters, and the clusters gathered in long strings with humongous, almost empty, voids in between. The first such string, named the Great Wall, was discovered in 1989 about 250 million light-years away. The newly discovered string lies in a southern constellation, Grus, at 10.8 billion light-years away, and represents what the universe looked like 10.8 billion years ago, or three billion years after the Big Bang. The international team of researchers identified 37 very bright galaxies in that region of space and found that they were not randomly distributed, as would be expected, but instead appeared to line up along the string. Such structures are rarely seen in computer simulations of the early universe, said Dr. Bruce E. Woodgate of the NASA Goddard Space Flight Center, a member of the team. We think it disagrees with the theoretical predictions in that we see filaments and voids larger than predicted, Dr. Woodgate said. Dr. Robert P. Kirshner of the Harvard-Smithsonian Center for Astrophysics said the findings were interesting, but that it was too early to eliminate any theories. What is probably needed was a better understanding how of a clump of dark matter leads to the formation of stars. What we're seeing here, Dr. Kirshner said, is the beginning of the investigation how structure grows. At the astronomy meeting on Monday, another team of researchers reported finding a large number of large elliptical galaxies. As part of an investigation known as the Gemini Deep Deep Survey, the astronomers explored 300 faint galaxies dating from when the universe was three billion and six billion years old. The large elliptical galaxies are supposedly a merged product of smaller spiral galaxies. Yet not only did they exist that early in the universe, but the stars within these galaxies also appeared a couple of billion years old already, implying that they had formed as early as a billion and a half years after the Big Bang. Massive galaxies seem to be forming surprisingly early after the Big Bang, said Dr. Roberto Abraham of the University of Toronto and a co-principal investigator on the team. It is supposed to take time. It seems to be happening right away. The data actually fit better with the views that astronomers held before the rise of the current dark-matter models, when they theorized that the largest galaxies formed first. If we presented this to astronomers 25 years ago, Dr. Abraham said, they wouldn't have been surprised. A third team of astronomers found two clusters of galaxies that also point to a precocious universe. Using the Hubble telescope, the astronomers spotted a cluster of at least 30 galaxies dating from when the universe was younger than two billion years old and extending three million light-years across. Which is similar in size to what
Re: Why no white talking rabbits?
Jesse Mazer wrote: Why, out of all possible experiences compatible with my existence, do I only observe the ones that don't violate the assumption that the laws of physics work the same way in all places and at all times? Eric Hawthorne replied: Because a universe whose space-time was subject to different physical laws in different regions would not have been able to generate you and sustain you, or more precisely I suppose would only be able to generate and sustain you with infinitesimal probability. What about a universe whose space-time was subject to all the same physical laws as ours in all regions - except in the vicinity of rabbits? And in those other regions some other laws applied which allow rabbits to behave magically? Hal Finney
Re: Is the universe computable?
Georges Quenot writes: I would be interested in reading the opinions of the participants about that point and about the sense that could be given to the question of what happens (in the simulated universe) in any non- synchronous simulation when the simulation diverges ? I'll make two points. First, you're right that there are other ways of computing a universe than simply starting with some initial conditions and evolving time forward step by step, computing the state of the universe at each subsequent instant. You list several ways this might happen and I agree that this concept makes sense. We might call this non-sequential or non-temporal simulation. But, given the specific temporal structures that exist in our universe, there are limitations to how this computation can be done. Specifically, we are able to construct physical computers in this universe which perform complex calculations. And among these calculations are those which are believed to be inherently sequential and lengthy, calculations for which the answer cannot be computed without spending a great deal of time from the initial values. Given that our universe contains systems like this, it constrains the amount of computation which must be done in any kind of non-sequential simulation. Specifically, the non-sequential simulation must do at least as much computation in order to produce our universe as the more traditional kind of sequential simulation. This demonstrates a limit on the power of non-sequential simulation. My second point is with regard to your specific question, what would happen if we tried to simulate a universe which diverged in some space-time region from the conventional physical laws? This is our often-discussed flying rabbit paradox (we have other names as well), where it seems that if all universes exist, we might as well be living in a universe which was lawful everywhere except in some small region, or up until a certain time, as in one where the laws are truly universal. Your question is whether this concept makes sense in a non-sequential simulation, or whether it assumes sequential simulation. I think it makes just as much sense in the context of non-sequential simulation. The non-sequential simulator is trying to find or create a universe which satisfies certain physical laws. It may be iteratively solving a differential equation or using some other non-temporal method, but that is its goal, its mechanism. The case at hand is simply a matter of defining the physical laws to be different in different regions of space-time. We could define the physical laws which the non-sequential simulator is trying to solve in some such terms. We'd say, observe these laws in this region, but these other laws in that region. For example, we might say to observe the true laws of our universe (whatever they turn out to be) up to simulated time T, and then to observe other laws after time T. Or similarly we could have one set of laws up to spatial coordiate X, and another set of laws on the other side of X. The non-sequential simulator would have no more difficulty in creating a universe which satisfied such non-uniform physical laws than in one where the laws were the same everywhere. So I'd say that the issue of sequential vs non-sequential simulation is irrelevant to the question of the existence of flying rabbit universes and does not shed light on the issue. Hal Finney
Re: Is the universe computable?
You asked what I meant: (- Original Message - From: Georges Quenot To: John M Cc: [EMAIL PROTECTED] Sent: Thursday, January 08, 2004 3:50 AM) ( John M wrote: [earlier excerpts from GQ's post]: A.the universe in which I live according to the current intuition I have of it and B: the possibility to simulate the universe at any level of accuracy. Snip, and later: Now if A is true, I wonder upon WHAT can you simulate?) [GQ remark]: I don't understand the question. [JM]: Your reply points to first person processes. If you consider (the) (your) universe, something according to YOUR current intuition what YOU have of it, then there is nothing else upon which you can simulate it. You definitely need something ELSE on which a simluation can be based. More than just your intuition-based universe. (I didn't say: 'outside reality'!). My (rethorical) question pointed to this dichotomy. It may be wrong, but probably understandable now. Further on : [GQ]: I don't believe I can isolate something like 'me'. Full agreement here. However: If you expand further - well, I did not find a limit. [GQ]: I am not sure of that. If many universes do exist, they might well be considered independent of each other (because of lack of spatio-temporal continuity or particle interaction or the like). [JM]: I don't restrict my views to spatio-temporal continuity, or to the 'particle-interaction' views of reductionistic human science. We MAY not know everything by today (ha ha). I leave open my 'scientific agnosticism' - the potential answer: I dunno. So you mat find a limit what I didn't. No argument here. To your remark on my narrative (watch the name I use): This sounds very speculative (not to say mystical) to me. Not more than the white or pink elephants/rabbits. Or some computation that takes infinite time and infinite virtual memory . Finally I like to use instead of triggers (in causality #2) 'facilitates' and must occur - may occur, leaving open changing circumstances to alter what we may postulate upon our closed model. With best regards John Mikes SNIP the rest
