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Is it possible to accurately predict the future? watch

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    (Original post by Donald Duck)
    Why? I can think of a theory, predict a given result, and then the result shows up. My prediction came true.

    Predicion and guess depends on the intention of author. You'd just say my prediction tends to be wrong.
    Because I refuse to apply the word "prediction" to the "predictions" of witches and the likes.
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    nope. quantum mechanics puts a spanner in the works here.
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    (Original post by Smaug123)
    Well, AFAIK, we aren't sure to what extent the universe is probabilistic. Certainly on large (micro or bigger) scales, the universe appears to be essentially deterministic; we don't actually know whether quantum physics is truly random processes
    As I've said before here, the only hope of escaping randomness here is through some sort of "hidden variables", a large class of which have already been ruled out. Conditions for these are stringent enough for most of the scientific community to have given up on them, although there are a few widely respected (Nobel Prize winners) scientists who still believe in that.

    It appears to be an open question as to whether the brain is essentially quantum-mechanical; I've seen pretty convincing arguments on both sides (from Douglas Hofstadter and Roger Penrose, specifically; I come down on Hofstadter's side, that there is no a priori reason to believe that the brain is quantum). If it's not, then the brain is probably deterministic, unless you're a dualist (which is a pretty tenuous view to hold, given all the evidence we have that the brain is doing computations that result in consciousness).
    Maybe. The brain is messy. But the brain is surely not ruled by classical physics, so even if it's not exactly quantum mechanical it might not be deterministic. Still, in order to be able to accurately predict the future you need to be able to predict everything, so the brain alone doesn't damage the QM argument.

    Correct me if I'm wrong - I'm a lowly maths student who doesn't know much beyond the woefully inadequate A-level syllabus on quantum stuff.
    I'll just end with a note on one of your notes here: "it appears on preliminary evidence to be that way, but given that at least one of quantum mechanics and general relativity is incomplete or wrong…"

    Most physicists will argue that general relativity is the wrong one. Not only because it is essentially very classical, but also because it is incompatible with the kind of formalism that enables unification of the other forces (i.e. it is nor renormalizable). That and quantum mechanics/ quantum field theories have survived the most demanding experimental tests - whereas many think the problems of dark energy and dark matter could be solved by improving on GR.

    Of course, QM can be the wrong one, but even if it is wrong it is unlikely that the theory to substitute it would be deterministic (kind of like quantum theories of gravity all try to mantain the essential features of GR).
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    (Original post by viriol)
    Maybe. The brain is messy. But the brain is surely not ruled by classical physics, so even if it's not exactly quantum mechanical it might not be deterministic. Still, in order to be able to accurately predict the future you need to be able to predict everything, so the brain alone doesn't damage the QM argument.
    I'm happy to go with your other points - they sound plausible to me, a non-expert But "the brain is surely not ruled by classical physics" is a very strong claim - do you have correspondingly strong evidence for it? Free will, etc, can be "explained" (for certain values of "explain") without requiring non-determinism, by (for instance) pointing to other instances of emergent behaviour (such as ant colonies). Of course, this doesn't "explain" free will in the sense that it doesn't tell us how to reproduce it; but then nor does any other hypothesis at the moment. (Response predicated on the assumption that you believe in "free will", for some messily-defined version of that concept; I currently believe that we are deterministic, but only because it seems neater that way to me.)
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    The problem is that quantum indeterminacy affects particles' behaviour on a fundamental level, making it impossible to know with certainty what the state of matter will be in the future, but only probabilistically.
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    (Original post by Smaug123)
    I'm happy to go with your other points - they sound plausible to me, a non-expert But "the brain is surely not ruled by classical physics" is a very strong claim - do you have correspondingly strong evidence for it? Free will, etc, can be "explained" (for certain values of "explain") without requiring non-determinism, by (for instance) pointing to other instances of emergent behaviour (such as ant colonies). Of course, this doesn't "explain" free will in the sense that it doesn't tell us how to reproduce it; but then nor does any other hypothesis at the moment. (Response predicated on the assumption that you believe in "free will", for some messily-defined version of that concept; I currently believe that we are deterministic, but only because it seems neater that way to me.)
    I'm not sure whether it qualifies as "strong evidence", but here goes (perhaps most is more like a strong clue) and you tell me:

    Firstly, let me clarify my point: I mean that the microscopic behaviour of the brain is surely not ruled by classical physics. This I strongly believe to be true because of one simple fact: there is no known physical/chemical/biological system whose behaviour can be explained by classical physics at a microscopic level. After all, there isn't a (known) valid classical microscopic theory.

    My second point is a bit more detached from experience. That question about the brain is in the air because of the role observation plays in quantum mechanics. I've heard "the brain is the one system shrodinger's equation doesn't describe". Even if that is true, that surely doesn't mean quantum mechanics is wrong (we have enough evidence to say that QM is less bound to fall than any other physical theory) but rather incomplete. A complete theory wold therefore not be one that "restored" classical physics - it would be one which could account for the role of counsciousness in quantum mechanics (and such an account is almost surely beyond the reach of classical theories due to their intrinsic deterministic limitations - once again, it would require "hidden variables", whose experimental situation is not the best, bla bla...).

    Finally, I'd like to remind that, although we are really far from knowing how the brain works, we do know a bit about its most basic functioning - electromagnetic phenomena are taking place by chemical means. Since the most fundamental (and only "completely" working) physical theory of electromagnetism is a quantum field theory I find it very unlikely that a classical description of the brain is possible.
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    (Original post by viriol)
    Firstly, let me clarify my point: I mean that the microscopic behaviour of the brain is surely not ruled by classical physics. This I strongly believe to be true because of one simple fact: there is no known physical/chemical/biological system whose behaviour can be explained by classical physics at a microscopic level. After all, there isn't a (known) valid classical microscopic theory.
    Yep, true, but we can model chemical reactions without resorting to Schrödinger - the mechanism for the reactions may be QM, but that doesn't make the product of the reaction unknowable. I agree that it's not yet known whether the brain is fundamentally quantum-mechanical (as opposed to incidentally quantum-mechanical in the same way that a bouncing ball is incidentally quantum-mechanical). [Also take my statements here with the caveat that I'm not a chemist or biologist or neuroscientist.]
    (Original post by viriol)
    My second point is a bit more detached from experience. That question about the brain is in the air because of the role observation plays in quantum mechanics. I've heard "the brain is the one system shrodinger's equation doesn't describe".
    But observation in the quantum mechanical sense just means "disturbance of a system by a mechanism with relatively far-reaching consequences" - an electron moving through a system could count as observation, if that electron went on to move outside the system. There's nothing special about the brain in that sense; the fact that there happens to be a large web of complicated dependencies on initial conditions concentrated into a smallish volume seems to me not to be much different from a *very* large web of complicated dependencies on initial conditions in a large volume (that is, some subsection of the universe).
    (Original post by viriol)
    Finally, I'd like to remind that, although we are really far from knowing how the brain works, we do know a bit about its most basic functioning - electromagnetic phenomena are taking place by chemical means. Since the most fundamental (and only "completely" working) physical theory of electromagnetism is a quantum field theory I find it very unlikely that a classical description of the brain is possible.
    But I can use ordinary classical experimentation to determine the behaviour of, say, an electrical wire when a current is run through it, without working out any quantum field theory. It's like saying "friction happens through electromagnetic forces, so to understand a ball rolling down a hill, I have to develop a theory of electromagnetism" - it *may* be true, but on the other hand we may not need such a powerful theory.
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    (Original post by Smaug123)
    Yep, true, but we can model chemical reactions without resorting to Schrödinger - the mechanism for the reactions may be QM, but that doesn't make the product of the reaction unknowable. I agree that it's not yet known whether the brain is fundamentally quantum-mechanical (as opposed to incidentally quantum-mechanical in the same way that a bouncing ball is incidentally quantum-mechanical). [Also take my statements here with the caveat that I'm not a chemist or biologist or neuroscientist.]
    That is an interesting point you are raising. It is true that most (not all: see dense stars, liquid helium, superconductors, superfluids, low-temperature solids, etc) phenomena can be explained by classical physics at a macroscopic scale. However, that doesn't mean you can predict everything about that system using classical physics. It's only enough when you're interested in predictions in "human" scales of time, energy, etc...

    As an example, let us consider the case of a diamond at rest. It is macroscopic, and classical physics is more suitable to its study than to the study of chemical reactions (I can tell you that despite your not needing QM to predict the products/rates of simple reactions, it is widely used by computational chemists in more complex - including biochemical - reactions). According to classical physics, predicting the future of this isolated diamond is pretty simple - all it does is be there, and nothing happens to it at all, no matter how many times you check! However, if you take QM into account, after enough time (more than the current age of the Universe), over 99% of that diamond will have turned into graphite, the stable form of carbon. Surely you'll agree that, if classical physics is insufficient to accurately predict the fate of one "lousy" diamond, then it is powerless when faced with the future of the Universe.

    But observation in the quantum mechanical sense just means "disturbance of a system by a mechanism with relatively far-reaching consequences" - an electron moving through a system could count as observation, if that electron went on to move outside the system. There's nothing special about the brain in that sense; the fact that there happens to be a large web of complicated dependencies on initial conditions concentrated into a smallish volume seems to me not to be much different from a *very* large web of complicated dependencies on initial conditions in a large volume (that is, some subsection of the universe).
    Not exactly. Observation actually means measurement. The thing is that, in QM, if you never try to find out the value of any observable quantity, then everything is deterministic. This is because Shrodinger's equation is actually a deterministic equation ruling the "state" of the system. This "state" can be thought of as an infinite vector whose coordinates are probabilities for specific observable quantities of the system. When you measure a specific quantity, that's when indetermination arises - your state "collapses", i.e., it randomly chooses one possible "direction" and forgets the rest. Then everything will be deterministic again until you try another measurement.

    So your electron moving through a system does not qualify as an observation, although looking at that electron does. There is a subtle yet radical difference.

    Bearing this in mind, what may be special about the brain is whatever it is that makes observations this special. If it doesn't have to do with the brain, then the brain is most likely just the same as everything else and obeys QM.

    But I can use ordinary classical experimentation to determine the behaviour of, say, an electrical wire when a current is run through it, without working out any quantum field theory. It's like saying "friction happens through electromagnetic forces, so to understand a ball rolling down a hill, I have to develop a theory of electromagnetism" - it *may* be true, but on the other hand we may not need such a powerful theory.
    This point is basically answered in my first pragraph. But I'll take the opportunity to note that classical electromagnetism is incapable of, for example, telling you the current through a classical wire when there is a sufficiently low applied voltage (basically, it doesn't care that the electron is the fundamental source of charge and starts predicting arbitrary fractions of the electron charge passing). But it's worse than that - conduction through a metal wire can actually only be explained using QM (Drude's model, the closest there is in classical physics, makes a couple of predictions that glaringly contradict easily observed properties, although it miraculously makes many accurate predictions).

    Just don't underestimate the relevance of powerful microscopic theories to our understanding and modelling of macroscopic phenomena.
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    (Original post by viriol)
    Just don't underestimate the relevance of powerful microscopic theories to our understanding and modelling of macroscopic phenomena.
    Your diamond example is a very long-term thing - the brain is nothing like so long-term, although I do see that the brain (being much more active in terms of chemical reactions) is many orders of magnitude more likely than a diamond to react in the first place. OK, I think you might have persuaded me - it does indeed sound like the brain is fundamentally quantum-mechanical. I still think that it is possible to build a non-quantum version (a classical AI) - that is, I still think that consciousness is not a strictly quantum property - and, relatedly, I'm still a bit reserved about "observation as collapser of quantum states" - it seems strange that such a tiny subset of reality (the brain) is privileged above everything else in its ability to collapse wave functions. I read something fairly recently about this (in qualitative terms, not mathematical - I'm only in my first year) but I can't remember where, which said that any sufficiently broad consequences to a system would collapse a wave function. I realise that this is very weak evidence!
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    (Original post by Smaug123)
    You're thinking on a less physicsy level than the OP. The OP is saying "if you knew the position etc of every particle, could you simulate the universe accurately?" - the assumption being that if you know where every particle is, you know whether it's raining or not.
    Never say never; humans are very predictable in many circumstances, even without knowing their brain states. I can predict that if I poke you with a needle, you will be annoyed (although I don't know the exact form that the annoyance will take). If I knew your brain state, I could predict what form your annoyance would take, by simulating the input to your brain.
    It's nice that someone got the idea
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    (Original post by viriol)
    I was taken aback a little bit by this reply. How can you conclude this from what I wrote?
    Deduction being the process by which you move fom two true premises or propositions to a conclusion (Aristotle the Syllogism), a logically valid method of gaining knowledge, yet if you cannot know the momentum and position of a particle (Schroedinger (if that is how you spell it)) then rationalism as a means of gaining knowledge is somewhat obselete. However induction seems to be still valid. For an example of induction if you were standing on a bridge and you saw 10 white swans swim past, you could predict (hypothesis) that all swans are white, with a small amount of accuracy, et.c. for 100, 1000...However it only takes one black swan to prove this wrong. Hence, Karl Popper, a contemporary philosopher said that scientific knowledge is implicitly disprovable only. Yet it is the only method that we can use in our search for knowledge
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    (Original post by Donald Duck)
    Why? I can think of a theory, predict a given result, and then the result shows up. My prediction came true.

    Predicion and guess depends on the intention of author. You'd just say my prediction tends to be wrong.
    that's modelling, I was talking of certainty
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    (Original post by Smaug123)
    Your diamond example is a very long-term thing - the brain is nothing like so long-term, although I do see that the brain (being much more active in terms of chemical reactions) is many orders of magnitude more likely than a diamond to react in the first place. OK, I think you might have persuaded me - it does indeed sound like the brain is fundamentally quantum-mechanical. I still think that it is possible to build a non-quantum version (a classical AI) - that is, I still think that consciousness is not a strictly quantum property - and, relatedly, I'm still a bit reserved about "observation as collapser of quantum states" - it seems strange that such a tiny subset of reality (the brain) is privileged above everything else in its ability to collapse wave functions. I read something fairly recently about this (in qualitative terms, not mathematical - I'm only in my first year) but I can't remember where, which said that any sufficiently broad consequences to a system would collapse a wave function. I realise that this is very weak evidence!
    Viriol and Smaug thanks for the discussion, it is informative and interesting. I would have to say though that I think that consiousness is due to quantum randomness, (I'm not a physicist so I've only gathered a small amount of generalities here). Yet I don't see why focusing on the brain will highlight any particular properties of determanism et.c. It's just a lump of (mostly) fats and sugars. (would love to discuss more but not got the time )
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    Just to add to all the quantum physics naysayers, it may still be possible to predict a possible and maybe likely future. You just can't be certain about it. It may not be accurate at all.
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    (Original post by Smaug123)
    Your diamond example is a very long-term thing - the brain is nothing like so long-term, although I do see that the brain (being much more active in terms of chemical reactions) is many orders of magnitude more likely than a diamond to react in the first place. OK, I think you might have persuaded me - it does indeed sound like the brain is fundamentally quantum-mechanical. I still think that it is possible to build a non-quantum version (a classical AI) - that is, I still think that consciousness is not a strictly quantum property - and, relatedly, I'm still a bit reserved about "observation as collapser of quantum states" - it seems strange that such a tiny subset of reality (the brain) is privileged above everything else in its ability to collapse wave functions. I read something fairly recently about this (in qualitative terms, not mathematical - I'm only in my first year) but I can't remember where, which said that any sufficiently broad consequences to a system would collapse a wave function. I realise that this is very weak evidence!
    That is only (too) strange if you think about quantum mechanics as modelling some "absolute" reality. Physics is all about observation. Quantum mechanics was built to account for weird observations, so it's not entirely strange that observations (not the brain directly) have a "special" role. There are a couple of ways you can interpret it to make it sound more or less weird, but they're all equivalent in terms of observable consequences.

    BTW, regarding the brain example, even if it took very long, QM would be evident in brains after a sufficient (arbitrarily large) number of generations.
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    (Original post by aidanhaslam)
    Deduction being the process by which you move fom two true premises or propositions to a conclusion (Aristotle the Syllogism), a logically valid method of gaining knowledge, yet if you cannot know the momentum and position of a particle (Schroedinger (if that is how you spell it)) then rationalism as a means of gaining knowledge is somewhat obselete. However induction seems to be still valid. For an example of induction if you were standing on a bridge and you saw 10 white swans swim past, you could predict (hypothesis) that all swans are white, with a small amount of accuracy, et.c. for 100, 1000...However it only takes one black swan to prove this wrong. Hence, Karl Popper, a contemporary philosopher said that scientific knowledge is implicitly disprovable only. Yet it is the only method that we can use in our search for knowledge
    That's not correct. In QM, it simply does not make sense to talk of momentum and position at the same time. However, you can know a particle's "exact" state with arbitrary accuracy at any given time. The price to pay is simply disturbing the "natural" evolution of this state. But there is still a lot of deducing that can be done! (although the other comments were true)
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    (Original post by viriol)
    That's not correct. In QM, it simply does not make sense to talk of momentum and position at the same time. However, you can know a particle's "exact" state with arbitrary accuracy at any given time. The price to pay is simply disturbing the "natural" evolution of this state. But there is still a lot of deducing that can be done! (although the other comments were true)
    Sorry for the confusion I meant that you cannot know the position and momentum/velocity (if that is correct) at the same time. As for the other bit would it be more accurate if I refined it to saying that for use as a starting point or reference point observation is the accepted method rather than working from metaphysics (like Descartes).
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    (Original post by aidanhaslam)
    Sorry for the confusion I meant that you cannot know the position and momentum/velocity (if that is correct) at the same time. As for the other bit would it be more accurate if I refined it to saying that for use as a starting point or reference point observation is the accepted method rather than working from metaphysics (like Descartes).
    I'm not sure I completely understand what you're trying to convey here. I'm saying that the reason it is not "possible to accurately predict the future" is not because of Heisenberg's uncertainty principle (momentum and position can't be specified at once, nor can energy and time, etc). Heisenberg's principle just tells you that there are "complementary" quantities that cannot be specified (don't make physical sense) at the same time. However, the state of a system can be defined using alternative quantities just as well. For example, an isolated quantum mechanical pendulum is as deterministically bound by the laws of QM as a classical pendulum is by the laws of mechanics. The difference is that in the latter case you specify the pendulum's state using its coordinates (position at a given time) and its corresponding momentums (linear momentum and energy) whereas in the former you do so using quantum numbers of energy (specifying an energy level, much like an atomic quantum number) and spin. Determinism cannot be attacked via this front. Only when you add observers does determinism crumble.
 
 
 
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