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I Need Convincing

  1. Jul 24, 2009 #1
    Okay, I'm a firm believer in a fixed future. I believe that every event is caused and affected by a preceding event and that if the state of everything in the universe (infinite or otherwise) was known, the next states would be predictable.

    I am willing to accept that perhaps I only believe this because I am ignorant to Quantum Mechanics, which if I'm correct suggests that everything is probabilistic. I simply cannot imagine a world where there are a number of possible outcomes each with a probability of occurring. I know it only really applies to quantum level particles, but this would effect the greater world as we know it and therefore directly affect our future lives. As far as I'm concerned, there is only a single future ahead of me, not multiple.

    So to allow you to convince me otherwise, I'm going to present you with a simple problem:
    I have a particle that apparently has a 50% probability of being in each of states 0 or 1, according to Quantum Mechanics. When I observe the particle, it is in state 0. I say "This particle was always going to be in state 0 when I observed it and that was the only future ahead of the particle."

    So the question is:
    How could any scientist possibly disprove my statement through experiment? Yeah, you could show me something that happens approx. 50% of the time and doesn't happen the rest of the time. But I could say it was always going to be like that. That's not a probabilistic future. That's just the way the laws of (non-quantum) physics made it happen (which happens to have a statistically 50% chance).

    I hope you all understand and I hope that if I've totally misinterpreted quantum physics that you'll set me on the right path.

    Thank you.
     
  2. jcsd
  3. Jul 24, 2009 #2

    Pengwuino

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    It looks like you're asking whether or not QM is simply incomplete, and that infact the particle had a "destiny" and our theory simply isn't enough to tell what that is. This is a massive philosophical debate, although as far as I know there has just been no theories that have any good evidence behind them that state that nature is deterministic. More educated people can guide you further into what that's all about however.
     
  4. Jul 24, 2009 #3
    There are two possibilities, that you'll go to Heaven or you'll go to hell. It depends on your choices. You can let the missionaries in when they come, or continue down the path to hell. :smile: Sorry, couldn't resist.
     
  5. Jul 24, 2009 #4
    Look up "Bell's inequalities". Once you reach a level where you can read Joy Christian, you may re-consider your position.

    Basically, LEP has collided electron-positron in a (for all purposes) identical initial state, and got gazillions of different final states. So, it does not look likely that any single initial state gives always the same final state. That's a major shift, sure. Welcome to the quantum world.
     
  6. Jul 24, 2009 #5

    HallsofIvy

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    It is ironic that when "Newtonian physics" became established, many people offered the same argument but in reverse- it implied that the future of everything in the universe was "fixed" by the present which they considered outrageous.
     
  7. Jul 24, 2009 #6

    Indeed. People thought it was an attack on the concept of free will (how does a person have free will if everything is deterministic). In regards to quantum we can demonstrate that IF there was, what we call, hidden variable theory it would have to be non-local (which would violate relativity). That doesn't rule it out but it does put bounds (it is either probabolistic or communication between particles can occur faster than the speed of light).
     
  8. Jul 24, 2009 #7
    I think there are two different issues here that are usually not separated when discussing this subject. One is the distinction between a one-world (or one-history) model and the many-worlds (many-histories) model. The other is the possibility of predicting the future (could be the near-future of a small number of particles) based on the present. (I am being vague on purpose here).
    You may say: Well, if you can predict the future that implies one world. (and you would be right). But it is not necesarily so the other way around. You can have one world (or history) and not be able to predict the future.
    A good paradigm for the one-world model is a roll of movie film. You can point to a certain frame in the film which is your present. You know what the frames before this one contain (to a certain extent). But what about the future? There are two possibilities:
    (1) If you have a causal deterministic model then looking at the present and inmediate past you could predict at least a very near future. This would imply causality in the sense that given certain present conditions there is only one "possible" outcome (which we can predict if we know the laws involved and we have sufficient computing power). I said "possible" because we are assuming one history and therefore we assume that "only one thing" is going to happen (which is contained in the subsequent frames of the film).
    (2) Knowing that there is certain outcome, which is "already" (excuse me for using this word) contained in the film does not mean that we can predict it. If the frames in the film are not related in a causal way then you can't predict with precision what comes next. Maybe there are some rough rules that prohibit certain things from happening given the present circumstances, but there may be other things that could happen in a number of ways without connection to what happened before. This seems to be the way quantum systems work. We can predict the evolution of the wave function (or state vector) but not the exact result of individual measurements.
    Between the above models, we would have to choose the second, which agrees with all the experience we have of quantum phenomena. But this does not tell you if there is one future or several futures. Maybe there is only one future which we can only approximate using the laws of quantum mechanics but which we can't predict exactly due to the probabilistic nature of these laws. But there is also the possibility that there are many different futures each containing a "copy" of yourself. This is the Many Worlds Interpretation of quantum mechanics. With respect to the "one future" model, I think we could say that both the Copenhagen interpretation as well as Gravitational Collapse and Bohm's interpretation belong to this category. But I am not sure that they are 100% compatible with this idea.
    With respect to the philosofical implications, in the "one world" model, even if the future can't be predicted due to the lack of causality exhibited by quantum systems, there is still determinism in the sense that the future is "one". It is there in the film and we'll know what it is when we get there but we can't do anything to change it. If you try to change it, you think that you have the "freedom" to do this but that is only an illusion because your intentions, decisions and actions are also already "in the film". (most people don't like this but they don't realize that it is implied in their one-world model of the universe).
    See this link: http://en.wikipedia.org/wiki/Determinism
     
    Last edited: Jul 24, 2009
  9. Jul 25, 2009 #8
    How do you differentiate ? If you can not, what is your point ?
     
  10. Jul 25, 2009 #9
    this is impossible according to QM since the state of the particle is consistent, it never changes. It is impossible for anything to be consistent including the state of a particle.
     
  11. Jul 25, 2009 #10
    So what you're saying is: There will be only one future, QM just says that we can't predict what it will be?

    Thanks for all the brilliant answers, people!
     
  12. Jul 25, 2009 #11
    How would you suppose if you knew your own 'destiny', and by knowing it you've changed it, you really haven't predicted anything.
     
  13. Jul 25, 2009 #12
    I believe that if you were to see your genuine future, then that would happen with 100% certainty. No matter how you tried to avoid it, because that avoiding would be part of making that future happen.

    If you saw "the future" and changed it, then what you saw wasn't really the future, was it? It was just a meaningless vision that got you to where you are now.
     
  14. Jul 25, 2009 #13

    Well this is certainly standard sci-fi fair but it really has nothing to do with physics. There is nothing in current physical theory that would allow breaches in causality nor could an atomic level breach in causality every be projected to macroscopic events (see chaos theory). This makes discussions like this really excercises in logic (the dickens/tale of two cities phenomena and such) that really have very little to do with physical reality as we understand it. Should physical theory ever find means of causality breach then we would have our answer in terms of how it would all "work". Which really makes any speculation a moot point. That being said, I've certainly been guilty of having my share of causality discussion after seening an episode of star trek or the movie primer or some such.
     
  15. Jul 25, 2009 #14
    Hey, they asked. :P I'm pretty sure my original post was physics related.
     
  16. Jul 25, 2009 #15
    It is certainly natural to project the weirdness and possibility of the quantum universe to everyday life but I have to say I've never understood these kinds of "philosophical" arguments. There are people who talk about what effect a quantum vs. newtonian universe has on free will and then go on to talk about what the lack of free will means. And then they go on to talk about how we can be right in prosecuting a murderer for their actions if all physical states are pre-determined vs. a quantum universe and stuff because the murderer really had no "choice" and all this stuff. At which point I spew what ever beverage I have in my mouth all over my monitor in disbelief. Questions of whether we are responsible for our choices as humans and whether "our futures are ours to change" and such and whether there are pausible causality violations in QM are entirely disjoint discussion and IMHO anyone who says otherwise is trying to pull the proverbial wool over your eyes. This venting is certainly not leveled at you sftrabbit i'm just pointing out that these kind of discussion can often take you to very questionable places.
     
  17. Jul 25, 2009 #16

    Pythagorean

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    How do you think it would affect the great world and our future lives? I mean, the probabilistic nature does bleed through a little bit, but in the end:

    If you throw a stick through the air, it's going to follow it's path unless acted on by a force. Most of the matter that you know, on the scale you know it on, obeys Newtonian physics well enough. You can leave your car in neutral at the bottom of a valley and random perturbations aren't going to suddenly jettison it up a hill. You don't have to worry about plates or cups jumping off the table without an external force being applied to them.

    Quantum Physics doesn't play into neurology either. Of course, neurons are made of atoms which are quantum particles, but ignoring reductionism, neurons can be modeled classically. Even chaotic systems have a determined path.
     
  18. Jul 25, 2009 #17

    What pythagorean is discussing is decoherence which is essentially the phenomena that even quantum systems of 3 or 4 particles tend to lose their quantumness as they entangle with the 'environment' thus something that is macroscopically visible will contain trillions of atoms and thus have entirely lost its quantum character.

    However, that does NOT rule out the possibility of quantum level perturbations effects macroscopic phenomena. In fact this is the essence of emergence. Also, in regards to the brain, Penrose is a proponent of such a quantum theory of mind, and that's a name that is not easily ignored.
     
  19. Jul 25, 2009 #18

    Quantum Mechanics is a method of predicting the statistical results of certain experiments. So far we do not have much of an inkling why such experiments appear to have a random element. There are three schools of thought on this:

    1. God does roll dice and the Universe is truly random and we may never understand why. The "Copenhagen interpretation" of QM basically leans this way but doesn't really stress it. Its also similar to the "shut up and calculate" interpretation, which really isn't even an interpretation at all--its more an "attempting to interpret QM is taboo" mindset. Anyway, IMO, although it might be true, its arrogant to concude it at this early stage: "If I can't figure it out then its not figure-outable".

    2. There is some complex process occurring within the particles of the experiment which we do not yet understand, and thus results appear random but are really just pseudo-random. We refer to this as local hidden variables. Certainly its possible that there is some chaotic process going on within the particles, but it seems that if there were, then we should also see variations in things like the masses of otherwise identical particle types, for example. Also that process would have to be extremely complex and chaotic because of the smooth statistics we see. But that's just my opinion.

    3. There is some process in the universe working among many or all particles which we do not understand, so when we examine the behavior of a couple of "local" particles, there is some effect from other particles in the universe. This is "non-local hidden variables".


    I lean strongly toward number (3). Entanglement and Mach's principle require either that there be some medium of instantaneous information exchange between distant objects (with certain restrictions), or that we must revise our understanding of the concepts of distance and time. I believe it is that our concepts of distance and time are not correct. Consider that the ideas of distance, time, continuums, manifolds, and even non-integer numbers were ALL learned/created for the purpose of predicting the general behavior of many tiny machines (particle-particle interactions), which is classical mechanics. So it is not logical to presume those same rules must be the founding principles in understanding how a single one of those machines behaves.

    EDIT: I keep forgetting to point out, though, that there are some non-local hidden variable interpretations that attempt to apply classical rules. I do not agree with these because, again, it is not logical to apply rules to a single machine that were designed simply to predict the large-scale, average behavior of a lot of those machines.
     
    Last edited: Jul 25, 2009
  20. Jul 25, 2009 #19

    DrChinese

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    As mentioned, Bell's Theorem addresses this. I definitely recommend you learn about this.

    If you believe in a "fixed" future, then Bell's Theorem requires that you abandon the concept of locality. You will accept a non-local view of nature. This is considered scientifically acceptable as an interpretation. It is called a non-local hidden variable perspective, and it best described by what are called pilot wave or Bohmian interpretations.
     
  21. Jul 27, 2009 #20
    I am saying that QM puts a limit to our capacity to predict the future. In some cases where a quantum event is amplified, the macroscopic result may be totally unpredictable. Take for instance Schodringer's cat. But I am not saying that there is only one future. But I am saying that even if there were only one future, this future may be unpredictable.
    Please note that I mention Schodringer's cat here for a different reason than the one it is usually brought up. I am not concerned here with when exactly the wave function collapses or how or if decoherence makes it collapse. All I am saying is that the end-result can't be predicted. That would be also true for some Stern-Gerlach experiments or even sending a photon through a half-silvered mirror to two detectors.
    I think most people have a model of the universe which has only one past, one present and one future. But people who adhere to the Many-worlds interpretation of quantum mechanics prefer to consider the "existence" of many different pasts, presents and futures.
    I, personaly favor the Many Worlds interpretation because I think it provides the most elegant explanation of quantum phenomena and solves many of the paradoxes.
    I think when we examine the diferent interpretations of quantum mechanics, the main difference between them is the belief in "one world" or "many worlds"
    Given the fact that a difference between one world and many worlds has great implications way outside the realm of quantum mechanics, I think this criterion should be used also for a general clasification of philosophical ideas about the nature of existence.
    But it appears that most philosofical ideas are currently based on the assumption of "one world". Perhaps we'll see the "many worlds" idea getting a greater influence on philosophy in the future. The many-worlds idea would allow you to examine the problem of determinism and free-will from a different angle.
    Which interpretation do you prefer? (this question goes to everybody on this thread).
     
    Last edited: Jul 27, 2009
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