Schrodinger's Cat

Discussion in 'Physics & Math' started by chuk15, Jan 2, 2010.

  1. Pandaemoni Valued Senior Member

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    To be fair, there is no "contradiction" as it is all perfectly self consistent. In fact most of the interpretations remain non-deterministic (except for Bohm's and other "hidden variable" approaches, and those have their own philosophical baggage).

    What is really important to remember is that these are, scientifically, not "theories", they are merely interpretations of the single agreed upon theory. They are, in and of themselves, not science as they are not falsifiable. The interpretations of quantum mechanics are just philosophical positions--metaphysical glosses on the established scientific theory.

    If it were important to maintain that cause and effect are always preserved, then it is a problem in any event as all science can say on that point is "there is no evidence sufficient to establish the proposition." One is free to maintain that as a philosophical position, just as one is free to maintain that God determines all of the outcomes and they *seem* random. Neither position is really "scientific", even though the former avoids (at least overtly) the non-naturalistic aspect of the latter.
     
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  3. RJBeery Natural Philosopher Valued Senior Member

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    The "Many-Worlds Interpretation" has many problems, the biggest of which is that I don't believe there is a universal definition of what it means exactly. Others...
    - Do the worlds "split" or not? Can they continue to interfere with each other?
    - Do the wavefunctions ever collapse? When they are observed? What qualifies as an observer? Any surrounding atom capable of absorbing any photon should qualify as an "observer" which means that the unitary propagation time of the wavefunction is effectively zero. No unitary propagation time means that the wavefunction itself is meaningless.
    - A photon traveling through a half-silvered mirror may "split" the universe into two "possibilities", but what about a mirror silvered in a ratio of 1/pi? How many "splintered worlds" result from this?

    With apologies, MWI is absurd. My prediction is that within 20 years science will accept that cause-and-effect is directional in the same way that entropy is - it's a "habit" more than a law - and all of QM is easily understood when you look at is in this fashion.

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  5. kurros Registered Senior Member

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    Actually, none of those things are problems with Many-Worlds. Let us go through them:

    1. "the biggest of which is that I don't believe there is a universal definition of what it means exactly."
    The version described at http://www.hedweb.com/everett/everett.htm and http://en.wikipedia.org/wiki/Many-worlds_interpretation is the only version I am familiar with.

    2. "Do the worlds "split" or not? Can they continue to interfere with each other?"
    Yes they split, in the sense that no, they cannot continue to interfere with each other. They all remain part of the same wavefunction however. Their seperation is ensured by the linearity of QM. (well in some sense they never TOTALLY split, because most processes don't have a definite start and finish time, but after a while you can say they are effectively completely seperate worlds)

    3." Do the wavefunctions ever collapse? When they are observed? What qualifies as an observer?"
    a) No, they never collapse. b) There is no special event called "observing", these are just another quantum (perfectly unitary) interaction. c) see b), i.e. observers aren't special.

    4."Any surrounding atom capable of absorbing any photon should qualify as an "observer" which means that the unitary propagation time of the wavefunction is effectively zero. No unitary propagation time means that the wavefunction itself is meaningless."
    I'm not sure why you think this is non-unitary. Small scale quantum interactions don't cause the worlds to split, in the same way they don't cause wave-function collapse in Copenhagen. The "amount" of world-splitting is exactly the same as the "amount" of wavefunction collapse that occurs in Copenhagen, i.e. if a process only partially collapses a wavefunction, then it only partially splits the worlds, i.e. they still interact but to a reduced degree.
    There is one difference; in Copenhagen the wavefunction collapses across the whole universe violating our instincts about causality (but isn't a problem since no causal effects can propagate through it), while universe splitting occurs locally and propagates at the speed of light (unless the splitting part of the universe is isolated in some way, then it may be slower)

    5. "A photon traveling through a half-silvered mirror may "split" the universe into two "possibilities", but what about a mirror silvered in a ratio of 1/pi? How many "splintered worlds" result from this?"
    There are still two worlds in this picture, as there are only two possibilities of where the photon may go. The worlds just aren't equally weighted (this part gets a bit tricky, but one can show that the probabilistic rules still come out just fine). More interesting are systems which don't undergo total wavefunction collapse, i.e. that decohere a bit but not totally. As mentioned above, the worlds involved with this still interact with each other through the remaining quantum degrees of freedom.

    I am not saying I believe in many-worlds, it is pretty crazy after all, I am just pointing out that all your objections to it are in fact not problems at all, and in fact are much better answered by many-worlds than Copenhagen.

    If you want a REAL problem with many-worlds, it is that the world separation is maintained only because quantum mechanics (and quantum field theory by extension) are linear theories. Gravity, however, is not a linear theory, so it seems likely that a quantum theory of gravity will also not be linear. I'm not sure about string theory...I don't think it is linear in this sense... hmm maybe someone else knows about that. Anyway if quantum gravity is non-linear is seems like the worlds should still be able to interact gravitationally, which doesn't seem to happen. I think there are ways of arguing ones way around this but I don't know how exactly.
     
    Last edited: Feb 3, 2010
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  7. Dinosaur Rational Skeptic Valued Senior Member

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    BobG: The following implies that the alternatives to Copenhagen are reasonable.
    I do not see any contradictions Copenhagen. Could you explain?

    Many worlds implies multi-billions of universes created every second. One for each possible outcome of a quantum process. Each new universe then creates multi-billions more per second. This seems absurd, although it also seems to be consistent with the mathematics & experimental data as well as easy to understand. Advocates of Many Worlds are willing to accept an absurd interpretation which seems more understandable & complete than Copenhagen.

    The various pilot wave interpretations accept what seems to be reverse causality in order to avoid lack of causality. They seem to ignore the probabilistic nature of the data. To me, reverse causality is less believable than lack of causality when you consider that quantum processes produce random (probabilistic) data. Random data certainly looks like support for lack of causality.

    Why not accept the concept that the quantum world is counterintuitive & not subject to classical-like explanations? That is what the experimental data indicates: Counterintuitive processes obeying probabilistic laws.

    At least nobody here claims that the Uncertainty Principle describes some limitation in measurement technology. Does the UC not strongly support the notion of a counterintuitive reality lacking causality?
     
  8. RJBeery Natural Philosopher Valued Senior Member

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    I don't understand your point here Dinosaur. Rolling a die under a cup produces probabilistic outcomes yet most would agree that it is clearly not truly random or non-causal. Accepting that the outcome of a quantum process may be retro-causal could produce an effect that to us would appear to be perfectly random without actually being so.

    Kurros, thanks for the reply and references. I'd like to read through these before I pose more questions...
     
  9. RJBeery Natural Philosopher Valued Senior Member

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    Kurros, again, thanks for the MWI reference. Many of my issues were indeed addressed. I'm not saying that you claim to be the local MWI expert, but I was wondering if you could help me understand a couple of things...

    My issue about a the "1/pi" silvered mirror is apparently dealt with here.
    Unless I am misinterpreting the link, it is saying that over time the non-random worlds tend to zero (they are basically overwhelmed by those that behave the way we expect them to due to sheer numbers). This makes sense, but I still don't believe it is addressing the behavior of an individual quantum event with unequal likelihood causing a world-split. I think of it as the "branch thickness"...what determines the "thickness" and more importantly what is the mechanism which drives a world to the "thicker" branch more frequently? Think about that for a second, either there are split worlds or there are not. What does it mean to have one world exist on a "thicker" branch? (One answer I had anticipated was that more copies of the thicker-branch world exist than the thinner-branch one which is why I chose the irrational silver-mirrored ratio of 1/pi.)

    I have other questions but I'll wait to read anyone's responses to this if you think you can explain...
     
  10. kurros Registered Senior Member

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    Yeah this is the part I understand the least. I'm not really clear what the meaning of an amplitude is in many-worlds. The arguments they give are based on frequentist views of probability, in which probability is defined in terms of some theoretical infinite series of identical trials. Thus, the system they use to get out their probability rules is composed of infinitely many identical sub-systems, and they then look at the possible outcomes of observations on those systems. Clearly in this case the random-looking outcomes vastly outnumber the highly organised outcomes.
    But yes, what the heck this means for world splitting if you only have ONE of these subsystems I don't know. I prefer the Bayesian view of probability, in which we should be able to assign some "degree of belief" to the amplitude for various events, even single trials, but I don't know how to apply this to many-worlds. It seems to suggest the amplitude weights the worlds somehow, so you are more likely to end up in one than another, but I don't really think this is what they are suggesting...
    The Bayesian thing is tricky too because it is subjective, one person may have different beliefs to another regarding the outcome of an event (i.e. one might know a dice is weighted while the other doesn't, but you can't tell after only one roll...), which is why they are sticking to the frequentist objective thing I guess.

    I suppose the answer has something to do with Q25:
    "Why am I in this world and not another?
    Why does the universe appear random?"
    I.e. there is no weighting, and it is only in the limit of large numbers of events that the probability rules make sense, and at this time they will turn out to have worked perfectly well due to the combinatorics of the possible universes generated by then.
    I think that's about where I am at with this question atm.
     
    Last edited: Feb 3, 2010
  11. RJBeery Natural Philosopher Valued Senior Member

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    I'm hoping someone with some experience "defending" MWI might shed more light on this issue. Until this is resolved, here's the consequence of MWI as described in the link (not really an objection, more of a complaint):

    As sentient, living beings subject to MWI branching we are inevitably exposed to an infinitude of the most horrific deaths imaginable (and unimaginable!). Somewhere in the multiverse there is a version of you whose eye spontaneously explodes, or falls through the ground and suffocates*. You will be afflicted with every type of cancer, every stray bullet, every fatally rotten piece of food whose genesis hinged upon a chance quantum fluctuation. On the flip side (or maybe equally horrible?) is that there are entire worlds where you are "blessed", where every quantum outcome has gone your way, steering your life to a virtual paradise...and yet here you remain, unable to touch that world.

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    *You may claim that macro-level quantum behavior (such as large scale tunneling, spontaneous combustion, etc) is not permitted in MWI, but QM suggests that it is merely extraordinarily unlikely rather than impossible. Since MWI grants equal reality status to all possibilities then these worlds plus the infinite others that I can't even dream of are all valid realities.
     
  12. kurros Registered Senior Member

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    Probably true. So long as a world is possible within the laws of physics it seems that it exists. I wouldn't worry too much though, being stuck here and everything

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    . Also, the statistics are presumably such that the vast, vast majority of worlds are essentially indistinguishable from this one anyway.
     
  13. Dinosaur Rational Skeptic Valued Senior Member

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    RJBeery: To me, the following suggests a naive concept of probability theory.
    The most who would agree that a dice throw is not truly random have an intuitive notion of a die as a solid cube bouncing against solid planes. They do not view a die as a collection of atoms appearing to be solid objects, but which are actually interacting with their environment via the repulsive effects of like charges (Id est: Repulsion of electron fields surrounding the nucleus of atoms).

    There are those who claim that given enough data & calculating power, dice throws would be predictable. I disagree, but that issue is not really pertinent to quantum randomness & I see no point in our arguing about dice throws.

    Radioactive decay is probably the easiest quantum process to analyze. It displays all the characteristics of a probability distribution (a Poisson distribution, I think). If you consider the assumptions & logic supporting probability theory, you should conclude that radioactive decay is governed by probabilistic laws, not deterministic ones. Probabilistic laws strongly imply lack of causality.

    A person can believe in Many Worlds, pilot wave interpretations, different laws of logic at the quantum level, observer created reality, or any other interpretation (including Copenhagen). No interpretation can explain away the implications of probabilistic quantum data.

    Many Worlds hides (actually ignores) the implications of the probabilistic data. Photons, electrons, whatever are more likely to be observed in certain places on a detection screen. Many Worlds must accept that some Worlds are much more likely than others. Quantum tunneling effects produce universes which are very unlikely to occur compared with those universes in which tunneling does not occur.

    While the hiding of probabilistic data is more obvious in the analysis of Many Worlds, it still exists in the other interpretations.

    Many view probability theory as a practical approach to dealing with processes for which cause-effect analysis is impractical due to lack of data, insufficient computing power, and/or lack of knowledge of pertinent analytical algorithms. For quantum processes, this is a naive (silly?) point of view. All the experimental evidence supports the Uncertainty Principle & the probabilistic nature of quantum processes (as evidenced by the data resulting from quantum processes).

    UC plus random data indicates lack of causality & a quantum reality which is counterintuitive. Many Worlds & various other non-Copenhagen interpretations attempt to hide, deny, or disguise the counterintuitive nature of quantum reality. Copenhagen might not be the final answer, but it seems better than its competitors until some genius comes up with TOE, Quantum-Gravity, GUT, or another better theory.

    If some interpretation finally wins over the others, it will still be counterintuitive & probabilistic. I do not expect either the UC or the random data to go away.
     
  14. Pete It's not rocket surgery Registered Senior Member

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    Why? Brownian motion is wonderfully probabilistic, for example.

    I had the vague impression that they predicted probabilistic data. That Many Worlds, for example, naturally predicts such probabilistic results.
     
  15. BobG Registered Senior Member

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    Can you point to any experimental data which excludes Pilot Wave Theory? If you can't then I don't see how you can claim that it is what the experimental data indicates. I'm not saying that PWT is necessarily correct but you are claiming that people should accept that the world is like the Copenhagenists essentially because they say so. Why should it be accepted?

    Besides one of the postulates of Quantum Mechanics in the CI says that the state vector obeys the Schrodinger equation H|psi> = ihbar d|psi>/dt . Looks fairly deterministic to me. In fact it is the CI which is forced to introduce a classical-like 'non Quantum' measuring system to facilitate the collapse of the wavefunction despite the fact that this contradicts another one of the postulates.
     
  16. RJBeery Natural Philosopher Valued Senior Member

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    What you seem to be saying is that anything that exhibits probabilistic behavior is non-causal. I disagree with both this and the concept that dice rolls are unpredictable (although I'll agree to "drop the dice"

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    ) A well-behaved pseudo-random number generator displays probabilistic behavior; do we agree that a PRNG is indeed causal?

    First, I don't think you should conflate the Uncertainty Principle with non-causality (or even randomness necessarily). And why you think radioactivity proves non-causality I'm not sure. If a fisherman has a 10% chance of catching a fish within an hour, and he continues to fish until he catches one yet quits when he does, you simply collect the fishing data of 1,000,000 such fishermen and you will find that the graph looks identical to the remaining mass of a radioactive material over time.
     
  17. Dinosaur Rational Skeptic Valued Senior Member

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    RJBeery: Do you know why they are called pseudo-random number generators?
    A PRNG is causal, but it does not generate truly random numbers.

    For certain simulations, researchers use quantum processes (usually radioactive decay) to generate random numbers due to the subtle lack of randomness inherent in PRNG's.

    MathCad (& I am sure Mathematica) includes about 15 or so random number generators because one size does not fit all simulation scenarios. Random & probability theory are more subtle than the view most people have of this subject matter.

    If you simulate dice throws with the random number generator built into Visual Basic 6.0, it does not give results conforming to the true odds. The DOS Basic random number generator resulted in the conclusion that craps favors the shooter, not the casino. I have yet to try the random number generator built into VB.net 2008, which might be better than that used by VB 6.0

    My experiences with writing & using simulation software written by others has indicated that some very intelligent people have naive views of randomness & probability theory.

    I do not consider Copenhagen to be the final answer to QT interpretations. I like it because it admits to being an imcomplete explanation & acknowledges a limit to our ability to devise a model which seems intuitively correct.

    The other interpretations seem to ignore or disguise the capriciousness & probabilistic nature of quantum reality. They seem silly to me compared to Copenhagen-like interpretations. Many Worlds, in particular, seems absurd. I still fail to understand how reverse causality can be viewed as more plausible than lack of causality. I also deny that the reverse causality (pilot wave) interpretations do away with the probabilistic nature of the data.

    Most who dislike Copenhagen seem to be upset by the notion that quantum objects do not have certain properties until some experimental results indicate values for such properties. The copenhagen view on this issue does not seem far off base.

    Probabilistic data strongly supports the notion of lack of cauasality. I do not understand how this can be denied. The Uncertanity Principle provides further support for capriciousness & lack of causality. The wave function is universally viewed as providing probabilities, not predictions of the outcomes of individual events. The precsion of Quantum Laws are due to the large number of quantum entities relating to any classical level process.

    You can build a very accurate clock based on the measurement of radioactive decay. The accuracy is due to the large number of atoms being measured. It is an excellent example of a quantum level random process resulting in the illusion of a causal process at the classical level.
     
  18. BobG Registered Senior Member

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    This is a completely circular argument. The 'probablistic nature of quantum reality' is a feature of some interpretations of quantum mechanics. You are justifying the CI on the basis that quantum reality is inherently probablistic. In other words your justification for the Copenhagen interpretation requires you to assume that a significant part of the CI is true. But since it is possible to construct non contradictory theories with the same results without assuming non determinism then it is a completely unjustified assumption.

    I don't know what you mean by 'reverse causality'. Pilot Wave Theory is explicitly non-local but why does that violate causality?

    As I pointed out above the postulates are inherently contradictory since the Schrodinger equation is deterministic whilst wavefunction collapse isn't.
     
  19. RJBeery Natural Philosopher Valued Senior Member

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    Yes I do, Dinosaur, and it's not because they are unable to produce probabilistic data. It's because they are (generally) describable and even predictable by the writer of the PRNG algorithm. Recall I said "well-behaved" PRNG*, which would clearly fit your criteria for non-causal behavior. Randomness can be a subjective function depending upon the information available to you. Whether the information is unavailable to you because it is lost in chaotic obfuscation (like predicting weather), because there are fundamental limits to what information you can have (like HUP), whether Bob won't share his PRNG algorithm with you, or whether that information isn't available to you until a future point in time, it's ALL subjective. Strictly speaking, a deterministic Universe makes true randomness a nonsensical concept, and the Universe is only non-deterministic if you presume that QM is non-causal.
    As I said, I agree with BobG here that you are using circular logic by presuming that QM is non-causal. What if, say, God is using a PRNG to determine QM behavior?? (Or, to be less sarcastic, what if pilot waves determine QM behavior?)

    I've already given you examples of macro-level real world examples of sources for probabilistic data: dice throws, fishermen fishing times and PRNGs. It seems you are claiming that one of the following is true, but not both:
    A) Dice throws, fishermen and PRNG's do not produce probabilistic data or
    B) Dice throws, fishermen and PRNG's are non-causal

    Or maybe you're saying that all real-world examples not related to QM are simply exceptions to the rule? I notice that you say "strongly implies" which seems like a squishy word to me. Actually what you seem to be saying is, if we can identify the cause of something then it is causal, yet if it is QM then it is non-causal...and that's a weak argument to me. :shrug:

    * The discussion of whether a perfectly well-behaved PRNG is achievable is a separate subject. My degree is in Computer Science so if you wish to discuss this I would be happy to in another thread in the appropriate forum.
     
  20. phyti Registered Senior Member

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    Regarding the 'cat in the box', the best
    explanation I've read is this:
    the geiger counter detects the decay,
    the possibilities become one reality.
    The wavefunction ends here, and does not include the cat.
    Remember, the uncertainty is in the radioactive
    substance, not the cat.
     
  21. CptBork Valued Senior Member

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    It's really too bad Schrodinger's Cat is so widely misunderstood- the misunderstandings in popular conception have led to a wealth of junk science spiritualist propaganda, which now seems more profitable (in terms of selling BS) than the actual field of physics itself. Go to amazon.com and type "Quantum Physics" into the search, and check out the amount of top-ranked nonsense you can buy there.
     
  22. RJBeery Natural Philosopher Valued Senior Member

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    CptBork: I'd agree with that, I have some friends (in California of course) that adhere to some pretty deep spiritual 'holistic' beliefs. I think it's great until they start mentioning quantum foam, wave functions, singularities, etc, and then I start cringing.
     
  23. CptBork Valued Senior Member

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    Well tell your friends I have a book I'd like to sell them, it's called "The Path Integral Approach to Uniting All Spiritual Teachings". Yuk yuk, get it? I have some beachfront property in Louisiana as well but that can wait

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