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Reality, locality and determinacy.

  1. Aug 18, 2009 #1
    I would like to get some opinions from those of you who prefer a One-World interpretation of QM (CI,Bohm,Transactional,Relational, etc) about the following:
    1) I understand it is already clear that QM puts a limit on our ability to predict the future. But if you believe that the universe is a 4-dimensional space, it seems like macroscopic events in the future should be there, some place in the 4-D manifold and even though we can't predict them, they are determined. This determinacy would be acausal but determinacy nevertheless.
    2) The same could be said about events in any other part of the 4-D universe. We could say with certainty that some macroscopic event in the past must have had a unique outcome even though we don't know which of the possible outcomes did actually happen. (maybe we can't get to a conclusion from the available data because this information has been somewhat scrambled). But we can nevertheless say that this past event must have had a unique outcome and if we had the right tools we could find out what it was.
    3) We could say that some macroscopic event considered at this instant on the other side of the earth (we can assume to be able to define instantaneity with respect to a frame of reference fixed to the earth) is or is not happening. We will have to wait until electromagnetic waves have a chance to reach us to know the outcome, but we can assume that there is only one outcone.
    So, in 1) and 2) I am considering time-like events and in 3) I am considering space-like events. It seems to me that the usual realist scientific approach and most philosofies (except perhaps positivism and solipsism?) imply the above statements. If you are a One-world proponent, I would like to get your opinion about the above. Do these statements reflect your thinking? Are they all true or maybe one or two are true but not all three?
    I think this could initiate an interesting debate. If you know about opinions on this topic explicitly expressed by known physicists it would be useful if you post a reference to the article or book. Thanks.
     
  2. jcsd
  3. Aug 18, 2009 #2
    Some thoughts on this... relativity and locality follow from holding space-time as basic. They don't follow from a 3d Newtonian world, but they do once you add in time. In this situation you are right to say that events could not be traced causally. Any evidence for any sort of determinism can therefore only be rational and metaphysical. Bohr holds space-time as basic and gets the result that real basic events must occur without cause. There is no "why." Bohm holds causality as basic. He gets results inconsistent with finding basic reality in space-time and eventually claims nonlocal signals are inherently mind-like and occur outside of the physical realm. For Bohm the 4d universe is real but incomplete and only an approximation of basic reality.

    Holding space-time as basic forces a denial of deterministic physical causation. It's space-time or deterministic causation, not both :smile:.

    By definition an event can only be or not be. You have "X happened" which can have a value of true or false. I don't think QM is involved here, just our evolving knowledge of the situation. I'm not quite sure I'm understanding you correctly here though.

    I've got some Bohr / Bohm quotes around anyways, but I've posted some elsewhere. I can go digging when I get some objections :smile:.

    Some good causation links:
    http://en.wikipedia.org/wiki/David_Hume#Causation
    http://plato.stanford.edu/entries/hume/#CauIndInfNegPha
    http://plato.stanford.edu/entries/causation-metaphysics/
     
  4. Aug 18, 2009 #3

    DrChinese

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    The way you have phrased these, you are assuming a lot: 1) Acausal events can lead to determinate outcomes; 2) Realism holds even though there seems to be observer dependence. If you define things so these are true regardless of the facts, what have you really accomplished. Clearly, 1) and 2) are not your usual axioms. Usually, if acausal events occur then one would throw out determinism. Ditto for realism when you presuppose observer dependence.

    I don't push many worlds, so I guess by your standards I am a "one-worlder". But I don't accept your premise(s).
     
  5. Aug 18, 2009 #4
    Your objections ( Kote, DrChinese) are interesting.
    For the moment I would like to respond to one on which you both seem to agree.
    It is that causality implies determinism. I understand this may just boil down to the use of words, but I would like to clarify what I meant.
    It seems like we are not in dissagreement as to what causality means.
    Now, with respect to determinism, if we think of a 4-D space-time manifold, we could assume that things that happen "are there" (on the manifold). Not being able to predict does not mean that events are not determined. I am not saying "predetermined" because that would imply being determined by some events which occured before.
    I understand you may be used to the most common use of the word determinism which is in connection with causality. But I used this word in a more general way.
    Well, I just looked up "determinism" in wikipedia. They use this word mainly to imply causal determinism and when they describe a different meaming, this does not include "acausal determinism". So I have learned a lesson here (about the use of this word).
    However, I still would like to have some word that can describe what I called "acausal determinism". This would imply that events are "recorded" in this 4-D object that we call space-time. We could envision someone with some super-natural power who could be able to go to each place in the manifold and see what "happens" there. When we got to that point (if it is within our ligh-cone) what we experience should coincide with this person's description. To give you another example, imagine that you are driving down a road. But lets imagine that this road really represents time. So things are there in front of you. You can't see them until you get there. You can't predict them because there is no causality. But things are still there and they don't change. (In order for them to change you would need another dimension). Even if you say that this kind of situation is not what actually happens, what would you call it?
     
  6. Aug 18, 2009 #5
    I think the problem here may be that no one I can think of has disputed the idea that definite events actually occur. "X happened." It's true or it's not true. Only our knowledge can be fuzzy (assuming an objective world). In an experiential ontology (reality is defined by our experiences) there isn't even such a thing as incomplete knowledge because there's nothing else out there to know about. Both views have definite basic events that they each describe as reality.
     
  7. Aug 18, 2009 #6
    I think people who adhere to MWI do think that there are different versions of the same event in different "worlds". Now, I can understand that believing in one world implies that there is only one version of the event. As you said: "it is true or not". So, given the fact that there are some people who dispute this (it doesn't matter if they are crazy), it would be good to have a word to distinguish between the the two ideas so that we can communicate better.
     
  8. Aug 18, 2009 #7
    I do think that according to most interpretations acausal events can lead to determinate outcomes. When you measure the z-component of spin for an atom that is in a 50/50 superposition, the outcome will be totally random and therefore acausal. However, once you measure, you get a determinate result, which is recorded in your instrument. By determinate here I mean only one result, which is contained in space-time.
    You say: "1) and 2) are not your usual axioms" I am not trying to present them as axions. I am just making a classification of how people think. Of course my criterion for classification may not be the one that you would choose. And this is exactly what I was looking for. To have your opinions.
    With respect to observer dependence, I think that in the macroscopic world we can compare observations and agree on some underlying "reality". I special relativity, two observers may obtain different measurements if they are in different frames of reference, but they can always think of these different results as a consequence of looking at the same reality from different angles. In QM, when you measure the spin of a silver atom and you get "up" or "down", the person standing next to you will usually agree. (unless he or she is trying to give you a hard time). If someone has a way to look at the result of your measurement from some distant place, they'll see the same result. Now, I can understand that the result you get depends on the basis you use for your measurement. So we could say that the interaction of the system with the apparatus + environment will determine the kind of results you get. But once the measurement is made, all observers agree and we may say that this result is part of "reality". I am here talking about macroscopic realism. I am not talking about things such as the reality of the wave function, etc. So, to summarize, I think that observer dependence applies only to the kind of result we get the first time we measure but does not throw away macroscopic realism.
     
  9. Aug 18, 2009 #8
    In the usual sense there is no such thing as different versions of real events. We simply call these distinct events. When formalizing logical or mathematical systems there is a common method to treating events as if they can't have multiple versions. We define them as single basic variables with no variable sub-properties that could create differences between them. We are allowed to say things like "let P represent the statement 'the cat died.'" We can't then say that P is true, but given some versions of P, the cat lived. In order for there to be such things as different versions of events, we would have to qualify every truth statement ever constructed. There would be no such thing as absolute truth.

    If this usual method of formalizing events is used for "versionable" events, or if the two definitions of events are confused in any way, any resulting formalism will be logically invalid and contradictory.

    I don't know if this confusion has or has not happened in MWI, but defining events as being able to have multiple versions does lead to the elimination of unqualified or absolute truth.
     
    Last edited: Aug 18, 2009
  10. Aug 18, 2009 #9
    A few more thoughts on MWI and the definition of an event... MWI seems fully aware of the fact that it is incompatible with absolute truths. What if, then, we are only interested in truth in our universe, x? With a versionable definition of events, we can meaningfully still ask "is P(x) true" even if it's meaningless to ask "is P true." If we specify that we are always only interested in variables qualified by x, then MWI events reduce to usual distinct events, and MWI reduces to standard QM.

    Why add these extra universes (and disallow absolute truths) when they are totally irrelevant to the only universe we can actually test? Surely synthetic truth statements must have at least enough empirical weight to be theoretically falsifiable. Why go through all the trouble to be able to ask, meaninglessly, about the unfalsifiable synthetic truth in other universes? It's arguable whether "unfalsifiable synthetic truth" is even a contradiction itself.
     
    Last edited: Aug 18, 2009
  11. Aug 18, 2009 #10
    I am not advocating on this thread for the MWI. I am just trying to understand different mental pictures people have of the universe. I understand your reasoning and I understand how discusting MWI is for you (and for most people).
    Now, going back to our discussion, If we forget about the many worlds and go back to one world, our experience would indicate that things happen or don't happen. We would assume that that is also true for the past and the future and distant places. This may seem like a truism, but I think that sometimes it is good to make statements about things that seem too obvious. Things that seem obvious to us may not seem that obvious to others and once in a while may turn out wrong. (At least it has happened to me)
    Now, reading DrChinese's post, it appears that he is questioning realism. I was thinking about his position and I can see some reasons why he may think this way. I would speculate that things like the Aspect experiment, may represent some evidence that realism is does not hold. Now, when we look at the Aspect experiment and other similar experiments, we see some problem with the realist assumption because the numbers of outcomes don't agree with what we would expect. Now, I am not sure that these experiments challenge realism on a macroscopic level, but they do question the possibility of an underlying microscopic reality behind the random outcomes of measurement.
     
  12. Aug 19, 2009 #11
    Is it only by my standards? Given the fact that there is a considerable number of people that prefer the MWI, Isn't it reasonable to expect those who reject it to state clearly that they adhere to a One-World view?. The same transparency could be expected from those who adhere to the MWI. There are many who do consider MWI as a better choice but are hessitant to say it out of fear of being ridiculed. Of course there will be some people who are undecided or who want to keep an open mind without commiting to one view or the other. I myself try to keep my mind open even though I have a preference for the MWI.
    So I would say, Yes, I am a many-worlder, but I might change if I find evidence that this interpretation is not the best. If you call me a many-worlder, I won't take it as an insult. I hope you don't take it as an insult if I call you a one-worlder.
    If I asked you: How many worlds do you believe exist? . You might answer: That's a ridiculus question, of course only one.
    So I would classify you as a one-worlder and myself as a many-worlder so that we can distinghish between our ideas. I know we have very different points of view, but probably you would agree with me that when classifying interpretations, the number of worlds is an important criterion. The article in Wikipedia on "Interpretations of Quantum Mechanics" (http://en.wikipedia.org/wiki/Interpretation_of_quantum_mechanics) has a table towards the end that classifies the different interpretations.
    The columns are labeled:
    1) Deterministic?
    2) Wavefunction real?
    3) Unique history?
    4) Hidden variables?
    5) Collapsing wave functions?
    6) Observer role?
    I think "unique history" would be the same as "one-world". I was surprised to see "consisten histories" classified as non-unique history. I thought this interpretation took in consideration the possible histories but considered only one as being "real", making it more similar to the other "one-world" interpretations (at least on an ontological level).
     
    Last edited: Aug 19, 2009
  13. Aug 19, 2009 #12
    I made some comments on your position about realism in my reply to one of Kote's posts.
    I was saying that you may be considering experiments such as Alain Aspect's which negate the existence of a definite value of some variable before a measurement is made. After I made that post I realized that delayed-choice experiments might be even more compelling. From this you can see that I am not necessarily ignoring the facts. Now, even though QM seems to indicate the indeterminateness of certain variables before measurement, it gives a more determinate character to the result of measurement. The correspondence principle would imply a high level of determinateness at the macroscopic level. So the standard interpretation of QM seems to deny realism to some variables such as the position or polarization of a photon before it is measured but it seems to be compatible with realism at the macroscopic level. We could argue that even at the macroscopic level there is a small uncertainty in the position and momentum of objects but this is nevertheless a microscopic uncertainty. When I was talking about definite events in my original post (which you reasonably identify with realism) I was referring to the macroscopic realm and I stated it in that post. So it wasn't that I was choosing to ignore experimental evidence in order to make a flawed classification of ideas but it was a failure in communication.
     
  14. Aug 19, 2009 #13

    DrChinese

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    Well, my own impressions are as follows:

    Determinism implies that a set of initial conditions invariably leads to the same results every time. So in my mind, if there are acausal factors, then these must be independent of the initial conditions (by definition). So determism cannot result if acausal factors influence the outcome in any way.

    But let's suppose that somehow there IS determinism anyway. I wouldn't expect that, but I guess it might be possible (maybe there is something behind the acausal factors that is related to the initial conditions). But why would I assume this out of hand? My definition above definitely pulls me the other way.

    Regarding realism: OK, now you have made a measurement. But according to the HUP, some of the other properties of the system are no longer definite after the measurement. Now we have a new set of initial conditions with indefinite values for some variables - not just unknown but indefinite. So it seems we are back where we started.
     
  15. Aug 19, 2009 #14
    I agree with this point, but it's based on the assumption that the properties that we say we are measuring are basic. If instead realism (separable objective reality) or determinism are assumed, we are led to deny that measurable properties are basic. I also believe an assumption of realism or of determinism implies an assumption of the other... they are almost the same thing.

    As for MWI being disgusting... I don't think that, and I'm certainly open to new ideas. My questions were not rhetorical, and I see no necessary reason to preclude any unfalsifiable assumptions from a theory (such as an assumption of determinism or an assumption of multiple universes). While I find it more semantically accurate to minimize any unnecessary assumptions and deny separability (realism), I see a practical reason for always assuming that there is some underlying level to be probed, as per Bohm. Additionally, rational arguments can be made for an assumption of determinism, as per Spinoza and other rationalists.

    I just think I have yet to see what metaphysical or practical problems are solved by MWI that make it potentially worth the extra baggage.

    Edit: The determinism / realism equivalence is pretty easy to derive from Einstein's Criterion of Reality, so I'll add it in :smile:.

    The criterion for reality from the EPR paper:
    If, without in any way disturbing a system, we can predict with certainty (i.e., with probability equal to unity) the value of a physical quantity, then there exists an element of reality corresponding to that quantity.

    If we know deterministic laws, we know reality. If determinism exists, objective reality exists. Conversely, if reality exists, as defined by separably objective properties, those properties must be predictable by deterministic laws. The first point follows directly from the criterion and the second follows indirectly with an added assumption that this criterion is necessary as well as sufficient - a claim explicitly denied (as being irrelevant to their point) but implicitly accepted by EPR.
     
    Last edited: Aug 19, 2009
  16. Aug 19, 2009 #15

    jambaugh

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    I think you'll find it better (especially when considering QM) to not think of the universe "as a 4-dimensional space" but rather think of 4-dimensional space as our conceptual scaffolding from which we pull label to attach to the "universe of events/phenomena".

    I like the analogy of a heads-up-display ovelaying gridlines on the viewport. We catch events with our eyes (photons) resolving some momentum information (direction and frequency) and compare it to our HUD. We then can assign numbers to each event: "Bogie at 4 oclock High!!!"

    So with regard to your comments/questions I would say you are confusing a conceptual 4-D universe (which exists now in our heads) with the yet to occur events we would associate with some points in that universe. To say something exists contradicts it being in (associated with) the future part of that 4-D universe. To say that 4-D universe already exists is to acknowledge it as a present conceptualization rather than a future physical manifestation. To combine both with your inference is to make a serious category error.

    Clearify this in your head before you go on to consider determinism et al. Now you can assume a physical 4-D universe if you like but first acknowledge the conceptual one I mentioned and make sure you know to which you are referring when you speak of it. For example let me translate the tenses in the quote above (without -I hope- changing the explicit meanings):

    Does the argument make as much sense now? Do you see how present tenses and objectification of events (which are not objects themselves but phenomena) can invoke hidden implications?
     
  17. Aug 19, 2009 #16
    Before I respond to your questions, I would like to make a comment.
    I noticed that you are all talking to me (not to each other). I understand I am the most irritating person in this thread. However, I think your objections to my statements follow different lines of reasoning that sometimes don't agree with those of the other posters. I don't see a complete agreement between DrChinese , Kote and Jambaugh. I think many of these disagreements may have to do with your different interpretations of QM. Sometimes it helps to say what interpretation your argument is inspired in (to give it a name). Also, if I am not mistaken and there are disagreements, it would be interesting to know what these disagreents are in your view.
    Now I have to go back to my job search... But I'll come back later to answer to your posts.
    Thanks.
     
  18. Aug 19, 2009 #17

    DrChinese

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    You're not irritating. :smile:

    A lot of my posts are aimed at specific comments someone makes, but it is not intended to correct anyone or otherwise defend my position. My hope is to make sure that good balance is provided and especially that relevant physical theory and experiment are presented. And perhaps a good reference here or there.
     
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