Essay Abstract

Quantum measurement predictions are consistent with relativity for macroscopic observations, but there is no consensus on how to explain this consistency in fundamental terms. The prevailing assumption is that the relativistic structure of spacetime should provide the framework for any microphysical account. This bias is due, in large part, to our intuitions about local causality, the idea that all physical processes propagate through space in a continuous manner. I argue that relativity is not a guarantor of local causality, and is not about ontological features of spacetime. It is, rather, an expression of the observational equivalence of spacetime descriptions of physical processes. This observational equivalence is due to the essentially probabilistic nature of quantum theory.

Author Bio

I hold a Bachelor's degree in Philosophy from the University of Michigan and a Ph.D. in Physics from the University of Colorado. I have worked as an engineer in the design of sensor systems for automotive applications, (both safety and engine control), and I have done powertrain and thermal modeling.

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Dear Edward,

Thank you for an interesting and well written essay. I look forward to following what is virtually certain to be an interesting and lively exchange of ideas between yourself and other readers who are more thoroughly steeped in the subtleties and nuances of relativity and quantum physics than myself. Your topic is indeed a fascinating one.

Good luck in the competition!

jcns

    Dear Edward

    I found your essay well written and researched, but the only statement I could wholeheartedly and unreservedly agree with in it was "Whether through genetic endowment or constant habituation, nature has equipped us with deep intuitions about how the world works. These intuitions, together with the historical path of discovery, have induced us to grant spacetime geometry a special status." I wish I had you erudition to defend my ideas, but for what they are worth I have concluded that since 1905 this "historical path of discovery" for all its success, consists of a comedy of erroneous assumptions.

    They 'work' to describe certain phenomena, but only because of the brilliant way Einstein and Born and others have developed them. Such assumptions as the photon-as-a-point and probability have led us astray from the simple causal local deterministic way that the "world works". I would be happy if you can read my fqxi essay and give your thoughts.

    With best wishes, Vladimir

      Edward,

      In his SEP article on the Copenhagen Interpretation Jan Faye says this, which I immediately thought of when I read your paper:

      "In general, Bohr considered the demands of complementarity in quantum mechanics to be logically on a par with the requirements of relativity in the theory of relativity. He believed that both theories were a result of novel aspects of the observation problem, namely the fact that observation in physics is context-dependent. This again is due to the existence of a maximum velocity of propagation of all actions in the domain of relativity and a minimum of any action in the domain of quantum mechanics. And it is because of these universal limits that it is impossible in the theory of relativity to make an unambiguous separation between time and space without reference to the observer (the context) and impossible in quantum mechanics to make a sharp distinction between the behavior of the object and its interaction with the means of observation (CC, p. 105)."

      Just curious as to whether you see it as analogous to your own approach. Incidentally, I was also led to download your longer July 2011 paper from the Arxiv and am chewing on it.

        Vladimir,

        Thank you for your post. I read your paper, and it is well written.

        It covers a lot of ground, so I will not try to comment on all of it.

        Regarding Q5, on the point particle vs. wave issue, I have not had a chance

        to look at Eric Reiter's results, but it would be interesting to see how

        the photon (or photon wave) was detected in two places. I assume that it

        was a nondestructive detection, since an absorption of a single photon

        in two places would violate conservation of energy. Aharonov and his colleagues

        have described weak measurement techniques which in some cases can be interpreted

        as (more or less) direct observations of the wave function, so some types of

        double detections are possible.

        Regarding Q6, you say that "the true explanation is that the two photons are in

        the same state from beginning to end", but Bell's theorem shows that this

        cannot be the case. Maudlin's book (Quantum Non-Locality and Relativity) gives an

        excellent presentation of the argument, and there are several simple on-line

        descriptions, for example, the Wikipedia entry on the Clauser-Horne-Shimony-Holt

        (CHSH) inequality.

        This is an excellent question (and therefore not an easy one to answer).

        I would not agree with the analogy that Bohr was trying to draw. Although I am

        arguing that we need to adopt a substantially new perspective toward relativity,

        Bohr was working in the context of the standard spacetime view of relativity. It

        is against this viewpoint that we have to judge his attempts to interpret quantum

        theory. The standard view of relativity as a description of spacetime is logically

        coherent, even if, ultimately, it cannot be successfully merged with quantum theory.

        For all his struggles to do so, I don't think that Bohr succeeded in constructing

        a logically coherent interpretation of quantum theory. Although relativity had some

        surprising consequences (particularly regarding the nature of time), it is fully

        comprehensible (as a classical theory). We cannot make an unambiguous separation

        between time and space, but we understand fully why this is so.

        In interpreting Bohr's views it is important to keep in mind that he was

        writing before Bell demonstrated the radically nonlocal nature of what occurs

        during some quantum measurements. Clearly, In the wake of the EPR paper, and in

        formulating his reply to it, Bohr had some rough idea of the challenge posed by

        nonlocality, and Faye makes the point that Bohr appears to have seriously changed

        his interpretation of the quantum formalism in response to the challenge. But it

        does not appear that he fully grasped the need to explain the nonlocal correlations

        that Bell (later) clearly identified.

        As I said, this is a very good question, and it probably will require

        more discussion.

        Hi Edward,

        this is an interesting and nicely written essay. I have the following thought for you: when one takes the different physical scales involved, things may look different. Example: I can make an apparatus where when I press a switch, an impulse is sent down two signalling paths that have been very carefully manufactured to be identical in length, to reach identical activators, say 5cm apart, that each send out a laser pulse when they receive the signal. These pulses will be emitted simultaneously if the signalling paths are equal to sufficient accuracy. From the micro-viewpoint this will look acausal (light is emitted simultaneously from spacelike separated objects), but from a macro viewpoint there is no problem; it is the macro structure that has enabled the simultaneity at the microlevel (and that chain of causation can off course be traced at the micro level). This is an example of the interscale effects that can occur in quantum physics: from the Copenhagen view you just regard the macro apparatus as a single entity whose internal workings are of no concern, and then macro apparatuses can reach down in an a-casual way to the micro level.

        Overall the comment is that any physical description has averaging scales associated with it. The interscale interactions resulting can be interesting.

        George Ellis

          Dear Edward Gillis,

          A well written essay. I think you are correct that both space-time, relativity and non deterministic physics have to be accepted. How they can co-exist without contradiction has been an interest of mine for a long time. I agree with Vladimir Tamari in particularly liking your conclusion.

          Good luck in the competition.

            Edward,

            "But, in order to make current theory logically coherent, we need to realize that relativity is rooted as much in the indeterminism that characterizes quantum theory as in the structure of space and time."

            Do time and space both have a role in relativity's indeterminism and are causal relationships dubious or non-existent as time passes?

            I'm somewhat confused.

            Jim

              4 days later

              Professor Ellis:

              Thank you for your interest.I have long admired your work in cosmology and your willingness to deal with controversial scientific issues. Your work outside academia is truly laudable.

              Your essay on top-down causation is interesting and insightful. You present a very nice explanation of how causation on different levels operates by defining constraints.

              I would agree with your overall comment that "any physical description has averaging scales associated with it", and that the interscale interactions are interesting. But I think that it is important to be able to explain, at least in principle, how these interactions work. My problem with the Copenhagen Interpretation (C.I.) is that it says that we really cannot analyze what happens across the micro-macro interface. Your example of the two simultaneously firing lasers illustrates this nicely. It is clearly causal on a macroscopic scale, and it is true that at least some versions of C.I. would treat the apparatus as a single "black box",so that the precise operation on a micro level might be viewed as acausal. However, as you point out, the chain of causation can be traced at the micro level. So we can construct a locally deterministic account of the process in which all influences propagate within the light cone. There is no genuine superluminal or acausal influence in this case, even if some versions of C.I. suggest this.

              In contrast, Bell-EPR correlations indicate that, in certain situations,

              there are real superluminal effects. To explain these on a micro level we need to revamp our understanding of spacetime structure to allow for these nonlocal

              processes. I believe that we can do this and still preserve the relativistic

              description of spacetime because of the symmetric character of the probabilistic law governing these processes [ P(A|B) = P(B|A) ].

              Ed

              Jim,

              Thanks for your question. I believe that we should look at space as a 3 dimensional manifold that evolves in time. This would disrupt the (partial) unification of space and time that is achieved in conventional views of relativity, but it makes it possible to understand what happens in quantum measurements. Bell's work and subsequent analysis have shown that the effects of measurements are both nonlocal (superluminal), and nondeterministic. These are extremely difficult to fit within a conventional 4-dimensional relativistic spacetime. Fortunately the form of indeterminsism that occurs is regulated by a special probability rule (the Born Rule). This rule has the special property that it is symmetric with respect to possible outcomes of measurements. So if 2 spacelike-separated measurements are made on an entangled system, the probability of a B outcome of measurement 2, given that an A outcome of measurement 1 has already occurred, is equal to the probability of an A outcome of measurement 1, given that a B outcome of measurement 2 has already occurred. This means that there is no way to determine which of the 2 measurements occurred first. So the relativistic description of spacetime which allows us to sequence spacelike separated events in either order remains consistent with all physical observations. It is the special form of indeterminism that insures this consistency.

              Ed

              Ed,

              "I argue that relativity is not a guarantor of local causality, and is not about ontological features of spacetime." What impact would this have on my belief that the forces of gravitation might be cancelled, at least by advanced civilizations? Are message carriers like the graviton and the embedded anti-graviton -- assuming they exist -- possibly discontinuous?

              Jim

              Your paper makes a salient point. I will be posting an essay here in the near future which touches on this problem. I think the question that needs to be raised is how fundamental is locality. Quantum mechanics has a representation according to configuration variables in spacetime, or the momentum conjugate, but quantum state are fundamentally independent of such representations. Quantum wave equations are partial differential equations which define an oscillator at every point on a spatial manifold. Locality is "imposed" by assigning equal time commutators on this spatial slice. However, the wave equation is defined according to partial derivatives with time ∂_t which is a local time direction determined by the frame of an observer. If we were to quantize spacetime itself there would be no manner in which a Born rule exists in general. The reason is that light cones near the Planck scale become indistinct. A propagator of quantized spacetime according to standard QFT propagates this on spacetime, which runs into trouble.

              I think then that spacetime is emergent from nonlocal or noncommutative geometry on a deeper level. In the reasoning of noncommutative geometry, geometry is replaced with groups. Underneath spacetime I think exists a quantized system of nonlocal amplitudes. At lower energy with the emergence of spacetime this enforces the Born rule for quantum waves at this larger scale.

                Edward,

                While your essay is quite dense for those of us with little formal education in physics, it does contain some interesting insights and seems to go in the right direction in terms of correcting the various misconceptions built into the current structure. I especially found your analogy of information with temperature quite interesting, since it mirrors some of my own perceptions and thus provides some deeper insight into the issue of non-locality, which seems to be a bit of a mathematical artifact, but difficult to unravel. I do think the concept of temperature is greatly overlooked, as a window into non-linear systems. While the focus is usually on its formal molecular definition, everything from cosmic background radiation, to economic statistics could be thought of as forms of temperature. E.O. Wilson described the insect brain as a thermostat and it could be argued that radios, as well as many other forms of electronic devices are also, as your profession suggests you well understand.

                My own essay goes into a slightly different form of sensory misconception, the perception of time. We experience it as a series of events, from past to future and physics re-enforces this assumption by treating it as a measurement, but the actual physical process is the changing configuration of what is extant, collapsing probabilities into actualities. The future becoming the past. This makes it an effect of action(rate of change), similar to temperature(level of activity). Digging down into this, time dilation is due to changes in the level of atomic activity affecting the rate of macroscopic change.

                Spacetime is then correlation of distance and duration, not causation of action. One could easily use ideal gas laws to formulate "temperaturevolume," but we don't confuse the needle with the scale, as we do with time.

                Good luck.

                  5 days later

                  Jim,

                  I don't think that what I am saying has any direct implications one way

                  or the other concerning possible ant-gravity effects. There was a very nice

                  paper by Scott Menary posted on the physics archive this past week,

                  explaining why we are fairly sure that there are no anti-gravity effects:

                  http://arxiv.org/abs/1207.7358.

                  Concerning "messenger" particles: they generally have to propagate in a

                  continuous manner.

                  Ed

                  Lawrence,

                  I look forward to reading your paper. What you say about the Born

                  rule is interesting. I would agree that the rule applies at the level of

                  macroscopic observations, and that it should be explainable in terms of more

                  fundamental processes. One key feature of it, however, is its symmetry: the

                  probability of A, given a B outcome is equal to the probability of B, given

                  an A outcome. I believe that this symmetry at a macroscopic level probably

                  stems from some more fundamental symmetry principle.

                  The possibility that spacetime is emergent is interesting to

                  consider. I have not really addressed it here, other than to speculate that

                  the partial unification of space and time that is achieved in relativity is

                  dependent on the probabilistic nature of quantum theory.

                  Ed