Entangled Quantum States

Keith B Miller (kbmill@ksu.edu)
Sun, 5 Jul 1998 15:15:47 -0600

More on entangled quantum states for those in the group who are physically
inclined. :-) I will resist posting any more on this from the Templeton
listserve. Any further discussion will have to generated from our own
local universe.


>Meta 126. 7/3/98. Approximately 117 lines.
>Below are three messages from Carl Helrich from the Physics Department at
>Goshen College continuing the thread on Entangled Quantum States.
>Helrich's first posting is a good review of the history and conflict
>between Bohr (the Copenhagen School) and Einstein, Podolsky and Rosen
>(EPR). He goes on to talk about the Bell Theorem and the seeming
>experimental vindication of Bohr in the 1980s. "Spooky connections"
>between quantum phenomena are "real". Other physicists might well skip
>this section, but I found it a helpful review for this layman.
>The second message from Carl Helrich is in response to Nick Saunders and
>John Dale (see Meta 124). Here, Helrich engages in some more philosophical
>and theological reflection on Quantum Mechanics and the Cosmos.
>In the third message, Helrich recommends a recent article in NATURE that
>presents an un-entangled and clear overview of the current state of cosmology.
>Please note that I now have a back log of some twenty messages on a variety
>of subjects. For those of you have submissions to Meta outstanding, please
>be patient and I will get to them over the next two weeks. Thank you.
>-- Billy Grassie
>From: "Carl S. Helrich" <carlsh@mail.goshen.edu>
>Got a chance to consider your last note and thought I'd add a couple of words.
>I'm sorry I didn't hear this discussion (Bill Wootters' talk at the Chicago
>Workshop). I would have very much enjoyed it. Since my note hear goes on a
>bit, let me say three things up front:
>1. Read the end first to see my position.
>2. I am preparing a thermodynamics outline for presentation to Zygon
>(teacher's section) which deals with some of the related problems to which
>I allude here.
>3. Part of the problem is the quantum measurement problem. This is an
>unsolved problem which still attracts considerable interest. We must have
>some idea of what quantum measurement means before there are any observers.
>This is not at all easy. Physics Today a month or so back has an article
>on the problem.
>Now to what I want to say ...
> First, I'm very hesitant to jump to conclusions about the entire
>universe. As I understand the problem, entangled states are those
>corresponding to entities (Quantum particles, photons, and the like) which
>single location (point) in space. The problem goes back to the Einstein,
>Podolsky and Rosen paper of 1935 (Phys Rev ... something). This was
>something of the final challenge to the Bohr (Copenhagen) interpretation of
>the quantum theory. And it (almost) did just that. Einstein, Podolsky and
>Rosen (EPR) selected an entangled quantum state (two electrons emitted from
>a single point ... a box) and chose to look at one of them at a later time.
> The humor is in that they could decide at their leisure, on any day,
>whether to measure momentum or position. The point is that the measurement
>of one or the other would define the corresponding value for the unmeasured
>electron moving in the4 other direction. The conclusion of EPR was that
>this makes no physical sense, since it would require "spooky connections"
>between the particles. The premises are a little more involved. EPR
>outline a meaning of "reality" as they claim it philosophically. This was
>the real challenge to the Copenhagen interpretation, as the EPR reality
>required that the property to be measured have a "real" ness. That is, the
>measurement was of an actual physical "something" that the particle
>possessed. Our problem is only to measure that something. The conclusion
>of EPR was that quantum mechanics is incomplete. Not wrong, just incomplete.
>The difference is that in the Copenhagen picture, a measurement is only
>defined in terms of dta obtained form pointers (digital readouts at this
>time) and must be conveyed in the language of classical physics and use
>HUMAN LANGUAGE. (Danish ... or German, perhaps). That is, there is no real
>something to be measured, just a result obtained. This is, of course, all
>very intriguing. It leaves us with this epistemological ... and maybe
>ontological limit. But it got nowhere with "uncle Albert."
>Answers to the EPR challenge failed until J.S. Bell provided a possibility
>to measure entangled systems. Bell's mathematical inequality involves what
>is called a correlation function, which provides a probability that a
>certain outcome occurs given that another has occurred. Of course that's
>what we want. The actual experimental results were obtained by the French
>group under Aspect at, I believe, Grenoble in the early 80's. Our intiial
>understanding of this was that "quantum mechanics wins .. and Albert
>loses." The issue seems more complicated. You see, Bell worked with a
>picture more akin to Einstein's. Bell considered what would happen if
>there were a hidden variable that determined what would be measured,
>although itself is not that measured quantity. I have only myself (finally)
>begun working through the Bell stuff. I once thought I understood it, but
>I am no longer so sure.
>If it is true that the quantum description "wins", which I believe is the
>case, we need only confront the epistemological question of quantum
>measurement. That's challenging enough. But we can avoid the problem of
>spooky connections. On the other hand, if we want to have a hidden
>variable theory, in other words that the quantum particle has a real
>something that determines what is measured before it is measured, then we
>must have spooky connections to obtain the quantum results. Any way we cut
>the pie we have quantum mechanics.
>We are always tempted to jump to conclusions. If it is true that entangled
>states demand "spooky connections", which I am not sure about at all, then
>we are tempted to joyously jump, with complete abandon, to the conclusion
>that all particles were connected at the point of the "Big Bang" and are
>forever entangleds. All that seems like far too much of a jump for me. In
>less kind moments, I would say that is fantasy. You see, we MUST AT ALL
>TIMES HAVE AN EXPERIMENT!!! I am tempted to claim that we have no
>measurements at the time of the Big Bang, which is probably true. But I
>need not go that route. I think the problem is far simpler than that. You
>see, we must ultimately consider something which is measurable and speak in
>terms of that. We can only measure the ENSEMBLE. So we really should cast
>our speculations in that language. There the difficulties of even speaking
>of particles rear their heads. Prigogine has pointed to a complementarity
>between particle description and thermodynamic description. It seems to me
>that we are confronted here by something we must take as seriously as we
>have taken Heisenberg. The practical result is that we shouldn't really
>speak about the individual particles of a large non-equilibrium system at
>all. The consequence is really that any discussion of entanlement of the
>states of all entites in the universe is a discussion which has little
>basis in anything beyond pure speculation, interesting though that may be.
>Peace, Carl
>From: "Carl S. Helrich" <carlsh@mail.goshen.edu>
>Subject: Re: Meta 124: Entangled Quantum States
>I read over the responses to entangled states with interest, although
>quickly. First a comment for John Dale. We do why the sky is blue. Yes,
>QM helps there.
>I appreciated particularly Nick Saunder's point on how unclear it is when
>we talk about measurements of the entire univers. That is my problem, to
>some degree, as well. His point is more theological than mine. Mine is
>scientific. I am definitely concerned about what we are trying to say when
>we contend that a measurement is made. The point Bohr was making is how
>careful we must be in specifying exactly what we mean by measurement is
>linked to specifying the detailed procedure undertaken in performing the
>measurement. The term "measurement" entails the entire setup. Bohr's
>position has been criticized because he said little about the actual
>division between apparatus and object. But it seems to me that this
>criticism misses the point. The point is that we, as human beings, cannot
>say anything about the border between the quantum and what we call the
>apparatus. All we can talk about is the apparatus. To pretend to know
>something about the detailed interacton of, say, the electron with the
>apparatus is to prestend to know more than we actually can know.
>Heisenberg pointed out that the atom is actually a mathematical model. I
>have said this often to my students. For my philosophically inclined
>physicists this is not a difficult point. But for my chemists it is.
>Heisenberg's point is that we only have scattering experiments on the atom
>(or molecule). These we correlate using a mathematical model. In other
>words, what we understand as structure of the atom is the structure we have
>in our mathematical picture. We have only interpreted this for the comfort
>of our mental picture. But that does not, in any sense, mean that the atom
>would "look like this" if we could ever decide what "looking at the atom"
>might entail, if we meant the same as "looking at a tree." Indeed, as
>Freeman Dyson once said, we physicists are not real sure about what matter is!
>I find the issues become really sticky when we start talking about photons.
>Those beasts are really a bit on the fringes. In the fifties, Einstein
>pointed out that many young physicists think they know what photons are,
>but that he had been thinking about these for fifty years and still didn't
>understand them. I've always seen that as a cautionary statement. The
>photon is a non-localizable quantum of the electromagnetic field. Yeah ...
>but what are those terms? We like to picture fuzzy little particles.
>Before I ramble, which I'm dangerously close to doing, let me raise a point
>that Hava Samuelson raised at Chicago. I believe Nick Saunders is probably
>leaning toward this as well. As a physicist I naturally try to find
>explanations in terms of physics. I think the issue we are about in trying
>to understand the action of God in the universe is, however, a little
>different. We are trying to see where God could be acting, within the
>limits of our physics, in a way that we can not detect. In other words we
>are seeking the epistemological and, perhaps, ontological limit beyond
>which we cannot go, but God may. Or may elect not to go, as Peacock points
>out. In principle I have seen this as not coming into conflict with the
>concept of transcendence. I have seen this as trying to point to a pathway
>by which we may see, from our observational point and with our apparatus,
>how this may work. I was struck by Hava's comment because it focused once
>again the realization that we must deal with the issue of transcendence. We
>claim to do this with the acceptable idea of "panENtheism." But is it not
>true that in so doing we walk a very thin tightrope. We use the words, but
>can we really find comfort in them.
>It seems to me that there is real genuine difficulty in claiming that we
>have a material substrate and yet understand a transcendence.
>I'll leave you with that. You probably know more about these issues than I
>do, since I am but a poor physicist. Enjoy the fireworks.
>Peace, Carl
>From: "Carl S Helrich" <carlsh@goshen.edu>
>I just read an articlae in Nature (Peter Coles, pp 741-744, 25 June, 1998).
> It's readable by all. Provides an overview of the present state of
>Cosmology and particularly deals with cold dark matter. Evaluates the
>present state of the model indicating that things are becoming a little
>unravelled. Of particular interst might be the nonumiformities.
>I am concerned that some of us may see the early universe as a homogeneous
>situation. There's a lot to account for. You might find this fun.
>Carl S. Helrich, Ph.D.
>Professor and Chair
>Department of Physics
>Phone: 219-535-7302
>FAX: 219-535-7509
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Keith B. Miller
Department of Geology
Kansas State University
Manhattan, KS 66506