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Making Meaning Out of Entanglement:
A Conversation

On the morning of 29 March 2006, Al Albano, a member of the Physics faculty at Bryn Mawr College, presented material on the quantum physics phenomena of entanglement to the emergence working group of the College's Center for Science and Society. Following the talk, Sandy Schram, a political scientist in the College's School of Social Work and Social Research, initiated a burst of email exchanges with several other members of the working group, including Al, computer scientist Doug Blank, and biologist Paul Grobstein. The exchanges, excerpted here with permission of all participants, provide an interesting documentation of interdisciplinary exchange as well as of the intersection of scientific observations and more general perspectives in intellectual inquiry. For additional conversation see the emergence group's on line forum

Sandy to all - 29 March, 11:53 pm

hi all, i read the following zeilinger article which covers everything we discussed today. i also visited the colgate webpage (http://departments.colgate.edu/physics/research/Photon/root/photon_quantum_mechanics.htm) and read the history on the experiments. the major problem for me remains the math. but then there is also the continual mixing of ontological and epistemological claims as when, say, zeilinger discusses how the newer experimental technologies allow for very rich entangled states of decomposing paired photons or alternatively these are really questions of shared information registered at any time in the form of very rich perfect correlations. one sounds like a description of the physical state of the photons and the other as a product of how they are measured. last, is the tendency to talk about experimental design and then jump up at the last minute with statements like:

"I hope that the reader can sympathize now with my viewpoint that quantum physics goes beyond Wittgenstein, who starts his Tractatus Logico-Philosophicus with the sentence, "The world is everything that is the case." This is a classical viewpoint, a quantum state goes beyond. It represents all possibilities of everything that could be the case."
http://www.physik.fu-berlin.de/~simons/Publikationen/RevModPhys99.pd

So, help me out here, is zeilinger saying that how reality is seen depends on how we measure it or is he saying that reality changes depending on how we measure it?

I do totally agree with his warning midway in the article. It is perfectly clear and at the end totally consistent with what paul said at our session today:

"This possibility of deciding long after registration of the photon whether a wave feature or a particle feature manifests itself is another warning that one should not have any realistic pictures in one’s mind when considering a quantum phenomenon. Any detailed picture of what goes on in a specific individual observation of one photon has to take into account the whole experimental apparatus of the complete quantum system consisting of both photons and it can only make sense after the fact, i.e., after all information concerning complementary variables has irrecoverably been erased."

i think i have been trying to resist having a pre-conceived notion of light or matter, or even energy whatever that is. But the question is are we to take those to be changeable because we measure them or that our view of them changes depending on how we measure them. or is that a false dichotomy itself? and was this kind of non-thinking common to our deliberations today? i still feel like i am missing something. that may be a big understatement!!

Sandy to all - 29 March, 12:28 pm

okay, i will stop now with this genealogical analysis of emergence that suggests that there can be ontological versus epistemological forms of emergence:

http://plato.stanford.edu/entries/properties-emergent/

here both ilya prigogine and robert laughlin are depicted as not necessarily choosing one over the other. i would add that for me the difference between ontological and epistemological emergence parallels the weak and strong versions of entanglement. i gather from the listservs i have looked at others have already made this parallel. it could be that this parallel is it own form of entanglement/emergence--i.e., another mutually exclusive complementarity!

Al to Sandy/all - 29 March, 12:49 pm

Sandy -- you really wasted no time!

So, help me out here, is zeilinger saying that the how reality is seen depends on how we measure it or is he saying that reality changes depending on how we measure it? I think what he is saying is that our description of reality depends on how we measure it. Recall Bohr -- the referent of quantum mechanics is not reality .. but what can be said about it. Of course, a lot of people still disagree with that.

It seems that despite the warning you quote ... , you still start with a "realistic picture" of what's happening out there before the measurements are completed. I must confess, though, that in Zeilnger's experiment, the idea that what is recorded by the detector behind the double slit is influenced by what is going to happen in the other detector at a later time violates my preconceived notions of causality, etc. But starting with these preconceived notions is what we are being warned against. And it's true that once the complete experiment has been done, there is a unique story line.

Sandy to Al/all - 29 March, 12:56 pm

thanks al. it seems that you highlighted what is also perplexing me when you say: "in Zeilnger's experiment, the idea that what is recorded by the detector behind the double slit is influenced by what is going to happen in the other detector at a later time violates my preconceived notions of causality, etc." i still do not understand how that can be. how does one detector influence another? i totally am befuddled by that one.

Doug to Sandy/all - 29 March, 1:42 pm

I imagine that, for some reason that still *needs* to have a story behind it, there can only be a single bit of information extracted from this experimental setup. Or, maybe a better way of saying it is that there really is only a single bit of information "out there" in the reality being measured. By measuring one of the split pieces, you get THE bit of information, so there is no more. Because there isn't anymore (and you can't just create information from nothing), then the other split piece's behavior is set.

Altering time and space don't seem to be able to affect this. However, the physics also don't seem to allow any contradictions either. That is, the experiments show that even though this quantum world is very different from the one that emerges from it, it is still self-consistent and logical. In this sense, it seems that it is still "normal" and normal science will continue to work away at discovering its nature. The only difference is that we are part of the equation.

Sandy to Doug/all - 29 March 2:32 pm

thanks doug. but i still dont understand how extracting the one bit of information one way changes the one bit that the other split piece gets recorded as. it almost sounds as if what is really being said is that there potentially two bits of information that a photon could be recorded as having and when you record it one way it changes what the other split piece can be seen as. how does it change it is my question?

Sandy to all - 29 March, 9:33 pm

please explain the dice. this more than anything explains my concern. hey, einstein himself called it "spooky."

http://www.quantum.at/typo/index.php?id=254&tx_jppageteaser_pi1[backId]=191

Paul to Sandy/all - 30 March

Sorry to be a little late in getting into this conversation. I needed to get some of my own questions/thoughts in order before I felt comfortable responding to your questions. Having done so (http://serendip.brynmawr.edu/forum/viewforum.php?forum_id=356#18720) let me see what that does (or doesn't) do about your quite legitimate and generative concerns.

"i still dont understand how extracting the one bit of information one way changes the one bit that the other split piece gets recorded as. it almost sounds as if what is really being said is that there potentially two bits of information that a photon could be recorded as having and when you record it one way it changes what the other split piece can be seen as. how does it change it is my question?"

"please explain the dice. this more than anything explains my concern. hey, einstein himself called it "spooky."
http://www.quantum.at/typo/index.php?id=254&tx_jppageteaser_pi1[backId]=191

"this article, produced regionally, argues that a post-particle quantum metaphysics creates the basis for imagining a non-linear, emergent causality:
http://www.lehigh.edu/~mhb0/emergence.html
The key here, I think, is Bohr's "what can be said about the world" as the referent of physics (and, for me, the referent of science/inquiry in general), as opposed to the referent being a description of "reality". "Entanglement" is a description of observations (or, more properly, a consequence of some equations which were in turn developed to account for a set of observations that in turn predicted something new that was subsequently observed). "Entanglement" is a story to account for a set of empirical observations. And, in this sense, entanglement "explains" dice and related things that were not originally part of the observations. This is how "story" works; the task is to account for observations, look at implications of that account, test those, keep the story if it still works, revise it if it doesn't.

Seen in these terms, your questions are actually meta-questions, not about the dice themselves but rather about entanglement (as would be the question, why was there a big bang?). The dice do what they do because of entanglement. What you are asking is why is there entanglement? Its a legitimate and potentially generative question but one for which the story has at the moment no answer. One might be bothered by this or not, depending on how it relates to other stories one has on one's mind. If one has somewhere in one's mind the story of a relatively simple deterministic universe, one in which some finite number of laws governing local interactions can in principle account for everything, then one may be bothered (as Einstein indeed was) by quantum formalisms that imply both some measure of genuine indeterminacy and some connectednesses not reducible to local interactions. In this case, as indeed has happened, one might try to account for the observations in some way more compatible with one's other story (Al's "you still start with a realistic picture" with the supposition that things have to make sense in terms of story elements one already and so the question "how does it change?" needs an answer in those terms). The Zeilinger observations in fact represent the latest in a series of efforts to find out if there is some explanation of entanglement in terms more compatible with the simple deterministic universe that Einstein liked, and add to a list of ways it is turning out that can't be done. If, on the other hand, one does not have the simple deterministic universe story somewhere in one's mind, then one can contentedly accept the quantum formalisms as a very very very good "story" in its own right (one that summarizes a huge number of observations in an elegant compact form, and in turn motivates new observations).

All this seems to me, in turn, to relate interestingly to an earlier exchange of ours, in which you expressed concern about the impact of science on other areas of inquiry because "most science is practiced as a form of scientism--defined here as an ideology that is in denial about its narrativity and insistent on its ability to directly represent reality, nature, the objective world, etc.". Might we equally define "scientism" as commitment to "the story of a relatively simple deterministic universe, one in which some finite number of laws governing local interactions can in principle account for everything'? An advantage of doing so is that this would disconnect "scientism" from science and so allow Wheeler, Zeilinger, Al (I think, though I don't want to put words in his mouth), and myself, among others, to go on calling ourselves scientists despite a disinclination toward "scientism". And it might allow one to acknowledge that "scientism" is not the exclusive domain of scientists but rather has home-grown versions in the social sciences and humanities as well? Which might in turn allow those of us who favor a story telling posture to make common cause, irrespective of our disciplinary backgrounds? I'm happy to have physics contribute to a "non-linear, emergent causality" but am equally convinced there are other equally viable ways to get to that perspective (eg "Getting It Less Wrong: The Brain's Way", "Science as Story Telling and Story Revising", and "Emerging Emergence").

Maybe, in fact, there is a bit of the inclination toward liking "a relatively simple deterministic universe" in all of us? And so the tension between "scientism" and a wholesale commitment to the story telling posture is constantly being played out not only between disciplines and within disciplines but within each of our own lives, professional and otherwise, as well (cf Making the Unconscious Conscious and Vice Versa"?

Sandy to Paul/all - 30 March

Thanks. Your comments are very helpful. But my problem is not so much either why is there entanglement or even what is it, as much as whether I am asking the right question when I say: how does it come to be that simply looking at the electron spin on one half/side of the entangled photon to see its location/direction that that automatically changes what the result will be recorded on the other side. it seems like a magician's trick. the beginning of understanding for me on this is starting to emerge with the quotation from Anton Zeilinger that I posted this morning:

"When, say, two electrons are entangled, it is impossible even in principle to describe one without the other. They have no independent existence. This seems bizarre until you use Zeilinger's principle. Concentrating on their spins, a two-electron system contains two bits. For example, they might be "The spins in the z direction are parallel," and "The spins in the x direction are antiparallel". The two bits are thereby used up, and the state is completely described--yet no statement is made about the direction of spin of one electron or the other. The entire description consists of relative statements, or correlations. This means that as soon as one spin is measured along a certain direction, the other one is fixed, even if it happens to be far away."

"Zeilinger's single, simple principle leads to these three cornerstones of quantum mechanics: quantisation, uncertainty and entanglement. What, then, of the more formal elements of quantum mechanics such as wave functions and Schršdinger's equation--the bread and butter of atomic physicists? The road promises to be long and steep, but Zeilinger and his student `«Caslav Brukner, have now begun the ascent."
I think if I can get more help in understanding this one quotation, I will be in better place about just what is the story that Bohr, Born, Bohm, Bell, de Broglie, Heisenberg, Shrodinger, Einstein and the others right up to Wheeler and now Zeilinger are wrestling with.

Al to Sandy - Monday 3 April

Sandy, I think you should change your question, or restate the answer, slightly. It is not that measuring a property of one of the entangled electrons changes a property of the other. Suppose that two electrons are entangled by the condition that their total energy has a fixed value, E. It means that if one of the electrons has energy, x, then the other has energy E-x. Measuring that one of the electrons does have energy x does not change the value of the other electron's energy from some other value to E-x. The entangled state, A = "one-electron-has-energy-x-and-the-other-electron-has-energy-(E-x)" is one of the possible states of the system. The probability of finding such a state, contained in its wave function, is what is calculated by Schroedinger's equation. If a measurement shows that the energy of one electron is x, then that tells us that the entangled system is in state A, and therefore the energy of the other electron is E-x. Before the measurement, we did not know the energy of either electron; all we could know are the probabilities for being in one of the possible entangled states.

The predominant opinion now is that Einstein, Born and their fans have lost this argument.

Sandy to Al/all - Monday 3 April

that helps tremendously. there is now though still the question how measuring location vs. direction on one end affects what we see on the other. i suspect that is a similar issue of entanglement but remains for me to explain. thanks for helping me get to this point or process (i guess it is undecideable where i am at, but here i am nonetheless)!

Paul to Sandy/all - Monday 3 April

Its interesting to look back over this conversation. "Is Zeilinger saying that how reality is seen depends on how we measure it or is he saying that reality changes depending on how we measure it?" was your original question. And yet we have still for you "the question of how measuring on one end affects what we see on the other". That in turn is interestingly connected to a conversation that's been going in a philosophy of science course I'm teaching (cf week 10). So let me borrow something from there and see if I can do better for you than "physics is a description of observations, not a description of the world" and therefore you can start over with the observations and derive an entirely new story , one for which the question you're asking is meaningful only in the older story and hence premature to ask in the new one (it may not exist).

The key notion here may be that one "has to take into account the whole experimental apparatus" and that that INCLUDES the experimenter. Its not either that "how reality is seen depends on how we measure it" OR that "reality changes depending on how we measure it" but rather that one needs probably to drop the concept of "reality" as distinct from the experimenter altogether. The two electrons, as Al says, have together a property of entanglement such that the observation of a particular value for one necessarily requires that the other be observed to have a particular property. And the experimenter is a inextricable part of this story of reality. Without an observer (of some sort) neither entanglement nor its consequences would exist. Is it "how reality is seen" or "reality changes" isn't a meaningful distinction in this case. There is only interactions between investigator and electrons, with no independent perspective from which to pose the question you're asking.

That any better? Want to get back to my earlier curiosity about how come a political scientist seems more inclined than either a biologist or a physicist to hold onto notions of simple unidirectional causal relations and a sharp observer/subject distinction?

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