Nobel Prize to Haroche and Wineland

By Sean Carroll | October 9, 2012 8:32 am

Nobody comes to these parts (at least, they shouldn’t) looking for insight into atomic physics, quantum optics, and related fields, but hearty congratulations to Serge Haroche and David Wineland for sharing this year’s Nobel Prize in Physics. Here are helpful stories by Alex Witze and Dennis Overbye.

One way of thinking about their accomplishments is to say that they’ve managed to manipulate particles one at a time: Haroche with individual photons, and Wineland with trapped ions. But what’s really exciting is that they are able to study intrinsically quantum-mechanical properties of the particles. For a long time, quantum mechanics could be treated as a black box. You had an atomic nucleus sitting there quietly, not really deviating from your classical intuition, and then some quantum magic would occur, and now you have several decay products flying away. The remoteness of the quantum effects themselves is what has enabled physicists to get away for so long using quantum mechanics without really understanding it. (Thereby enabling such monstrosities as the “Copenhagen interpretation” of quantum mechanics, and its unholy offspring “shut up and calculate.”)

These days, in contrast, we can no longer refuse to take quantum mechanics seriously. The experimentalists have brought it up close and personal, in your face. We’re using it to build things in ways we wouldn’t have imagined in the bad old days. This prize is a great tribute to physicists who are dragging us, kicking and screaming, into a quantum-mechanical reality.

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  • Joah

    Sean, do you have any place you can point me to where you explained why the Copenhagen Interpretation is monstrous? I understand that you have a Many Worlds affinity, but there are certain aspects of the Copenhagen Interpretation I’ve always liked. It seems to me that Copenhagen gives a straightforward explanation for things such as the Born Rule and the Heisenberg Uncertainty Principle while I don’t see a simple explanation for this coming out of my basic understanding of Many Worlds. Do you just find its ontology aggravating?

    • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean Carroll

      Joah– The objection to Copenhagen is just that it’s completely incoherent. It imagines a distinct “classical” realm, doesn’t tell you what’s in that realm and what’s truly quantum, doesn’t explain when wave functions collapse, etc. The Born Rule isn’t “explained” at all — it’s just postulated. And the Uncertainty Principle is exactly the same in MWI as it is in Copenhagen, so I’m not sure what the distinction is there.

      MWI has its own issues, certainly, as do all other known versions of QM. But at least it’s well-defined, whereas Copenhagen is kind of a joke.

  • CERNicist

    It’s a shame more physicist aren’t interested in interpretations of quantum theory, but as I understand it very few interpretations make testable predictions (or at least ones that would set them apart from other interpretations). So we can’t really blame physicist for wanting to do science rather than philosophy (not that there’s anything wrong with that).

  • Pete

    Copenhagen Interpretation is “monstrous”? Please collapse my assumptions as to it’s usefulness.

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  • Markk

    What version of the Copenhagen interpretation are you using? There is no idea of “classical” or “Quantum” in it that I understand – just models and observations. You calculate models, make observations which cause the function in the model to change “quantumly” that is discontinuously. That was the whole point – observations rule and models are just models. The idea of discontinuity is built into the Copenhagen interpretation, but removed from many worlds or hidden. I find that troubling.

  • Brett

    @Markk

    I think your first sentence is exactly the problem with the Copenhagen interpretation.

    I think the problem with MWI is that people try to explain it in terms of classical mechanics.

  • http://www.eshib.in Shibin Dinesh

    Here is a simple ,non technical description on the basic science upon which this years NP winning work in Medicine is based on-
    http://wp.me/p1z4hZ-d6
    Please do read and leave your reply!

  • Jeff

    Haroche and Wineland are very deserving, but wasn’t this the year when Peter HIggs was supposed to win the prize? At 83, he’s not getting any younger.

  • Ysan

    I also thought of this. It would be a a it tragic considering one of the other people already wasn’t around anymore for the discovery. But from what I’ve seen they seem to wait a bit before handing out the prize. Nevertheless this is a great discovery and I had no idea that they managed to do this.

  • Joah

    Thanks for clarifying, Sean.

    My (perhaps flawed) understanding of the Copenhagen Interpretation is that observables are all that matters and the underlying formalism is just that. This reminds me of Phasor Diagrams in that the actual observable values of the current, charge, or voltage are only the real parts of the particular phase vector that you are considering while in quantum mechanics it is the value of the observable operator when it operates on the wavefunction. It’s the emphasis on the operator being important that I found most satisfying in my elementary quantum mechanics courses. The Born Rule seems to me to fall out of the mathematics rather nicely: since solutions to the Eigenvalue Equation are constants that are subject to normalization, they must be simply the probabilities. This isn’t to say that the Many Worlds’ Interpretation doesn’t emphasize the operator, only that I find the proposal that there is somehow a split to p percentage of alternative timelines at every instance of the operator being applied to be a bit hard to justify in terms of Ockham’s Razor.

    To me, Copenhagen has encouraged me to look at concepts like commutators and the associated concepts of uncertainty as something closely related to calculability. That is, I see the fact that a Fourier Transform of a function in position space yields a function in momentum space to satisfactorily explain the problems with switching back and forth and why a uncertainty inequality should exist.

    I guess it’s true that Many Worlds doesn’t deny this perspective any more than Copenhagen requires it: it’s only that I’m not sure that given Many Worlds as a concept the connections that I made that help me understand how quantum mechanics works would have been apparent. Then again, maybe other concepts I do not have would be more clear.

    I will have to look more into this, but I’m afraid of falling down this rabbit hole (perhaps being an unfortunate acolyte of the unholy shut up and calculate brigade).

  • Rick

    Joah@11,

    “I find the proposal that there is somehow a split to p percentage of alternative timelines at every instance of the operator being applied to be a bit hard to justify in terms of Ockham’s Razor”

    But doesn’t this “fall out” of the math rather nicely as well? As for Ockham’s Razor, I would think that putting in a non-physical collapse of the wavefunction by hand (since it really doesn’t “fall out of the math” at all), is a much bigger issue as far as that goes.

  • Jess Tauber

    In atomic physics Pascal’s Triangle is behind much of the math- all the spherical nuclear magic (mostly weak) numbers are double tetrahedral numbers- and the other batch (mostly strong) involving spin-orbit splits are double tet minus double triangular numbers directly above them in the Pascal Triangle. I’ve now found similar links to the shifted magics in deformed nuclei. People already knew that the Pascal Triangle’s horizontal rows link to NMR effects. And there is much more besides (and also in the electronic system). I’m still trying to work out exactly how the Triangle’s internal systematicity relates to the quantum equations, but any such link must be quite regular. What does this ultimately reveal about the quantum world?

  • http://darkbuzz.blogspot.com/ Roger

    So Sean promotes MWI and says that Copenhagen is an incoherent monstrosity? Sean is the one who refuses to take quantum mechanics seriously. MWI is a fantasy.

  • Brett

    meh, trolls.

  • http://mike.pirnat.com Mike Pirnat

    Can someone please correct “sitting their quietly” to use “there” instead? My spelling OCD would appreciate it.

  • David

    It has always shocked me how people tend to say MWI goes against Ockham’s razor because it predicts multiple universes. This is like saying a line goes against Ockham’s razor because it has infinite points: you’re forgetting a line can be described with a single equation, which defines how simple it is.
    The same goes for MWI: you’re removing a postulate, period. It’s simpler than Copenhagen and definitely more coherent (define “classical observer”!). It doesn’t matter how many universes it predicts. It has less postulates. End of the story.

  • http://www.astro.multivax.de:8000/helbig/helbig.html Phillip Helbig

    “Haroche and Wineland are very deserving, but wasn’t this the year when Peter HIggs was supposed to win the prize? At 83, he’s not getting any younger.”

    Well, it is not yet clear that the Higgs Boson has actually been detected. So, the committee wisely didn’t jump the gun. Also, the rule “at most 3″ applies here; Higgs has the name recognition, but there were three others who did similar work at the same time, so the question is whom to leave out.

  • Rezso

    “The objection to Copenhagen is just that it’s completely incoherent. It imagines a distinct “classical” realm, doesn’t tell you what’s in that realm and what’s truly quantum, doesn’t explain when wave functions collapse, etc.”

    Decoherence theory explains these things!!!

    During the measurement process, the system, the measuring device and the environment become entangled, and when you trace over the environment degrees of freedom, you obtain a density operator with the classical probabilities. So, you get wave function collapse in an effective way.

    The MWI is not needed to explain the measurement process.

  • Lee

    David, I agree completely.

    The idea that MWI is ontologically heavy strikes my as a subtler shade of a gentleman, stuck at a fork in the road, shaking his head in incredulity, “the road doubles, surely this violates conservation of mass!” Or maybe Zeno’s paradox echoing down the ages.

    My interpretation is that the universe comprises all possible states and all possible transitions between those states. Nothing is ever created or destroyed, it only looks that way from narrow perspectives.

    That may seem ontologically heavy to some, but no moreso than the endless variety of mathematical “stuff” which must exist simply because there is no reason for it to be otherwise.

  • martenvandijk

    I guess that US wineproducers are happy also with this Nobel Prize. Wineland and a Frenchman probably make France happy enough to continue the right of US wineproducers to put ”Chateau” on their bottles. :-)

  • the clayton peacock

    A couple typos: in the first paragraph “atomic nucleus sitting *their* quietly” and in the last paragraph “We’re using ** to build things” (were you intending to write an “it” where the asterisks are?).

    In related news, I sure hope Peter Higgs doesn’t pass away in the next calendar year.

    • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean Carroll

      Typos fixed!

  • Gene

    The pioneers of the Copenhagen interpretation were nothing short of heroic in their interpretation of quantum mechanics. The only thing “missing” in CI is the modern understanding of decoherence, the rest is prejudice. Contrary to what is widely believed, Bohr did not need to explain how the wave function collapsed because it was never, to him, a physical wave to begin with.

  • Kostas

    Hi,
    all comments seem very interesting to me. To understand it better, as my knowledge is very basic: the results by Haroche and Wineland mean that “Copenhagen interpretation” is now severely weakened in favor of MWI theory ? Or that is not clear yet (i.e. both are applicable) ?

  • Joah

    Rick@12

    I don’t really understand what is “unphysical” about the collapse of a wavefunction. Rezso@19 more-or-less summarizes my prejudice in that regard. I can understand the simplicity of a decision tree that is discrete for a simple 50/50 spinor set, for example, but it is hard for me to understand the simplicity of a decision tree where an uncountable number of bifurcations happen at the moment of collapse, the limit of which is some irrational probability calculated for each Eigenstate. Perhaps I’m relying too much on my own conceptual bias and not enough on the MWI realization that David@17 and Lee@20 seem to prefer.

  • http://www.scottaaronson.com Scott Aaronson

    Kostas #25: The experiments of Haroche and Wineland, phenomenal as they are, have zero implications one way or the other for the MWI/Copenhagen debate (nor, for that matter, for third-party candidates like Bohm :-) ). In other words, while doing these experiments is a tremendous challenge requiring lots of new ideas, no sane proponent of any interpretation would have made predictions for their outcomes other than the ones that were observed. To do an experiment about which the proponents of different interpretations might conceivably diverge, it would be necessary to try to demonstrate quantum interference in a much, much larger system — for example, a brain or an artificially-intelligent quantum computer. And even then, the different interpretations arguably don’t make differing predictions about what the published results of such an experiment would be. If they differ at all, it’s in what they claim, or refuse to claim, about the experiences of the subject of the experiment, while the experiment is underway. But if quantum mechanics is right, then the subject would necessarily have forgotten those experiences by the end of the experiment — since otherwise, no interference could be observed!

    So, yeah, barring any change to the framework of quantum mechanics itself, it seems likely that people will be arguing about its interpretation forever. Sorry about that. :)

  • Rezso

    “To understand it better, as my knowledge is very basic: the results by Haroche and Wineland mean that “Copenhagen interpretation” is now severely weakened in favor of MWI theory ?”

    NO, their work is based on decoherence theory. Decoherence is a physical phenomena, you can measure it in the lab, and it solves the “preferred basis problem” of the Copenhagen interpretation. So the Copenhagen interpretation actually became stronger.

  • Rick

    “Decoherence is a physical phenomena, you can measure it in the lab, and it solves the “preferred basis problem” of the Copenhagen interpretation. So the Copenhagen interpretation actually became stronger.”

    What Scott said. QM became stronger — as if it needed any strengthening.

    “Bohr did not need to explain how the wave function collapsed because it was never, to him, a physical wave to begin with.

    Yeah, it just about our knowledge of world, not the world itself . . . ?

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  • David

    Decoherence explains how a superposed state “splits” into two classical ones, but I don’t see it as endorsing CI. In fact, decoherence does not predict a collapse but a splitting, which is much more in line with MWI! For the collapse you still need the measurement postulate.
    Here’s the picture: there is only one wave function carrying all the information about the experimental device and the experimenter. When the measurement is performed, two “regions” of the function decohere, meaning they become unable to interact with each other, therefore seeming like two effective separate wave-functions. These we call “parallel universes”, which is probably a misnomer since we’re only talking about different parts of one wave-function. That is, decoherence taken seriosuly is MWI.
    If you want to explain the classical outcome without retorting to MWI, you have to postulate the collapse of the original wave-function, that is, the fact that after decoherence the wave-function “chooses” one of its parts and discards the other. That seems to me as completely ad-hoc and unjustified, since the previous interpretation already gave the results we see!

  • Rezso

    29. Rick

    “QM became stronger — as if it needed any strengthening.”

    The Copenhagen interpretation was not able to derive the preferred basis, it was chosen by an ad hoc rule. This was an important problem of the interpretation.

    In decoherence theory, the preferred basis of the system+measuring device Hilbert-space is generated by the unitary dynamics of the system+measuring device+environment.

    So QM needed strengthening and it is stronger now.

    32. David

    Sorry, but I completely disagree with you.

    “Decoherence explains how a superposed state “splits” into two classical ones, but I don’t see it as endorsing CI. In fact, decoherence does not predict a collapse but a splitting, which is much more in line with MWI! For the collapse you still need the measurement postulate.”

    No, decoherence theory gives you a density operator and the eigenvalues of this operator are classical probabilities.

    And classical probabilities collapse by definition, when you learn the outcome of a measurement. This fact has nothing to do with quantum mechanics. If I throw a classical dice, then the probabilitiy distribution is (1/6, 1/6, 1/6, 1/6, 1/6, 1/6). But when I learn that the result is 3, then the probability distribution collapses to (0, 0, 1, 0, 0, 0). In my opinion, there is nothing more to explain here.

    “These we call “parallel universes”, which is probably a misnomer since we’re only talking about different parts of one wave-function. That is, decoherence taken seriosuly is MWI.”

    A superposition has nothing to do with parallel universes. I can represent the motion of a classical guitar string with a Fourier-series, but this doesn’t mean that there are infinitely many guitar strings in parallel universes, there is only one.

  • David

    33. Reszno, decoherence explains how the system-experimenter state is split into two orthonormal states, both of which keep existing as a superposition. Nowhere in the equations can you see you’re allowed to interpret their squared amplitudes as classical probabilities, unless you explicitly use the Born rule. Decoherence does not solve the measurement problem. You need an interpretation on top (CI or MWI) to do that.
    I think our main source of disagreement is you assume once you see a measurement outcome, it is obvious the probability distribution has collapsed. To me, all that’s obvious is you’re entangled with that particular outcome and you have no way of accessing the other, which nonetheless keeps existing as an unaccessible part of the system’s state, thus effectively splitting into two separate realities.
    “This doesn’t mean there are infinitely many guitar strings in parallel universes”: precisely. That’s why “parallel universes” is a misnomer. There is only one wave function one can split into many components which cannot interact.

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  • Rezso

    “Reszno, decoherence explains how the system-experimenter state is split into two orthonormal states, both of which keep existing as a superposition. Nowhere in the equations can you see you’re allowed to interpret their squared amplitudes as classical probabilities, unless you explicitly use the Born rule.”

    I’m not interpreting the squared amplitudes of a superposition as probabilities!

    My whole point is that in decoherence theory, there are no probabilities at level of the system+measuring device+environment wavefunction.

    Classical probabilities only emerge after we trace over the environment. After that, we obtain a density operator wich describes the system+measuring device.

    The classical probabilities are the eigenvalues of the density operator.

  • mks

    Sean Carroll,

    would you say the Copenhagen Interpretation is still the Orthodox interpretation of QM?

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Cosmic Variance

Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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