Guest Post: Terry Rudolph on Nature versus Nurture

By Sean Carroll | August 27, 2012 1:07 pm

Everyone always wants to know whether the wave function of quantum mechanics is “a real thing” or whether it’s just a tool we use to calculate the probability of measuring a certain outcome. Here at CV, we even hosted a give-and-take on the issue between instrumentalist Tom Banks and realist David Wallace. In the latter post, I linked to recent preprint on the issue that proved a very interesting theorem, seemingly boosting the “wave functions are real” side of the debate.

That preprint was submitted to Nature, but never made it in (although it did ultimately get published in Nature Physics). The story of why such an important result was shunted away from the journal to which it was first submitted (just like Peter Higgs’s paper where he first mentioned the Higgs boson!) is interesting in its own right. Here is that story, as told by Terry Rudolph, an author of the original paper. Terry is a theoretical physicist at Imperial College London, who “will work on anything that has the word `quantum’ in front of it.”

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There has long been a tension between the academic publishing process, which is slow but which is still the method by which we certify research quality, and the ability to instantaneously make one’s research available on a preprint server such as the arxiv, which carries essentially no such certification whatsoever. It is a curious (though purely empirical) observation that the more theoretical and abstract the field the more likely it is that the all-important question of priority – when the research is deemed to have been time-stamped as it were – will be determined by when the paper first appeared on the internet and not when it was first submitted to, or accepted by, a journal. There are no rules about this, it’s simply a matter of community acceptance.

At the high-end of academic publishing, where papers are accepted from extremely diverse scientific communities, prestigious journals need to filter by more than simply the technical quality of the research – they also want high impact papers of such broad and general interest that they will capture attention across ranges of scientific endeavour and often the more general public as well. For this reason it is necessary they exercise considerably more editorial discretion in what they publish.

Topics such as hurdling editors and whether posting one’s paper in preprint form impacts negatively the chances of it being accepted at a high-end journal are therefore grist for the mill of conversation at most conference dinners. In fact the policies at Nature about preprints have evolved considerably over the last 10 years, and officially they now say posting preprints is fine. But is it? And is there more to editorial discretion than the most obvious first hurdle – namely getting the editor to send the paper to referees at all? If you’re a young scientist without experience of publishing in such journals (I am unfortunately only one of the two!) perhaps the following case study will give you some pause for thought.

Last November my co-authors and I bowed to some pressure from colleagues to put our paper, then titled The quantum state cannot be interpreted statistically, on the arxiv. We had recently already submitted it to Nature because new theorems in the foundations of quantum theory are very rare, and because the quantum state is an object that cuts across physics, chemistry and biology – so it seemed appropriate for a broad readership. Because I had heard stories about the dangers of posting preprints so many times I wrote the editor to verify it really was ok. We were told to go ahead, but not to actively participate in or solicit pre-publication promotion or media coverage; however discussing with our peers, presenting at conferences etc was fine.

Based on the preprint Nature themselves published a somewhat overhyped pop-sci article shortly thereafter; to no avail I asked the journalist concerned to hold off until the status of the paper was known. We tried to stay out of the ensuing fracas – is discussing your paper on blogs a discussion between your peers or public promotion of the work?

In December the three referee reports came back. Two were very positive and comprehensive (one was longer than the paper!), and the negative one was just silly. The editor chose to ignore the negative one, and we were happy to be told

Your manuscript entitled “The quantum state cannot be interpreted statistically” has now been seen by our referees, and in the light of their advice (enclosed below) I am delighted to say that we can in principle offer to publish it.

We then began to revise the paper considerably along the lines suggested by the referees, something clearly necessary given the multiple misinterpretations of the result we had encountered.

Now the fun started. As this revision was ongoing, two of us submitted a preprint to the arxiv with another of our students, a paper with a somewhat tongue-in-cheek contrary title: The quantum state can be interpreted statistically. Later I will explain a bit more carefully the relation between the physics of the two papers. For the moment I will outline the unexpected connection in the publishing process.

A few weeks later we resubmitted the first paper – the revised version explained the result much more along the lines of Matt Leifer’s discussion. It was sent back to the two referees who had been positive, and they opined

The Authors made all the changes I recommended. The letter now reads really nicely. I am thus happy to support publication in Nature of this nice letter.

and

I think the paper is substantially improved, more accessible both to the general reader and to the expert on hidden-variable models for quantum mechanics. In particular, the key assumptions, that there is an [sic] state-related ontology underneath quantum mechanics and preparation independence, are laid out more clearly, and this is a major improvement.

We were therefore somewhat bemused that the editor decided:

While we appreciate that the new paper does not invalidate the results of your Nature submission, we feel that it nevertheless significantly reduces its impact. In a way, the Nature paper only tells one side of the story – its central claim is no longer true if one of the key assumptions is dropped. The discussion that the papers have generated within the community leave us in no doubt as to their value for specialists; however, there is no longer in our view a compelling reason to publish the original study in Nature.

Let me briefly explain the interesting science that lies at the heart of the “key assumption” the editor is alluding to in the above. I will call this assumption preparation independence.

Suppose an experiment at one lab reproduces the results of an earlier experiment at another. This would righty be called an “independent” verification of the first lab’s results. No scientist would attempt to refute this by appealing to correlations between random events at the two labs, there being no realistic mechanism for such to be established. Even in a single lab, repeated runs of an experiment must be assumed independent in order to estimate probabilities based on the results. Preparation independence is simply the assumption that we have the ability to build independent, uncorrelated experimental apparatuses to act as preparation devices of microscopic systems, and that any deeper theory of nature than quantum theory will not overthrow this principle by virtue of “hidden super-correlations” where to date scientists have always successfully assumed there are none.

The theorem we prove – that quantum states cannot be understood as merely lack of knowledge of an underlying deeper reality described by some as yet undiscovered deeper theory – assumes preparation independence. It is an important insight that this assumption is necessary for the theorem, and the point of our second paper was to show this explicitly. That second paper is, however, simply making a mathematical/logical point – it is not a serious proposal for how the physical world operates.

We are in a similar position with Bell’s theorem, which I consider the most important insight into the nature of physical reality of the last century, an honour for which there are some serious competitors! That theorem relies on a presumed ability to make independent choices of measurements at separated locations. Denial of such is the “super-determinism” loophole, and while intelligent people can and do consider its plausibility, and while it is an important insight into Bell’s theorem that this assumption is necessary, the jury is still out (‘t Hoofts efforts notwithstanding) as to whether a super-deterministic theory agreeing with all experiments to date can even be constructed, never mind be a plausible theory of nature.

Denial of preparation independence or invocation of super-determinism throws into question the basic methods of all science carried out to date. Most physicists would, I believe, consider the “cure” (extremely convoluted correlations between seemingly unrelated events leading to a conspiratorial interpretation of the nature of reality) worse than the “disease” (non-locality in the case of Bell’s theorem, the reality of the quantum state in the case of ours). If our theorem fails because the assumption of preparation independence fails, it is a far more amazing insight into nature than the theorem itself provides.

So of course we responded to the editor, making these points. But after another two weeks of consideration (that I presume involved conversations with experts, but we were never made privy to them) the editor confirmed that they still felt the second paper lessened the impact of the first, and that the paper was only suited to a more specialist journal.

However, they also said:

Moreover, from an editorial viewpoint, we find it hard to see what publication of the paper in Nature would achieve at this stage (we cannot help but feel that its timeliness and impact are now considerably reduced, as it has already been debated widely within the community).

Put simply, the buzz matters – this objection by the editor would not have arisen had we not posted to the arxiv.

While it mildly rankles that my own participation in that “wide debate” was curbed by the blurry lines of their own policies, I’m not particularly upset by the episode – perhaps indicative of my well documented own laissez-faire attitude to publishing, but perhaps because I know the result is ultimately more important than the journal it appears in.

But one thing is for sure – every single paper published in Nature this year will implicitly be making an assumption that independent preparations and independent verification of experiments are possible. The authors of those papers will have been smart enough not to explicitly say so!

(By the way, the paper appears now in Nature Physics and has been the subject of a second news article by Nature!).

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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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