Category Archives: Paper writing

Physics and the bumper sticker

In the remote preparation for my Coursera on randomness, I read Nate Silver‘s The signal and the noise. I am not sure how much of it will enter my course, since I don’t plan to enter into the topics he deals with (politics, the stock market, climate change, prevention of terrorism, baseball and poker). But the conclusion struck a cord.

The author lists seven approximations to describe the “efficient market hypothesis”, which run: 1. No investor can beat the stock market, 2. No investor can beat the stock market over the long run, and so on until approximation 7 which a is five lines long sentence. Then he adds (emphasis is mine):

“The first approximation — the unqualified statement that no investor can beat the stock market — seems to be extremely powerful. By the time we get to the last one, which is full of expressions of uncertainty, we have nothing that would fit on a bumper sticker. But it is also a more complete description of the objective world.”

Sounds familiar? Let’s give it a try:

Example 1:

  • Bumper sticker: No extension of quantum theory can have improved predictive power
  • Expression full of uncertainty: the authors work under the assumption of no-signaling (so, if you are Bohmian, don’t worry, our result does not concern you).  Then they assume a lot of quantum physics, but not all of it, otherwise the claim would be tautological. Beyond the case of the maximally entangled state, which had been settled in a previous paper, they prove something that I honestly have not fully understood. Indeed, so many other colleagues have misunderstood this work, that the authors prepared a page of FAQs (extremely rare for a scientific paper) and a later, clearer version.
  • Comment: the statement “Colbeck and Renner have proved that quantum theory cannot be extended” is amazingly frequent in papers, referee reports and discussions. Often, it comes in the version: “why are people still working on [whatever], since Colbeck and Renner have conclusively proved…?” It is pretty obvious however that many colleagues making that statement are not aware of the “details” of what Colbeck and Renner have proved: they have simply memorized the bumper sticker statement. I really don’t have a problem with Colbeck and Renner summarizing their work in a catchy title; what is worrisome is other experts repeat the catchy title and base decisions solely on it.

Example 2:

  • Bumper sticker: The quantum state cannot be interpreted statistically [Yes, I know that the title of the final version is different, but this is the title that sparked the curiosity of the media]
  • Expression full of uncertainty: the authors work with a formalization of the notions of “ontic” and “epistemic” that is accepted by many people, though not by Chris Fuchs and some of his friends. They add a couple of other reasonable assumptions, where by “reasonable” I mean that I would probably have used them in a first attempt to construct an epistemic model. Then they prove that such an epistemic model is inconsistent.
  • Comment: too many people have commented on this paper. The latest contrary claim has been posted online today, I have not read it because I am really not following the debate, but for those who are interested, here it is.

Example 3:

  • Bumper sticker: either our world is fully deterministic or there exist in nature events that are fully random [the use of “either-or” makes it too elaborated for a real bumper sticker, but for someone who browses these papers, the sentence is basic enough]
  • Expression full of uncertainty: the authors consider a very weak source of randomness, something like a very biased coin; in fact, it can be more perverse than that, because it can have correlation over various tosses. But it cannot be completely perverse: the authors make an assumption about its structure (technically known as “Santha-Vazirani” by the names of the first two persons who proposed it). Then they prove that, if this source is used as seed for a specific quantum experiment, the outcomes of the experiment are guaranteed to be much more random. In the limiting case of an experiment lasting infinitely long time, and whose results do not deviate by any amount from the optimal result allowed by quantum physics, the source can contain almost no randomness, while the final list will be almost fully random.
  • Comment: in a paper just published, we studied what happens if we remove the Santha-Vazirani assumption, so that the source can be as perverse as you wish. Not surprisingly, the conclusions become more pessimistic: now, one would need a fair amount of initial randomness in order for the quantum step to produce further randomness. Nothing wrong at all: some guys get a good result with an assumption, others test the limit of the assumption, this is the normal course of science. But read again the bumper-sticker statement: taken in itself, out of the paper where it belongs, that statement has not been “scientifically proved” — it even sounds closer to being impossible to prove, without the crucial assumption

A tale of 2011

Many things happened in 2011, of which I can only be thankful. I wanted to consign one to record, which may otherwise be missed, because it is about a “failure” — or better said: a beautiful reaction to a disappointing realization.

Starting in August 2010, a student of mine, Thinh, had been studying a new class of protocols for quantum cryptography, inspired by a previous work. By April, he had managed to define the key mathematical objects to very general scenarios. This was his Final Year Project (FYP), which was awarded as “Outstanding” by the university. A few months later, together with Lana (post-doc), we prepared a paper and submitted to Physical Review Letters (PRL; for the unaware: one of the most prestigious journals for physics).

When the referee report came, the tone was expected: “good work but not of enough broad interest” — very common nowadays for quantum cryptography. The referee stressed how he/she liked very much our generalization, i.e. Thinh’s result. With a few modifications, we could have had the paper published in Physical Review A (PRA; a very good journal still, edited by the same society; a Tier 1 journal in NUS, for the sake of the bureaucrats who care about these classifications).

However, one of the small comments of the referee caught our attention: we realized that the family of protocols we had considered was uninteresting! In a nutshell, these protocols collect a lot of information, but then discard much of it and rely on the rest. Why should one do so?? In other words, all that we did was correct and even elegant, but the object of our study was sort of pointless.

Now you see the alternatives we were facing: (1) skip this awareness under the carpet, do the modifications suggested by the referees and submit to PRA, with quasi-certainty of being accepted; (2) forget about this paper and write rather a technical note, explaining why these protocols are not interesting, to be sent to a very specialized (i.e. less visible) journal. For me, there was no doubt that (2) was the correct course, but I let Thinh and Lana decide — and I am very proud to say that they took the right decision 🙂 The paper has duly been re-written and is under consideration in a specialized journal of our field.

Now comes the scary part of it. I told this story to several friends working in the academic world, over coffees or lunches or other informal meetings. Many of them, especially the younger one, were astonished: “Wow, you guys are so honest! I know many who would never had dropped the chance of publishing in a Tier 1 journal”. For myself, I am sure that Thinh and Lana have made a bigger step in their career by choosing the right course: if you keep your standards high, Tier 1 publications will come.

Happy New Year!


“We” in scientific prose

The exaggerated use of “we”, “our”, etc. may make scientific prose pretty heavy (I mean, more than it should) and show the authors as very self-proud fellows (which they probably are, but it is good manner to try to keep a level of false modesty). Here is my suggestion: use “we” for matters that are really the author’s choice. For instance:

  • we investigate this topic; our paper shows…
  • we choose these numerical values for the simulation

For other matters, try rather the passive form:

  • Result of a calculation: “the result is found to be”, “the calculation yields”, rather than “we obtain” (after all, you expect everyone to obtain the same)
  • Observation: “the expected peak is observed” rather than “we observe the expected peak”.

Of course, enjoy flexibility 🙂