Wednesday, August 15, 2012

"Rapid streamlined peer-review" and its results

Contains 0% Quantum Gravity.
"Scientific Reports" is a new open access journal from the Nature Publishing Group, which advertises its "rapid peer review and publication of research... with the support of an external Editorial Board and a streamlined peer-review system." In this journal I recently found this article
"Testing quantum mechanics in non-Minkowski space-time with high power lasers and 4th generation light sources"
B. J. B. Crowley et al
Scientific Reports 2, Article number: 491
Note the small volume number, all fresh and innocent.

It's a quite interesting article that calculates the cross-section of photons scattering off electrons that are collectively accelerated by a high intensity laser. The possibility to maybe test Unruh radiation in a similar fashion has lately drawn some attention, see eg this paper. But this is explicitly not the setup that the authors of the present paper are after, as they write themselves in the text.

What is remarkable about this paper is the amount of misleading and wrong statements about exactly what it is they are testing and what not. In the title it says they are testing "quantum mechanics in non-Minkowski space-time." What might that mean, I was wondering?

Initially I thought it's another test of space-time non-commutativity, which is why I read the paper in the first place. The first sentence of the abstract reads "A common misperception of quantum gravity is that it requires accessing energies up to the Planck scale of 1019GeV, which is unattainable for any conceivable particle collider." Two sentences later, the authors no longer speak of quantum gravity but "a semiclassical extension of quantum mechanics ... under the assumption of weak gravity." So what's non-Minkowski then? And where's quantum gravity?

What they do in fact in the paper is that they calculate the effect of the acceleration on the electrons and argue that via the equivalence principle this should be equivalent to testing the influence of gravity. (At least locally, though there's not much elaboration on this point in the paper.) Now, strictly speaking we do of course never make any experiment in Minkowski space - after all we sit in a gravitational field. In the same sense we have countless tests of the semi-classical limit of Einstein's field equations. So I read and I am still wondering, what is it that they test?

In the first paragraph then the reader learns that the Newton-Schrödinger equation (which we discussed here) is necessary "to obtain a consistent description of experimental findings" with a reference to Carlip's paper and a paper by Penrose on state reduction. Clearly a misunderstanding, or maybe they didn't actually read the papers they cite. They also don't actually use the Schrödinger-Newton equation however - as I said, there isn't actually a gravitational field in their setup. "We do not concern ourselves with the quantized nature of the gravitational field itself." Fine, no need to quantize what's not there.

Then on page two the reader learns "Our goal is to design an experiment where it may be possible to test some aspects of general relativity..." Okay, so now they're testing neither quantum mechanics nor quantum gravity, nor the Schrödinger-Newton equation, nor semi-classical gravity, but general relativity? Though, since there's no curvature involved, it would be more like testing the equivalence principle, no?

But let's move on. We come across the following sentence: "[T]he most prominent manifestation of quantum gravity is that black holes radiate energy at the universal temperature - the Hawking temperature." Leaving aside that one can debate how "prominent" an effect black hole evaporation is, it's also manifestly wrong. Black hole evaporation is an effect of quantum field theory in curved spacetime. It's not a quantum gravitational effect, that's the exact reason why it's been dissected since decades. The authors then go on to talk about Unruh radiation and make an estimate showing that they are not testing this regime.

It follows the actual calculation, which, as I said, is in principle interesting. But at the end of the calculation we are then informed that this "provid[es], for the first time, a direct way to determine the validity of the models of quantum mechanics in curved space-time, and the specific details of the coupling between classical and quantized fields." Except that there isn't actually any curved space-time in this experiment, unless they mean the gravitational field of the Earth. And the coupling to this has been tested for example in this experiment (and in some follow-up experiements to this), which the authors don't seem to be aware of or at least don't cite. Again, at the very best I think they're proposing to test the equivalence principle.

In the closing paragraph they then completely discard the important qualifier that the space-time is not actually curved and that it's in the best case an indirect test by claiming that, on the contrary, "[T]he scientific case described in this letter is very compelling and our estimates indicate that a direct test of the semiclassical theory of quantum mechanics in curved space-time will become possible." Emphasis mine.

So, let's see what have we. We started with a test of quantum mechanics in non-Minkowski space, came across some irrelevant mentioning of quantum gravity, a misplaced referral to the Schrödinger-Newton equation, testing general relativity in the lab, further irrelevant and also wrong comments about quantum gravity, to direct tests of quantum mechanics in curved space time. All by looking at a bunch of electrons accelerated in a laser beam. Misleading doesn't even begin to capture it. I can't say I'm very convinced by the quality standard of this new journal.


  1. You could ask whether the journal accepts rapid streamlined comments on published papers...

    Incidentally the captcha image for this comment is extremely weird - looks like recaptcha is trying to deciper house numbers from blurry photographs. I wonder how legit that is.

  2. Does the fact that it mentions its impact factor on its main webpage (even though it is not yet eligible) disqualify it?

  3. Thanks for mentioning Carlip's paper. (I'm familiar with Carlip because he is a contributor to sci.physics.research, which for you young dudes is a newsgroup.) This is actually something I have always thought about myself: maybe the success of unification has been so great that it seems automatic that gravity must be unified with other forces as well. What do you think of Carlip's paper?

  4. Another instance of the B. brothers?


  5. "calculate the effect of the acceleration on the electrons and argue that via the equivalence principle this should be equivalent to testing the influence of gravity" Careful. A Beckman Coulter Optima Max-XP ultracentrifuge pulls 1,019,000 gees at the rotor rim, but that is NOT Equivalence Principle.

    Phys. Rev. 129(6) 2371 (1963)

    Should these folks be trusted with that laser? They might condense a photon black hole with unknown hazards,

    Rev. Mex. Fis. 52(6) 515 (2006)

  6. Hi Bee,

    Despite this paper's and journal's suspect quality with this review B. J. B. Crowley et al have managed to have garnered at least one citation :-)



  7. Bee, recall that Scientific Reports is the journal of the Nature Publishing Group to compete with PLoS ONE. Both journals have similar criteria for publication. In fact, "to be published in Scientific Reports, a paper must be technically sound."

    Let me emphasize the point: "judgments about the importance of a paper will be made by the scientific community after publication."

    Source: Guide to referees

  8. Francis,

    Yes. My point was that "technically sound" can leave a paper full of misleading and wrong explanation about what is actually being done. Best,


  9. All those papers will be lost in time like tears in rain...

  10. bee, just found this:


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