Thursday, July 13, 2017

Nature magazine publishes comment on quantum gravity phenomenology, demonstrates failure of editorial oversight

I have a headache and
blame Nature magazine for it.
For about 15 years, I have worked on quantum gravity phenomenology, which means I study ways to experimentally test the quantum properties of space and time. Since 2007, my research area has its own conference series, “Experimental Search for Quantum Gravity,” which took place most recently September 2016 in Frankfurt, Germany.

Extrapolating from whom I personally know, I estimate that about 150-200 people currently work in this field. But I have never seen nor heard anything of Chiara Marletto and Vlatko Vedral, who just wrote a comment for Nature magazine complaining that the research area doesn’t exist.

In their comment, titled “Witness gravity’s quantum side in the lab,” Marletto and Vedral call for “a focused meeting bringing together the quantum- and gravity-physics communities, as well as theorists and experimentalists.” Nice.

If they think such meetings are a good idea, I recommend they attend them. There’s no shortage. The above mentioned conference series is only the most regular meeting on quantum gravity phenomenology. Also the Marcel Grossmann Meeting has sessions on the topic. Indeed, I am writing this from a conference here in Trieste, which is about “Probing the spacetime fabric: from concepts to phenomenology.”

Marletto and Vedral point out that it would be great if one could measure gravitational fields in quantum superpositions to demonstrate that gravity is quantized. They go on to lay out their own idea for such experiments, but their interest in the topic apparently didn’t go far enough to either look up the literature or actually put in the numbers.

Yes, it would be great if we could measure the gravitational field of an object in a superposition of, say, two different locations. Problem is, heavy objects – whose gravitational fields are easy to measure – decohere quickly and don’t have quantum properties. On the other hand, objects which are easy to bring into quantum superpositions are too light to measure their gravitational field.

To be clear, the challenge here is to measure the gravitational field created by the objects themselves. It is comparably easy to measure the behavior of quantum objects in the gravitational field of the Earth. That has something to do with quantum and something to do with gravity, but nothing to do with quantum gravity because the gravitational field isn’t quantized.

In their comment, Marletto and Vedral go on to propose an experiment:
“Likewise, one could envisage an experiment that uses two quantum masses. These would need to be massive enough to be detectable, perhaps nanomechanical oscillators or Bose–Einstein condensates (ultracold matter that behaves as a single super-atom with quantum properties). The first mass is set in a superposition of two locations and, through gravitational interaction, generates Schrödinger-cat states on the gravitational field. The second mass (the quantum probe) then witnesses the ‘gravitational cat states’ brought about by the first.”
This is truly remarkable, but not because it’s such a great idea. It’s because Marletto and Vedral believe they’re the first to think about this. Of course they are not.

The idea of using Schrödinger-cat states, has most recently been discussed here. I didn’t write about the paper on this blog because the experimental realization faces giant challenges and I think it won’t work. There is also Anastopolous and Hu’s CQG paper about “Probing a Gravitational Cat State” and a follow-up paper by Derakhshani, which likewise go unmentioned. I’d really like to know how Marletto and Vedral think they can improve on the previous proposals. Letting a graphic designer make a nice illustration to accompany their comment doesn’t really count much in my book.

The currently most promising attempt to probe quantum gravity indeed uses nanomechanical oscillators and comes from the group of Markus Aspelmeyer in Vienna. I previously discussed their work here. This group is about six orders of magnitude away from being able to measure such superpositions. The Nature comment doesn’t mention it either.

The prospects of using Bose-Einstein condensates to probe quantum gravity has been discussed back and forth for two decades, but clear is that this isn’t presently the best option. The reason is simple: Even if you take the largest condensate that has been created to date – something like 10 million atoms – and you calculate the total mass, you are still way below the mass of the nanomechanical oscillators. And that’s leaving aside the difficulty of creating and sustaining the condensate.

There are some other possible gravitational effects for Bose-Einstein condensates which have been investigated, but these come from violations of the equivalence principle, or rather the ambiguity of what the equivalence principle in quantum mechanics means to begin with. That’s a different story though because it’s not about measuring quantum superpositions of the gravitational field.

Besides this, there are other research directions. Paternostro and collaborators, for example, have suggested that a quantized gravitational field can exchange entanglement between objects in a way that a classical field can’t. That too, however, is a measurement which is not presently technologically feasible. A proposal closer to experimental test is that by Belenchia et al, laid out their PRL about “Tests of Quantum Gravity induced non-locality via opto-mechanical quantum oscillators” (which I wrote about here).

Others look for evidence of quantum gravity in the CMB, in gravitational waves, or search for violations of the symmetries that underlie General Relativity. You can find a little summary in my blogpost “How Can we test Quantum Gravity”  or in my Nautilus essay “What Quantum Gravity Needs Is More Experiments.”

Do Marletto and Vedral mention any of this research on quantum gravity phenomenology? No.

So, let’s take stock. Here, we have two scientists who don’t know anything about the topic they write about and who ignore the existing literature. They faintly reinvent an old idea without being aware of the well-known difficulties, without quantifying the prospects of ever measuring it, and without giving proper credits to those who previously wrote about it. And they get published in one of the most prominent scientific journals in existence.

Wow. This takes us to a whole new level of editorial incompetence.

The worst part isn’t even that Nature magazine claims my research area doesn’t exist. No, it’s that I’m a regular reader of the magazine – or at least have been so far – and rely on their editors to keep me informed about what happens in other disciplines. For example with the comments pieces. And let us be clear that these are, for all I know, invited comments and not selected from among unsolicited submissions. So, some editor deliberately chose these authors.

Now, in this rare case when I can judge their content’s quality, I find the Nature editors picked two people who have no idea what’s going on, who chew up 30 years old ideas, and omit relevant citations of timely contributions.

Thus, for me the worst part is that I will henceforth have to suspect Nature’s coverage of other research areas is equally miserable as this.

Really, doing as much as Googling “Quantum Gravity Phenomenology” is more informative than this Nature comment.


  1. Thanks Sabine for saving my time before it was wasted on such a misleading and poor piece of work. I call it academic fascism when you get a chance to publish not because of quality but the stamp that you carry e.g. oxford, cambridge, mit etc..

  2. Sabine, you forgot to mention a few papers in your post:

    Probing a Gravitational Cat State: Experimental Possibilities
    M. Derakhshani, C. Anastopoulos, and B. L. Hu
    Journal of Physics: Conference Series, Volume 701, conference 1 (2016)

    which is an experimental feasibility study based on

    Probing a Gravitational Cat State
    C. Anastopoulos, B. L. Hu
    Class. Quantum Grav. 32, 165022 (2015)

    Also relevant are:

    Probing Gravitational Cat States in Canonical Quantum Theory vs Objective Collapse Theories
    M. Derakhshani (2016)

    Magnetic Skatepark for Quantum Interference of a Superconducting Microsphere
    H. Pino, J. Prat-Camps, K. Sinha, B. P. Venkatesh, O. Romero-Isart (2016)

    I know this isn't the first time you've seen these papers.....

  3. Hi Sabine,
    Have you brought this article to the attention of the authors (or the nature article)? If not, I hope some of the readers do.
    Anyhow I have also been shocked when I see many papers not citing previous literature, but usually most of them do after you email them.

  4. maaneli,

    Thanks, I updated the references.

  5. Shantanu,

    I wrote a letter to the editors, but the guidelines limit those to 300 words, hence this blogpost to add more context.

    1. Hi Sabine,

      Did the editors reply to your letter? What did they say? I find it really sad that funding agencies and universities care so much about Nature and similar journals. They screw up the incentives and I expect ultimately have a negative impact on science

  6. Hi Dr. Hossenfelder,

    I'm happy that you're here to set the record straight on these kinds of nonsensical articles that don't even cite previous work.

    On another note, as a reader on your RSS feed, I was wondering if it was possible to enable full text posts on the feed? At the moment, I believe only an excerpt is available, which means I can't read your posts without going on your site and exiting my app. Nonetheless, thanks for the great work!

  7. Alas one negative outcome of the internet has been a race to the bottom in terms of the cost of publishing and conversely what the few remaining magazines pay their editorial staffs. It costs money to check a contributor's work. Nature not the only magazine abandoning editorial integrity for the sake of saving money.

  8. My area of research was (I'm retired) intramolecular vibrational relaxation,
    starting in 1971. There were about 100 people either in it or seriously interested,
    plus maybe 1000 others more into intermolecual vibrational relaxation but a bit interested in the intra stuff.

    Depending on the molecule size it could be either quantum or classical. The key area
    is the boundary. The is related to but not identical with, "quantum entanglement".

    It was always a big laugh to read or listen to people with no clue.

    Today it is interesting to see how the entanglement people could benefit, at least a little, from thinking about bigger "systems".

  9. bee:

    if you haven't googled it yet but in case you didn't, Chiara Marletto is the collaborator of David Deutsch on his Constructor Theory. I can't make any sense out of Constructor Theory but it's described ( as follows:

    Constructor Theory is a new approach to formulating fundamental laws in physics. Instead of describing the world in terms of trajectories, initial conditions and dynamical laws, in constructor theory laws are about which physical transformations are possible and which are impossible, and why. This powerful switch has the potential to bring all sorts of interesting fields, currently regarded as inherently approximative, into fundamental physics. These include the theories of information, knowledge, thermodynamics, and life.

    if you can make any sense of it, i'd like to know your opinion of it.


  10. " measure the gravitational field of an object in a superposition of, say, two different locations" "two scientists who don’t know anything about the topic they write about" Montessori science! Sub-atomic test masses' quantum jingle-jangle; in-tight for gravitation, degenerate rearrangement – superpositions of nothing net changing.

    George Olah’s "Magic Acid"(1:1 molar HSO_3F and SbF_5) creates CH_5^(+), methanium, which degenerately Berry pseudorotates with a small activation energy (runs at low temperatures).
    ...degenerate protons’ jingle-jangle.

    Methanium also obtains ~2 torr gas phase,

    Observe a temperature-dependent quantum gravitational anomaly - left as an exercise for the alert reader.

  11. I think you're right to point the finger directly at the editors, if only because proper editing protects contributors as well as the public. (I was puzzled by the article as I once heard Vlatko give a very nice seminar on quantum information..).
    In a slightly similar vein, I have been contacted more than once by book reviewers, seeking clarification on technical details. I find myself wondering why prestigious publications hand out book reviews to writers who don't have the appropriate technical expertise...
    Regards, Cormac

  12. I had heard of Marletto from her work on David Deutsch's "Constructor Theory" idea. So she's not all bad :)

  13. Hi Sabine-- is there any news about another Experimental Search for QG conference this year? (I did google and didn't find anything :))

  14. Also, sorry, forgot the main point: I agree, this article is horrific.

    Quanta was publishing stuff about similar ideas years ago... (

  15. Another troubling oversight by Marletto and Vedral. They write:

    Happily to answer Feynman’s question we do not need a full theory of quantum gravity. All we need is to witness quantum behaviour in the gravitational field.

    As I'm sure you know, that was already accomplished in a beautiful experiment published in 1975:

    Observation of Gravitationally Induced Quantum Interference. R. Colella, A. W. Overhauser, and S. A. Werner. Phys. Rev. Lett. 34, 1472

    That showed a shift in the fringes of a neutron interferometer due to Earth's gravity.

  16. This is so typical. It happens in a lot of fields. I don't know how often I read an overview or proposal and realized that the author had no idea of what had already been done in the field. Granted, that was before Google and the like, but some of this stuff was common knowledge in the field.

  17. Jeremy,

    I used to have full-text sharing but disabled it on purpose. The problem is, if you don't visit this page, it won't count in the stats and the ads won't show either. I will enable full-text feed if this blog brings in enough money to pay the rent, which by my own extrapolation means never. Meanwhile, please have a close look at the donate button in the top right corner.

  18. Dan,

    David Mattingly is supposed to do the next one next year somewhere on the East Cost. I totally encourage you to bug him about it :o)

  19. naivetheorist, antimatter,

    As you may have noticed, I didn't blame the authors for this. It's clear that they aren't from the field and they just didn't know any better. Yes, I know they have a quantum information background. But it's really beyond me how the editors approved this without doing a first-order check on whether authors know what they are talking about.

  20. At least for a few decades, Nature has been more about sensationalism and less about good science. There is even a YouTube video with a former editor who openly admits this.

    "Getting into Nature" demonstrates much of what is wrong with the current publication culture. Even important work which does get published there is published in more detail elsewhere. The days in which people used Nature to get an overview of important work in other fields than their own is long gone.

    Although the emphasis is different, there is another "ignoring the literature" post in the blogosphere today.

  21. You're a good sport not to blame the authors. I figured that the minimum check on similar prior work would be to Google "superposition quantum gravity" which brought up one of your previous blog pages on this subject listing prior work. So the authors cannot even have performed the minimum check on whether something similar has been suggested. For an article they knew was going to be published in Nature. And they're professional physicists. Absolutely unacceptable and staggering.

  22. For a decade or more, quantum information theorists annoyed the hell out of condensed matter physicists by 'rediscovering' old results in a new (and often trivial) terminology, and not citing the old works. Meanwhile papers recasting some well-known result get hundreds of citations from within the quantum information community, so it is a self-reinforcing phenomena.

  23. They're in David Deutsch's group. He follows his own individual path deciding he has unlocked the secret of the universe so there's no point looking at what anyone else is doing. And I reckon it's a style which is rubbing-off on everyone in that group,

  24. Phillip,

    Interesting video. Yes, I saw Peter's post this morning. Another case in which several people had the same idea almost simultaneously? I think of that as surfacing of the collective consciousness of the community, quite a remarkable phenomenon.

  25. Well the field exists after a fashion but there's not been any noteworthy progress. People should trailblaze onto that turf if they have energy for the space
    Ruffle feathers yes. IGNORE or skim the literature yes. Keep the distance between you and a body of work and it's authors wanting respect for all hours they've clocked and to instruct you on their amazing assumptions, orthodoxies and all the other heroic feats performed in the face of the great mediocracycy. Don't be bitten

  26. piein,

    Well, we went from "it's not possible" to "a few orders of magnitude away" in 10 years. How is that no progress?

  27. Thanks Bee, as always, for these updates regarding Quantum Gravity.


  28. Sabine,

    Even a non - full time quantum and gravity person like me knows that there have been many papers on superposition tests, not to mention all the other things discussed at meetings like the Experimental Search for Quantum Gravity conference.

    The exiting part is that the experimental state is wide open. While the classical electromagnetic spin down of the 1916 planetary style H atom would occur in 10^-11 secs, the gravitational radiation equivalent takes 10^20 times the age of the Universe. So there is no need to quantize gravity at all in order to ensure the stability of matter. If atoms constantly radiated gravitational waves, there would be no experimental signature. In the nucleus, the energy loss from a Fermi model of nucleons is about an eV per year or so, if (its a big if!) these nucleons constantly radiate gravitational waves classically. This quantum gravity possible phenomena (or lack of) is in the experimental realm.

  29. (comment is based on oversight failure, not quantum gravity)
    As for oversight failure, I wonder how long the IAU and other astronomical organizations will keep Soter's planetary discriminant. Soter's paper the discriminant is taken from actually has some good ideas, but Soter missed the elephant in the room.

    The planetary discriminant is defined as the ratio between an object's mass and the mass of all bodies with non-resonant orbits partially within the object's orbital zone with the orbital period within one order of magnitude. If that ratio is above 100, the object would be a planet.

    It works with the bodies so far known, but would fail as soon as it's confronted with a body that another planetary classification method would consider a planet. It's actually likely that it will satisfy Soter's criterion, but - it cannot be proven. Since the object itself is already so hard to see that we haven't seen it yet, how should we see the asteroids and dwarf planets on a similar orbit?

    In such a case the information that the body would be a planet would need to come from a different method - but if Soter's method cannot classify even one additional planet by itself, why use it in the first place? But the method is still widely used.

  30. Thanks for the well-deserved rant. In addition to the problems you accurately describe, it also seems to me as if the references provided in the comment were just randomly assigned to the sentences where they are cited. At least for references 5 (which is, by the way, cited with a wrong journal name) and 10, I do not see the slightest relation between the content of these papers and the context in which they are cited.
    I have no experience with Nature's comments, are these usually peer reviewed?

  31. "For a decade or more, quantum information theorists annoyed the hell out of condensed matter physicists by 'rediscovering' old results in a new (and often trivial) terminology, and not citing the old works."

    Yes - I noticed that tendency to parachronism in the QIT community when I read a recent Quanta Magazine article (which I won't link to because Quanta Magazine is a despicable, comment deleting, rag). The "data science" community's 'rediscovery' of (parts of) statistics is also notorious.

  32. Sabine,

    Thanks for the tip! I emailed David and he tells me that the target is sept 2018, on the east coast some place. So presumably more details available closer to then ;)


  33. Andre,

    I doubt that the comments are peer reviewed. It's kind of an opinion column.

  34. Sadly, it is to be feared that Nature is following in the steps of SciAm.
    I unsbscribed fro the latter in 2007.

  35. Bee says 'Well, we went from "it's not possible" to "a few orders of magnitude away" in 10 years. How is that no progress?'

    'Progress' is obviously decided retrospectively. The quantity you point toward is necessary in any time-line that yields progress, but insufficient as a candidate yield of progress, in and of itself, because it's not exclusively a marker for progress.

    I think you know this but just that it's tough and never gets less tough to face up to when there is a large amount of personal investment in play.
    I'm not psychologically guessing at you here but simply taking seriously what else you say(e.g. why talk about a crisis when there's buckets more progress out there on similar criteria as that?)

  36. piein,

    It's literally the only part of quantum gravity research in which there has been tangible, quantifiable, progress. I am actually not myself involved in that particular research direction (as with the massive quantum things etc).

  37. This comment by Marletto may provide a kernel of insight.

    "here is a new fundamental theory of physics that’s called constructor theory, and was proposed by David Deutsch who pioneered the theory of the universe of quantum computer. David and I are working this theory together. The fundamental idea in this theory is that we formulate all laws of physics in terms of what tasks are possible, what are impossible, and why. In this theory we have an exact physical characterization of an object that has those properties, and we call that knowledge. Note that knowledge here means knowledge without knowing the subject, as in the theory of knowledge of the philosopher, Karl Popper."

  38. > Nature magazine
    Magazine, not Journal! Good pun :) Awaiting hot babes and dudes in the following issues of the Nature Magazine!

  39. I find this absurdly amazing. Even more, these two persons apparently work in Oxford University, which I thought is a good university. It seems that there is a growing need for a wide-spread discussion about what science and scientific method is. Discussion near that Nature article is also quite fascinating... Especially this Pentcho Valev guy. To be absolutely clear: I am not really complaining about theories they are coming up with. But as in this blog spot, I find it terrifying that previous work is not properly acknowledged.

    Unfortunately this sort of events can really put down a motivation for making a career in science...

    Keep up the good work, Sabine. Your work certainly is on the right side of science.

  40. As you wish - a further difficulty talking about this sort of thing is that one of many serious impacts decades of no progress in the fundamental sense, is to the linguistic component. There's effectively an infinite number of equally legitimate ways to inflect words like 'progress'. One might think context will help, or convention, or precedent, but same goes for all that, and all the others too.

  41. Ugis Lacis: "It seems that there is a growing need for a wide-spread discussion about what science and scientific method is. Discussion near that Nature article is also quite fascinating... Especially this Pentcho Valev guy."

    If Sabine Hossenfelder had not systematically deleted my comments, I would have shown here, on this blog, that the scientific method in theoretical physics can only be DEDUCTION. A deductive theory can be presented as two lists:

    1. The list of all initial assumptions (postulates).

    2. The list of all arguments, each having the form:

    Premise 1: ...
    Premise 2: ...
    Premise N: ...
    Conclusion: ...

    Any premise is either an initial assumption (postulate) or the conclusion of some previous argument.

    Critics look for false postulates and invalid arguments. If they are unable to find any, all the conclusions of the theory are regarded as true.

  42. I basically never delete comments, I just don't approve them in the first place. Pentcho Valev has in the past submitted several obviously wrong and ill-informed comments that demonstrate lack of knowledge about basic physics. Of course I don't approve this. The above comment is, needless to say, also wrong, but mostly demonstrates a lack of familiarity with the philosophy of science, which I think is a milder form of wrongness.

  43. FYI: The authors of the Nature 'comment' have posted a preprint regarding their proposal on the arXiv:

  44. Yes, I've seen it. Haven't read it, but already 3rd sentence of abstract is wrong. Also, reference list is a joke.

  45. Without reading their arXiv preprint, just with a quick look at the "experiment" they propose:
    I assume, they would need a spatial superposition that is at least comparable to the diameter of the quantum system (a 10^-14 kg particle, i.e. order of 1 micron). To the best of my knowledge, such a superposition is far from being feasible in any actual experiment. It doesn't seem likely that they really thought this through. For example, if you compare the numbers for mass and superposition size with the harmonic oscillator ground state, this corresponds to a particle trapped at a frequency of 10^-8 Hz, which is not anywhere close to actual experiments.
    That is the main problem with the type of experiments they propose: you have either massive systems with small spatial superpositions or large superpositions with small masses, but you need both in order to test quantum effects of the gravitational field.
    That is, unless I missed some brilliant new insight in their proposal.

  46. I don't read Nature myself, but I'd always understood it to be a top-notch journal so I am honestly surprised by such editorial oversight. Shame on them! Hopefully some kind of apology will be winging its way to you soon.

  47. Sabine Hossenfelder (2:15 AM, July 20, 2017)

    What is wrong with 3rd sentence in arXiv:1707.06036 ? It looks rather like linguistic problem with interpretation of “in” for me. I found helpful to look briefly at they previous work arXiv:1704.00120 and also to a work arXiv:1707.07974 with discussion about mentioned Marletto and Vedral e-print and Bose e-print arXiv:1707.06050 . Maybe the novelty is using three bodies in the experiments.

  48. The gravitational coupling constant is dimensionful. Taking the ratio to the coupling constant of QED isn't even meaningful. The number they refer to is usually quoted for the ratio of gravitational to electric force between electron and proton.

  49. "The gravitational coupling constant is dimensionful."

    "Really, doing as much as Googling ..."

  50. J,

    Well, what can I say. It's not a coupling constant. Like, write down the Lagrangian. Of course the coupling constant doesn't depend on the mass of the electron! What sense does that even make? But thanks for pointing out that the nomenclature doesn't seem to be all that uncommon. I don't know anyone who works in quantum gravity who uses it though.

  51. In abstract they are likely indeed have used analogue of wikipedian idea about dimensionless \alpha_G, to obtain a value 10^{-43} (- ratio gravitational to electric force between two electrons). On the other hand, they are also using “gravitational coupling constant” for G in expression for a phase after equation (1) on page 3, but that looks like usual dimensionful constant.

  52. Sabine,

    Just read your correspondence to Nature. Thanks.

    Have you read the paper by Vinante and others about a millimetre sized cantlilever at 40 mK that has a noise source that does not want to go away, evan as temp -> 0. They use it to support a 'continuous spontaneous localization' CSL quantum theory of Adler.

    The finite intercept, clearly visible in the inset of
    Fig. 3 implies that the data are not compatible with
    a pure thermal noise behavior, and a nonthermal ex-cess noise is present. "

    I think its related to quantum gravity, as many continuous collapse theories are related to gravity.


  53. Tom,

    The paper's on my pile, but I'm presently a little behind with everything, so haven't read it.

  54. in my area of immunology, it can be if you know the editor, and how many times you are willing to undergo revisions. Ben Lewin, who started Cell, instructed that an editor should consider ONE round of revisions, then make an up or down decision, editorially, considering the comments of the reviewers of the revised article, but not being handcuffed by them. But what has actually happened at Nature is the editors now will go back and forth multiple times asking for ever more work as the reviewers move the bar incrementally in an attempt to stop the paper.

  55. Apparently they've published this work in PRL now :-/ Here's the link:

    Sad thing is that the media coverage about this is quite univocal, see the recent quanta article:

  56. Dear Prof. Sabin
    Thank you for clarifying the subject, specially for a none physicist like me. But I believe you have totally missed the point :
    Dr Marletto is elegantly Gorgeous.


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