Saturday, June 23, 2018

Particle Physics now Belly Up

Particle physics. Artist’s impression.
Professor Ben Allanach is a particle physicist at Cambridge University. He just wrote an advertisement for my book that appeared on Aeon some days ago under the title “Going Nowhere Fast”.

I’m kidding of course, Allanach’s essay has no relation to my book. At least not that I know of. But it’s not a coincidence he writes about the very problems that I also discuss in my book. After all, the whole reason I wrote the book was that this situation was foreseeable: The Large Hadron Collider hasn’t found evidence for any new particles besides the Higgs-boson (at least not so far), so now particle physicists are at a loss for how to proceed. Even if they find something in the data that’s yet to come, it is clear already that their predictions were wrong.

Theory-development in particle physics for the last 40 years has worked mostly by what is known as “top-down” approaches. In these approaches you invent a new theory based on principles you cherish and then derive what you expect to see at particle colliders. This approach has worked badly, to say the least. The main problem, as I lay out in my book, is that the principles which physicists used to construct their theories are merely aesthetic requirements. Top-down approaches, for example, postulate that the fundamental forces are unified or that the universe has additional symmetries or that the parameters in the theory are “natural.” But none of these assumptions are necessary, they’re just pretty guesses.

The opposite to a top-down approach, as Allanach lays out, is a “bottom-up” approach. For that you begin with the theories you have confirmed already and add possible modifications. You do this so that the modifications only become relevant in situations that you have not yet tested. Then you look at the data to find out which modifications are promising because they improve the fit to the data. It’s an exceedingly unpopular approach because the data have just told us over and over and over again that the current theories are working fine and require no modification. Also, bottom-up approaches aren’t pretty which doesn’t help their popularity.

Allanach, as several other people who I know, has stopped working on supersymmetry, an idea that has for a long time been the most popular top-down approach. In principle it’s a good development that researchers in the field draw consequences from the data. But if they don’t try to understand just what went wrong – why so many theoretical physicists believed in ideas that do not describe reality – they risk repeating the same mistake. It’s of no use if they just exchange one criterion of beauty with another.

Bottom-up approaches are safely on the scientific side. But they also increase the risk that we get stuck with the development of new theories because without top-down approaches we do not know where to look for new data. That’s why I argue in my book that some mathematical principles for theory-development are okay to use, namely those which prevent internal contradictions. I know this sounds lame and rather obvious, but in fact it is an extremely strong requirement that, I believe, hasn’t been pushed as far as we could push it.

This top-down versus bottom-up discussion isn’t new. It has come up each time the supposed predictions for new particles turned out to be wrong. And each time the theorists in the field, rather than recognizing the error in their ways, merely adjusted their models to evade experimental bounds and continued as before. Will you let them get away with this once again?

Tuesday, June 19, 2018

Astrophysicists try to falsify multiverse, find they can’t.

Ben Carson, trying to
make sense of the multiverse.
The idea that we live in a multiverse – an infinite collection of universes from which ours is merely one – is interesting but unscientific. It postulates the existence of entities that are unnecessary to describe what we observe. All those other universes are inaccessible to experiment. Science, therefore, cannot say anything about their existence, neither whether they do exist nor whether they don’t exist.

The EAGLE collaboration now knows this too. They recently published results of a computer simulation that details how the formation of galaxies is affected when one changes the value of the cosmological constant, the constant which quantifies how fast the expansion of the universe accelerates. The idea is that, if you believe in the multiverse, then each simulation shows a different universe. And once you know which universes give rise to galaxies, you can calculate how likely we are to be in a universe that contains galaxies and also has the cosmological constant that we observe.

We already knew before the new EAGLE paper that not all values of the cosmological constant are compatible with our existence. If the cosmological constant is too large, the universe either collapses quickly after formation (if the constant is negative) and galaxies are never formed, or it expands so quickly that structures are torn apart before galaxies can form (if the constant is positive).

New is that by using computer simulations, the EAGLE collaboration is able to quantify and also illustrate just how the structure formation differs with the cosmological constant.

The quick summary of their results is that if you turn up the cosmological constant and keep all other physics the same, then making galaxies becomes difficult once the cosmological constant exceeds about 100 times the measured value. The authors haven’t looked at negative values of the cosmological constant because (so they write) that would be difficult to include in their code.

The below image from their simulation shows an example for the gas density. On the left you see a galaxy prototype in a universe with zero cosmological constant. On the right the cosmological constant is 30 times the measured value. In the right image structures are smaller because the gas halos have difficulties growing in a rapidly expanding universe.

From Figure 7 of Barnes et al, MNRAS 477, 3, 1 3727–3743 (2018).

This, however, is just turning knobs on computer code, so what does this have to do with the multiverse? Nothing really. But it’s fun to see how the authors are trying really hard to make sense of the multiverse business.

A particular headache for multiverse arguments, for example, is that if you want to speak about the probability of an observer finding themselves in a particular part of the multiverse, you have to specify what counts as observer. The EAGLE collaboration explains:
“We might wonder whether any complex life form counts as an observer (an ant?), or whether we need to see evidence of communication (a dolphin?), or active observation of the universe at large (an astronomer?). Our model does not contain anything as detailed as ants, dolphins or astronomers, so we are unable to make such a fine distinction anyway.”
But even after settling the question whether dolphins merit observer-status, a multiverse per se doesn’t allow you to calculate the probability for finding this or that universe. For this you need additional information: a probability distribution or “measure” on the multiverse. And this is where the real problem begins. If the probability of finding yourself in a universe like ours is small you may think that disfavors the multiverse hypothesis. But it doesn’t: It merely disfavors the probability distribution, not the multiverse itself.

The EAGLE collaboration elaborates on the conundrum:
“What would it mean to apply two different measures to this model, to derive two different predictions? How could all the physical facts be the same, and yet the predictions of the model be different in the two cases? What is the measure about, if not the universe? Is it just our own subjective opinion? In that case, you can save yourself all the bother of calculating probabilities by having an opinion about your multiverse model directly.”
Indeed. You can even save yourself the bother of having a multiverse to begin with because it doesn’t explain any observation that a single universe wouldn’t also explain.

The authors eventually find that some probability distributions make our universe more, others less probable. Not that you need a computer cluster for that insight. Still, I guess we should applaud the EAGLE people for trying. In their paper, they conclude: “A specific multiverse model must justify its measure on its own terms, since the freedom to choose a measure is simply the freedom to choose predictions ad hoc.”

But of course a model can never justify itself. The only way to justify a physical model is that it fits observation. And if you make ad hoc choices to fit observations you may as well just chose the cosmological constant to be what we observe and be done with it.

In summary, the paper finds that the multiverse hypothesis isn’t falsifiable. If you paid any attention to the multiverse debate, that’s hardly surprising, but it is interesting to see astrophysicists attempting to squeeze some science out of it.

I think the EAGLE study makes a useful contribution to the literature. Multiverse proponents have so far argued that what they do is science because some versions of the multiverse are testable in our universe, for example by searching for entanglement between universes, or for evidence that our universe has collided with another one in the past.

It is correct that some multiverse types are testable, but to the extent that they have been tested, they have been ruled out. This, of course, has not ruled out the multiverse per se, because there are still infinitely many types of multiverses left. For those, the only thing you can do is make probabilistic arguments. The EAGLE paper now highlights that these can’t be falsified either.

I hope that showcasing the practical problem, as the EAGLE paper does, will help clarify the unscientific basis of the multiverse hypothesis.

Let me be clear that the multiverse is a fringe idea in a small part of the physics community. Compared to the troubled scientific methodologies in some parts of particle physics and cosmology, multiverse madness is a minor pest. No, the major problem with the multiverse is its popularity outside of physics. Physicists from Brian Greene to Leonard Susskind to Andrei Linde have publicly spoken about the multiverse as if it was best scientific practice. And that well-known physicists pass the multiverse off as science isn’t merely annoying, it actively damages the reputation of science. A prominent example for the damage that can result comes from the 2015 Republican Presidential Candidate Ben Carson.

Carson is a retired neurosurgeon who doesn’t know much physics, but what he knows he seems to have learned from multiverse enthusiasts. On September 22, 2015, Carson gave a speech at a Baptist school in Ohio, informing his audience that “science is not always correct,” and then went on to justify his science skepticism by making fun of the multiverse:
“And then they go to the probability theory, and they say “but if there’s enough big bangs over a long enough period of time, one of them will be the perfect big bang and everything will be perfectly organized.””
In an earlier speech he cheerfully added: “I mean, you want to talk about fairy tales? This is amazing.”

Now, Carson has misunderstood much of elementary thermodynamics and cosmology, and I have no idea why he thinks he’s even qualified to give speeches about physics. But really this isn’t the point. I don’t expect neurosurgeons to be experts in the foundations of physics and I hope Carson’s audience doesn’t expect that either. Point is, he shows what happens when scientists mix fact with fiction: Non-experts throw out both together.

In his speech, Carson goes on: “I then say to them, look, I’m not going to criticize you. You have a lot more faith than I have… I give you credit for that. But I’m not going to denigrate you because of your faith and you shouldn’t denigrate me for mine.”

And I’m with him on that. No one should be denigrated for what they believe in. If you want to believe in the existence of infinitely many universes with infinitely many copies of yourself, that’s all fine with me. But please don’t pass it off as science.

If you want to know more about the conflation between faith and knowledge in theoretical physics, read my book “Lost in Math: How Beauty Leads Physics Astray.”

Friday, June 15, 2018

Physicists are very predictable

I have a new paper on the arXiv, which came out of a collaboration with Tobias Mistele and Tom Price. We fed a neural network with data about the publication activity of physicists and tried to make a “fake” prediction, for which we used data from the years 1996 up to 2008 to predict the next ten years. Data come from the arXiv via the Open Archives Initiative.

To train the network, we took a random sample of authors and asked the network to predict these authors’ publication data. In each cycle the network learned how good or bad its prediction was and then tried to further improve it.

Concretely, we trained the network to predict the h-index, a measure for the number of citations a researcher has accumulated. We didn’t use this number because we think it’s particularly important, but simply because other groups have previously studied it with neural networks in disciplines other than physics. Looking at the h-index, therefore, allowed us to compare our results with those of the other groups.

After completing the training, we asked how well the network can predict the citations accumulated by authors that were not in the training group. The common way to quantify the goodness of such a prediction is with the coefficient of determination, R2. The higher the coefficient of determination, the stronger the correlation of the prediction with the actual number, hence the better the prediction. The below figure shows the result of our neural network, compared with some other predictors. As you can see we did pretty well!

The blue (solid) curve labelled “Net” shows how good the prediction
of our network is for extrapolating the h-index over the number of years.
The other two curves use simpler predictors on same data. 

We found a coefficient of determination of  0.85 for a prediction over ten years. Earlier studies based on machine learning found 0.48 in the life-sciences and 0.72 in the computer sciences.

But admittedly the coefficient of determination doesn’t tell you all that much unless you’re a statistician. So for illustration, here are some example trajectories that show the network’s prediction compared with the actual trend (more examples in the paper).

However, that our prediction is better than the earlier ones is only partly due to our network’s performance. Turns out, our data are also intrinsically easier to predict, even with simple measures. You can for example just try to linearly extrapolate the h-index, and while that prediction isn’t as good as that of the network, it is still better than the prediction from the other disciplines. You see this in the figure I showed you above for the coefficient of determination. Used on the arXiv data even the simple predictors achieve something like 0.75.

Why that is so, we don’t know. One possible reason could be that the sub-disciplines of physicists are more compartmentalized and researchers often stay in the fields that they started out with. Or, as Nima Arkani-Hamed put it when I interviewed him “everybody does the analytic continuation of what they’ve been doing for their PhD”. (Srsly, the book is fun, you don’t want to miss it.) In this case you establish a reputation early on and your colleagues know what to expect from you. It seems plausible to me that in such highly specialized communities it would be easier to extrapolate citations than in more mixed-up communities. But really this is just speculation; the data don’t tell us that.

Having said this, by and large the network predictions are scarily good. And that’s even though our data is woefully incomplete. We cannot presently, for example, include any papers that are not on the arXiv. Now, in some categories, like hep-th, pretty much all papers are on the arXiv. But in other categories that isn’t the case. So we are simply missing information about what researchers are doing. We also have the usual problem of identifying authors by their names, and haven’t always been able to find the journal in which a paper was published.

Now, if you allow me to extrapolate the present situation, data will become better and more complete. Also the author-identification problem will, hopefully, be resolved at some point. And this means that the predictivity of neural networks chewing on this data is likely to increase some more.

Of course we did not actually make future predictions in the present paper, because in this case we wouldn’t have been able to quantify how good the prediction was. But we could now go and train the network with data up to 2018 and extrapolate up to 2028. And I predict it won’t be long until such extrapolations of scientists’ research careers will be used in hiring and funding decisions. Sounds scary?

Oh, I know, many of you are now dying to see the extrapolation of their own publishing history. I haven’t seen mine. (Really I haven’t. We treat the authors as anonymous numbers.) But (if I can get funding for it) we will make these predictions publicly available in the coming year. If we don’t, rest assured someone else will. And in this case it might end up being proprietary software.

My personal conclusion from this study is that it’s about time we think about how to deal with personalized predictors for research activity.

Tuesday, June 12, 2018

Lost in Math: Out Now.

Today is the official publication date of my book “Lost in Math: How Beauty Leads Physics Astray.” There’s an interview with me in the current issue of “Der Spiegel” (in German) with a fancy photo, and an excerpt at Scientific American.

In the book I don’t say much about myself or my own research. I felt that was both superfluous and not particularly interesting. However, a lot of people have asked me about a comment I made in the passing in an earlier blogpost: “By writing [this book], I waived my hopes of ever getting tenure.” Even the Spiegel-guy who interviewed me asked about this! So I feel like I should add some explanation here to prevent misunderstandings. I hope you excuse that this will be somewhat more personal than my usual blogposts.

I am not tenured and I do not have a tenure-track position, so not like someone threatened me. I presently have a temporary contract which will run out next year. What I should be doing right now is applying for faculty positions. Now imagine you work at some institution which has a group in my research area. Everyone is happily producing papers in record numbers, but I go around and say this is a waste of money. Would you give me a job? You probably wouldn’t. I probably wouldn’t give me a job either.

That’s what prompted my remark, and I think it is a realistic assessment. But please note that the context in which I wrote this wasn’t a sudden bout of self-pity, it was to report a decision I made years ago.

I know you only get to see the results now, but I sold the book proposal in 2015. In the years prior to this, I was shortlisted for some faculty positions. In the end that didn’t pan out, but the interviews prompted me to imagine the scenario in which I actually got the job. And if I was being honest to myself, I didn’t like the scenario.

I have never been an easy fit to academia. I guess I was hoping I’d grow into it, but with time my fit has only become more uneasy. At some point I simply concluded I have had enough of this nonsense. I don’t want to be associated with a community which wastes tax-money because its practitioners think they are morally and intellectually so superior that they cannot possibly be affected by cognitive biases. You only have to read the comments on this blog to witness the origin of the problem, as with commenters who work in the field laughing off the idea that their objectivity can possibly be affected by working in echo-chambers. I can’t even.

As to what I’ll do when my contract runs out, I don’t know. As everyone who has written popular science books will confirm, you don’t get rich from it. The contract with Basic Books would never have paid for the actual working time, and that was before my agent got his share and the tax took its bite. (And while I am already publicly answering questions about my income, I also frequently get asked how much “money” I make with the ads on this blog. It’s about one dollar a day. Really the ads are only there so I don’t feel like I am writing here entirely for nothing.)

What typically happens when I write about my job situation is that everyone offers me advice. This is very kind, but I assure you I am not writing this because I am asking for help. I will be fine, do not worry about me. Yes, I don’t know what I’ll do next year, but something will come to my mind.

What needs help isn’t me, but academia: The current organization amplifies rather than limits the pressure to work on popular and productive topics. If you want to be part of the solution, the best starting point is to read my book.

Thanks for listening. And if you still haven’t had enough of me, Tam Hunt has an interview with me up at Medium. You can leave comments on this interview here.

More info on the official book website:

Monday, June 11, 2018

Are the laws of nature beautiful? (2nd book trailer)

Here is the other video trailer for my book "Lost in Math: How Beauty Leads Physics Astray". 

Since I have been asked repeatedly, let me emphasize again that the book is aimed at non-experts, or "the interested lay-reader" as they say. You do not need to bring any background knowledge in math or physics and, no, there are no equations in the book, just a few numbers. It's really about the question what we mean by "beautiful theories" and how that quest for beauty affects scientists' research interests. You will understand that without equations.

The book has meanwhile been read by several non-physicists and none of them reported great levels of frustration, so I have reason to think I roughly aimed at the right level of technical detail.

Having said that, the book should also be of interest for you if you are a physicist, not because I explain what the standard model is, but because you will get to hear what some top people in the field think about the current situation. (And I swear I was nice to them. My reputation is far worse than I.)

You find a table of contents, and a list of people who I interviewed, as well as transcripts of the video trailers on the book website.

Saturday, June 09, 2018

Video Trailer for "Lost in Math"

I’ve been told that one now does video trailers for books and so here’s me explaining what led me to write the book.

Friday, June 08, 2018

Science Magazine had my book reviewed, and it’s glorious, glorious.

Science Magazine had my book “Lost in Math” reviewed by Dr. Djuna Lize Croon, a postdoctoral associate at the Department of Physics at Dartmouth College, in New Hampshire, USA. Dr. Croon has worked on the very research topics that my book exposes as mathematical fantasies, such as “extra natural inflation” or “holographic composite Higgs models,” so choosing her to review my book is an interesting move for sure.

Dr. Croon does not disappoint. After just having read a whole book that explains how scientists fail to acknowledge that their opinions are influenced by the communities they are part of, Dr. Croon begins her review by quoting an anonymous Facebook friend who denigrates me as a blogger and tells Dr. Croon to dislike my book because I am not “offering solutions.” In her review, then, Dr. Croon reports being shocked to find that I disagree with her scientific heroes, dislikes that I put forward own opinions, and then promptly arrives at the same conclusion that her Facebook friend kindly offered beforehand.

The complaint that I merely criticize my community without making recommendations for improvement is particularly interesting because to begin with it’s wrong. I do spell out very clearly in the book that I think theoretical physicists in the foundations should focus on mathematical consistency and making contact to experiment rather than blathering about beauty. I also say concretely what topics I think are most promising, though I warn the reader that of course I too am biased and they should come to their own conclusions.

Even leaving aside that I do offer recommendations for improvement, I don’t know why it’s my task to come up with something else for those people to do. If they can’t come up with something else themselves, maybe we should just stop throwing money at them?

On a more technical note, I find it depressing that Dr. Croon in her review writes that naturalness has “a statistical meaning” even though I explain like a dozen times throughout the book that you can’t speak of probabilities without having a probability distribution. We have only this set of laws of nature. We have no statistics from which we could infer a likelihood of getting exactly these laws.

In summary, this review does an awesome job highlighting the very problems that my book is about.

Update June 17th: Remarkably enough, the editors at Science decided to remove the facebook quote from the review.

Physicist concludes there are no laws of physics.

It was June 4th, 2018, when Robbert Dijkgraaf, director of the world-renown Princeton Institute for Advanded Study, announced his breakthrough insight. After decades of investigating string theory, Dijkgraaf has concluded that there are no laws of physics.

Guess that’s it, then, folks. Don’t forget to turn off the light when you close the lab door for the last time.

Dijkgraaf knows what he is talking about. “Once you have understood the language of which [the cosmos] is written, it is extremely elegant, beautiful, powerful and natural,” he explained already in 2015, “The universe wants to be understood and that’s why we are all driven by this urge to find an all-encompassing theory.”

This urge has driven Dijkgraaf and many of his colleagues to pursue string theory, which they originally hoped would give rise to the unique theory of everything. That didn’t quite pan out though, and not surprisingly so: The idea of a unique theory is a non-starter. Whether a theory is unique or not depends on what you require of it. The more requirements, the better specified the theory. And whether a theory is the unique one that fulfils these or those requirements tells you nothing about whether it actually correctly describes nature.

But in the last two decades it has become popular in the foundations of physics to no longer require a theory to describe our universe. Without that requirement, then, theories contain an infinite number of universes that are collectively referred to as “the multiverse.” Theorists like this idea because having fewer requirements makes their theory simpler, and thus more beautiful. The resulting theory then uniquely explains nothing.

Of course if you have a theory with a multiverse and want to describe our universe, you have to add back the requirements you discarded earlier. That’s why no one who actually works with data ever starts with a multiverse – it’s utterly useless; Occam’s razor safely shaves it off. The multiverse doesn’t gain you anything, except possibly the ability to make headlines and speak of “paradigm changes.”

In string theory in particular, to describe our universe we’d need to specify just what happens with the additional dimensions of space that the theory needs. String theorists don’t like to make this specification because they don’t know how to make it. So instead they say that since string theory offers so many options for how to make a universe, one of them will probably fit the bill. And maybe one day they will find a meta-law that selects our universe.

Maybe they will. But until then the rest of us will work under the assumption that there are laws of physics. So far, it’s worked quite well, thank you very much.

If you want to know more about what bizarre ideas theoretical physicists have lately come up with, read my book “Lost in Math.”

Sunday, June 03, 2018

Book Update: Books are printed!

I had just returned from my trip to Dublin when the door rang and the UPS man dumped two big boxes on our doorstep. My husband has a habit of ordering books by the dozens, so my first thought was that this time he’d really outdone himself. Alas, the UPS guy pointed out, the boxes were addressed to me.

I signed, feeling guilty for having forgotten I ordered something from Lebanon, that being the origin of the parcels. But when I cut the tape and opened the boxes I found – drumrolls please – 25 copies “Lost in Math”. Turns out my publisher has their books printed in Lebanon.

I hadn’t gotten neither galleys nor review copies, so that was the first time I actually saw The-Damned-Book, as it’s been referred to in our household for the past three years. And The-Damned-Book is finally, FINALLY, a real book!

The cover looks much better in print than it does in the digital version because it has some glossy and some matte parts and, well, at least two seven-year-old girls agree that it’s a pretty book and also mommy’s name is on the cover and a mommy photo in the back, and that’s about as far as their interest went.

I’m so glad this is done. When I signed the contract in 2015, I had no idea how nerve-wrecking it would be to wait for the publication. In hindsight, it was a totally nutty idea to base the whole premise of The-Damned-Book on the absence of progress in the foundations of physics when such progress could happen literally any day. For three years now I’ve been holding my breath every time there was a statistical fluctuation in the data.

But now – with little more than a week to go until publication – it seems exceedingly unlikely anything will change about the story I am telling: Fact is, theorists in the foundations of physics have been spectacularly unsuccessful with their predictions for more than 30 years now. (The neutrino-anomaly I recently wrote about wasn’t a prediction, so even if it holds up it’s not something you could credit theorists with.)

The story here isn’t that theorists have been unsuccessful per se, but that they’ve been unsuccessful and yet don’t change their methods. That’s especially perplexing if you know that these methods rely on arguments from beauty even though everyone agrees that beauty isn’t a scientific criterion. Parallels to the continued use of flawed statistical methods in psychology and the life sciences are obvious. There too, everyone kept using bad methods that were known to be bad, just because it was the state of the art. And that’s the real story here: Scientists get stuck on unsuccessful methods.

Some people have voiced their disapproval that I went and argued with some prominent people in the field without them knowing they’d end up in my book. First, I recommend you read the book before you disapprove of what you believe it contains. I think I have treated everyone politely and respectfully.

Second, it should go without saying but apparently doesn’t, that everyone who I interviewed signed an interview waiver, transferring all rights for everything they told me to my publisher in all translations and all formats, globally and for all eternity, Amen. They knew what they were being interviewed for. I’m not an undercover agent, and my opinions about arguments from beauty are no secret.

Furthermore, everyone I interviewed got to see and approved a transcript with the exact wording that appears in the book. Though I later removed some parts entirely because it was just too much material. (And no, I cannot reuse it elsewhere because that was indeed not what they agreed on.) I had to replace a few technical terms here or there that most readers wouldn’t have understood, but these instances are marked in the text.

So, I think I did my best to accurately represent their opinions, and if anyone comes off looking like an idiot it should be me.

Most importantly though, the very purpose of these interviews is to offer the reader a variety of viewpoints rather than merely my own. So of course I disagree with the people I spoke with here and there – because who’d read a dialogue in which two people constantly agree with each other?

In any case, everything’s been said and done and now I can only wait and hope. This isn’t a problem that physicists can solve themselves. The whole organization of academic research today acts against major changes in methodology because that would result in a sudden and drastic decrease of publishing activity. The only way I can see change come about is public pressure. We have had enough talk about elegant universes and beautiful theories.

If you still haven’t made up your mind whether to buy the book, we now have a website which contains a table of contents and links to reviews and such, and Amazon offers you can “Look Inside” the book. Two video trailers will be coming next week. Silicon Republic writes about the book here and Dan Falk has a piece at NBC titled “Why some scientists say physics has gone off the rails.”

Thursday, May 31, 2018

New results confirm old anomaly in neutrino data

The collaboration of a neutrino experiment called MiniBooNe just published their new results:
    Observation of a Significant Excess of Electron-Like Events in the MiniBooNE Short-Baseline Neutrino Experiment
    MiniBooNE Collaboration
    arXiv:1805.12028 [hep-ex]
It’s a rather unassuming paper, but it deserves a signal boost because for once we have an anomaly that did not vanish with further examination. Indeed, it actually increased in significance, now standing at a whopping 6.1σ.

MiniBooNE was designed to check the results of an earlier experiment called LSND, the Liquid Scintillator Neutrino Detector experiment that ran in the 1990s. The LSND results were famously incompatible the results of a bulk of other neutrino experiments. So incompatible, indeed, that the LSND data are usually excluded from global fits – they just don’t fit.

All the other experimental data could be neatly fitted with assuming that the three known types of neutrinos “oscillate,” which means they change back and forth into each other as they travel. Problem is, in a three-neutrino oscillation model, there are only maximally nine parameters (the masses, mixing angles, and a few phases, the latter depending on the type of neutrino). These parameters are not sufficient to also fit the LSND data.

See figure below for the LSND trouble: The turquoise/yellow areas in the figure do not overlap with the red/blue ones.

[Figure: Hitoshi Murayama]

The new data from MiniBooNE, now, confirms that this tension in the data is real. It’s not a quirk of the LSND experiment. This data can (to my best knowledge) not be fitted with the standard framework of three types of neutrinos (one for the electron, one for the muon, and one of the tau). Fitting this data requires either new particles (sterile neutrinos) or some kind of symmetry violation, typically CPT violation or Lorentz-invariance violation (or both).

This is the key figure from the new paper. See how the new results agree with the earlier LSND results. And note the pale grey line indicating that this area is “ruled out” by other experiments (assuming the standard explanation).

[Figure 5 from arXiv:1805.12028]

So this is super-exciting news: An old anomaly was re-examined and confirmed! Now it’s time for theoretical physicists to come up with an explanation.

Monday, May 28, 2018

What do physicists mean when they say the laws of nature are beautiful?

Simplicity in photographic art.
“Monday Blues Chat”
By Erin Photography
In my upcoming book “Lost in Math: How Beauty Leads Physics Astray,” I explain what makes a theory beautiful in the eyes of a physicist and how beauty matters for their research. For this, I interviewed about a dozen theoretical physicists (full list here) and spoke to many more. I also read every book I could find on the topic, starting with Chandrasekhar’s “Truth and Beauty” to McAllister’s “Beauty and Revolution in Science” and Orrell’s “Truth or Beauty”.

Turns out theoretical physicists largely agree on what they mean by beauty, and it has the following three aspects:


A beautiful theory is simple, and it is simple if it can be derived from few assumptions. Currently common ways to increase simplicity in the foundations of physics is unifying different concepts or adding symmetries. To make a theory simpler, you can also remove axioms; this will eventually result in one or the other version of a multiverse.

Please note that the simplicity I am referring to here is absolute simplicity and has nothing to do with Occam’s razor, which merely tells you that from two theories that achieve the same you should pick the simpler one.


A beautiful theory is also natural, meaning it does not contain numbers without units that are either much larger or much smaller than 1. In physics-speak you’d say “dimensionless parameters are of order 1.” In high energy particle physics in particular, theorists use a relaxed version of naturalness called “technical naturalness” which says that small numbers are permitted if there is an explanation for their smallness. Symmetries, for example, can serve as such an explanation.

Note that in contrast to simplicity, naturalness is an assumption about the type of assumptions, not about the number of assumptions.


Elegance is the fuzziest aspect of beauty. It is often described as an element of surprise, the “aha-effect,” or the discovery of unexpected connections. One specific aspect of elegance is a theory’s resistance to change, often referred to as “rigidity” or (misleadingly, I think) as the ability of a theory to “explain itself.”

By no way do I mean to propose this as a definition of beauty; it is merely a summary of what physicists mean when they say a theory is beautiful. General relativity, string theory, grand unification, and supersymmetry score high on all three aspects of beauty. The standard model, modified gravity, or asymptotically safe gravity, not so much.

But while physicists largely agree on what they mean by beauty, in some cases they disagree on whether a theory fulfills the requirements. This is the case most prominently for quantum mechanics and the multiverse.

For quantum mechanics, the disagreement originates in the measurement axiom. On the one hand it’s a simple axiom. On the other hand, it covers up a mess, that being the problem of defining just what a measurement and a measurement apparatus are.

For the multiverse, the disagreement is over whether throwing out an assumption counts as a simplification if you have to add it again later because otherwise you cannot describe our observations.

If you want to know more about how arguments from beauty are used and abused in the foundations of physics, my book will be published on June 12th and then it’s all yours to peruse!

Wednesday, May 23, 2018

This is how I pray

I know, you have all missed my awesome chord progressions, but do not despair, I have relief for your bored ears.

I am finally reasonably happy with the vocal recordings if not with the processing, or the singing, or the lyrics. But working on that. The video was painful, both figuratively and literally; I am clearly too old to crouch on the floor for extended periods and had to hobble stairs for days after the filming.

The number one comment I get on my music videos is, sadly enough, not "wow, you are so amazingly gifted" but "where do you find the time?". To which the answer is "I don't". I did the filming for this video on Christmas, the audio on Easter, and finished on Pentecost. If it wasn't for those Christian holidays, I'd never get anything done. So, thank God, now you know how I pray.

Friday, May 18, 2018

The Overproduction Crisis in Physics and Why You Should Care About It

[Image: Everett Collection]
In the years of World War II, National Socialists executed about six million Jews. The events did not have a single cause, but most historians agree that a major reason was social reinforcement, more widely known as “group think.”

The Germans who went along with the Nazis’ organized mass murder were not psychopaths. By all accounts they were “normal people.” They actively or passively supported genocide because at the time it was a socially acceptable position; everyone else did it too. And they did not personally feel responsible for the evils of the system. It eased their mind that some scientists claimed it was only rational to prevent supposedly genetically inferior humans from reproducing. And they hesitated to voice disagreement because those who opposed the Nazis risked retaliation.

It’s comforting to think that was Then and There, not Now and Here. But group-think think isn’t a story of the past; it still happens and it still has devastating consequences. Take for example the 2008 mortgage crisis.

Again, many factors played together in the crisis’ buildup. But oiling the machinery were bankers who approved loans to applicants that likely couldn’t pay the money back. It wasn’t that the bankers didn’t know the risk; they thought it was acceptable because everyone else was doing it too. And anyone who didn’t play along would have put themselves at a disadvantage, by missing out on profits or by getting fired.

A vivid recount comes from an anonymous Wall Street banker quoted in a 2008 NPR broadcast:
“We are telling you to lie to us. We’re hoping you don't lie. Tell us what you make, tell us what you have in the bank, but we won’t verify. We’re setting you up to lie. Something about that feels very wrong. It felt wrong way back then and I wish we had never done it. Unfortunately, what happened ... we did it because everyone else was doing it.”
When the mortgage bubble burst, banks defaulted by the hundreds. In the following years, millions of people would lose their jobs in what many economists consider the worst financial crisis since the Great Depression of the 1930s.

It’s not just “them” it’s “us” too. Science isn’t immune to group-think. On the contrary: Scientific communities are ideal breeding ground for social reinforcement.

Research is currently organized in a way that amplifies, rather than alleviates, peer pressure: Measuring scientific success by the number of citations encourages scientists to work on what their colleagues approve of. Since the same colleagues are the ones who judge what is and isn’t sound science, there is safety in numbers. And everyone who does not play along risks losing funding.

As a result, scientific communities have become echo-chambers of likeminded people who, maybe not deliberately but effectively, punish dissidents. And scientists don’t feel responsible for the evils of the system. Why would they? They just do what everyone else is also doing.

The reproducibility crisis in psychology and in biomedicine is one of the consequences. In both fields, an overreliance on data with low statistical relevance and improper methods of data analysis (“p-value hacking”) have become common. That these statistical methods are unreliable has been known for a long time. As Jessica Utts, President of the American Statistical Association, pointed out in 2016 “statisticians and other scientists have been writing on the topic for decades.”

So why then did researchers in psychology continue using flawed methods? Because everyone else did it. It was what they were taught; it was generally accepted procedure. And psychologists who’d have insisted on stricter methods of analysis would have put themselves at a disadvantage: They’d have gotten fewer results with more effort. Of course they didn’t go the extra way.

The same problem underlies an entirely different popular-but-flawed scientific procedure: “Mouse models,” ie using mice to test the efficiency of drugs and medical procedures.

How often have you read that Alzheimer or cancer has been cured in mice? Right – it’s been done hundreds of times. But humans aren’t mice, and it’s no secret that mice-results – while not uninteresting – often don’t transfer to humans. Scientists only partly understand why, but that mouse models are of limited use to develop treatments for humans isn’t controversial.

So why do researchers continue to use them anyway? Because it’s easy and cheap and everyone else does it too. As Richard Harris put it in his book Rigor Mortis: “One reason everybody uses mice: everybody else uses mice.”

It happens here in the foundations of physics too.

In my community, it has become common to justify the publication of new theories by claiming the theories are falsifiable. But falsifiability is a weak criterion for a scientific hypothesis. It’s necessary, but certainly not sufficient, for many hypotheses are falsifiable yet almost certainly wrong. Example: It will rain peas tomorrow. Totally falsifiable. Also totally nonsense.

Of course this isn’t news. Philosophers have gone on about this for at least half a century. So why do physicists do it? Because it’s easy and because all their colleagues do it. And since they all do it, theories produced by such methods will usually get published, which officially marks them as “good science”.

In the foundations of physics, the appeal to falsifiability isn’t the only flawed method that everyone uses because everyone else does. There are also those theories which are plainly unfalsifiable. And another example are arguments from beauty.

In hindsight it seems perplexing, to say the least, but physicists published ten-thousands of papers with predictions for new particles at the Large Hadron Collider because they believed that the underlying theory must be “natural”. None of those particles were found.

Similar arguments underlie the belief that the fundamental forces should be unified because that’s prettier (no evidence for unification has been found) or that we should be able to measure particles that make up dark matter (we didn’t). Maybe most tellingly, physicists in these community refuse to consider the possibility that their opinions are affected by the opinions of their peers.

One way to address the current crises in scientific communities is to impose tighter controls on scientific standards. That’s what is happening in psychology right now, and I hope it’ll also happen in the foundations of physics soon. But this is curing the symptoms, not the disease. The disease is a lacking awareness for how we are affected by the opinions of those around us.

The problem will reappear until everyone understands the circumstances that benefit group-think and learns to recognize the warning signs: People excusing what they do with saying everyone else does it too. People refusing to take responsibility for what they think are “evils of the system.” People unwilling to even consider that they are influenced by the opinions of others. We have all the warning signs in science – had them for decades.

Accusing scientists of group-think is standard practice of science deniers. The tragedy is, there’s truth in what they say. And it’s no secret: The problem is easy to see for everyone who has the guts to look. Sweeping the problem under the rug will only further erode trust in science.

Read all about the overproduction crisis in the foundations of physics and what you – yes you! – can do to help in my book “Lost in Math,” out June 12, 2018.

Tuesday, May 15, 2018

Measuring Scientific Broadness

I have a new paper out today and it wouldn’t have happened without this blog.

A year ago, I wrote a blogpost declaring that “academia is fucked up,” to quote myself because my words are the best words. In that blogpost, I had some suggestions how to improve the situation, for example by offering ways to quantify scientific activity other than counting papers and citations.

But ranting on a blog is like screaming in the desert: when the dust settles you’re still in the desert. At least that’s been my experience.

Not so this time! In the week following the blogpost, three guys wrote to me expressing their interest in working on what I suggested. One of them I never heard of again. The other two didn’t get along and one of them eventually dropped out. My hopes sank.

But then I got a small grant from the Foundational Questions Institute and was able to replace the drop-out with someone else. So now we were three again. And I could actually pay the other two, which probably helped keeping them interested.

One of the guys is Tom Price. I’ve never met him, but – believe it or not – we now have a paper on the arXiv.
    Measuring Scientific Broadness
    Tom Price, Sabine Hossenfelder

    Who has not read letters of recommendations that comment on a student's `broadness' and wondered what to make of it? We here propose a way to quantify scientific broadness by a semantic analysis of researchers' publications. We apply our methods to papers on the open-access server and report our findings.

    arXiv:1805.04647 [physics.soc-ph]

In the paper we propose a way to measure how broad or specialized a scientists’ research interests are. We quantify this by analyzing the words they use in the title and abstracts of their arXiv papers.

Tom tried several ways to quantify the distribution of keywords, and so our paper contains four different measures for broadness. We eventually picked one for the main text, but checked that the other ones give largely comparable results. In the paper, we report the results of various analyses of the arXiv data. For example, here is the distribution of broadness over authors:

It’s a near-perfect normal distribution!

I should add that you get this distribution only after removing collaborations from the sample, which we have done by excluding all authors with the word “collaboration” in the name and all papers with more than 30 authors. If you don’t do this, the distribution has a peak at small broadness.

We also looked at the average broadness of authors in different arXiv categories, where we associate an author with a category if it’s the primary category for at least 60% of their papers. By that criterion, we find physics.plasm-ph has the highest broadness and astro-ph.GA the lowest one. However, we have only ranked categories with more than 100 associated authors to get sensible statistics. In this ranking, therefore, some categories don’t even appear.

That’s why we then also looked at the average broadness associated with papers (rather than authors) that have a certain category as the primary one. This brings physics.pop-ph to the top, while astro-ph.GA stays on the bottom.

That astrophysics is highly specialized also shows up in our list of keywords, where phrases like “star-forming” or “stellar mass” are among those of the lowest broadness. On the other hand, the keywords “agents”, “chaos,” “network”, or “fractal” have high values of broadness. You find the top broadest and top specialized words in the below table. See paper for reference to full list.

We also compared the average broadness associated with authors who have listed affiliations in certain countries. The top scores of broadness go to Israel, Austria, and China. The correlation between the h-index and broadness is weak. Neither did we find a correlation between broadness and gender (where we associated genders by common first names). Broadness also isn’t correlated with the Nature Index, which is a measure of a country’s research productivity.

A correlation we did find though is that researchers whose careers suddenly end, in the sense that their publishing activity discontinues, are more likely to have a low value of broadness. Note that this doesn’t necessarily say much about the benefits of some research styles over others. It might be, for example, that research areas with high competition and few positions are more likely to also be specialized.

Let me be clear that it isn’t our intention to declare that the higher the broadness the better. Indeed, there might well be cases when broadness is distinctly not what you want. Depending on which position you want to fill or which research program you have announced, you may want candidates who are specialized on a particular topic. Offering a measure for broadness, so we hope, is a small step to honoring the large variety of ways to excel in science.

I want to add that Tom did the bulk of the work on this paper, while my contributions were rather minor. We have another paper coming up in the next weeks (or so I hope), and we are also working on a website where everyone will be able to determine their own broadness value. So stay tuned!

Friday, May 11, 2018

Dear Dr B: Should I study string theory?

Strings. [image:]
“Greetings Dr. Hossenfelder!

I am a Princeton physics major who regularly reads your wonderful blog.

I recently came across a curious passage in Brian Greene’s introduction to a reprint edition of Einstein's Meaning of Relativity which claims that:
“Superstring theory successfully merges general relativity and quantum mechanics [...] Moreover, not only does superstring theory merge general relativity with quantum mechanics, but it also has the capacity to embrace — on an equal footing — the electromagnetic force, the weak force, and the strong force. Within superstring theory, each of these forces is simply associated with a different vibrational pattern of a string. And so, like a guitar chord composed of four different notes, the four forces of nature are united within the music of superstring theory. What’s more, the same goes for all of matter as well. The electron, the quarks, the neutrinos, and all other particles are also described in superstring theory as strings undergoing different vibrational patterns. Thus, all matter and all forces are brought together under the same rubric of vibrating strings — and that’s about as unified as a unified theory could be.”
Is all this true? Part of the reason I am asking is that I am thinking about pursuing String Theory, but it has been somewhat difficult wrapping my head around its current status. Does string theory accomplish all of the above?

Thank you!

An Anonymous Princeton Physics Major”

Dear Anonymous,

Yes, it is true that superstring theory merges general relativity and quantum mechanics. Is it successful? Depends on what you mean by success.

Greene states very carefully that superstring theory “has the capacity to embrace” gravity as well as the other known fundamental forces (electromagnetic, weak, and strong). What he means is that most string theorists currently believe there exists a specific model for superstring theory which gives rise to these four forces. The vague phrase “has the capacity” is an expression of this shared belief; it glosses over the fact that no one has been able to find a model that actually does what Greene says.

Superstring theory also comes with many side-effects which all too often go unnoticed. To begin with, the “super” isn’t there to emphasize the theory is awesome, but to indicate it’s supersymmetric. Supersymmetry, to remind you, is a symmetry that postulates all particles of the standard model have a partner particle. These partner particles were not found. This doesn’t rule out supersymmetry because the particles might only be produced at energies higher than what we have tested. But it does mean we have no evidence that supersymmetry is realized in nature.

Worse, if you make the standard model supersymmetric, the resulting theory conflicts with experiment. The reason is that doing so enables flavor changing neutral currents which have not been seen. This became clear in the mid 1990s, sufficiently long ago so that it’s now one of the “well known problems” that nobody ever mentions. To save both supersymmetry and superstrings, theorists postulated an additional symmetry, called “R-parity” that simply forbids the worrisome processes.

Another side-effect of superstrings is that they require additional dimensions of space, nine in total. Since we haven’t seen more than the usual three, the other six have to be rolled up or “compactified” as the terminology has it. There are many ways to do this compactification and that’s what eventually gives rise to the “landscape” of string theory: The vast number of different theories that supposedly all exist somewhere in the multiverse.

The problems don’t stop there. Superstring theory does contain gravity, yes, but not the normal type of gravity. It is gravity plus a large number of additional fields, the so-called moduli fields. These fields are potentially observable, but we haven’t seen them. Hence, if you want to continue believing in superstrings you have to prevent these fields from making trouble. There are ways to do that, and that adds a further layer of complexity.

Then there’s the issue with the cosmological constant. Superstring theory works best in a space-time with a cosmological constant that is negative, the so-called “Anti de Sitter spaces.” Unfortunately, we don’t live in such a space. For all we presently know the cosmological constant in our universe is positive. When astrophysicists measured the cosmological constant and found it to be positive, string theorists cooked up another fix for their theory to get the right sign. Even among string-theorists this fix isn’t popular, and in any case it’s yet another ad-hoc construction that must be added to make the theory work.

Finally, there is the question how much the requirement of mathematical consistency can possibly tell you about the real world to begin with. Even if superstring theory is a way to unify general relativity and quantum mechanics, it’s not the only way, and without experimental test we won’t know which one is the right way. Currently the best developed competing approach is asymptotically safe gravity, which requires neither supersymmetry nor extra dimensions.

Leaving aside the question whether superstring theory is the right way to combine the known fundamental forces, the approach may have other uses. The theory of strings has many mathematical ties with the quantum field theories of the standard model, and some think that the gauge-gravity correspondence may have applications in condensed matter physics. However, the dosage of string theory in these applications is homeopathic at best.

This is a quick overview. If you want more details, a good starting point is Joseph Conlon’s book “Why String Theory?” On a more general level, I hope you excuse if I mention that the question what makes a theory promising is the running theme of my upcoming book “Lost in Math.” In the book I go through the pros and cons of string theory and supersymmetry and the multiverse, and also discuss the relevance of arguments from mathematical consistency.

Thanks for an interesting question!

With best wishes for your future research,


Thursday, May 03, 2018

Book Review: “The Only Woman In the Room” by Eileen Pollack

The Only Woman in the Room: Why Science Is Still a Boys Club
By Eileen Pollack
Beacon Press (15 Sep 2015)

Eileen Pollack set out to become an astrophysicist but switched to a career in writing after completing her undergraduate degree. In “The Only Woman In The Room” she explores the difficulties she faced that eventually led her to abandon science as a profession.

Pollack’s book is mostly a memoir, and an oddly single-sided one in that. At least for the purpose of the book, she looks at everything from the perspective of gender stereotypes. It’s about the toys she didn’t get, and the teachers who didn’t let her skip a year, and the boys who didn’t like nerdy girls, and the professors who didn’t encourage her, and so on.

I had some difficulties making sense of the book. For one, Pollack is 20 years older than I and has grown up in a different country. In the book she assumes the reader understands the context, but frankly I have no idea whatsoever how American school education looked like in the 1960s. I also missed most of the geographic, religious, and cultural references but wasn’t interested enough to look up every instance.

Leaving aside that Pollack clearly writes for people like her to begin with, the rest of the story didn’t make much sense to me either. The reader learns in a few sentences that Pollack in her youth develops an eating disorder. She also seems to have an anxiety disorder, is told (probably erroneously) that she has too high testosterone levels, and that later she regularly sees a therapist. But these asides never reappear in her narrative. Since it’s exceedingly unlikely her problems just disintegrated, there must have been a lot going on which the reader is not told about.

The story of the book is that Pollack sets out to track down her former teachers, professors, and classmates, and hear what they’ve been up to and what, if anything, changed about the situation for women in physics. Things did change, it turns out: The fraction of female students and faculty has markedly increased and many men have come to see the good in that. Pollack concludes with a somewhat scattered list of suggestions for further improvement.

Pollack does mention some studies on gender disparities, but her sample seems skewed to confirm her beliefs and she does not discuss the literature in any depth. She entirely avoids the more controversial questions, like whether some gender differences in performance are innate, whether it’s reasonable to assume women and men should be equally represented in all professions, or whether affirmative action is compatible with constitutional rights.

Despite this, the book has its uses. It sheds light on the existing problems, and (as Google will tell you) in reaction many women have spoken about and compared their experiences. For me, the value of the book has been to let me see my discipline through somebody else’s eyes.

I found it surprising just how different Pollack’s story is from my own, though my interests seem to be very close to hers. I’ve been told from as early as I can recall that I’m not social enough, that I don’t play with the other kids enough, that I’m too quiet, don’t integrate well, am bad at group work, and “will never make it at the university” unless I “learn to work with others.” I am also the kind of person who doesn’t give a shit what other people think I should do, so I went and got a PhD in physics.

The problem that Pollack blames most for her dropping out – that professors didn’t encourage her to pull through courses she had a hard time with – is a problem I never encountered because I didn’t get bad marks to begin with. I didn’t have friends among the students either, but I was just glad they left me alone. And where I am from, university is tuition-free, so while my money was short, financing my education was never a headache for my family.

Like Pollack, I have a long string of DSM classifiers attached to me and spent several years in therapy, but it never occurred to me to blame my profs for that. When doctors checked my testosterone levels (which has happened several times over the decades) I didn’t conclude I must be a man, but that it’s probably a standard check for certain health problems. And since now you wonder, my hormone levels are perfectly normal. Or at least that’s what I thought until I read that Pollock had a crush on pretty much every one of her profs. Maybe I’m abnormal in that I never fancied my profs. Or that I never worried I might not find a guy if I study physics.

Nevertheless, Pollack is right of course that we have a long way to go. Gender disparities which reinforce stereotypes are still omnipresent, and now that I am mother of two daughters I don’t have to look far to see the problems. The kids’ teachers are all women except for the math teacher. The parents who watch their toddlers at the playground are almost exclusively mothers. And I get constantly told I am supposedly aggressive, sometimes for doing nothing more than looking the way I normally look, that is, mildly dismayed at the bullshit men throw at me. But I’m not quite old enough to write a memoir, so let me leave it at this.

I’d recommend this book for anyone who wants to understand why some women perceive science and engineering as extremely unwelcoming workplaces.

Monday, April 30, 2018

Me, Elsewhere

  • I spoke with Iulia Georgescu, who writes for the Nature Physics blog, about my upcoming book “Lost in Math.
  • The German version of the book now also has an Amazon page. It sells me as “Ketzer,” meaning “heretic.” Well, I guess I indeed make some blasphemous remarks about other people’s beliefs.
  • Chris Lee has reviewed my book for Ars Technica. He bemoans it’s lacking dramatic turns of plot. Let me just say it’s really hard to be surprising if your editor puts the storyline in the subtitle.
  • It seems there will be an audio version after all. Will let you know if details emerge.
  • When I was in New York last year, the Brockmans placed me in front of a camera with the task to speak about what has been on my mind recently, just that I shouldn’t mention my book, which of course has been the only thing on my mind recently. I did my best.

Wednesday, April 25, 2018

A black hole merger... merger... merger

For my 40th birthday I got a special gift: 2.5 σ evidence for quantum gravity. It came courtesy of Niayesh Afshordi, Professor of astrophysics at Perimeter Institute, and in contrast to what you might think he didn’t get the 2.5 σ on Ebay. No, he got it from a LIGO-data analysis, results of which he presented at the 2016 conference on “Experimental Search for Quantum Gravity.”

Frankly I expected the 2.5 σ gift to quickly join the list of forgotten anomalies. But so far it has persisted, and it seems about time I unwrap this for you.

Evidence for quantum gravity is hard to come by because quantum fluctuations of space-time are so damn tiny you can’t measure them. To overcome this impasse, Afshordi and his collaborators looked at a case where the effects of quantum gravity can become large: Gravitational waves produced by black hole mergers.

Their idea is that General Relativity may not correctly describe black hole horizons. In General Relativity, the horizon bounds a region that, once entered, cannot be left again. The horizon itself has no substance and indeed you would not notice crossing it. But quantum effects may change the situation.

Afshordi and his group therefore studied that quantum effects turn the horizon into a physical obstacle that partly reflects gravitational waves. If that was so, the gravitational waves produced in a black hole merger would bounce back and forth between the horizon and the black hole’s photon sphere (a potential barrier at about 1.5 times the Schwarzschild radius). This means the waves would slowly leak out in each iteration rather than escape in one bang. If that’s what’s really going on, gravitational wave interferometers like LIGO should detect echoes of the original merger signal.

2.5 σ means that roughly one-in-a-hundred times random fluctuations conspire to look like the observed echo. It’s not a great level of significance, at least not by physics standards. But it’s still 2.5σ better than nothing.

Afshordi’s group extracted the echo signal from the LIGO data with their own analysis methods. Some members of the LIGO collaboration criticized this method and did their own analysis, concluding that the significance is somewhat lower. Afshordi’s group promptly complained the LIGO people make misleading statements and the results are actually consistent. You see they’re having fun.

Bottomline is there’s some quarrel about exactly what the level of significance is, and exactly what’s the right way to analyze the data, but the results of both groups are by and large comparable. Something is there, but at this point we cannot be sure it’s a real signal.

I will admit that as a theorist, I am not enthusiastic about black hole echoes because there are no compelling mathematical reasons to expect them. We know that quantum gravitational effects become important towards the center of the black hole. But that’s hidden deep inside the horizon and the gravitational waves we detect are not sensitive to this. That quantum gravitational effects are also relevant at the horizon is speculative and pure conjecture, and yet that’s what it takes to have black hole echoes.

But theoretical misgivings aside, we have never tested the properties of black hole horizons before, and on unexplored territory all stones should be turned. Indeed the LIGO collaboration has now included the search for echoes into their agenda.

There is even another group, this one in Toronto, which has done their own scan of the LIGO data. They found echoes at 3 σ. The Toronto group’s analysis has the benefit of being largely model-independent. But they advocate the use of periodic window-functions which induce spurious periodic signals. The authors show that in certain frequency regimes the side-effect of the windowing can be neglected and that in simulations they were able to extract the actual signal. But I suspect it will take more than this to convince anyone that imposing a periodic signal on data is a good way to look for a periodic signal.

Afshordi and his collaborators meanwhile have put out another paper, claiming that indeed the evidence is as high as 4.2 σ. That’s a pretty high significance, inching close to an actual discovery. I am, however, not convinced by their latest study. The reason is that the more they doctor on their model, the better they will get at finding specific types of echo in the noise. To correctly evaluate the significance they’d then have to take into account the number of different models which they tried. Without doing that, the significance is bound to increase simply because they’ve tested more hypotheses.

So I’d advise you to not read too much into the 4.2 σ. On the other hand, the LIGO people probably tried very hard to make the signal go away but didn’t manage to. Therefore I think at this point we can be confident there is something in the data. But to find out whether it’s more than just funny-looking random fluctuations, we will have to wait for more black hole mergers.

[I wrote about black hole echoes previously for Aeon and more recently for Quanta Magazine, and the story will probably come back a few times more.]

Monday, April 23, 2018


I am giving (another) seminar in Heidelberg on Wednesday (April 25th), this time about my upcoming book.

May 1st is a national holiday in Germany (labor day) and I’ll be off-grid due to family affairs for some days.

May 7th to 9th I am in Stockholm to get yelled at (it’s complicated).

On May 26th I am in Hay-on-Wye which is a village someplace UK that hosts an event called How The Light Gets In at which I am supposed to debate how “the pursuit of beauty drive[s] the evils that hold back a better society.” I wouldn’t go as far as calling grand unification an evil, so please don’t judge me by the tagline.

I have also been asked to share this image below. Hope it makes more sense to you than to me.

On May 28th I am giving a public lecture in Dublin at the Irish Quantum Foundations conference.

In summary this means May will be a very slow month on this blog.

Wednesday, April 18, 2018

Guest Post: Brian Keating about his book “Losing the Nobel Prize"

My editor always said “Don’t read reviews”... But given that I’ve received some pretty amazing reviews lately, how bad could it be? Nature even made a delightfully whimsical custom-illustration of my conjecture: that some of my fellow astronomers look to the skies for the Nobel Prize:

Illustration by Stephan Schmitz for Nature.

When I saw Sabine had finally gotten round to reading my book, I was thrilled! This is sure to be an awesome review from a fellow-traveller: a first-time author herself.

Gulp. After reading Sabine’s blog, I immediately regretted not taking my editor’s advice. But, Sabine was kind enough to offer me a chance to reply to her review (a review of a review?) so here goes.

First off, speaking of not reading things, the cover of the version I sent to Sabine explicitly says “don’t quote without checking against the final version” (See the white cover version in the upper left hand corner of this photograph on Medium).

Unfortunately, Sabine never read the finished version. In fact, the few times I asked her about her progress reading the “ADVANCE UNCORRECTED” review copy’ book sent to her in August, she only replied “I’ve not started it”. Fair enough, she was writing her own book about things being Lost. And she did pass it on to a German publisher on my behalf, which was terribly kind of her.

But the version Sabine read was not even proof-read, nor copyedited, nor fact-checked. Right on the cover it implores the reader to “not quote for publication without checking against the finished book”. This is something she, as an author, probably should have realized before writing her review. I’ve reviewed multiple books for fellow physicists long before writing my own -- as has she -- and always make sure to cross-check against the final version(s) [plural because often I’ve read and listened to the audio book before writing my review].

[[SH: I quoted a single sentence, and I assume that sentence is still in the book because otherwise hed have rubbed it in by now.]]

But, what about the substance of her review? Well, much of what’s inaccurate about it stems from unwarranted or incorrect assumptions. For example, she complains that I did not inquire as to what “Swedish Royal Academy has to say about the reformation plans”.

First of all, I’m not sure how she could possibly know with whom I’ve been in communication with...she’s not Zuckerberg!

[[SH: I guessed that much from my exchange with him, and reading the book confirmed it because if he had been in touch with them he’d have mentioned it.]]

Secondly, not only did I seek (and receive permissions from the Swedish Academy), I corresponded with a member of the Swedish Academy...and they agreed with my proposal:

“Thanks for sending me your interesting piece in the Scientific American. Although I, for obvious reasons, cannot comment on any details concerning the Nobel prize, I can assure you that all the points that were rised [sic] in your article are actively discussed in the Committee and the Academy, and have been so for a long time. We are acutely aware of both challenges and difficulties related to revising the self-imposed rules for how the prize is awarded. We also very much welcome debate about these issues, so I thank you for caring about the future of the Nobel prize, and I will forward you article to the other members of the committee.

How’s that for seeing what “they have to say”?

[[SH: I was the one who got Brian in contact with the above quoted member of the Swedish Academy after it became clear to me that Brian had not bothered communicating them.]]

Some of this appears in the final book version.

[[SH: I am so happy I could be of help.]]

And all of this I would have been happy to share with Sabine...had she asked. I was gratified to see that my concerns were shared by them and that they had not, as Sabine asserted, ignored my ideas: “I’d be surprised if the Royal Academy even bothers responding to Keating’s book.”

I agree with her: I’m not convinced anything will come of it...until the day the Nobel Prize in physics is boycotted or sued. And I think that day is coming.

Why? It relates to two objections Sabine raised early in her review:

“I have found Keating’s book outright perplexing. To begin with let us note that the Nobel Prize is not a global community award. It’s given out by a Swedish committee tasked with executing the will of a very dead man.”

It really not that perplexing, Sabine. The Nobel Prize is a global event, not just a simple Swedish smorgasbord. The prize for peace, for example, is for world peace, not merely to implore Norsemen to stop making war with their many conniving enemies, right?

Fact: According the Nobel Foundation, 100 million people tune into the festivities each year...ten times the population of Sweden and about 10% of the audience the Oscars receive. Winners become celebrities and the Nobel Committees revel in the fame and adoration the events receive.

Why, they’re even moving into a brand, spanking new $150M building in Stockholm next year, designed by a fancy architecture firm, for all their many festivities (the old venue is too small apparently).

The winners are disproportionately non-Scandinavian and the prize aims to reward those who have benefitted “all mankind”, not just Swedes. In fact, the prize for literature is currently undergoing a bonafide sex scandal:

“STOCKHOLM — A sexual abuse and harassment scandal roiling the committee that awards the Nobel Prize in Literature deepened on Wednesday, as the king of Sweden and the foundation that finances the prize warned that the scandal risked tarnishing one of the world’s most important cultural accolades.” [emphasis mine]

The Nobel Prize leaders and the King recognize the power of the prize. It is not only science’s greatest accolade, it’s the greatest one humanity has to offer as well. As such it should be held to a higher standard.

With respect to the many comments others have made about me having sour grapes, no one who reads the book could come away thinking I actually still want to win it. Of course, after reading Sabine’s review, many have cancelled their orders so they may never learn!

But even that notwithstanding, I’m often criticized for writing about it without having won the Nobel. I find that a bit silly. Can one not criticize Harvey Weinstein without being an member of the Academy? Can one not criticize President Trump if one has not been president?

As to this snarky bit: “Keating apparently thinks he knows better what Alfred Nobel wanted than Alfred Nobel himself. Maybe he does. I don’t know, my contacts in the afterworld have not responded to requests for comments.”

I resonate with Sabine’s admission that she has no direct lines to the afterworld; neither do I. And that’s the exact purpose of a will, isn’t it? “A last will and testament is a legal document that communicates a person's final wishes pertaining to possessions and dependents

Alfred died without any children or spouse...his will specified what was to be done with the money he made from the (world wide) patent on dynamite. After providing some kroner for his friends, and his nephews and nieces (the nieces got only ½ of what his nephews received...perhaps an early source of the prize’s legendary sexism?), he left money for the titular prizes. Reading the will, we learn:

“The whole of my remaining realizable estate shall be dealt with in the following way: the capital, ...shall be annually distributed in the form of prizes to those who, during the preceding year, shall have conferred the greatest benefit to mankind. ... one part to the person who shall have made the most important discovery or invention within the field of physics…”

One sees three conditions for awarding the prize:

1. The person [in the singular]
2. Who in the Preceding year
3. Conferred “the greatest benefit to mankind”

I don’t need to have clairvoyance into the netherworld because Alfred did it for me. It is abundantly clear what he wanted and all three of these rules are routinely ignored and have been for over a century.

As for the power of the prize to affect the judgement and career choices of scientists, let me just say it affects non-astronomers too: "With physicist Peter Mansfield, Lauterbur in 2003 bested Damadian to Nobel recognition of magnetic resonance imaging (MRI). This outcome prompted the appearance of full-page ads financed by the Friends of Raymond Damadian in a number of newspapers, including The New York Times.” [emphasis mine].

Wherever there is an idol, people will bow down to it, the Nobel is no baal [Warning: another Old Testament reference], but it is no exception either.

As for the pro-experimental bias of my book “Keating for example suggests that the Nobel Prize only be given to “serendipitous discoveries,” by which he means if a theorist predicted it then it’s not worthy.” Sabine, how could you miss the lovely pie chart I made for you and your fellow brainiacs as well as the accompanying text: “A serendipity criterion would mean Nobel Prizes would go to the theorist(s) who predict new phenomena, though they should win only after experimental verification.”

[[SH: He also explains that if a theorist predicted it, then the experimental verification wasn’t serendipitous, so what gives? And yeah, I was about to make a joke about that pie chart but then felt sorry for the graphics designer who probably just did what Brian asked for.]]

In the book I am advocating that more theorists should win it, and experimentalists should not win it if they/we merely confirm a theory...that leaves them/us susceptible to confirmation bias. For reference, this was in the copy Sabine read.

Alas, time is fleeting and the launch of my book is few short days away, so I must take leave of back reacting.

But I am thankful that Sabine has permitted me this chance to address some of her concerns. And I am grateful for the many kind words she did employ in her review. I enjoy your work and I wish you best of luck with your book...may you never read a review you have to react to!