# Chasing Einstein

Last night I went to a showing of Chasing Einstein, a new documentary about the search for dark matter. It’s quite well done, and if you’re near New York, Berkeley or LA, you might want to take the opportunity to go see it in a theater.

The film starts out with a segment on LIGO, talking to Barry Barish and Rainer Weiss. Later on there are scenes from their Nobel celebration ceremony at Caltech and the award ceremony in Stockholm. There are no claims made that LIGO’s results are related to dark matter. Rather, this material functions as a counterpoint to the dark matter material, contrasting a great success story to the rather frustrating lack of success that physicists have had with dark matter.

Attention then turns to Elena Aprile and the Xenon1T experiment. Aprile is in the physics department at Columbia, and attended the screening I was at. I think she’s the great heroine of this film, although a bit of a tragic one. She and her collaborators have done a fantastic job of getting a series of highly sensitive detectors to work. If a WIMP particle responsible for dark matter had existed in the region advertised by many theories, they would have found it and followed the LIGO people to Stockholm. Instead they put a strong limit on the possible properties of such a conjectured particle. The film includes a heart-breaking scene when they unblind their data, quickly realizing that their years of effort haven’t been rewarded with the discovery that they had been hoping for. Aprile has a realistic take on the prospects for future experiments of this kind: they can be make somewhat more sensitive, but it’s hard to be optimistic that the remaining accessible parameter space contains a new particle.

Attention then turns to Erik Verlinde and his “Emergent Gravity” explanation for the dark matter phenomenon. I’ve never found the motivation for this compelling, so haven’t followed his work carefully. For someone who has, see Sabine Hossenfelder’s blog where she has written on the topic quite a few times (and has her own version of a model here). Grad student Margot Brouwer worked on this attempt to experimentally test Verlinde’s ideas, and she is also featured in the film. My understanding is that the positive results her group found are matched by other more negative results, see here.

Tech entrepreneur Cree Edwards appears at various points in the film, and I’m guessing that he’s the one who brought together the physicists and filmmakers to make the film (and probably financed it). He has an amateur’s interest in fundamental physics, and his questioning of the physicists reminds one of how people’s fascination with the subject is often deeply connected to their desire to make sense of the world, hoping to find explanations of the great puzzles of human existence. I fear he’s not likely to find much of what he’s looking for in physics, but glad to see that his questioning led to an excellent film.

Finally, the film contains scenes of observing a solar eclipse, an added attraction.

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### 15 Responses to Chasing Einstein

1. A_saint says:

I was hoping by reading this post I’d know how you thought about the film. This reminds me a bit about Dirac style of lecturing 😛 … Would you recommend others to watch it too?

2. Peter Woit says:

A_saint,
I enjoyed the film, and I hope that came out in the posting, but I’m always leery of telling others that they will too, so should definitely see a certain film. Tastes differ, and what I find charming others might find annoying. So, I try to give enough information about what’s in the film to let you make up your own mind.

In any case, right now the film has only a very limited theatrical release, so relatively few people are going to have it available nearby.

3. More Anonymous says:

1.Just re-read the whole post and found one sentence that does describe your views: “… but glad to see that his questioning led to an excellent film.”

2.Also about ” So, I try to give enough information about what’s in the film to let you make up your own mind.” Is there anything in the movie you have left out from the plot? Maybe add a spoiler in the title (if not)?

3. “… “Emergent Gravity” explanation for the dark matter phenomenon. I’ve never found the motivation for this compelling … ” I’m also curious what your view on the dark matter phenomenon is? Where should physicists be placing their bets?

4. Also chrome is showing me a red sign with “Not secure” in the URL place (for this site). And if I click on the learn more: https://support.google.com/chrome/answer/95617?visit_id=637042412030042076-2172091136&p=ui_security_indicator&rd=1

4. A_saint/More Anonymous says:

That was quick!
I just saw it go from:
Not secure to Info to Secure

Did you do anything on your end? I swear I’m not lying (and wasn’t when I made that comment) … Interestingly it didn’t remember my details despite the ”
Save my name, email, and website in this browser for the next time I comment.” in the comment box.

Also just noticed the username change in the 2nd post to More Anonymous must have accidentally done something .

5. Peter Woit says:

A_saint/More Anonymous,
Yes, I did just fix the https warning, it was doing that because of an http rather than https in one of the buttons on the right hand side. The change in the site may have temporarily disrupted the “save your name” feature.

There’s not really a plot to “spoil” for this film. The one moment of drama is the Xenon1T unblinding, but unless you’re unaware that that experiment hasn’t found dark matter, the outcome isn’t a surprise.

I don’t want to get into a general discussion about dark matter, it’s a huge, endlessly debated topic, and unfortunately there hasn’t been anything really new to say about it for quite a while (and I certainly have no new idea about it). My generic question about “emergent gravity” claims like those of Verlinde is “emergent from what?” Without a non-trivial answer to that question (and I don’t see that Verlinde has one), it seems unlikely you are going to get anything interesting. Not mentioned in the film is the all too possible frustrating scenario that dark matter is a new particle, but one that has no interactions other than gravitational, so can effectively never be directly seen in a feasible experiment. If I had to place a bet, it might be there.

6. GoletaBeach says:

Perhaps the movie presents Elena Aprile in a tragic light, but I’m not aware of anyone in the actual dark matter field who shares that view. Everyone knows when they start a search program that the most probable outcome (by a lot!) is no discovery.

There is a very weird and contrafactual attitude out there… typified by a Malcolm Browne article in 1993 that ran under the headline “315 Physicists Report Failure In Search for Supersymmetry”.

There was no failure. They (as LHC now, and Xenon-1T too) completely succeeded in doing exactly what they said they were going to do… achieve sensitivity to new physics within a certain parameter space. It is science… “Eliminate all other factors, and the one which remains must be the truth.” Just as Michelson and Morley did. It is a recurring cynical joke that theorists on modern review panels would have defunded Michelson and Morley.

Everyone in the dark matter field knows that there are at least 8 orders of magnitude more to go before SUSY explanations of dark matter are close to inconsistent with SUSY. Anyone who says otherwise is confused about what some call the “Canadian Border Effect”. Canadian population clusters around the southern border, it is the most desirable real estate. US population is sparse right there… for Americans, the northern border is not desirable.

A la mode SUSY dark matter theories always cluster just below the current experimental sensitivity for the same reason. For dark matter and for the LHC. Thinking “a la mode” is the only reason to build experiments is immature, although theorists want to be able to say “I predicted it!”, so they find models just over the limit. Only other theorists take that seriously.

Aprile got involved in liquid xenon detector technology when it was mainly going to be used for x-ray astronomy at Columbia. She wasn’t initially using the dual phase technique, invented in Russia. She had the insight to see and push for implementation of that technique with her liquid xenon ability to search for dark matter. She is not the only one, actually… Dolgoshien’s old group in Russia and groups in UK simultaneously began the push. Aprile’s group did get the first really good results out.

The technique has achieved 4-5 orders of magnitude in new sensitivity… imagine finding a technique that raised beam energy in proton-proton collisions by 4 to 5 orders of magnitude. And the liquid xenon can go a lot further; many groups are planning to continue… progress will be slowed (but not stopped entirely) when neutrino interactions start to show up.

The tragic element really is: both this blog (and Sabine Hossenfelder) portray vast improvements in experimental sensitivity without a transformational discovery as “failures”. It is a lack of understanding as to how real experimental work and discovery works… the top quark didn’t appear for 15-20 years post prediction, and its method of discovery was pretty much unheralded at its inception, for example. Real experimentation and experimental discovery entails quite a bit of persistence, and skepticism of all theorists.

Ruling things out has a huge value… Luis Alvarez answered this question in the 1960’s when the muon intensity experiment in the pyramid of Khafre found “no large unknown chambers exist”… the technique did map the big chamber where they set up the experiment. He was asked about his “failure”… he pointed out that the experiment was a complete success, and would prevent explorers and drillers from mounting expeditions to look for new chambers… of no small value. And now, the technique has been refined and found a new chamber in the pyramid of Khufu.

These portrayals of “tragedy” and “failure” mildly annoy many experimentalists… and further convince them that theorists and mathematicians don’t deeply comprehend what empirical science is. Sitting on a review panel with folks who don’t get it can be quite painful… another topic Luis Alvarez used to write about. It may be that forums like this blog (and Hossenfelder) are suppressing discovery.

A portion of what Hossenfelder lobbies for is experimental testing of alternate DM theories. That is good…

7. Peter Woit says:

Goleta Beach,
I’m afraid the posting does not make my point of view clear, but I’m not sure why. To quote myself above:
“I think she’s the great hero of this film, although a bit of a tragic one. She and her collaborators have done a fantastic job of getting a series of highly sensitive detectors to work. If a WIMP particle responsible for dark matter had existed in the region advertised by many theories, they would have found it and followed the LIGO people to Stockholm. Instead they put a strong limit on the possible properties of such a conjectured particle.”

The reference to “tragic” is to the portrayal in the film, where she is interviewed and gives a nuanced explanation of what it is like to work on an experiment like this.

I agree completely that the achievement of huge increases in sensitivity and investigation of large new areas of parameter space by Xenon1T and others is a huge experimental success (while still being, undeniably, a failure to find an hypothesized new particle state). Arguably, this sort of achievement, not just discoveries, should be rewarded by the Nobel.

Similarly, the LHC results ruling out large new regions where there could have been new particles is a huge experimental success, while at the same time being a failure to find SUSY states. When I refer to such a failure, what I’m referring to is a theoretical prediction being successfully disconfirmed by experiment, and the failure is on the theorist’s side, the success on the side of the experimentalists.

On the topic of where to expect SUSY states, my opinion has always been “nowhere”, since such states don’t explain anything, just make the SM more complicated. The regions heavily advertised for such states pre-LHC have now been ruled out, puncturing I hope the hype behind the whole subject. This doesn’t rule them out in other regions, and if experimentalists can investigate some of those regions they should, but I think the argument for doing this increasingly is because something unexpected might turn up, not because unconvincing models will get ruled out.

8. GoletaBeach says:

Thank you Peter. The 3 families (e,mu,tau) and/or (u/d,c/s,t/b) also just make the SM more complicated too… who ordered that? Actually, “Who Ordered That?” might be the complementary experimental blog (if it existed) to “Not Even Wrong”.

That the relative – sign between loops of symmetrical fermions & bosons in SUSY isn’t the worst motivation I’ve ever heard of.

The WIMP motivation always has been: we doubt the dark matter has explicit strong and electromagnetic interactions. We believe the dark matter (DM) has gravitational interactions. That leaves one interaction to probe… the weak interaction. Slight bias if the DM has a weak interaction then it should have rest mass in the W/Z/Higgs ballpark.

That idea also helps in one scenario of the early universe, if the DM was in thermal equilibrium with us.

Experimentally that defines a program. The first “natural” experimental sensitivity benchmark was passed in the 1980’s… if the (massive) DM had the couplings of a Dirac neutrino, it would have been discovered then. Experiments stopped for a while.

Gradually the idea that maybe the DM was not Dirac but Majorana seeped in, and the “natural” sensitivity plummeted to well below what we have lately achieved, because one needs to mediate through Higgs to top pairs to gluons, or through the Z0, and inevitably through interferences. Still no SUSY is needed. If anything SUSY makes *even tinier* cross sections *more* likely… also makes large cross sections more likely… just broadens everything.

Somehow Sabine Hossenfelder and Stacy McGaugh still write in the August 2018 Scientific American…
“But after three decades of failed attempts to detect any of these particles, ignoring alternative hypotheses is no longer reasonable.”

First, there were no “failed attempts”. Note they do not say “failed theories”. “Failed attempts” implies the experiments failed. Most of the experiments succeeded admirably.
(I do know that you, Peter, are not equal to Hossenfelder and McGaugh, and I appreciate that).

The second clause of their sentence is always reasonable. Keep thinking about everything. Keep suggesting experiments to test the ideas.

A bunch of earthbound experimental effort actually did go into testing MOND… but turns out the loophole is… MOND depends on *absolute* acceleration. Relative acceleration is empirically proven to show no MOND effect.

So although lab experiments possess a sensitivity level sufficient to test MOND, we can’t get them into the right reference frame without a rocket that gets out of the solar environment. To do that you are talking a billion $at least. But just writing this has made me wonder if far out in the Kuiper belt or beyond their might be a system of binary snowballs that Hubble could study to test MOND. A bit puzzling that Hossenfelder and McGaugh *ever* felt non-WIMP ideas were *ever* ignored. Nobody felt strongly the collapsing binary signal would be large enough for this generation of LIGO to see the chirp. Great that unexpectedly massive black holes turned out to exist, but “Who Ordered That?” What is the formation mechanism? Post LIGO, no lack of theories, will be the same if WIMPs are seen at a cross section of 10-52 cm^2. As for Nobels… only time will tell. Charpak’s chambers did not work at all at first. It took non-Charpak adopters to correct their deficiencies.. but Charpak got the Nobel Prize. Yes, Nobels get awarded in particle physics for innovation without direct responsibility for a new particle or force. The vast sensitivity improvement pioneered by Elena Aprile (and others) might yet get awarded a Nobel somehow. 9. shantanu says: GoletaBeach: Some comments on your post. we don’t have even a single shred of evidence from astrophysical observational that dark matter is a WIMP or has weak scale couplings. (The only argument is WIMP miracle, which is at best a numerical coincidence) Also the goal posts for WIMP direct dark matter detection have changed in the last decade. This is best exemplified in Figure 1 of https://arxiv.org/pdf/1703.02389.pdf 10. Ron Avitzur says: I saw the ads for the film and was going to skip it, then saw your review and walked downtown to see it. Gorgeous film, loved the scenery, and awesome giving the physicists so much screen time. So thanks for changing my mind! 11. GoletaBeach says: shantanu…. “we don’t have even a single shred of evidence from astrophysical observational that dark matter is a WIMP or has weak scale couplings. ” You are right… we don’t even have evidence that dark matter is a particle, or obeys our quantum mechanics or relativistic quantum field theory, or obeys any of our conservation laws. But we assume some of that to test hypotheses. Gotta start somewhere. That dark matter might have weak scale couplings is a conjecture, but has at least one very simple motivation you overlook: electromagnetic and strong couplings are very unlikely, gravitational couplings are likely (although could just be MOND or something like it), leaving the weak interaction as “the remaining one to check”. Sherlock Holmes logic: test the untested hypothesis. The WIMP miracle *may* be a coincidence, or not. You may feel that it is, but your feelings are not scientific evidence. The paper you refer to is nice but culls out the lower limits for cross sections, which for unconstrained SUSY models go down far below the bottom of those plots, down to at least 10-56 cm^2 or so. Not sure why the author forgot to mention that. That (eventually) popular models tend to lurk just under the current experimental sensitivity has been true ever since models and sensitivity got on to a plot. The popular models of any particular moment do not even close to comprising a “complete set” of pertinent models. For WIMPs there are always many models just below whatever the experimental sensitivity happens to be, and those models get popular when experiment gets there. But the knowledgeable know that those models are still lurking there right now, where experiment will be in 5 or 10 or 20 years. The WIMP situation may not fit in a simplistic Kuhn or Popper-esque notion of science. They didn’t describe real scientific discovery so that is no problem. In real scientific discovery, the majority of new particles… the electron, the proton, the alpha-particle, the neutron, the electron neutrino, the muon, the muon neutrino, the tau, the strange quark, and the bottom quark were unheralded by theorists and dominantly discovered by experimentalists. The photon, the gluon, the tau neutrino, the Z0 and W, the top quark, and the Higgs were predicted by theorists. The charm quark is about 50-50. So 10.5 particles for aphilosophical experimental exploration, 7.5 particles for textbook scientific philosophy. For fundamental symmetries: C is definitely a theorists prediction, while P violation is about 50-50 (observed early by Cox and the tau-theta puzzle, then fleshed out by Lee and Yang), CP violation pure experiment, CPT on the theory side. So for these kind of symmeteries… 2.5 theory/philosophy, 1.5 experiment/aphilosophy. Other symmetries… baryon number, lepton number… harder to say. Deep interplay throughout it all. 12. shantanu says: Goleta Beach The dark matter could be a non-thermal relic. It could be a massive graviton. It could be even be a SM particle (see the collection of papers on Macro dark matter). There is no evidence from any astrophysical observational to distinguish between these (and other such possibilities) and a WIMP (for which so much of investment has taken place) 13. GoletaBeach says: shantanu… you are right, the dark matter could be a non-thermal relic, which some WIMPs can be too, and there have long been experiments (ADMX, for example) among many others who have looked for non-thermal relics. WIMP hunts, if you fairly account for all the dark matter effort going on at accelerators, with QIS sensors, with AMS and Fermi in space, with other indirect techniques… constitute a small fraction of all dark matter search funds. MOND got innovative attention in the 2000’s but to really test it is in the billion-$ class now.

Whether the relative abundance of dark matter to our matter is astrophysical evidence that supports (to a certain extent) a weak interaction for dark matter is something you feel is a coincidence, but others feel is a bonafide observation.

Investment in experimental endeavor takes one input from perceived discovery likelihood, but there is another input which is innovation… innovation isn’t perfectly correlated with $. Experimentalists push to innovate all the time, and deep insights by folks like Aprile have led to huge advances in WIMP sensitivity per dollar. Other WIMP techniques have hit barriers and don’t advance much even with the substantial$ that have been granted to them.

14. Dan says:

I saw Chasing Einstein, mixed feeling about this movie, mostly of the motives of the gathering these physicist in Montana and Carmel by Cree. Didn’t get anything out of the Couch interview, and Carmel interview was uncomfortable to watch (poor Verlinde, just couldn’t say what he really was thinking it seemed). Wish they would have gone more into the theory that Verlinde was putting forth. Aprile I feel was edited in the wrong light.

To A_saint, do not see this film, it was lackluster, and to be honest, I got more out of reading comments from GoletaBeach, shantanu and Peter Woit.

15. Bernhard says:

Thanks for pointing to Sabine’s model, I didn’t know it. I spent some time reading it – what a really cool article. Beyond me how someone who writes the number of high quality (many single authored by her!) articles she did not get tenure yet. In any case, I think “yet” is the word here.