Now back from traveling, regular blogging will resume. Here are a few items:
- I was going to write something yesterday, explaining that this year’s physics Nobel would surely go to the LIGO trio who have gotten every other major physics prize this year. Luckily I was too lazy to do that yesterday, since this morning’s news is that it instead went to Haldane, Kosterlitz and Thouless, work going way back to the early 1970s. When I was doing my thesis work trying to figure out how to find a lattice version of topological invariants of gauge fields, I started out looking at the case of the 2d XY model which they had studied, where the topology is much simpler.
Congratulations to them, probably next year for the LIGO guys…
- My colleague Daniel Litt has started up a really nice blog.
- Some sort of time warp back to the days of pre-LHC hype of the last decade seems to have occurred while I was in Germany, leading to lots of media stories like this one.
- In Heidelberg among the people I met were Dirk Huylebrouck, who reminded me that there’s lots of great material in the Mathematical Intelligencer, including his “Mathematical Tourist” column, and Barry Cipra, one of the authors of the AMS’s What’s Happening series.
- John Baez is involved with a new project, funded by DARPA, that he describes here.
- Last week there was a conference in Madrid devoted to the question Is SUSY Alive and Well?. Of the talks I looked at, the only one with a sensible answer to the question was that of Alessandro Strumia.
Update: A commenter points to this very interesting survey of the participants.
- In case you haven’t heard what’s going on in Leicester, Tim Gowers explains here.
- I was very sorry to hear of the passing last Saturday of Joseph Birman, a theorist at CCNY, and husband of my colleague Joan Birman. Some information about one aspect of Joe’s work is here, perhaps more about other aspects will appear soon.
The Leicester story gets a sad ironical twist with this year’s Nobel prize going to three Brits who left the country during the Thatcher madness. Doesn’t seem they have learned anything. To make matters worse, the “good citizenship” requirement nowadays includes spying on your students to spot potential “terrorists”. A colleague of mine grew up in the GDR and finds these practices eerily familiar.
The survey results from that conference are interesting
Thanks, very interesting. I’ve added a link to that to the posting. Interesting to see that even among experts on SUSY still working on it, “alive and well” is the opinion of less than 30%.
There may actually be some wisdom in giving the LIGO discovery another year to mature. Not least because that gives a clear opportunity for another clear event or more to be identified.
The first event GW150914 is always associated with that slight niggle because it was almost immediately seen on switch on, nothing so clear since, and no corroboration from any other observation type. The subsequent GW151226 event is so buried in the noise that a skeptic may believe that reverse engineering the result cannot be entirely ruled out. And again no corroborating gamma ray burst or the like. Yes I realise that some very sound statistics have been employed, but in the end we still have only two events.
The room for doubt may be tiny, but hopefully this time next year it will be non-existent.
“Alive and Well” is the opinion of less than 30%, but on the other hand, “Alive” in some form is the opinion of over 85% of those surveyed. A survey question not asked, to which I would have liked to see the results, is “Under what circumstances would you be likely to consider SUSY dead?” with options for not seeing any evidence from various runs of the LHC or other future events.
I wonder how many would pick “I will never agree that SUSY is dead”?
And again no corroborating gamma ray burst or the like.
If these are black hole collisions happening hundreds millions of LY away, one might suppose that there would never be anything to put on a photographic plate (these are blacks holes, after all). On the other hand… Modeling the afterglow of the possible Fermi-GBM event associated with GW150914
More information about the survey included many comments here
What’s this “suppressed SUSY” business?
Well, curiouser and curiouser. If you Google “suppressed SUSY” you hit a ton of papers by a John Dixon. If you check these papers, the recent ones have no affiliation listed for him. Go back a bit, and the affiliation is a law firm. Back further, and he was at Texas A&M. Anyone care to explain?
In the comments from that survey, it appears to be the most-cited reason to continue to expect natural SUSY. Or, at least, the notion of “suppressed SUSY” is deemed to be both sufficiently promising, despite being poorly understood, to not dismiss the notion of SUSY being a viable solution to the hierarchy problem. From what little I can understand, “suppressed SUSY” seems to provide a “natural” explanation for why sparticles have not been, will not be seen by the LHC. It also seems qualitatively different than other ideas (e.g. sparticles “hiding in plain sight” because the masses of the LSP and the next-to-LSP are nearly equal) explaining away the non-appearance of SUSY.
Lacking the needed expertise/IQ/what-have-you, I’m unable to determine if my limited understanding is correct. I’m also unable to determine how desperate a measure”suppression” is to rescue “naturalness”, compared to the others in the SUSY field.
The problem with those comments is that you don’t know whether they reflect anything other than the views of one particular participant. In this case, John Dixon is listed as a participant at this conference, and the comments about “suppressed SUSY” may just be his enthusiasm for his own idea.
Got it. Didn’t factor in such a powerful, uh, selection bias. Rather, figured those comments might reflect a broader sample.
Speaking of “Alive and Well” can anybody confirm whether the LIGO “trio” (Rainer Weiss (age 84), Kip Thorne (76) , Ronald Drever (85) ) need to survive until the end of nominations in January or if they have to still be alive next October at the time of the award of the Nobel?
I am the John Dixon of whom you are speaking, in relation to Suppressed Susy, and the recent Madrid conference on `Is SUSY alive and well’. A friend pointed out these remarks to me. This is a test to see if this gets online. If it does, then I will probably make a short reply to your remarks about the conference, and also about my own work.
Well OK then. I tend to agree with Peter Woit, that the talk of Alessandro Strumia, which gave a short answer NO to the question `Is SUSY alive and well?’ made some valid points. Alessandro did get a lot of flack for that answer at the conference. But SUSY is certainly in trouble, using the usual ideas, in my opinion.
The purpose of a conference of course is to create a venue where people can exchange ideas. The Madrid conference did that, and I enjoyed it.
The problem for SUSY, at present, is that the popular view at the conference was that SUSY can get spontaneously broken in an invisible sector, which is then manifested in the visible sector (our world) by some unknown messenger sector. The trouble is that this is supposed to give rise to some hundred and fifty new undetermined parameters.
Much of the conference was a discussion of these parameters, and how the present experiments constrict the huge space that these occupy. It does not look very good for the theory in my opinion. Also I do not think that the theory makes much sense anyway. It is rather like the Emperor’s new clothes as things stand–you can’t see the invisible sector, and that is where everything important is supposed to happen.
It is true that I do not presently hold an academic position. Recently I was at Oxford for six months or so as a visitor. My recent papers have been published however by a reputable refereed journal, Physics Letters B. It is also true that these are not yet widely known or cited. They are very new and the ideas are new too. However, this does not mean that they are necessarily wrong or crackpot. I went to the conference and also the SUSY 2016 conference in Australia in July, to discuss these ideas with colleagues. I did give a talk at SUSY 2016. People at the conferences seem somewhat interested, but as the comments above note, the thing is complicated, and I expect progress to be slow.
Suppressed SUSY is an idea that amounts to a way of splitting SUSY masses without spontaneous breaking of SUSY. The next step is to calculate the one-loop corrections.
So I do not know yet how successful it will be. It depends on the Master Equation for the BRST formulation of SUSY, as explained in the papers.
Other papers are in preparation.
I believe, but someone correct me if I’m wrong, that you have to be alive when the prize is awarded. You don’t have to make it to the presentation ceremony.
More precisely, the Nobel committee must think that you are alive when the prize is awarded. On 3 October 2011, the laureates for the Nobel Prize in Physiology or Medicine were announced; however, the committee was not aware that one of the laureates, Ralph M. Steinman, had died three days earlier. The committee was debating about Steinman’s prize, since the rule is that the prize is not awarded posthumously. The committee later decided that as the decision to award Steinman the prize “was made in good faith”, it would remain unchanged. [Wikipedia]
***I tried to post this earlier but it didn’t show up, possibly due to the spam filter, so I am trying again. I mean no annoyance if it did not show up due to being considered off topic. I would like to see some discussion of this issue somewhere though.***
>MikeS: “Yes I realise that some very sound statistics have been employed”
I’m not so sure the headline stats (that really small p-value) were interpreted correctly:
“We present the analysis of 16 days of coincident observations between the two LIGO detectors from September 12 to October 20, 2015.
The significance of a candidate event is determined by the search background—the rate at which detector noise produces events with a detection-statistic value equal to or higher than the candidate event. Estimating this background is challenging for two reasons: the detector noise is nonstationary and non-Gaussian, so its properties must be empirically determined; and it is not possible to shield the detector from gravitational waves to directly measure a signal-free background. The specific procedure used to estimate the background is slightly different for the two searches, but both use a time-shift technique: the time stamps of one detector’s data are artificially shifted by an offset that is large compared to the intersite propagation time, and a new set of events is produced based on this time-shifted data set. For instrumental noise that is uncorrelated between detectors this is an effective way to estimate the background.”
“Even though the routine data quality checks did not indicate any problems with the data, in-depth checks of potential noise sources were performed around the time of GW150914…No data quality vetoes were active within an hour of the event.
Following the event, the detectors were maintained in the same configuration to ensure that detector changes would not cause unanticipated consequences which might bias the background estimation for the event.”
So the hypothesis being tested is that their model of background noise accurately describes what the detectors were sensing at the time of GW150914. Also, note the model of background noise is based on data collected primarily after the detection. However, members of the LIGO team have described that this was not the case, the processing pipeline was changed in response to GW150914:
“At 11:23:20 UTC, an analyst follow-up determined which auxiliary channels were associated with iDQ’s decision. It became clear that these were un-calibrated versions of h(t) which had not been flagged as “unsafe” and were only added to the set of available low latency channels after the start of ER8. Based on the safety of the channels, the Data Quality Veto label was removed within 2.5 hours and analyses proceeded after restarting by hand.”
So that statistical test doesn’t mean much to me, the hypothesis it tested was rendered false by altering the configuration. That numerical relativity simulations could easily reproduce the signal is far more convincing than their statistical argument.
This comment is off-topic for this post, but it’s the easiest way to bring it to your kind attention:
I just, for the first time, came across a blog by Sabine Hossenfelder called “backreaction”, and there is a post there on “Demystifying Spin-1/2”
I didn’t think the discussion there demystified spin-1/2 particles at all. Hossenfelder first wrote that spin-1/2 particles are “…particles that have to be rotated twice to return to the same initial state.” She then made a statement I readily agreed with: “I don’t know if anybody who didn’t know the math already has ever been able to make sense of this explanation – certainly not me when I was a teenager.”
But then, instead of “demystifying” anything, she merely doubles down on the idea of “particles that have to be rotated twice to return to the same initial state”, by introducing how rotations (or, more generally symmetry transformations) act upon quantum states. She writes, “A symmetry transformation acting on a quantum state must be described by a unitary transformation …. And the full set of all symmetry transformations must be described by a ‘unitary representation’ of the group.” Then, “Symmetry groups, however, can be difficult to handle, and so physicists prefer to instead work with the algebra associated to the group. The algebra can be used to build up the group…. But here’s where things get interesting: If you use the algebra of the rotation group to describe how particles transform, you don’t get back merely the rotation group. Instead you get what’s called a ‘double cover’ of the rotation group. It means – guess! – you have to turn the state around twice to get back to the initial state.” So she’s gotten back to that original definition of a spin-1/2 particle. But in my view, she hasn’t “demystified” spin-1/2 particles, she has merely given a quick summary of why mathematical physicists define them that way (in other words, it’s just the mathematics used, not the physics). For anyone interested in what spin-1/2 particles are physically, surely it is simpler to say they are particles that are always (can only be) observed to have either “spin up” or “spin down” along any given axis. That doesn’t really explain what “(quantum) spin” is either, physically, but it captures the observable reality where “double cover of the rotation group” does not.
Why didn’t Hossenfelder give the traditional definition I just gave, and why did she call her post “demystifying spin-1/2”, when she did not do that at all? I would like to see a post by you on this, to see where you and your readers stand on it.
Harry Dale Huffman,
That is highly off-topic, and I don’t want to have a discussion of it here, not because it’s not interesting, but because it’s too interesting, and deserves something more serious. I did look at that blog posting, and it struck me as running into the standard problem such discussions always run into: you can get from knowing how SO(3) rotations act on vectors (which is what we have lots of intuition about) to all sorts of interesting things, but you can’t get the spin 1/2 representation this way. In particular, you can motivate the fact that \pi_1(SO(3))=Z_2, but this isn’t enough to tell you about the spinor representation.
I think this is an example of something I disagree with lots of physicists about. Yes, if you really understand something you should be able to explain it to your grandmother, but in cases like this you’re just going to confuse her (or mislead her into thinking she understands something she doesn’t) if you try and explain things in terms of her intuitions about rotating objects in 3-space. Granny is going to need to sit still and pay attention for quite a while, as you first explain to her some new ideas she has no intuition for. One of various ways of going about this is to start by telling her about complex numbers and show how you can use them to study rotations in the plane, then introduce quaternions and show how to think of rotations in terms of them. At that point you have the spinor representation, not just the vector representation (for the details of what I’m talking about, see chapter 6 of http://www.math.columbia.edu/~woit/QM/qmbook.pdf ).