Catching UpPostcards from the Energy Frontier by Prof Jon Butterworth
I have been too distracted to write much lately. This is partly due to the demoralising backdrop of UK politics, and partly because I have been having fun with physics and related matters. This is a quick catch up on a few of the good things from that side. I will avoid the politics, not because it isn’t important but because I am sick of it and we all need a break sometimes.
A few weeks ago I went to a workshop organised by Michela Massimi, a philosopher of science in Edinburgh, on “Cross disciplinary perspectives on model-independent searches“. I used to subscribe to Richard Feynman’s view that “philosophy of science is as useful to scientists as ornithology is to birds”, but I have changed my mind. Some of it is much worse, as though an ornithologist were on TV telling everyone birds can’t really fly. But some of it is much better. (Also, I reckon ornithologists do some good for the bird population in some circumstances, even if the birds remain oblivious. But I digress.)
Everyone, even Feynman, has a “philosophy” at some level. Right now, in my field we need to re-examine ours. From the moment I began in particle physics, until 2012, we had a shopping list of questions to answer from the theory, and a well-defined set of ways to address them. To give a few highlights:
- The Standard Model was thought to contain three “generations” of matter (progressively heavier duplicates of the fundamental particles). In 1990 the LEP collider at CERN showed that to be true, by measuring the number of neutrinos.
- The Tevatron collider at Fermilab discovered the top quark in 1995, the final particle in the third generation.
- The flux of neutrinos from the Sun was much smaller than expected. The SuperKamiokande and SNO experiments showed that this was due to the neutrino having a non-zero mass – contrary to the expectation of the Standard Model, and requiring significant new elements to be added to the theory to accommodate it.
- The existence of a quantum field even in the lowest energy state of “empty” space was needed to allow the fundamental particles to have mass; the discovery of the Higgs boson at CERN in 2012 vindicated that prediction.
Done, done, solved, done, and much more. There is more to learn both about neutrinos and the Higgs boson, and there are many open questions remaining, but we are off the map for the first time in decades as far addressing them goes. You can make a shopping list, but it doesn’t tell you which shops to visit. For example, one of the open questions is the nature of Dark Matter. There’s a very extensive review of this here from two of my ATLAS colleagues; as you can see from that, there are many ways to address the question but no guarantees any of them will be definitive.
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This situation is exposing some major differences in philosophy amongst physicists, which could turn out to be very important in deciding what to do next. These discussions are happening amongst particle physicists everywhere, ranging from a formal process in Europe through blogs and the media to coffee rooms in practically every lab and university with a physics department.
I think part of the answer is to make our measurements and explorations as model-independent as possible, on the basis that (to borrow a phrase¹) “all models are wrong but some are useful”. This was the topic of Michela’s workshop. In fact much of my recent distraction has been down to a project conceived at a previous meeting she convened, exploiting “Standard Model” measurements to generically probe for new physics, rather than doing dedicated optimised searches for specific models. More here if you are interested.
Other distractions… ATLAS continues to produce lots of results, and here’s one I am especially pleased with because of its model-independent nature. It is also possible to make measurements at the same time as searching, see for example here. All of this is an important part of our voyage, especially when we have no clear map.
Finally, while the LHC is currently closed for renovation, the first ATLAS result from our full “Run 2” data set is out. Many more to come.
¹From statistician George Box, which I first came across in Tamsin Edward’s excellent blog.
Professor Jon Butterworth is a physics professor at University College London and a researcher on the ATLAS experiment at CERN involved with, amongst other things, the discovery of the Higgs Boson. He is the author of two popular science books Smashing Physics and A Map of the Invisible. Postcards From the Energy Frontier is the successor to Jon’s hugely successful blog for The Guardian, Life and Physics. He is @jonmbutterworth on Twitter.
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Thank you for this interesting post prof. Butterworth. I wish some good catch to you and all other physicists engaged in fishing deep through the roaring 10s TeV sea!
I guess computer scientists will be particularly helpful for such a model-independent programme to be successful.
I wonder if it won’t be useful too for high energy physics to try harder on building geometric models of spacetime.
Of course the large/universal/warped extra dimensions hypotheses have not been successful yet to give a hint of an answer to theoretical issues like the Higgs naturalness or the eletroweak-Planck scales hierarchy problems. Then it could be theoretical physicists addressed too difficult questions for too rough tools or have not selected yet the proper hypotheses for spacetime geometry (*).
As the currently measured parameters of the Standard Model point to a plausible scenario where its quantum vacuum is stable up to the Planck scale, it may be not so naive anymore to think the Higgs boson knows something about unification of gravity and quantum physics in some sense!
History shows us that building on the XIXth century discovery of Maxwell equations and the technological development of electricity and optics, Einstein and Minkowski could find an efficient spacetime model where the full spectrum of electromagnetic waves lives naturally and interact with classical matter. Then thanks to Riemannian geometry (*), Einstein, Friedmann, Eddington… have paved the way to make cosmology a science.
Now building on the XXth century discovery of quantum mechanics & general relativity and the spectacular progress in electronics and photonics, is it not time to address the geometrisation of the full Standard Model gauge bosons and of the lonely 125 GeV beast living in the quantum fields that fill “empty” space (or rather spacetime)? Not for the sake of mathematical beauty or building a theory of everything but for the sake of high energy physicists to motivate with more confidence the building of the next colliders/detectors. To address in the most efficient way flavour physics (established neutrinos oscillations & purported flavour anomalies) and rejuvenate synergies with cosmological observations (dark matter/dark energy parameters of the concordance model & possible inflation/big bounce models) for instance…?
* Riemann’s philosophy in his own words: “We are therefore quite at liberty to suppose that the metric relations of space in the infinitely small do not conform to the hypotheses of geometry; and we ought in fact to suppose it, if we can thereby obtain a simpler explanation of phenomena.” (https://www.maths.tcd.ie/pub/HistMath/People/Riemann/Geom/WKCGeom.html)