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Is supersymmetry dead?

[“What’s changed in the last ~50 years” series]

As noted elsewhere, this blog is sort of a personal journey, a way to explore topics in physics, and milestones and achievements in the field. Advances in quantum physics. Open areas of research. Unresolved questions. And, in particular, the theme of what’s changed in the last ~50 years (and what’s not).

So, this recent online debate about the state of particle physics caught my attention. Not so much as to the future of colliders (quantum microscopes) per se, but regarding the ~50 year saga of supersymmetry. A retrospective.


• YouTube > The Institute of Art and Ideas > “The crisis of particle physics | Sabine Hossenfelder, John Ellis & Jim Baggott” (excerpt – see [1]) (Dec 22, 2020)

In pondering the mystery of reality, is supersymmetry dead?

YouTube description:

At the heart of our understanding of reality is physics, the cornerstone of science. But it appears to be in all sorts of trouble. For decades it has been predicted that we would find ‘supersymmetry‘ – a set of parallel particles for all those we currently understand to exist. It was the solution to many inconsistencies and deep puzzles in our current theory. 10,000 scientists collaborated to build The Large Hadron Collider to find the evidence. But year has followed year and no evidence of the predicted supersymmetric particles has been found. Is supersymmetry dead, and with it string theory, the theory of everything, and the life’s work of many leading particle physicists? Is our underlying theory, the Standard Model, fundamentally mistaken? Must we conclude that the whole framework of contemporary physics might be wrong? And if so, where can we turn for an alternative?

[From transcript]

[Ellis] … the issue is rather that the Standard Model leaves open a whole bunch of extremely important questions … the Standard Model is not mistaken. it has open questions, and for me that doesn’t mean to say that physics is in trouble. it means that there’s a fantastic opportunity. i would also take issue a little bit with you saying that the LHC was constructed to find supersymmetry – it was constructed to do many things …

my interest has always been in practical aspects of supersymmetry [as a tool to crack the mystery of reality], and that’s actually one reason why i don’t pay so much attention these days to strings. back in the 1980s i worked a bit on string theory and string model building, but i basically gave up on that because it seemed to be very difficult to make contact with reality.

[Baggott] … as a result of the hype surrounding supersymmetry and string theory for something like the last 30 or 40 years, there’s now a great confusion, i think, amongst the general public of the status of these theories.

[Hossenfelder] yeah, so i think i would like to directly answer your question: is super symmetry dead? the answer is: no. you could say it’s undead. you can’t kill it, and that’s a problem. so, it helps to look a little bit at the history that jim already outlines … super symmetry goes back to an entirely mathematical idea; or, actually, i should say ideas, because it was simultaneously discovered by several people sometime in the 70s, and it was then recognized (as john already said) that it would make a potential explanation for dark matter, and it would aid the unification of the interactions; and that, i think, excited a lot of particle physicists. however, super symmetry ran into conflict with experiment already in the 1990s very early, and it then had to be fixed by adding another assumption on top of it so that it would still be viable …


[1] The full video is available on The Institute of Art and Ideas’ site here.

The Institute of Art and Ideas site notes that their video was recorded at the Institute’s annual philosophy and music festival HowTheLightGetsIn on October 29, 2020.

From the YouTube description:

Sabine Hossenfelder is a research fellow at the Frankfurt Institute for Advanced Studies, author of Lost in Math: How Beauty Leads Physics Astray and regular contributor to Forbes and the popular physics blog Backreaction.

Jim Baggott is a science writer, writing on science, philosophy and science history. He is a regular contributor to New Scientist and Nature. Baggott is the author of nine books, including Farewell to Reality: How Modern Physics Has Betrayed the Search for Scientific Truth, Higgs: The Invention and Discovery of the God Particle and The Quantum Story: A History in 40 Moments.

John Ellis is the Clerk Maxwell Professor of Theoretical Physics at King’s College London who has worked extensively at CERN, and advocates the extension of the particle accelerator programme. His research focuses on phenomenological aspects of particle physics. Professor Ellis coined the term ‘theory of everything’, and in 1976 he coauthored the first paper on how to find the Higgs boson.

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3 thoughts on “Is supersymmetry dead?

  1. Here’s astrophysicist Paul Sutter’s take on the question.

    • > “From squarks to gluinos: It’s not looking good for supersymmetry” by Paul Sutter (Jan 7, 2021) – The future of the theory is in serious doubt.

    In supersymmetry, there’s a new kind of mathematical relationship that connects the fermions and the bosons. In fact, it’s more than a mere connection: supersymmetry states that fermions and bosons are really two sides of the same (supersymmetric) coin. Every single fermion has a mirror-like particle in the boson family, and every boson has a twin over the fermion world.

    In a perfectly supersymmetric world, we would see these twinned particles everywhere we look. For every fermion we could find an associated boson, and vice versa.

    After years of searching and loads of accumulated data from countless collisions, there is no sign of any supersymmetric particle. In fact, many [but not all] supersymmetry models are now completely ruled out, and very few theoretical ideas remain valid.

  2. A useful recap of matter-antimatter taxonomy and the (conservation) rules governing beta decay. Against the backdrop of cosmic baryon asymmetry. The role of W bosons, whether virtual or not.

    [includes visuals]

    • Forbes > “Not All Particles And Antiparticles Are Either Matter Or Antimatter” by Ethan Siegel (Dec 29, 2020) – Particles aren’t always matter, and antiparticles aren’t always antimatter. Here’s the science behind this counterintuitive truth about our Universe.

    When we talk about matter and antimatter, we’re talking only about the fermions in our Universe: the quarks and leptons. But there are bosons as well …

    What’s remarkable about this is where the idea of “matter” versus “antimatter” comes in. If you have a positive baryon or lepton number, you’re matter. If you have a negative baryon or lepton number, you’re antimatter. And if you don’t have either baryon or lepton number… well, you’re neither matter nor antimatter!

    … composite particles, like pions or other mesons that are made of quark-antiquark combinations, are neither matter nor antimatter; they’re equal amounts of both.

    And it means that, if supersymmetry were correct, we could have fermions like the supersymmetric counterpart of the photon — the photino — that are neither matter nor antimatter. Possibly, we could even have supersymmetric bosons, like squarks, whose particle and antiparticle versions really are matter and antimatter.

    … all of the bosons, which carry neither lepton nor baryon number, and all of the composite particles with a net baryon and lepton number of zero — lives in a nebulous area where they’re neither matter nor antimatter.

  3. Mathematics and science have a long history. Especially in modern cosmology, where mathematical simulations are increasingly used to cull theoretical models of exotic matter (like black holes). Mathematical methods have proved to be powerful in science and technology. Yet, mathematical facts are not facts about the physical world. Historical lessons?

    • Science News > “Physicists’ devotion to symmetry has led them astray before” by Tom Siegfried (March 31, 2021) – If dark matter WIMPs are mythical, they join the ancient idea that the planets moved in circles

    (caption) Ptolemaic model of planets – In ancient Greece, Aristotle deduced the existence of an exotic form of matter in space based on the circular symmetry of celestial motion, a symmetry preserved in the Ptolemaic model of planets orbiting the Earth in a combination of circular motions.

    (quote) If SUSY [supersymmetry] does turn out to be a myth, it won’t be the first time that symmetry has led science on a wild WIMP chase. Reasoning from the symmetry of circular motion originally suggested the existence of a new form of matter out in space more than two millennia ago. Devotion to that symmetry blinded science to the true nature of the solar system and planetary motion for the next 19 centuries.

    … all the known ordinary matter and force particles fit neatly into the mathematical patterns described by symmetry groups. But none of those particles can explain the dark matter.

    “You can’t really kill SUSY because it’s not a thing,” physicist Patrick Stengel of the International Higher School of Advanced Studies in Trieste, Italy, said at a conference in Washington, D.C., in 2019. “It’s not an idea that you can kill. It’s basically just a framework for a bunch of ideas.”

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