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The future of (particle) physics?

John Healy

I’ve encountered some articles recently about the current state of particle physics. Or, more broadly, “the direction of theoretical physics .” Concerns about its future. Whether new particle accelerators are needed (or even viable). An expensive rabbit hole. That research has become mired in wishful elegant mathematics. The absence of evidence being evidence of absence.

I didn’t record the first articles that I noticed on this topic. A footnote below [1], however, lists some examples of the negative sentiment.

In contrast, other articles (noted below) were optimistic about the situation.

• [Slate] Particle Physics Is Doing Just Fine: In science, lack of discovery can be just as instructive as discovery (January 31, 2019)

Recently, particle physics has become the target of a strange line of scientific criticism. … But the proposal that particle physicists are essentially setting money on fire comes with an insidious underlying message: that science is about the glory of discovery, rather than the joy of learning about the world. Finding out that there are no particles where we had hoped tells us about the distance between human imagination and the real world. It can operate as a motivation to expand our vision of what the real world is like at scales that are totally unintuitive. Not finding something is just as informative as finding something.

• [Forbes Senior Contributor Ethan Siegel] We Must Not Give Up On Answering The Biggest Scientific Questions Of All (February 5, 2019)

There’s an old saying in business that applies to science just as well: “Faster. Better. Cheaper. Pick two.” The world is moving faster than ever before. If we start pinching pennies and don’t invest in “better,” it’s tantamount to already having given up.

This morning, I noted that Chad Orzel weighed into the topic with an article summarizing the debate. He references some of the seminal posts.

• [Forbes Contributor Chad Orzel] The Thorny Question Of Whether To Build Another Particle Collider (February 5, 2019)

As I mentioned in that earlier post, though, this is a tricky topic to write about because it’s posing a genuinely difficult question about research priorities and resource allocation. As a result, while many of the arguments for and against are delivered with great passion and conviction, I don’t find any of them fully convincing. It’s just too easy to poke holes in most of the arguments being thrown around.

So, there’s a historical side to the topic — the struggle with prior “Big Science” projects. And a philosophical side — a debate about theory and scientific progress (which also has a long history).

Notes

[1] Examples of negative sentiment on research:

• [Vox] The $22 billion gamble: why some physicists aren’t excited about building a bigger particle collider: Particle accelerators have taught us so much about physics that the new one might have nothing to find (January 22, 2019)

• [NBC News] Why some scientists say physics has gone off the rails: Has the love of “elegant” equations overtaken the desire to describe the real world? (June 2, 2018)

• [Sabine Hossenfelder] How the LHC may spell the end of particle physics (December 27, 2018)

• [Sabine Hossenfelder] Particle Physics now Belly Up (June 23, 2018)

[2] Wiki: Relationship between mathematics and physics

“At this point an enigma presents itself which in all ages has agitated inquiring minds. How can it be that mathematics, being after all a product of human thought which is independent of experience, is so admirably appropriate to the objects of reality?” —Albert Einstein, in Geometry and Experience (1921).

On the relationship between mathematics and physics and the current state of affairs, see also: The Universe Speaks in Numbers: How Modern Maths Reveals Nature’s Deepest Secrets by science communicator Graham Farmelo (May 2019).

Since the 1970s … experiments at the world’s most powerful atom-smashers have offered few new clues. So some of the world’s leading physicists have looked to a different source of insight: modern mathematics. These physicists are sometimes accused of doing ‘fairy-tale physics’, unrelated to the real world. But in The Universe Speaks in Numbers, award-winning science writer and biographer Farmelo argues that the physics they are doing is based squarely on the well-established principles of quantum theory and relativity, and part of a tradition dating back to Isaac Newton.

[3] Physicist Jon Butterworth reviews Graham Farmelo’s book The Universe Speaks in Numbers in this Nature article “A struggle for the soul of theoretical physics” (16 April 2019).

The worry — expressed by a number of theorists and writers over several decades — is that theoretical physics has become a monoculture too focused on a small clutch of concepts and approaches. Those include string theory, overstated predictions of new discoveries, over-reliance on mathematical elegance as a guide and a general drift into what physicist and writer [science communicator] Jim Baggott, in Farewell to Reality (2013), called “fairytale physics” [multiverse, superstring theory, and supersymmetry*], divorced from its empirical base. Notable critiques have come from theoretical physicists including Peter Woit, Lee Smolin and, more recently, Sabine Hossenfelder … . Science writer Graham Farmelo clearly intends The Universe Speaks in Numbers as a riposte.

These [historical advances in physics] are brilliant successes of the mathematical approach, and Farmelo leads us through them adeptly, with a mixture of contemporary accounts and scientific insight. He also casts a sceptical eye on the stories the players tell about themselves — and here the tensions start to be felt.

During what Farmelo calls “the long divorce” between mathematics and theoretical physics from the 1930s to the 1970s, …

* Wiki: [Baggott stated:] “When you start asking ‘Do we live in a hologram?’ Then you are crossing into metaphysics, and you are heading down the path of allowing all kinds of things that have no evidence to back it up, like creationism.” … He [Baggott] feels that empirical data provides an anchor for these people to “return to reality” and that science without evidence is “most dangerous.” … Science writer Philip Ball, in a review of Farewell in The Guardian, stated that Baggott was right “although his target is as much the way this science is marketed as what it contains.”

15 thoughts on “The future of (particle) physics?”

  1. I found this Symmetry Magazine article (10/25/2018) interesting regarding particle research and the Standard Model: “Already beyond the Standard Model — We already know neutrinos break the mold of the Standard Model. The question is: By how much?”

    … in the search for physics beyond the Standard Model, one area of notably keen interest continues to be neutrinos.

    This extra neutrino — suggested by results from the Liquid Scintillator Neutrino Detector and the MiniBooNE experiment — wouldn’t match up with the generations of particles in the Standard Model. It would be “sterile,” meaning it likely wouldn’t interact directly with any Standard Model particles. It might even be a form of dark matter.

    Meanwhile, other oscillation experiments will continue to understand what gave neutrinos their mass in the first place — one of the first hints we have had of physics beyond the Standard Model.

  2. The future of particle physics at Fermilab:

    This U.S. Department of Energy podcast / article “S3 E7: DUNE: The Neutrinos Must Flow” (May 7, 2019) discusses the key role neutrinos play in the Standard Model regarding explaining why anything exists — why the symmetries of the Big Bang did not just result in matter and anti-matter annihilating, leaving nothing — as least no matter, only a “bath of energy.” This article contains some interesting pictures and [visualization] videos, as well as a transcript of the podcast. Over a 1000 scientists from around the world … a “megascience” experiment.

    Join Direct Current on a subatomic sojourn into the Deep Underground Neutrino Experiment (DUNE), a massive international research project aiming to unlock the secrets of the neutrino with help from more than 175 institutions in over 30 countries.

    We’ll take you from Fermilab to the home of the Large Hadron Collider in Switzerland to the bottom of a former gold mine a mile beneath the hills of South Dakota as we explore one of the most ambitious particle physics projects of our lifetime.

    From transcript:

    KREER: Neutrinos are the stars of the lab’s current research efforts. Bonnie is one of more than a thousand scientists from around the world involved in this “megascience” project called the Deep Underground Neutrino Experiment, or “DUNE.”

    KREER: We’re steering clear of dark matter this time around. There’s plenty to cover with neutrinos. As Bonnie said, neutrinos are everywhere, and they are connected to the stuff you are probably familiar with: things like protons, neutrons, and electrons. 

    KREER: The project that Lia is helping direct right here in the U.S. has the potential to be as much a pioneer in particle physics — and to our understanding of the universe — as CERN’s Large Hadron Collider in Switzerland. Except in the case of Fermilab, the new ground being broken — literally and figuratively — centers around the neutrino.

    References:

    Fermilab: “Long-Baseline Neutrino Facility pre-excavation work is in full swing” (May 2, 2019).

    Fermilab > Youtube: “Small Particles, Big Science: The International LBNF/DUNE Project” (March 28, 2016).

    Neutrinos are the most abundant matter particles in the universe, yet very little is known about them. This animation shows how the Department of Energy’s Long-Baseline Neutrino Facility will power the Deep Underground Neutrino Experiment to help scientists understand the role neutrinos play in the universe. DUNE will also look for the birth of neutron stars and black holes by catching neutrinos from exploding stars. More than 800 scientists from 150 institutions in 27 countries are working on the LBNF/DUNE project, including Armenia, Belgium, Brazil, Bulgaria, Canada, Colombia, Czech Republic, Finland, France, Greece, India, Iran, Italy, Japan, Madagascar, Mexico, Netherlands, Peru, Poland, Romania, Russia, Spain, Switzerland, Turkey, Ukraine, United Kingdom, USA.

  3. Department of Energy Announces $75 Million for High Energy Physics Research

    JUNE 4, 2019

    WASHINGTON, D.C. – Today, the U.S. Department of Energy (DOE) announced $75 million in funding for 66 university research awards on a range of topics in high energy physics to advance knowledge of how the universe works at its most fundamental level.

    The projects involve scientists at 51 U.S. institutions of higher learning across the nation, and include both experimental and theoretical research into such topics as the Higgs boson, neutrinos, dark matter, dark energy, and the search for new physics.

    Projects include experimental work on neutrinos at DOE’s Fermi National Accelerator Laboratory; the search for dark matter with the LZ (LUX-ZEPLIN) experiment one mile below the Black Hills of South Dakota; the analysis of observatory data relating to dark energy and the expansion of the universe; and investigation of the Higgs boson from data collected at the Large Hadron Collider at CERN.

  4. LiveScience: “Physicists Search for Monstrous Higgs Particle. It Could Seal the Fate of the Universe” by Paul Sutter, Astrophysicist, June 5, 2019

    Though we don’t have any evidence yet of a heavier Higgs, a team of researchers based at the LHC, the world’s largest atom smasher, is digging into that question …

    If the heavy Higgs does indeed exist, then we need to reconfigure our understanding of the Standard Model of particle physics … And within those complex interactions, there might be a clue to everything from the mass of the ghostly neutrino particle to the ultimate fate of the universe.

  5. This Interesting Engineering article “Fermilab is Still Alive After CERN – While it may no longer be the world’s premier atom smasher, interesting physics is still going on at Fermilab, and the neutrino might just be ready to give up its secrets” (June 23, 2019) is yet another look at ongoing research at Fermilab.

    The article includes a YouTube video by Don Lincoln: “Everything you need to know about Fermilab” (published on Jan 22, 2019).

    Fermilab is one of the world’s finest laboratories dedicated to studying fundamental questions about nature. In this video, Fermilab’s own Dr. Don Lincoln talks about some of Fermilab’s leading research efforts that will lead the field for the next decade or two. If you want to learn more about Fermilab’s research, there is more information here: http://www.fnal.gov/.

  6. An interesting interview by Quanta Magazine of Carlo Rubbia, “an Italian particle physicist and inventor who shared the Nobel Prize in Physics in 1984 with Simon van der Meer for work leading to the discovery of the W and Z particles at CERN: “A Call for Courage as Physicists Confront Collider Dilemma” by Thomas Lewton, Contributing Writer (August 7, 2019).

    The Higgs boson — the 17th piece in the Standard Model puzzle — materialized at the LHC in 2012, and now Rubbia wants to explore its characteristics in depth with a state-of-the-art “Higgs factory.”

    To Rubbia, the choice is clear: An innovative muon collider, he says, could produce thousands of Higgs bosons in clean conditions at a fraction of the time and cost of other experiments.

    – – –

    The Quanta Magazine article also is referenced by Ethan Siegel, who discusses the pros and cons of current colliders in his Forbes article > “Forget About Electrons And Protons; The Unstable Muon Could Be The Future Of Particle Physics” by Ethan Siegel Contributor, Starts With A Bang Contributor Group (August 22, 2019).

    One Nobel Laureate, Carlo Rubbia, has called for physicists to build something entirely novel: a muon collider. It’s ambitious and presently impractical, but it just might be the future of particle physics.

    In general, electron/positron colliders are better for precision studies of known particles, while proton/proton colliders are better for probing the energy frontier.

    Everything in this Universe is limited by the speed of light in a vacuum: 299,792,458 m/s. It’s impossible to accelerate any massive particle to that speed, much less past it. At the LHC, particles get accelerated up to extremely high energies of 7 TeV per particle. Considering that a proton’s rest energy is only 938 MeV (or 0.000938 TeV), it’s easy to see how it reaches a speed of 299,792,455 m/s.

    But the electrons and positrons at LEP went even faster: 299,792,457.9964 m/s. Yet despite these enormous speeds, they only reached energies of ~110 GeV, or 1.6% the energies achieved at the LHC.

    Even though the electrons and positrons are much closer to the speed of light, it takes nearly 2,000 of them to make up as much rest mass as a proton. They have a greater speed but a much lower rest mass, and hence, a lower energy overall.

    This is where the big idea of using muons comes in. Muons (and anti-muons) are the cousins of electrons (and positrons), being 206 times as massive as an electron (with a much smaller charge-to-mass ratio and much less synchrotron radiation).

    But there are issues with muons, e.g., instability – “a mean lifetime of just 2.2 microseconds before decaying away.”

  7. Fermilab also is involved in the hunt for dark matter.

    Fermilab > Department of Energy awards Fermilab funding for next-generation dark matter research (October 18, 2019 | edited by Leah Hesla)

    Earlier this month, the Department of Energy announced that it has awarded scientists at its Fermi National Accelerator Laboratory funding to boost research on dark matter, the mysterious substance that makes up an astounding 85% of the matter in the universe.

    The award will fund two Fermilab projects focused on searching for dark matter particles of low mass — less than the mass of a proton.

    The Fermilab-led initiatives funded through the DOE Basic Research Needs for Dark Matter New Initiatives grants are:

    1. Extending the search for axions with ADMX

    Collaborating institutions: Lawrence Livermore National Laboratory, Pacific Northwest National Laboratory, Los Alamos National Laboratory, University of Florida, University of Washington, Washington University, St. Louis, University of California, Berkeley and University of Western Australia.

    2. Toward unprecedented sensitivity with skipper CCDs

    One way to hunt for dark matter is to catch it in the act of bumping into a particle of ordinary matter, such as an electron [and detect energy-transfer signals].

    Collaborating institutions: Pacific Northwest National Laboratory, Stony Brook University, University of Chicago, University of Washington.

  8. And here’s a (more recent) retrospective by Chad Orzel on his view of the future of particle physics:

    Forbes > “What I Was Wrong About In Physics” by Chad Orzel Contributor (Sep 11, 2019)

    The point of physics I was most definitively wrong about is not a unique failure on my part: like many physicists, I was pretty sure the Large Hadron Collider would have seen some evidence of physics not incorporated in the Standard Model by now.

    There are scenarios in which precision measurements of electric dipole moments or anomalous magnetic moments end up being more sensitive than direct collider experiments, and as I have a lot of friends in the precision-measurement world, I’m rooting for them to win. In that sense, the crisis in particle physics is unexpectedly good news…

    A number of my changes of mind are not so much switches from “wrong” to “right” as they are oscillations between different views of a subject. This is pretty much the situation with regard to particle physics theory, where my opinion of the field goes back and forth a bit, particularly when it comes to the question of string theory. I was very down on the whole business in the mid-00’s, when it seemed to be just accumulating epicycles – adding more and more baroque and unobservable elements. My opinion moderated somewhat over the several years after that, with the development of the AdS-CFT correspondence, … My opinion is sort of trending downward again, because there doesn’t seem to have been as much progress as was being promised six or eight years ago. Cynics might note that this coincides with the publication of Sabine Hossenfelder’s Lost in Math, while the last minimum in my oscillating esteem happened around the time of the Lee Smolin and Peter Woit anti-string books.

  9. • YouTube > PBS Space Time > “Can Future Colliders Break the Standard Model?” – Matt O’Dowd (August 24, 2020)

    (description) In June, the consortium of Europe’s top particle physicists published their vision for the next several years of particle physics experiments in the EU. A big part of that is the Future Circular Collider, which, if it happens, will accelerate particles in a 100 kilometer circumference underground ring encircling Geneva. It’ll be nearly 4 times the size of the Large Hadron Collider, and it would be capable of colliding particle beams with 8 times the current LHC energy. The hope is that this will open the window to brand new physics – and perhaps break the current deadlock in our quest for a theory of everything. But do the FCC or other upcoming collider experiments really have a chance of succeeding? Today we’re going to discuss the incredibly ambitious plans for future colliders, and try to honestly evaluate their prospects.

  10. • Symmetry Magazine > “Defining the next decade of US particle physics” by Scott Hershberger (Oct 1, 2020) – The “Snowmass” process seeks to identify the most promising questions to explore in future research.

    This year, the topics for discussion are divided into 10 thematic “frontiers” representing the various facets of modern particle physics research: energy, neutrinos, precision, the cosmos, theory, accelerators, instrumentation, computation, underground facilities and community engagement. In a new part of the process, researchers were invited to submit two-page letters of interest outlining ideas to discuss at the community planning meeting and beyond. The organizers received over 1500 such letters.

  11. Re muons and the search for new physics … particle spin … magnetic moment … Feynman diagrams … QED, QCD … multi-photon (virtual) interactions (perturbative corrections) … W and Z bosons … gluons (self-interacting) … hadrons (particles bound by strong force) … (supercomputer) simulations vs. dispersion relation method …

    • Symmetry Magazine > “The many paths of muon math” by Daniel Garisto (Oct 20, 2020) – Here’s how physicists calculate g-2, the value that will determine whether the muon is giving us a sign of new physics.

    The goal of the experiment, Fermilab Muon g-2, is to better understand the properties of muons, which are essentially heavier versions of electrons, and use them to probe the limitations of the Standard Model of particle physics. Specifically, physicists want to know about the muons’ “magnetic moment” – that is, how much do they rotate on their axes in a powerful magnetic field – as they race around the magnet?

    “Contributions to the anomalous magnetic moment come from the three different interactions— the strong interaction, the weak interaction and quantum electrodynamics all contribute,” Blum [theoretical physicist at the University of Connecticut] says.

    There are two main types of hadronic corrections: “vacuum polarization” corrections and “light by light” corrections. In vacuum polarization, the muon emits a virtual photon, which decays into a quark and antiquark. These quarks and antiquarks exchange gluons, turning into a frothing blob of hadronic matter such as pions and kaons. Finally, the virtual blob of hadronic matter ends when a quark and antiquark annihilate back into a virtual photon, which is finally absorbed by the muon.

    Light by light contributions are perhaps some of the strangest. From the outside, it looks as if two virtual photons are emitted by a muon, interact, and are then absorbed. What’s going on here?

    But if the two virtual photons get caught in a quark loop, each converting to a virtual quark and virtual antiquark, they can form a blob of hadronic matter. If the virtual quarks and virtual antiquarks annihilate back into virtual photons, the two will appear to have bounced off of one another, interacting in a forbidden way.

  12. Re history of the Standard Model … the LHC … Higgs …

    • Inverse > “By Coming Together, 3,000 Scientists Changed The Course Of Physics Forever” by Grace Browne (Oct 22, 2020) – “Without this collaboration, it would not have been discovered.”

    The community fostered at CERN has been a subject of study for anthropologists and sociologists. The fact so many physicists manage to work and collaborate together within the same enterprise is incredible.

    One of the big questions scientists want to answer now is whether the particle they found is indeed the Higgs boson as predicted by the Standard Model, or something different and more complex.

  13. Another perspective on the Muon g-2 experiment at Fermilab … precision mapping of the magnetic field is critical throughout the 45-meter circumference ring … to achieve field measurements accurate to 70 parts per billion … a trolley system [holding 17 probes] to drive measurement probes around the ring and collect data …

    • Phys.org > “Scientists work to shed light on Standard Model of particle physics” by Savannah Mitchem, Argonne National Laboratory (Nov 5, 2020)

    As scientists await the highly anticipated initial results of the Muon g-2 experiment at the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory, collaborating scientists from DOE’s Argonne National Laboratory continue to employ and maintain the unique system that maps the magnetic field in the experiment with unprecedented precision.

    Just as the Earth’s rotational axis precesses – meaning the poles gradually travel in circles – the muon’s spin, a quantum version of angular momentum, precesses in the presence of a magnetic field. The strength of the magnetic field surrounding a muon influences the rate at which its spin precesses. Scientists can determine the muon’s g-factor using measurements of the spin precession rate and the magnetic field strength.

  14. I’ve sometimes wondered about beam quality in particle accelerators. Wrangling clusters of trillions of particles at relativistic speeds.

    It’s sort of like lasers, which I once imagined as purely monochromatic (coherent single frequency) light waves.

    Beam loss is a major issue – “beam halos” which stray outside confinement fields and might touch the walls of the accelerator. It wastes energy (among other things), like in many devices where energy is lost to heat rather than primary output.

    Phys.org > “After 20 years, physicists find a way to keep track of lost accelerator particles” by Jeremy Rumsey, Oak Ridge National Laboratory (February 23, 2021)

    A high-intensity accelerator beam is formed of trillions of particles that race at lightning speeds down a system of powerful magnets and high-energy superconductors. Calculating the physics of the beam is so complex that not even the fastest supercomputers can keep up.

    Terms

    6D space
    Maximum allowable density (for which beam halo is manageable)
    Computer modeling simulation (for understanding beam loss patterns)

  15. As a follow-up for some previous comments …

    In anticipation of the first results from Fermilab’s Muon g-2 experiment, this article recaps the history of the muon’s magnetic moment. Spectroscopy … Dirac equation … empirically a tad extra magnetism … Schwinger’s virtual photons … looking for a slight additional wobble in the rotation of their spins … a muon decays into an electron and two neutrinos.

    • Symmetry Magazine > “The mystery of the muon’s magnetism” by Brianna Barbu (03/30/2021) – A super-precise experiment at Fermilab is carefully analyzing every detail of the muon’s magnetic moment.

    The current Muon g-2 (pronounced g minus two) experiment is actually a sequel, an experiment designed to reexamine a slight discrepancy between theory and the results from an earlier experiment at Brookhaven National Laboratory, which was also called Muon g-2.

    The Fermilab Muon g-2 collaboration has announced it will present its first result on April 7. Until then, let’s unpack the facts of the case.

    All spinning, charged objects – including muons and their better-known particle siblings, electrons – generate their own magnetic fields. The strength of a particle’s magnetic field is referred to as its “magnetic moment” or its “g-factor.” (That’s what the “g” part of “g-2” refers to.)

    Over time, researchers discovered that there was an extensive network of “virtual particles” constantly popping in and out of existence from the quantum vacuum. … every particle and force in the Standard Model takes part [in these virtual interactions].

    It looked as if the same conspiracy of particles that affected the electron’s g-2 were responsible for the magnetic moment of the muon as well.

    But then, in 2001, the Brookhaven Muon g-2 experiment turned up something strange. … it also showed a tiny discrepancy—less than 3 parts per million—between the new measurement and the theoretical value.

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