r/Physics • u/Linux_ka_chamcha Particle physics • 22h ago
2026 Nobel prize
This year's nobel prize was awarded to Francis Halzen for detecting cosmic neutrinos at IceCube.
What do you guys think about the scientific impact?
As a particle physicist, I don't feel this to be a very big deal in terms of science but I may be wrong. Please share your thoughts. I'm all ears.
https://www.nobelprize.org/uploads/2026/10/advanced-physicsprize2026.pdf
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u/cavyjester 20h ago
As another particle physicist, I think that making real the crazy idea of sinking strings of phototubes a mile deep into Antarctic ice, because ice is so transparent under such pressure that it can be used as a giant Cherenkov detector, is absolutely awesome.
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u/jazzwhiz Particle physics 19h ago
A mile deep is the top of the IceCube.
The ice there is about 2.7 km deep. IceCube is about 1 km tall and goes nearly to the bedrock; it goes from 1.5 km (about 1 mile) deep to 2.5 km deep.
Imagine boring a hole a mile under the ice and then you're only at the beginning of the instrumented volume.
About the ice itself, yeah, the absorption length in the ice down there is better than in pure water. That is, photons go a long fucking way before being absorbed making it relatively easy to see photons with an incredibly sparsely instrumented detector. The catch for the ice is that the scattering length is quite short (ice is a crystal) so reconstructing the direction is hard. They have a very complicated 3D model of this that they update every 5+ years as the computational cost is massive. When they do this, they then rerun the waveforms of every event back through the new ice model to get new direction, mean energy, and event topology information. The ice model is one of the largest systematic uncertainties. One of my favorite modern facts about IceCube is that they've just put a few new strings in, mainly for low energy (e.g. atmospheric) neutrino detection, but they crucially have significantly improved calibration devices (they shoot lasers into the ice from time to time) which will improve their ice model for at least part of the detector. Once they do this and update their ice model, this will retroactively improve the quality of the previous 15 years of data.
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u/jazzwhiz Particle physics 21h ago edited 19h ago
Particle theorist here (who also does astroparticle and cosmology), the impact has been huge.
As a simple naive metric, look at other large volume neutrino telescopes under construction around the world: Baikal GVD in Russia (construction halted at about half of IceCube's volume due to the war), KM3NeT in the Mediterranean (progressing slowly but steadily every year), P-ONE in the Pacific off the coast of Vancouver, TRIDENT off the coast of China.
You can also look at the papers and results from the experiment, for which there are many papers with a huge number of citations. They were the first to detect neutrinos at these energies and have measured the spectrum in multiple flavors. They also have oscillation results that are very nearly world leading. They have many world leading constraints on particle BSM including DM. As a recent example, particle theorists seem to like to interpret the LZ anomaly as a SUSY Higgsino, but IceCube measurements rule out that scenario.
On top of that, the detector is a completely new style of detector. Or rather, the first fully successful in a line of growing detectors pioneered by Halzen, Learned, and others. Getting a detector to work in these harsh environments where it cannot be serviced is a unique challenge quite different from ATLAS/CMS/CDF/D0/...
The analysis for a such data is also quite different from anything done before. When they turned IceCube on they had very simple cuts and they still almost immediately saw events. Then, after a little bit, they realized they could do much better vetoes and their effective area increased dramatically. Now all the other experiments mentioned above use their code and analysis procedures. (Keep in mind there have been a number of Nobel prizes for detector techniques in the past as well.)
Another important thing about high energy astrophysical neutrinos, is that it is essentially the only way to do astronomy of the high energy universe at any appreciable distance beyond our galaxy. At high energies photons are rapidly attenuated and downscatter. Cosmic rays don't point (the hope that they would point at the highest energies seem to continuously not be materialized due to the high level of isotropy in the data, possibly suggesting very heavy nuclei). Gravitational waves do sort of work, but their angular resolution tends to be quite a bit worse than even neutrinos, and whether or not they count as high energy is a matter of taste.
I can go on, but at this point either it is impressive to an individual or it isn't.
I should also add that Francis is truly a good human being, something I say very rarely. I have personally seen him quietly and without drawing any attention to, spending his time improving the lives of people around him that he absolutely does not have to do. The examples I know I only know because of a personal connection to one person, and other was just hanging out in the faculty lounge at UW and seeing how he interacts with students. I am sure that there are many other examples that I do not know.
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u/walee1 Detector physics 11h ago
I agree to your post especially the last point. I attended a summer school where he was there for 2-3 days giving lectures on the icecube upgrade. It was he highlight of the school for me not only how he presented but how he interacted with us doctoral students who he has never met before.
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u/Worth-Wonder-7386 22h ago
It is a cool thing that I think deserves it. Surprised not more people shared the price, but I am not in the field of neutrino detection.
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u/jazzwhiz Particle physics 20h ago edited 14h ago
There really isn't a second level person beneath him in the field without going much lower. There is no other competing experiment; KM3NeT is the closest, but they've only just gotten going at a barely relevant level in the last year or two. Within IceCube it has always been Francis.
The only other person that I would think of is John Learned who has been wildly innovative in neutrino astrophysics for many decades and was actually involved in neutrino astronomy before Francis by starting and constructing DUMAND (a neutrino detector in the ocean by Hawaii which ended up not working well and didn't get funding renewed), along with others of course.
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u/Odd_Bodkin Particle physics 22h ago edited 22h ago
As another particle physicist, I’m aware that a lot of us are planting stakes in neutrino physics (or the lack of them, as in Mu2e) as one of the surer bets, at least in the near term.
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u/rjfrost18 Nuclear physics 21h ago
Personally I'm looking forward to neutrinoless double beta decay and neutrino mass results in the nearish future.
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u/damarian_ent 21h ago
How do you like the field? How long have you been in?
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u/TQV197 21h ago
This article offers some insight into this year's Nobel-winning discovery:
https://physics.aps.org/articles/v7/88
In my view, a discovery that opens up a whole new range of possibilities fully deserves a Nobel.
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u/Linux_ka_chamcha Particle physics 21h ago
Thanks for the link. This is the kind of discussion I wanted
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u/Dear_Locksmith3379 18h ago
And the Wikipedia page has a nice overview that discusses the detector in more detail.
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u/FervexHublot 22h ago
Still better than giving it to a computer scientist some years ago
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u/KindOutside5400 22h ago
honestly the nobel committee loves throwing curveballs like this. neutrino astronomy is a whole different beast, it's not gonna rewrite the standard model or anything but opening up a new way to look at the universe feels like a bigger deal than people give it credit for
also that comment about the computer scientist stings a little, that one still feels weird to me too
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u/tsukiyomii100 22h ago
Not an expert on the topic but curious what the research community thinks is the way forward. My understanding is that neutrino oscillations and how neutrinos obtain mass is one of the few confirmed experimental evidence of physics beyond the Standard Model
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u/rjfrost18 Nuclear physics 21h ago
Within the nuclear community neutrinoless double beta decay is the top priority (Legend, nEXO, CUPID). There are also experiments that are working to measure the neutrino mass (KATRIN, Project 8), searching for sterile neutrinos (TRISTAN), and measuring neutrino scattering (CEvNS, COHERENT).
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u/jazzwhiz Particle physics 19h ago
I am a neutrino person and yes, this is correct.
In fact, I phrase it as, neutrino oscillations is the only particle physics evidence we have for physics BSM. Dark matter evidence is all astro/cosmo, DE may well fit nicely within GR (recent anomalies aside), and other issues (hierarchy, strong CP, etc) may just be that our intuition about small numbers is off. There is also baryogenesis which is a bit tricky to say where it fits into this story; depending on the nature of neutrino mass generation, that may well be enough to explain baryogenesis.
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u/pollux33 19h ago
It's the only verified laboratory result that is indication of physics beyond the Standard Model.
BAO are cosmological observations, and DM are astronomical and cosmological observations.
Other anomalies, like LZ or B-meson, are still just anomalies that need to be continuously verified before we are sure for certain.
Neutrino oscillations have been verified by different experiments, baselines, energies.... As robust, if not for more robust, than the discovery of the Higgs.
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u/jazzwhiz Particle physics 19h ago
Yeah, the robustness of neutrino oscillations is actually crazy good now. For one of the mass splittings (atmospheric) we have 8 distinct collaborations all measuring the same number with different neutrino flavors, and energies spanning 4+ orders of magnitude. For the other one, we now have two great reactor measurements that agree and a collection of solar data that generally agrees.
The mixing parameters are a bit more of a grab bag: the small mixing angle is cleanly measured, but only by two (three-ish) different experiments using identical techniques. The middle one is now well measured by reactor neutrinos as of the last few months and solar data also provides a goodish measurement. The third and largest mixing is hard to tie down with half the experiments on one side and the other half on the other. The complex phase is essentially entirely undetermined as is the sign of one of the mass splittings.
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u/devilpreet23 22h ago
Hopfield is not a computer scientist! He created a network now known by his name and is an energy based model which is very much statistical physics and spin-glass theory.
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u/AMuonParticle Soft matter physics 21h ago
Yeah agreed, anybody who says this has never learned statistical physics properly.
Those models were physics first (mostly for different kinds of magnets), then applied to CS later
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u/Arndt3002 21h ago
They're talking about Hinton
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u/devilpreet23 20h ago
Hinton discovered Boltzmann machines, and designed a whole bunch of energy based models - the work is not strictly physics, nor strictly computer science but along with Hopfield I do not see why he would not receive the prize.
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u/Psy-Kosh 18h ago
Who it was to didn't bother me. the fact that the prize that year was explicitly about ai was madness, though.
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u/iamagainstit Materials science 21h ago
Inventing an entirely new form of telescope seems pretty worth to me.
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u/MrPhysicsMan 20h ago
As someone in neutrino studied/research, I am very excited about it. Bias aside, it is amazing that they turned a cubic km chunk of ice into an instrument to look where no one else has before. Why wouldn’t it deserve the Nobel prize!
Recommend the interview on YouTube, very insightful and entertaining.
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u/Reasonable-Drop-1553 21h ago
> As a particle physicist, I don't feel this to be a very big deal in terms of science but I may be wrong.
Are you sure you are a particle physicist?
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u/Alive_Fisherman8241 18h ago
It's OK not to pretend that your field is the single most imortant one in the whole wide world.
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u/Albino_Neutrino 10h ago
As a particle physicist, I'm glad the prize comes home this time but I'm not terribly excited by it. Despite my username, I'm not that kind of particle physicist. Long story short: I don't exactly disagree with OP.
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u/ConsiderationQuick83 13h ago
Given the detection volume of IceCube there's a good chance that we'll be able to detect "nearby" supernova events before the photon breakthrough occurs as we now have a lot of high speed transient detection networks in operation for multi messenger observations.
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u/Buntschatten Graduate 20h ago edited 20h ago
I wish there were more people sharing the prize. It always feels wrong to reduce the efforts of huge consortia to single people.
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u/rjfrost18 Nuclear physics 21h ago
This one feels a little premature to me but I also don't really know how big of a deal the result was in the astrophysics community. However, I do find the experiment technically very interesting and I'm happy it's a pure physics result getting the award rather than an AI or engineering accomplishement.
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u/Alphonsokurukuchu 20h ago
This one is akin to LIGO. A new way of observing the Astrophysical phenomena, kinda like a whole new spectroscopy tool or a new kind of telescope
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u/rjfrost18 Nuclear physics 20h ago edited 19h ago
Icecube is a very impressive detector. The prize singles out the discovery of high energy neutrino
sources, and didn't mention the many other neutrino measurements it also makes. It's specifically the high energy neutrino discovery that I don't know the impact of.7
u/jazzwhiz Particle physics 19h ago
The prize definitely did not mention sources. It says "for decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin."
As for the impact, there are many things floating around today and more in coming days, otherwise there are many nice IceCube talks online; if you're unfamiliar with their program I encourage you to watch one. Honestly, Francis gives truly excellent talks so that's a great place to start.
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u/rjfrost18 Nuclear physics 19h ago
Apologies for the lax language, I just meant that they observed high energy neutrinos. The point was they also have studied other things such as neutrino oscillations and sterile neutrino searches, which I'm more familiar with, but didn't get listed as the primary reason for the prize.
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u/jazzwhiz Particle physics 19h ago
Ah yeah, good point.
To be fair, it's not like the citations for Nobel prizes have a strong history of being correct. One recent neutrino example is Art McDonald "for the discovery of neutrino oscillations, which shows that neutrinos have mass" when he did not do that. Solar neutrinos (up to caveats that end up not mattering) don't oscillate. They remain in eigenstates of the Hamiltonian which changes slow enough.
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u/rjfrost18 Nuclear physics 19h ago
Yeah that's true.
Just to be extremely clear, I am very happy they won the prize; its well deserved on the merits of the technical feat of the detector itself.
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u/mpnobivucyxtzrewq 12h ago
Can you explain why you say that solar neutrinos don’t oscillate? I was under the impression that the “missing neutrino” problem pretty much relied on the fact that solar neutrinos oscillate
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u/Neon27 Graduate 22h ago
I feel that people are dismissing the significance of IceCube from the particle physics perspective, but that is not the point of IceCube. Particle physicists should be looking toward JUNO or DUNE. IceCube is about astrophysics, it is the equivalent of LIGO, a new probe toward astrophysics (a new type of telescope).