Our best model of particle physics is bursting at the seams as it struggles to contain all the weirdness in the universe. Now, it seems more likely than ever that it might pop, thanks to a series of strange events in Antarctica.
Mysterious particles spewing from Antarctica defy physics
Researchers prepare to launch the Antarctic Impulsive Transient Antenna (ANITA) experiment, which picked up signals of impossible-seeming particles as it dangled from its balloon over Antarctica.
(Image: © NASA)
The death of this reigning physics paradigm, the Standard Model, has been predicted for decades. There are hints of its problems in the physics we already have. Strange results from laboratory experiments suggest flickers of ghostly new species of neutrinos beyond the three described in the Standard Model. And the universe seems full of dark matter that no particle in the Standard Model can explain.
But recent tantalizing evidence might one day tie those vague strands of data together: Three times since 2016, ultra-high-energy particles have blasted up through the ice of Antarctica, setting off detectors in the Antarctic Impulsive Transient Antenna (ANITA) experiment, a machine dangling from a NASA balloon far above the frozen surface.
As Live Science reported in 2018, those events — along with several additional particles detected later at the buried Antarctic neutrino observatory IceCube — don’t match the expected behavior of any Standard Model particles. The particles look like ultra high-energy neutrinos. But ultra high-energy neutrinos shouldn’t be able to pass through the Earth. That suggests that some other kind of particle — one that’s never been seen before — is flinging itself into the cold southern sky.
Now, in a new paper, a team of physicists working on IceCube have cast heavy doubt on one of the last remaining Standard Model explanations for these particles: cosmic accelerators, giant neutrino guns hiding in space that would periodically fire intense neutrino bullets at Earth. A collection of hyperactive neutrino guns somewhere in our northern sky could have blasted enough neutrinos into Earth that we’d detect particles shooting out of the southern tip of our planet. But the IceCube researchers didn’t find any evidence of that collection out there, which suggests new physics must be needed to explain the mysterious particles.
To understand why, it’s important to know why these mystery particles are so unsettling for the Standard Model.
Neutrinos are the faintest particles we know about; they’re difficult to detect and nearly massless. They pass through our planet all the time — mostly coming from the sun and rarely, if ever, colliding with the protons, neutrons and electrons that make up our bodies and the dirt beneath our feet.
But ultra-high-energy neutrinos from deep space are different from their low-energy cousins. Much rarer than low-energy neutrinos, they have wider “cross sections,” meaning they’re more likely to collide with other particles as they pass through them. The odds of an ultra-high-energy neutrino making it all the way through Earth intact are so low that you’d never expect to detect it happening. That’s why the ANITA detections were so surprising: It was as if the instrument had won the lottery twice, and then IceCube had won it a couple more times as soon as it started buying tickets.
And physicists know how many lottery tickets they had to work with. Many ultra-high-energy cosmic neutrinos come from the interactions of cosmic rays with the cosmic microwave background (CMB), the faint afterglow of the Big Bang. Every once in a while, those cosmic rays interact with the CMB in just the right way to fire high-energy particles at Earth. This is called the “flux,” and it’s the same all over the sky. Both ANITA and IceCube have already measured what the cosmic neutrino flux looks like to each of their sensors, and it just doesn’t produce enough high-energy neutrinos that you’d expect to detect a neutrino flying out of Earth at either detector even once.
“If the events detected by ANITA belong to this diffuse neutrino component, ANITA should have measured many other events at other elevation angles,” said Anastasia Barbano, a University of Geneva physicist who works on IceCube.
But in theory, there could have been ultra-high-energy neutrino sources beyond the sky-wide flux, Barbano told Live Science: those neutrino guns, or cosmic accelerators.
“If it is not a matter of neutrinos produced by the interaction of ultra-high-energy cosmic rays with the CMB, then the observed events can be either neutrinos produced by individual cosmic accelerators in a given time interval” or some unknown Earthly source, Barbano said.
Blazars, active galactic nuclei, gamma-ray bursts, starburst galaxies, galaxy mergers, and magnetized and fast-spinning neutron stars are all good candidates for those sorts of accelerators, she said. And we know that cosmic neutrino accelerators do exist in space; in 2018, IceCube tracked a high-energy neutrino back to a blazar, an intense jet of particles coming from an active black hole at the center of a distant galaxy.
ANITA picks up only the most extreme high-energy neutrinos, Barbano said, and if the upward-flying particles were cosmic-accelerator-boosted neutrinos from the Standard Model — most likely tau neutrinos — then the beam should have come with a shower of lower-energy particles that would have tripped IceCube’s lower-energy detectors.
“We looked for events in seven years of IceCube data,” Barbano said — events that matched the angle and length of the ANITA detections, which you’d expect to find if there were a significant battery of cosmic neutrino guns out there firing at Earth to produce these up-going particles. But none turned up.
Their results don’t completely eliminate the possibility of an accelerator source out there. But they do “severely constrain” the range of possibilities, eliminating all of the most plausible scenarios involving cosmic accelerators and many less-plausible ones.
“The message we want to convey to the public is that a Standard Model astrophysical explanation does not work no matter how you slice it,” Barbano said.
Researchers don’t know what’s next. Neither ANITA nor IceCube is an ideal detector for the needed follow-up searches, Barbano said, leaving the researchers with very little data on which to base their assumptions about these mysterious particles. It’s a bit like trying to figure out the picture on a giant jigsaw puzzle from just a handful of pieces.
Right now, many possibilities seem to fit the limited data, including a fourth species of “sterile” neutrino outside the Standard Model and a range of theorized types of dark matter. Any of these explanations would be revolutionary.hjh But none is strongly favored yet.
“We have to wait for the next generation of neutrino detectors,” Barbano said.
The paper has not yet been peer reviewed and was published January 8 in the arXiv database.
Rad more at www.livescience.com
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Andy Rowlands
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It should not be much of an outrageous thought that the Standard Model may need revising. Science is never settled, and the debate is never over. There have been hints from Cern that there may be a seventh previously-unknown quark, and I believe when the LHC restarts it will try and look for them. If a seventh quark is found, it will require the search for an eighth, as quarks are supposed to come in pairs.
In the 70s, physicists Jogesh Pati and Abdus Salam hypothesized about what they termed ‘pre-quarks’ or ‘preons’, particles that they suggested were what quarks were made of. To date, no evidence of preons has been found, so it appears quarks are not made of any smaller particles. In the future, if evidence of such preons is discovered, that itself will require the Standard Model be revised.
This is how science works, when you uncover new information, you modify to your theory to take account of it, or if you cannot accomodate it in your theory, you have to devise a new one. The Standard Model may not be the correct explanation for how the Universe works, but for now at least, it’s the best we have.
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Tom O
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Quote – “The Standard Model may not be the correct explanation for how the Universe works, but for now at least, it’s the best we have.”
The only issue I have with that statement is that this is only true if you think the universe can be completely explained by mathematics. Even when I considered myself leaning towards atheism, I never felt the universe fits a mathematical model that requires everything to come from nothing, and that I would look to the farthest limits of the universe to see the beginning..
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Andy Rowlands
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I agree Tom, we will probably never understand the Universe completely, so I suspect the long sought after ‘Unified Field Theory’ may never be possible. Saying that, we have come a long way by uniting the various fundamental forces. Electromagnetism has now been united with the weak nuclear force, now renamed the ‘electro-weak’ force, and there are hints from the high-energy accelerators that we may be on the verge of uniting the strong nuclear force with the electro-weak force. That just leaves gravity, which is the big stumbling block to any unified field theory.
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Jerry Krause
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Hi Andy,
Accurate Definition!!! Rafi began: “The death of this reigning physics paradigm, the Standard Model, has been predicted for decades.”
I have no knowledge of what this Standard Model of physics is. Which I guess explains how it is some people comment that I know nothing about science. For if my knowledge of science must begin with this Standard Model of physics, it is true I know nothing about science.
I write what follows because I do not know if you are aware of the history of physics and chemistry. I do not know if you know that Tycho Brahe, the astronomer, was also an alchemist. I do not know if you know that Galileo wrote about what the alchemists had learned at his time. I do not know if you know that Newton, a physicist and astronomer, was also a practicing alchemist who avoided the controversy of whether matter was continuously divisible or was instead composed of ‘atoms’ which could not be further divided.
But clearly many of the early physical scientists were both physicists and chemists. And until graduate school I did not begin to see that in the 1960s that physicists and chemists did not see physical science in the same way. For the world of chemistry was that of experimentation with real matter and the world of the physicists was theoretical. But a fact is the chemist used the theories of the physicists while the physicists lost tough with the ‘actual’ practical world of the chemist.
Hence, I attended a lecture by Linus Pauling, a chemist at Caltech, who reported to the chemists in his audience, that the nuclear physicists at Caltech and else where, know nothing about the nucleus. For these physicists, based upon experiments, were inventing particles other than neutrons and protons with strange names with proposed properties which only the nuclear physicists imagined. And he claimed that they did this so no one outside their field could see that they understood nothing.
And I have made comments that Pauling considered that the results of the quantum mechanical ideas of a few physicists could be understood and used by freshman chemistry students to explain the descriptive chemistry that the earlier chemists had learned by observation (experiments). And the same time, Richard Feynman, a physicist at Caltech whose knowledge I much respect, considered that physic students should (could) not be taught quantum mechanical ideas until their junior year. This because of the mathematics involved in the quantum mechanical ideas (theories). Which mathematics Pauling considered could be ignored by chemists because it was the results of QM and not the mathematics which was practically important.
So I write about this history so you will be aware that Rafi seems to be agreeing with Pauling’s opinion of 5 or more decades ago.
Have a good day, Jerry
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Andy Rowlands
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I am indeed aware those people you mentioned were alchemists. They fell down by saying you could transmute elements at the chemical level, while we now know it can only be done at the atomic level. My Dad lectured on nuclear physics some years ago, which is what got me interested, and I acquainted myself with the history of particle predictions and discoveries at places like Cern and Fermilab and the development of the standard model. If you can get hold of a copy of ‘The Key To The Universe’ by Nigel Calder, who incidentally was a staunch climate skeptic, it is an invaluable tome. I followed the work at Fermilab where they discovered the top quark, and Cern with the Intersecting Storage Rings where they discovered the W & Z bozons from anti-proton collisions, the Large Electron-Positron Collider and now the LHC.
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Jerry Krause
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Hi Andy,
You wrote: “They fell down by saying you could transmute elements at the chemical level.” No, they are the ones that proved they could not transmute at the chemical level.
What you did not write was that they were accepting the ‘knowledge of the Aristotle and his fellow Greek philosophers who had rationally concluded that all matter could be made from (was composed of) the elementary matter of air, water, earth, and fire. I find it very interesting that you, as others seldom do, did not blame Aristotle for what the alchemists tried to ‘intellectually’ do.
Have a good day, Jerry
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Andy Rowlands
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Okay I used the wrong words about transmutation, and I didn’t think I needed to go back as far as Aristotle, though if you remember, Lord Percy in Blackadder did create some ‘green’ through transmutation 🙂
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Jerry Krause
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Hi Andy,
And I forgot to remind you that it was a alchemist, Robert Boyle, who gave us a better definition of elementary matter. Which was that which could not be broken apart by experiments into simpler forms of matter; instead of that which could not be made by combinations of air, water, earth, or fire.
Have a good day, Jerry
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