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The 2026 Nobel Prize in\u00a0Physics was awarded<\/a> to\u00a0Belgian physicist Francis Halzen for his \u201cdecisive contribution to\u00a0the IceCube neutrino observatory and the discovery of\u00a0high-energy neutrinos of\u00a0astrophysical origin.\u201d Neutrinos were long considered almost impossible to\u00a0detect, especially those arriving from deep space. Tracing them to\u00a0their cosmic sources is\u00a0even harder here on\u00a0Earth because the vast majority come from the Sun or\u00a0are produced in\u00a0the planet\u2019s magnetic field. Yet scientists managed to\u00a0detect them with a\u00a0project of\u00a0astonishing scale, first proposed by\u00a0Soviet physicist Moisey Markov in\u00a0the 1960s and built through Halzen\u2019s efforts in\u00a0recent decades: IceCube, an\u00a0observatory buried deep in\u00a0the Antarctic\u00a0ice. What should we\u00a0know about the project\u2019s history? How does a\u00a0cosmic neutrino detector work? And what can studying these particles tell us?<\/p>\n The Soviet roots of\u00a0the 2026 Nobel: How Moisey Markov\u2019s idea won over the physics world<\/p>\n Russian-language popular science writing about physics, like the field itself, is\u00a0in\u00a0much better shape than its counterparts in\u00a0the other Nobel science disciplines, biology and chemistry. Experts have already written many in-depth articles about neutrinos and the IceCube neutrino observatory, the brainchild of\u00a0this year\u2019s laureate, Francis Halzen. It\u2019s hard to\u00a0add anything new to\u00a0these accounts, so\u00a0they\u2019re a\u00a0sensible place to\u00a0start.<\/p>\n Readers are especially fortunate that Mark Bowen\u2019s book \u201cThe Telescope in\u00a0the Ice: Inventing a\u00a0New Astronomy at\u00a0the South Pole\u201d<\/a> was translated into Russian a\u00a0few years\u00a0ago. It\u00a0tells the story of\u00a0this remarkable project, conceived and built through Halzen\u2019s efforts. Written in\u00a02017, the book is\u00a0now quite dated, but only in\u00a0its account of\u00a0neutrino \u201cdiscoveries\u201d (modern physics moves fast). Its central story \u2014 that of\u00a0Halzen and his creation \u2014 remains accurate and fascinating.<\/p>\n , physicists Dmitry Naumov and Igor Ivanov of\u00a0the Joint Institute for Nuclear Research\u2019s Laboratory of\u00a0Nuclear Problems gave our readers a\u00a0detailed explanation<\/a> of\u00a0what neutrinos are and how scientists search for cosmic neutrinos in\u00a0the depths of\u00a0Russia\u2019s Lake Baikal. That article focused on\u00a0IceCube\u2019s counterpart, the Baikal-GVD neutrino observatory. This is\u00a0one of\u00a0the rare fields in\u00a0which Russian science contributes research that complements work elsewhere in\u00a0the world, rather than trying to\u00a0catch up.<\/p>\n Baikal-GVD is\u00a0in\u00a0the opposite hemisphere from IceCube and operates in\u00a0water rather than\u00a0ice. This is\u00a0a\u00a0major advantage, rather than a\u00a0compromise dictated by\u00a0circumstances (though working at\u00a0Lake Baikal is\u00a0certainly easier than working in\u00a0Antarctica). Data from the two facilities complement each other: Their positions on\u00a0opposite sides of\u00a0the Earth help pinpoint the sources of\u00a0incoming particles, while detectors in\u00a0water offer greater precision than those in\u00a0ice, where light scatters more readily.<\/p>\n The Russian \u2014 or, more accurately, Soviet \u2014 connection to\u00a0this year\u2019s prize is\u00a0clear. The USSR began building a\u00a0similar neutrino telescope back in\u00a0the early 1980s. More significantly, Soviet physicist and Academy of\u00a0Sciences member Moisey Markov proposed searching for traces of\u00a0neutrinos in\u00a0large natural bodies of\u00a0water or\u00a0ice, such as\u00a0lakes or\u00a0seas, as\u00a0opposed to\u00a0building purely laboratory-based detectors, which also exist.<\/p>\n Markov proposed the idea<\/a> at\u00a0a\u00a0conference in\u00a0Rochester in\u00a01960. This wasn\u2019t a\u00a0case<\/a> of\u00a0an\u00a0idea that occurred to\u00a0a\u00a0lone Soviet scientist, appeared in\u00a0an\u00a0obscure journal, and was rediscovered in\u00a0the West many years later. Markov presented it\u00a0in\u00a0Rochester himself, and many Western physicists immediately recognized its potential and embraced\u00a0it. Francis Halzen was among those who embraced\u00a0it. The laureate himself recalled<\/a> that moment:<\/p>\n How is\u00a0such a\u00a0detector built? That has also been known since 1960. I\u00a0like to\u00a0recall a\u00a0photograph [\u2026] of\u00a0Markov, who had the idea, together with , because Pontecorvo had basically every idea in\u00a0neutrino physics \u2013 except this\u00a0one. This one was Markov\u2019s idea. What you do\u00a0is\u00a0build a\u00a0. You go\u00a0deep in\u00a0the ocean, or\u00a0in\u00a0the case of\u00a0Russia, you go\u00a0deep into Lake Baikal. It\u00a0is\u00a0dark. You install light sensors, filling a\u00a0kilometer cube of\u00a0water with them. <\/p>\n You take your imaginary kilometer, and you detect particles coming through the Earth. If\u00a0a\u00a0particle comes through the earth, it\u00a0is\u00a0a\u00a0neutrino. No\u00a0other particle comes through the Earth. What does this neutrino\u00a0do? It\u00a0goes through the detector, and you do\u00a0not see anything. However, about one time in\u00a0a\u00a0million, in\u00a0the region we\u00a0are interested in, and where IceCube operates, the neutrino will crash into a\u00a0proton. Then you get a\u00a0nuclear reaction, and the water turns blue, precisely as\u00a0it\u00a0does in\u00a0a\u00a0nuclear reactor [\u2026]<\/p>\n These two paragraphs essentially explain everything you need to\u00a0know about how IceCube works and the idea that earned the Nobel Prize. To\u00a0unpack this concise description, we\u2019ll start with neutrinos.<\/p>\n What is\u00a0a\u00a0neutrino, and why look for it?<\/p>\n \u201cThe neutrino joined the ranks of\u00a0elementary particles tentatively and timidly,\u201d Moisey Markov wrote in\u00a0his 1964 monograph. \u201cFor several years, it\u00a0was unclear whether the neutrino was a\u00a0real particle or\u00a0a\u00a0theoretical concept that successfully described, in\u00a0quantitative terms, the disappearance of\u00a0energy and angular momentum in\u00a0various reactions.\u201d<\/p>\n In\u00a0plainer, modern language, this means that physicists initially just made neutrinos\u00a0up. They invented them to\u00a0save the law of\u00a0conservation of\u00a0energy in\u00a0certain radioactive decay processes that produced electrons. Under the conservation laws, these electrons should have had specific, fixed energies \u2014 but for some reason, they didn\u2019t: Their energies formed a\u00a0continuous spectrum rather than a\u00a0set of\u00a0discrete values. That was when, as\u00a0the story is\u00a0now understood, Austrian-German physicist Wolfgang Pauli proposed that these decays also produced a\u00a0hypothetical particle that carried away some of\u00a0the energy and angular momentum.<\/p>\n This saved the law of\u00a0conservation of\u00a0energy, but at\u00a0a\u00a0considerable cost: The \u201cinvented\u201d particle had to\u00a0have no\u00a0charge, no\u00a0mass, and almost no\u00a0interactions with anything at\u00a0all. Proving that it\u00a0even existed was virtually impossible at\u00a0the time, which naturally troubled physicists, who dislike such intangible things.<\/p>\n The neutrino\u2019s defining property \u2014 both its strength and its weakness as\u00a0a\u00a0tool for studying the world \u2014 is\u00a0that it\u00a0participates only in\u00a0what is\u00a0called the weak interaction. Gravity also affects it, but so\u00a0slightly that this effect can often be\u00a0ignored. The weak interaction is\u00a0one of\u00a0the four fundamental interactions, alongside the strong interaction, electromagnetism, and gravity. It\u00a0acts over an\u00a0extremely short distance, smaller even than an\u00a0atomic nucleus.<\/p>\n Neutrinos are often described as\u00a0light, almost ethereal particles that pass through matter like incorporeal angels. But that description isn\u2019t quite right. Nearly 65 billion neutrinos do\u00a0pass through every square centimeter of\u00a0our bodies every second without us\u00a0even noticing. But that isn\u2019t because these particles are so\u00a0light.<\/p>\n Although the neutrino\u2019s exact rest mass is\u00a0still unknown (another remarkable property of\u00a0these particles), its tremendous speed can give it\u00a0as\u00a0much energy as\u00a0a\u00a0tennis ball delivers on\u00a0impact. If\u00a0a\u00a0neutrino like that somehow decides to\u00a0interact with you, you\u2019ll certainly notice. The probability is\u00a0vanishingly small, however: It\u00a0has to\u00a0hit a\u00a0suitable atomic nucleus with precision down to\u00a0fractions of\u00a0. Only then does the neutrino have a\u00a0chance to\u00a0interact and release its energy at\u00a0the end of\u00a0its journey. The fact that this never happens to\u00a0people tells us\u00a0less about how light and insubstantial neutrinos are than about how people, like all visible matter, consist mostly of\u00a0empty space.<\/p>\n So\u00a0how did scientists prove that neutrinos exist, and even build detectors for them? As\u00a0you might guess, even very rare events can be\u00a0detected if\u00a0they have enough opportunities to\u00a0happen. For neutrinos, this means entering a\u00a0medium where they can interact to\u00a0produce other, more tangible particles that scientists can detect. Even in\u00a0a\u00a0detector, the neutrino itself remains invisible. What scientists can detect is\u00a0the electron, or\u00a0another, heavier charged particle called a\u00a0muon, produced by\u00a0the interaction.<\/p>\n From here, the physics becomes somewhat more familiar: Charged electrons and muons moving at\u00a0tremendous speeds through a\u00a0medium such as\u00a0water begin to\u00a0emit what is\u00a0called Cherenkov radiation. It\u00a0resembles the shock wave produced by\u00a0a\u00a0supersonic aircraft in\u00a0air and occurs when a\u00a0particle moves faster than light travels in\u00a0that particular medium \u2014 water, for example. (Don\u2019t worry: The speed of\u00a0light in\u00a0a\u00a0vacuum is\u00a0still unattainable!)<\/p>\n Cherenkov radiation is\u00a0what makes the water tanks in\u00a0nuclear reactors glow pale blue. Essentially, all that neutrino detectors such as\u00a0IceCube and Baikal-GVD do\u00a0is\u00a0record flashes of\u00a0this radiation.<\/p>\n Of\u00a0course, this makes everything sound too simple. In\u00a0practice, neutrino physicists\u2019 main challenge is\u00a0contending with constant noise from an\u00a0endless stream of\u00a0other particles. These particles also produce Cherenkov radiation that the detectors pick up, but they aren\u2019t neutrinos. Or\u00a0they are neutrinos but come from other sources: those same nuclear reactors, the center of\u00a0the Earth, where radioactive decay occurs, the center of\u00a0the Sun (the main source of\u00a0noise), or\u00a0space.<\/p>\n But cosmic neutrinos come in\u00a0different kinds. Some \u2014 the overwhelming majority by\u00a0number \u2014 are produced near Earth through the decay of\u00a0protons that have entered the region of\u00a0the planet\u2019s magnetic field. These are neutrinos too, of\u00a0course, but they aren\u2019t the ones most physicists and astronomers are interested in.<\/p>\n Much more interesting are particles produced outside our solar system, or, better still, outside our galaxy altogether. They are far, far less numerous than neutrinos from other sources, but only these can have extremely high energies, in\u00a0the hundreds of\u00a0teraelectronvolts. No\u00a0processes on\u00a0Earth can produce particles with such energies, but supernova remnants and the centers of\u00a0quasars\u00a0can. Detections of\u00a0these particles are fairly rare, and some remain unique, such as\u00a0the recent detection of\u00a0a\u00a0neutrino with an\u00a0energy of\u00a0120 petaelectronvolts<\/a> by\u00a0KM3NeT, a\u00a0deep-sea telescope in\u00a0the Mediterranean.<\/p>\n Exactly which processes produce these extraordinarily energetic particles remains a\u00a0mystery. IceCube, Baikal-GVD, KM3NeT, and other similar detectors are being built to\u00a0investigate that question. This means creating a\u00a0new kind of\u00a0astronomy in\u00a0which neutrinos take the place of\u00a0light or\u00a0radio waves. Gravitational waves recently opened a\u00a0second \u201cwindow\u201d onto the sky; detectors such as\u00a0IceCube have opened a\u00a0third, a\u00a0neutrino window. The Nobel Committee recognized the opening of\u00a0that window this year.<\/p>\n At\u00a0Meduza, we\u00a0are committed to\u00a0transparency about our use of\u00a0artificial intelligence in\u00a0the newsroom. The story you\u2019re reading was written by\u00a0one of\u00a0our living, breathing journalists and translated from Russian using an\u00a0AI\u00a0model configured to\u00a0follow our strict editorial standards. This translation process is\u00a0the result of\u00a0extensive testing and refinements to\u00a0ensure our English-language coverage is\u00a0timely and accurate. A\u00a0Meduza editor reviews every draft before publication.<\/p>\n If\u00a0you find any errors in\u00a0this translation, please contact us\u00a0at\u00a0[email\u00a0protected]<\/a>.<\/p>\n