Every second, trillions of neutrinos pass through your body. They slip through flesh, rock and even the entire Earth, leaving virtually no trace. You cannot feel them, and detecting them is extraordinarily difficult. Yet, these elusive particles could help scientists answer some of the biggest questions about the universe: What happens inside exploding stars? What powers the most extreme objects in space? And why is the universe made predominantly of matter when antimatter should also have been created?
The 2026 Nobel Prize in Physics, awarded to physicist Francis Halzen for his decisive contributions to the IceCube Neutrino Observatory and the discovery of high-energy neutrinos of astrophysical origin, has brought these ghost-like particles into the spotlight. By tracking particles rather than relying on light alone, scientists have opened a new window into the universe, one that could reveal things even powerful telescopes cannot easily see.
What makes neutrinos special?
Neutrinos are elementary particles produced in the Sun, nuclear reactions, supernova explosions and other energetic astrophysical processes. They have no electric charge and interact primarily through the weak nuclear force. This means they can travel enormous distances through matter and magnetic fields without being significantly absorbed or deflected.
Light can be blocked, scattered or absorbed on its journey through space. Neutrinos, by contrast, can escape dense cosmic environments and reach Earth carrying information about the processes that produced them.
“Neutrinos are extraordinarily abundant but interact so weakly with matter that they can travel through stars and planets largely undisturbed. They offer unique insights into stellar interiors, supernova explosions and extreme astrophysical environments,” said Prof Basudeb Dasgupta of the Department of Theoretical Physics at the Tata Institute of Fundamental Research (TIFR).
How do you catch a particle that passes through the Earth?
The very property that makes neutrinos valuable also makes them difficult to detect. Because they rarely interact with matter, scientists cannot simply observe them passing through a detector. Instead, they wait for the occasional collision that produces detectable signals.
At the IceCube Neutrino Observatory, thousands of light sensors are embedded deep within Antarctic ice, covering an instrumented volume of about a cubic kilometre. When a neutrino collides with an atom in the ice, it can produce charged particles that emit faint flashes of light. By studying these flashes, researchers can estimate the neutrino’s direction and energy.
“It is very hard because neutrinos interact very weakly. You need big detectors with lots of photomultiplier tubes, and you have to go to extreme environments such as the South Pole,” said Prof Shantanu Desai, professor in the Department of Physics at IIT Hyderabad and an adjunct faculty member in its AI department.
What has IceCube revealed?
Detecting neutrinos is only the beginning. Scientists also want to know where they come from and what produced them.
In 2017, IceCube detected a high-energy neutrino associated with a flaring active galactic nucleus, a region surrounding a supermassive black hole. The observation helped establish a link between such cosmic environments and high-energy neutrinos, offering researchers a way to investigate some of the universe’s most energetic processes.
But the mystery is far from solved. Scientists still do not know the origins of most high-energy astrophysical neutrinos detected by IceCube. Identifying their sources and understanding how they acquire such enormous energies remain major research challenges.
Can neutrinos explain why matter won?
Look around, and almost everything you see is made of matter. Yet, according to our understanding of the early universe, matter and antimatter were both produced. Antimatter particles have properties related to those of their matter counterparts, and when the two meet, they can annihilate each other.
So why did matter come to dominate the universe? Scientists have yet to establish the full explanation.
One possible clue lies in charge-parity (CP) symmetry, which concerns how physical processes compare with those involving antimatter. Researchers are investigating whether neutrinos violate this symmetry through a process called neutrino oscillation, in which they change from one flavour to another as they travel.
“Theoretically, there is an intimate connection between the question of matter-antimatter asymmetry and the properties of neutrinos. Experimentally, however, establishing this connection is hard,” said Dasgupta.
Prof Rukmani Mohanta, senior professor in the Department of Physics at the University of Hyderabad, said, “Neutrinos could help scientists investigate the origins of this matter dominance. The universe is composed predominantly of matter, but we do not yet fully understand what happened to antimatter. One possibility being investigated is whether additional sources of CP violation could be associated with neutrinos.”
What do scientists still not know?
Neutrinos have already challenged scientists’ understanding of fundamental particles, but several questions remain unanswered. Although researchers know that neutrinos have mass, their absolute masses and the ordering of their three mass states are not yet fully established.
The mass ordering refers to whether the third mass state is heavier or lighter than the other two. Determining it is a key goal of several ongoing and proposed experiments worldwide, Mohanta explained.
Another question is whether neutrinos are their own antiparticles. Establishing this could reveal important information about the fundamental nature of matter and help scientists test theories that go beyond the current understanding of particle physics.
India’s missed opportunity?
India’s neutrino research dates back to experiments at the Kolar Gold Fields in Karnataka, where cosmic-ray neutrinos were detected deep underground. The country later proposed the India-based Neutrino Observatory (INO) at Bodi West Hills in Tamil Nadu’s Theni district.
The proposed facility was designed primarily to study atmospheric neutrinos and determine their mass ordering. It was to house a 50-kilotonne magnetised iron calorimeter, but the project has faced prolonged delays and has not become operational.
Had INO materialised, it could have helped address important questions about neutrino oscillations and mass ordering, Mohanta said.
Desai, however, pointed out that INO was designed for neutrino oscillation research, not the high-energy astrophysical neutrino studies that led to the 2026 Nobel Prize. The two approaches address complementary questions, and INO would not have replicated IceCube’s research programme.
Where does India stand now?
Indian researchers continue to contribute to neutrino science through international collaborations, including IceCube and the Deep Underground Neutrino Experiment (DUNE) in the United States.
Desai said several researchers at IIT Hyderabad are working on theoretical questions involving neutrino masses and interactions. His own research examines possible astrophysical sources of high-energy neutrinos, including pulsars, magnetars and other extreme cosmic environments, to understand which could account for the signals observed by IceCube.
For India to strengthen its position in the field, experts say sustained funding, specialised infrastructure, institutional coordination and public outreach will be essential.
“Fundamental science need not promise immediate commercial applications to justify investment,” said Dasgupta. Large experiments also develop expertise in precision instrumentation, electronics, data acquisition and computational analysis, while training scientists and engineers to tackle complex technological challenges.
Neutrinos may pass through the world unnoticed, but scientists are learning how to listen to the faint signals they leave behind. Each detection offers another clue to the universe’s most energetic events and the fundamental laws governing matter. The challenge now is to turn those fleeting signals into answers.
