How much does a neutrino weigh? Scientists have finally weighed the lightest elementary particle known to physics.
Physicists have just broken another record. They managed to determine how much a neutrino — an elusive elementary particle — weighs.
We have succeeded in determining precisely how much a neutrino weighs, researchers at the Karlsruhe Institute of Technology (KIT) have announced. This elusive elementary particle has long fascinated physicists. The scientific work of German researchers was published in the journal “Nature Physics”.
Neutrino — history of discovery and properties
The existence of the neutrino was theoretically predicted in 1930 by Wolfgang Pauli. This physicist proposed the existence of such a particle to balance the energy of the so-called beta radioactive decay. The idea was that the energy of the neutron did not match the sum of the energies of the particles that were created from it.
This conflicts with one of the foundations of physics — the principle of conservation of energy. Pauli came up with the idea that the missing part of the energy is lifted by a particle that is difficult to detect (and, in his opinion, not detectable at all).
In time, it was called a neutrino. Its existence could not be confirmed for a very long time. The neutrino has no electric charge and interacts very little with other particles. It was not even certain that it had mass. Some physicists assumed that it might lack mass altogether, like the photon. Others thought the neutrino had mass, just very little.
How was the mass of the neutrino measured?
Whether a neutrino has mass is of great importance to physical theories. Determining that mass accurately will help us better understand the Universe. But how can we weigh an elementary particle that hardly interacts with the rest of the matter that we and our measuring instruments are made of?
Neutrinos constantly pass through us like ghosts. To be sure of stopping a single neutrino, one would have to place a slab of lead one light year (9.5 trillion kilometers) thick in its path. Huge detectors, hidden deep below the earth’s surface, are used to detect the existence of neutrinos.
Weighing the neutrino is the goal of the international KATRIN project, led by the Karlsruhe Institute of Technology. The project involves researchers from six countries, including the USA, Spain, the Czech Republic and Russia. Scientists use the phenomenon of beta radioactive decay, occurring in atoms of the hydrogen isotope called tritium.
KATRIN is a 70 m long research apparatus. It includes a tritium source and a huge spectrometer that precisely measures the properties of electrons produced during beta decay. The experiment began in 2019 and is collecting increasingly accurate data.
“Now we have been able to reduce interference and extract a clean signal. In this way, we have achieved new results,” says Prof. Christian Weinheimer of the Westphalian Wilhelm University in Münster, spokesman for KATRIN.
What is the mass of a neutrino?
The masses of elementary particles are specified in units called electron volts (eV). In particle physics, multiples of this unit are most commonly used: thousands (keV), millions (MeV), billions (GeV) or trillions (TeV).
Here are masses of some elementary particles:
However, the neutrino is so light that its mass is less than one electron volt. That’s why it has been so difficult to measure it accurately. The scientists running the KATRIN experiment announced that the mass of the neutrino is no more than 0.8 eV.
“This is the first time we have been able to go below the one-electron-volt limit in measurements. This is an exciting achievement”, comments John Wilkerson of the University of North Carolina, one of the scientists involved in KATRIN.
However, this is not the end of the research. They are to continue at least until 2024. Scientists hope to measure the neutrino mass even more precisely. The new TRISTAN detector will help them to do that. Thanks to it, scientists hope to weigh the so-called sterile neutrinos. These are particles that may be part of the mysterious dark matter that fills the Universe.
About the Creator
“Are You Dead?”: A New App Reflects the Loneliness of Young Chinese Living Alone
In China’s rapidly changing cities, living alone is no longer unusual—especially among young adults pursuing education, careers, and independence. But as solo living increases, so do concerns about isolation, safety, and what happens when no one is around to check in. Against this backdrop, a new app with a blunt, unsettling question—“Are you dead?”—has captured public attention and ignited debate. Despite its shocking name, the app is not designed to provoke fear. Instead, it aims to address a practical and emotional gap in modern urban life: how to ensure the well-being of people who live alone, and how technology is stepping in where traditional community networks have weakened. The Rise of Solo Living in China China has witnessed a dramatic shift in household structures over the past two decades. Urbanization, delayed marriage, rising housing costs, and changing cultural values have contributed to a growing number of single-person households, particularly among people in their 20s and 30s. For many young Chinese professionals, living alone represents freedom and self-reliance. It allows flexibility, privacy, and independence from family expectations. Yet this independence often comes with trade-offs: fewer daily social interactions, weaker neighborhood ties, and limited support in emergencies. In megacities like Beijing, Shanghai, and Shenzhen, it is increasingly common for neighbors not to know each other at all. In this environment, concerns about what happens if someone becomes ill, injured, or simply disappears from daily routines have become more pronounced. What the App Actually Does Despite its provocative name, the app’s purpose is surprisingly simple. It functions as a digital check-in system. Users set regular times to confirm they are okay—by tapping a notification or completing a brief check-in. If the user fails to respond after a certain period, the app automatically alerts designated contacts, such as friends, family members, or emergency responders. The stark question, “Are you dead?”, is intentionally designed to grab attention and prompt action. Developers argue that softer language is often ignored, while blunt phrasing cuts through digital noise and encourages consistent use. In essence, the app acts as a safety net, especially for people who live alone and may not have daily contact with others. Why Young People Are Downloading It The app’s popularity reflects deeper anxieties among young adults navigating modern life. Many users say they downloaded it not because they fear the worst every day, but because it provides peace of mind—both for themselves and for loved ones. For parents living far from their children, the app offers reassurance without constant phone calls. For users, it creates a sense of being quietly watched over, without sacrificing independence. Some users have also described the app as a form of emotional comfort. Even a routine notification can feel like a reminder that someone, somewhere, would notice if they vanished from daily life. A Name That Sparked Debate The app’s name has been its most controversial feature. Critics argue that the phrase “Are you dead?” is unnecessarily harsh and reflects a growing desensitization in digital culture. Others worry that such language could amplify anxiety rather than reduce it. Supporters, however, see the name as a reflection of reality rather than a provocation. In densely populated cities where people can go unnoticed for days or weeks, the question is uncomfortable—but relevant. They argue that avoiding blunt language does not eliminate the underlying problem of isolation. The debate highlights a broader tension in tech design: Should apps prioritize emotional sensitivity, or practical effectiveness—even if it makes people uncomfortable? Technology Filling a Social Gap The rise of this app points to a larger issue: technology increasingly compensates for weakened social structures. In the past, extended families, close-knit neighborhoods, and workplace communities naturally checked in on individuals. Today, those informal safety nets are often absent. Apps like this one are not just tools; they are symptoms of a society where digital solutions are replacing human presence. While convenient, this raises questions about whether technology is addressing the root causes of loneliness—or simply managing its consequences. Still, for many users, the app is not a replacement for relationships, but a supplement to modern life realities. Living Alone Does Not Mean Wanting to Be Alone An important takeaway from the app’s success is that living alone is not the same as wanting isolation. Many young Chinese adults value independence but still crave connection, security, and acknowledgment. The app’s routine check-ins, though minimal, provide a structured moment of contact. In a fast-paced, high-pressure environment, even small gestures of recognition can matter. This trend also reflects changing attitudes toward mental well-being and personal safety. Younger generations are more open to discussing vulnerability and using tools that previous generations might have dismissed. What This Says About Modern Urban Life The popularity of an app that asks such a stark question speaks volumes about the realities of contemporary urban living—not just in China, but globally. As cities grow larger and lives become more individualized, people are searching for new ways to ensure they are seen, remembered, and protected. The app’s success suggests that people are willing to engage with uncomfortable ideas if they address real needs. It also underscores the importance of designing technology that is honest about modern challenges, rather than masking them with euphemisms. Conclusion: A Wake-Up Call, Not a Warning While the phrase “Are you dead?” may sound alarming, the app behind it is less about fear and more about care. It reflects a generation navigating independence in a world where traditional support systems no longer function as they once did. Rather than signaling a morbid obsession, the app serves as a quiet reminder of something deeply human: the need to be noticed. In that sense, its blunt question is not about death at all—but about presence, connection, and the reassurance that someone would check if you were gone. As solo living continues to rise, tools like this app may become less shocking and more commonplace—symbols of how society adapts to changing ways of life in the digital age.
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