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Why does anything exist? And why is there something instead of nothing? The prevailing theory of how the universe began is the Big Bang theory. It states that some 13.8 billion years ago, a burst of growth created matter, space and time. And the Big Bang created not only matter, but antimatter.<\/p>\n
Matter and antimatter destroy each other when they meet, releasing energy. If the early universe contained equal amounts of both, they should have wiped each other out, leaving behind a universe filled with energy but no stars, planets or people.<\/p>\n
But on October 20, 2026, physicists from the University of Southampton and the Indian Institute of Technology Kanpur said they have a new theory to why everything \u2014 including us \u2014 exists. They said an often-forgotten particle, the decoupled heavy neutrino, might explain how matter dominated in the early universe.<\/p>\n
Co-author Rishav Roshan from the University of Southampton said:<\/p>\n
\nThis decoupled heavy neutrino has long been dismissed as an irrelevant background detail in particle physics.<\/p>\n
However, it decays incredibly slowly. As the cosmos cooled after the Big Bang, the particle lived long enough that it temporarily took over the energy density of the universe and triggered a matter-dominated period.<\/p>\n<\/blockquote>\n
The researchers published their peer-reviewed paper in the journal Physical Review Letters<\/em> on September 8, 2026.<\/p>\n
What is a decoupled heavy neutrino?<\/h3>\n
Neutrinos are tiny subatomic particles with no electric charge and almost no mass. They rarely interact with other matter. Trillions of them pass through your body every second without you noticing. Scientists sometimes call them ghost particles<\/em> because they are so difficult to detect.<\/p>\n
A decoupled heavy neutrino is a theoretical particle that\u2019s incredibly massive with a slow decay. It\u2019s called right-handed<\/em> because its quantum spin aligns with its direction of motion. It would interact only weakly with other particles, so it could have survived for a long time in the early universe.<\/p>\n
And because this particle would have lasted longer than other particles, it could have taken over the energy density of the cooling early universe. This would have allowed it to shift the balance to a matter-dominated universe.<\/p>\n
Let\u2019s go back to the beginning<\/h3>\n
In the moments after the Big Bang, the universe was extremely hot and dense. As it expanded, it cooled, allowing particles to interact and gradually form the building blocks of the universe we know today.<\/p>\n
The researchers propose that the heavy neutrino could have lived long enough to temporarily dominate the universe\u2019s energy. This would have changed how quickly the universe expanded and how its temperature evolved.<\/p>\n
Roshan said:<\/p>\n
\nThe decoupled neutrino shifted the temperature in the early universe at which fundamental particles \u2014 like electrons and other leptons \u2014 interacted with their antiparticles with the help of Standard Model Higgs boson.<\/p>\n
This temperature acts like a switch that shapes how the matter-antimatter imbalance was built up.<\/p>\n<\/blockquote>\n
A new look at the earliest universe<\/h3>\n
The researchers said the decoupled heavy neutrino could have profoundly altered the universe\u2019s expansion history. Besides matter and antimatter interactions, they said these special neutrinos also could have had an impact on the production of dark matter and the generation of primordial\u00a0gravitational waves.<\/p>\n
Co-author Sudipta Show from the Indian Institute of Technology Kanpur said:<\/p>\n
\nIt offers us a new explanation for how matter won.<\/p>\n
The dramatic shift in the early expansion of the cosmos leaves distinct but detectable imprints of changes, for example on primordial gravitational waves.<\/p>\n
These gravitational wave signatures open up new avenues for us to unravel the evolution of the early universe after the Big Bang.<\/p>\n<\/blockquote>\n
So does this answer the question of why does anything exist? For now, it\u2019s an intriguing theory but not a definitive answer. But it might bring us a step closer to understanding why the universe contains something rather than nothing.<\/p>\n
Bottom line: Why does anything exist? A new theory by physicists suggests a forgotten particle, the decoupled heavy neutrino, might have shifted the balance between matter and antimatter.<\/p>\n
Source: Delayed Charged Lepton Yukawa Equilibration in Minimal Seesaw<\/p>\n
Via University of Southampton<\/p>\n
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