Why does the Universe contain stars, planets, and living beings rather than only light? A hypothetical particle could provide part of the answer.
At the beginning of the Universe, matter and antimatter were present. They are very similar, but their particles have certain opposite properties. When a particle encounters its antimatter counterpart, both disappear completely, with their mass being fully converted into energy, according to the famous formula e=mc².
What is the origin of matter?
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Yet matter eventually prevailed. Enough remained to form galaxies, followed by stars and planets. Physicists are still trying to understand why this imbalance occurred, even though the two forms of matter should have been equal at the outset.
Two researchers, one in the United Kingdom and the other in India, focused on a particle often left out of calculations: a heavy neutrino. Known neutrinos are extremely light particles that interact very little with matter. Their more massive cousin remains hypothetical.
In the model studied, this heavy neutrino would interact so rarely with other particles that it could survive long after its formation. For a time, it might even have represented a significant part of the Universe. Its presence would then have altered the rate at which the Universe expanded.
This would have changed the time at which certain interactions between particles became effective. These interactions play a role in mechanisms capable of creating an excess of matter over antimatter. In other words, a particle almost absent from ordinary reactions could have influenced their outcome by changing the conditions under which they occurred.
The particle would eventually decay. But the effects of this particular period could still be reflected in the current distribution of matter.
For now, no one has observed this heavy neutrino or confirmed that it existed in the past. The study is theoretical work exploring what would happen if the particle had certain characteristics.
To test this hypothesis, physicists are considering looking for traces in very ancient gravitational waves, tiny distortions of space produced in the early cosmos. Future observations could help determine whether this scenario truly describes part of our history.