‘The oldest of the subatomic particles called neutrinos might each encompass a space larger than thousands of galaxies, new simulations suggest.
Neutrinos as we know them today are created by nuclear reactions or radioactive decay.
According to quantum mechanics, the “size” of a particle such as a neutrino is defined by a fuzzy range of possible locations. We can only detect these particles when they interact with something such as an atom, which collapses that range into a single point in space and time.
For neutrinos created recently, the ranges they can exist in are very, very small.
But over the roughly 13.7-billion-year lifetime of the cosmos, “relic” neutrinos have been stretched out by the expansion of the universe, enlarging the range in which each neutrino can exist.
“We’re talking maybe up to roughly ten billion light-years” for each neutrino, said study co-author George Fuller of the University of California, San Diego.
“That’s nearly on the order of the size of the observable universe.” ‘ (National Geographic)