Relic neutrinos are stretched out by the expansion of the universe just as the universe itself has stretched out from the “big bang” some 13.7 billion years ago. Today, these meganeutrinos could be as large as the Milky Way in contrast to the new neutrinos which are among the smallest particles known to science.
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Charles Q. Choi, National Geographic News
June 2, 2009
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.”
“Small” Physics, Writ Large Neutrinos have no charge, and their masses are so tiny they have yet to be accurately measured.
This means that neutrinos, which zip around at nearly the speed of light, can pass through normal matter largely undisturbed.
Most neutrinos that affect Earth come from the sun. Billions of solar neutrinos pass through the average human every second.
While trying to calculate masses for neutrinos, Fuller and his student Chad Kishimoto found that, as the universe has expanded, the fabric of space-time has been tugging at ancient neutrinos, stretching the particles’ ranges over vast distances.
Such large ranges can remain intact, the scientists suggest in the May 22 issue of Physical Review Letters, since neutrinos pass right through most of the universe’s matter.
An open question is whether gravity—say, the pull from an entire galaxy—can force a meganeutrino to collapse down to a single location.
“Quantum mechanics was intended to describe the universe on the smallest of scales, and now here we’re talking about how it works on the largest scales in the universe,” Kishimoto said.
“We’re talking about physics that hasn’t been explored before.”
According to physicist Adrian Lee at the University of California, Berkeley, who was not part of the study team, “gravity is a real frontier these days that we don’t really understand.
“These neutrinos could be a path to something deeper in our understanding with gravity.”
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