Particles Larger Than Galaxies Fill the Universe?

Charles Q. Choi
for 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.

Continued on Next Page >>


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