What is the smallest particle in the universe? (What about the largest?) - Livescience.com

At Fermilab, scientists use a particle accelerator to smash individual particles together and look at the debris — or possible new fundamental particles — that come out.

Lincoln said there are two ways to measure the size of particles: investigating their mass and measuring their physical size, like calculating the diameter of a ball.

The lowest nonzero-mass particle we know of is the neutrino, Lincoln said.

He pointed out, however, that we don't have the exact measurement of a neutrino's mass because the instruments used to calculate mass of fundamental particles aren't sensitive enough.

"A neutrino is a particle, sort of the ghost of the subatomic world," Lincoln said.

Physicists use electron volts (eV) to measure the mass of subatomic particles, Lincoln said.

To figure out the mass of a subatomic particle, then, you'd use Albert Einstein's famous equation E=mc^2 to get the mass (m) in kilograms.

An electron weighs 511,000 electron volts, which is equivalent to 9.11 x 10^-31 kilograms, according to Lincoln.

Conversely, the largest (in terms of mass) fundamental particle we know of is a particle called a top quark, measuring a whopping 172.5 billion electron volts, according to Lincoln.

Quarks are another fundamental particle that, as far as we know, cannot be broken down into more parts?

Up and down quarks make up protons and neutrons, and they weigh 3 million and 5 million electron volts, respectively.

We know the physical size of some particles, but not the smallest ones.

Currently, the smallest physical size scientists can measure with a particle accelerator is 2,000 times smaller than a proton, or 5 x 10^-20 m.