A universe is a big place, but it’s made out of small pieces. The periodic table includes carbon, oxygen, and other building blocks that makeup cups of coffee, cats, or stars. Since the start of the 20th century, scientists have been trying to find out smaller and smaller fundamental particles, those thinner than atoms that fill up the universe.
Don Lincoln, a senior scientist at Fermi National Accelerator Laboratory near Chicago, is one of the scientists answering this question. Over there, scientists use a particle accelerator to smash individual particles together and look at possible new fundamental particles or the debris that come out. According to Don, to measure the size of a particle, there are two ways to measure its physical size and investigate its mass.
In terms of mass, these questions are relatively simple to answer. Don said the lowest nonzero-mass particle know is the neutrino. The exact measurement of a neutrino’s mass is unknown because the instruments used to calculate the mass of fundamental particles aren’t sensitive enough.
“A neutrino is a particle, sort of the ghost of the subatomic world,” Lincoln said. With the matter, Neutrinos interact very weakly and are 2nd most abundant particle after photons. There are trillions of neutrinos passing through a person at this very second. They weigh nearly nothing and travel close to the speed of light.
An atomic nucleus is made up of electrons, protons, and neutrons. Protons and Neutrons themselves are about one-tenth the size of the nucleus as a whole, Don said. An electron has a near-zero mass, but it weighs 500,000 times more than a neutrino. Don said physicists use electron volts to measure the mass of subatomic particles. Technically, the unit is eV/c^2, in which c is the speed of light. One electron volt is equal to about 1.6×10^-19 joules. To make things easy, a set of units were used by physicists whereby the speed of light is 1. To figure out the mass of a subatomic particle, use E=mc^2 to get the mass (m) in kilograms (Albert Einstein’s equation). According to Don, an electron weighs 511,000 electron volts, equivalent to 9.11 x 10^-31 kilograms.
According to Don, the largest fundamental particle known is called a top quark, measuring a whopping 172.5 billion electron volts. They are another fundamental particle that cannot be broken down into more parts. Scientists have found six types of quarks: the top, bottom, charm, strange, down, up. Down and up quarks make up protons and neutrons, and they weigh 5 million and 3 million, respectively.