2.33. Fundamental Particles http://www.ck12.org
carrying fundamental particles. The different types of bosons and the forces they carry are shown inTable2.8.
Consider the examples of gluons, the bosons that carry the strong nuclear force. A continuous exchange of gluons
between quarks binds them together in both protons and neutrons. Note that force-carrying particles for gravity
(gravitons) have not yet been found.
TABLE2.8: Bosons and Fundamental Forces
Type of Bosons Fundamental Force They
CarryParticles They Affect Distance over Which
They Carry Force
Gluons strong nuclear force quarks only within the nucleus
W bosons
Z bosonsweak nuclear force leptons and quarks only within the nucleusPhotons electromagnetic force leptons and quarks all distances
Gravitons (hypothetical) force of gravity leptons and quarks all distancesQ:Which type of boson carries force between the negative electrons and positive protons of an atom?
A:Photons carry electromagnetic force. They are responsible for the force of attraction or repulsion between all
electrically charged matter, including the force of attraction between negative electrons and positive protons in an
atom.
Q:Gravitons have not yet been discovered so they have only been hypothesized to exist. What evidence do you think
leads scientists to think that these hypothetical particles affect both leptons and quarks and that they carry force over
all distances?
A:Gravity is known to affect all matter that has mass, and both quarks and leptons have mass. Gravity is also known
to work over long as well as short distances. For example, Earth’s gravity keeps you firmly planted on the ground
and also keeps the moon orbiting around the planet.
The Standard Model
Based on their knowledge of subatomic particles, scientists have developed a theory called thestandard modelto
explain all the matter in the universe and how it is held together. The model includes only the fundamental particles
in theTable2.8. No other particles are needed to explain all kinds of matter. According to the model, all known
matter consists of quarks and leptons that interact by exchanging bosons, which transmit fundamental forces. The
standard model is a good theory because all of its predictions have been verified by experimental data. However,
the model doesn’t explain everything, including the force of gravity and why matter has mass. Scientists continue
to search for evidence that will allow them to explain these aspects of force and matter as well. You can learn much
more about the standard model at the URL below. Click on “the standard model” and follow the sequence titled
“What is fundamental?”
Summary
- For centuries, scientists searched for the fundamental particles of matter and the “glue” that holds them
together. At first, scientists thought that atoms were the fundamental particles. Now they know that there
are smaller, simpler particles than atoms that make up matter and carry the forces that hold matter together. - Protons and neutrons are made up of fundamental particles of matter called quarks. Electrons are another type
of fundamental particles of matter called leptons. Bosons are fundamental particles that carry forces between
fundamental particles of matter.