Privacy and Security Notice
Particle Physics Bedtime
A Bedtime Primer on Particle Physics, with Links for Children and Adults Alike
This story is laden with links for education and entertainment in a particle physics sort of way. Physicists and other kids should read The Whole Thing before going to links. The story will be more enjoyable that way and, well, context is everything. After visiting a link, click the "Back" button on your browser to return to this page.
Once upon a time, there were three particles in the atom:
the proton, the electron, and the neutron. The electron would dance around the other two all day long and they were very happy together, even though no one knew why many protons could stay close to each other in the nucleus of the atom without pushing themselves apart. And since that early time it came to be understood that the proton charge is so positive, and the electron charge is so negative, and the neutron charge is just neutral.
Image Courtesy of CPEP/Lawrence Berkeley Laboratory
It was Rutherford, really, who discovered how much fun it could be to learn about the nuclei of atoms by firing alpha particles at them and seeing how they scattered. In doing so, he sort of let the cat (owned, no doubt, by Schrodinger) out of the bag.
Physicists, who are good scientists but are always curious, began to make devices to shoot particles at higher and higher energies at the nucleus, so as to understand more of what is inside. These devices are called accelerators because they accelerate particles up to high speeds and, more important, high energies.
Image Courtesy of Fermilab
Soon, the physicists began to notice that the protons and neutrons were made up of something, and that they were held together and bound in the nucleus by something else. And being so intensely curious, they began build bigger, more powerful accelerators to find out what these somethings were.
It was Gell-Mann, really, who figured out what the somethings were. He called them, whimsically,
quarks, even though he wasn't sure such things really existed. Well, those curious physicists went right on with their accelerators and showed that quarks do indeed seem to exist. There are up quarks, which are positive but not so positive as protons. There are down quarks, which are negative but not so negative as the electron. There are other quarks, too.
Two up quarks and a down quark make a very nice proton, thank you, and two down quarks and an up quark make up a fine, strapping neutron, you are very welcome. But electrons have no quarks at all and do not seem to be made up of anything smaller than themselves. What's more, electrons have a lot less mass than protons or neutrons. So we call electrons and their kin
leptons. We call protons, neutrons, and all their kin that are made of quarks hadrons.
Image Courtesy of CPEP/Lawrence Berkeley Laboratory
Hadrons are held together by the Strong nuclear force, carried by "exchange particles" called gluons. They can also interact by means of the
Weak nuclear force, carried by bosons and by the Electromagnetic force, carried by photons. It was Weinberg, really, who showed everyone that the Weak and the Electromagnetic forces are really parts of one force, called the Electroweak force. Weinberg understands this. I'm not sure I do, but I'm very curious.
So the quarks dance about inside the hadrons and the electrons never stopped twirling around the nucleus and the gluons and the bosons and the photons just seem to be flitting about everywhere, like so many messengers and royal pages and diplomatic attaches and newspaper reporters. And everyone is exceedingly happy with this
Standard Model of matter.
Except...
Image Courtesy of Fermilab
How do particles really get their masses? Why is the top quark 50,000 times the mass of the up quark? If we can unify Weak and Electromagnetic forces, can we find a way to include the Strong force? And what about
Gravity? Does it fit in anywhere?
It was all those curious physicists, really, who built the giant
Tevatron accelerator at Fermilab in Illinois and who are building the Large Hadron Collider at
CERN in Switzerland to try to answer some of these questions.
Photos Courtesy of CERN
And if you begin to explore some of these things too you will discover that they are, really, very curious and very happy.
To comment on this web page or to request more information on Education and Outreach by the Hampton University Particle Physics Group, please use the contact information below.
E-Mail:cecire@jlab.org
Tel: (757)269-5511
Fax: (757)269-6273
Contact Person: K. Cecire, HU
Last Updated: August 1999
...unless otherwise noted!