The Quark Theory of Matter
• Developed in early 1960s to help explain a proliferation of mysterious subatomic particles found in “atom smashers” [particle accelerators]
• Further developed up to present day
• Proton and neutron are no longer “fundamental” particles• They are composed of quarks
• “Free” quarks are not stable, they quickly recombine
• Quarks are bound together by “gluons”
Size Scales – a Comparison
Virus 10-7 m
Molecule 10-9 m
Atom 10-10 m
Nucleus 10-14 m
Proton 10-15 m
Electron 10-18 m
Quark 10-19 m
The Quarks
Name Charge
Up (u) +2/3
Down (d) -1/3
Charm (c) +2/3
Strange (s) -1/3
Top (t) +2/3
Bottom (b) -1/3
udu u dd
Proton Neutron
• Some particles are composed of 3 quarks (above)
• Some particles (mesons, found in cosmic rays) are made of 2 quarks
• No single quarks are observed in nature
What we don’t know ….
• Why quarks can have “fractional” charge when the electron (still thought to be “fundamental” has a charge of -1 ?
• Whether any of the exotic particles we know about now can account for “dark matter” that we believe is in most galaxies
• Whether there really is a graviton …
• How to reconcile gravity and quantum/subatomic physics
• and lots more besides …stay tuned ….