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 ….