Finishing things up

So what’s with that 14C?

Masses of isotopes (not “natural” stuff) truly are multiples of basic hydrogen.

Hydrogen is positively charged.

Could there be neutral particles, same mass as hydrogen atoms?

The neutron

Chadwick discovers the neutron (1930)

Explains isotopes => nucleus contains both protons and neutrons.

Neutrons subject to strong nuclear force.

Another look at EM and Gravity

Action at a Distance (Newton) vs. Fields (Faraday)

Light is a wave (Thomas Young, 1801)

Albert Einstein: The Photoelectric effect shows that light behaves as a particle!

So, is EM a wave, a field, a particle, or what?

Forces and “their particles”: mediators

The photon, a particle of light, is the “particle” associated with the force of electromagnetism.

How do mediators work?

Does each force have its own mediator?

Back to particles . . .

Trying to find the mediator of the strong force . . .

1937 – a new particle discovered in cosmic rays – the “mu meson”, or muon

Couldn’t be mediator of strong Force

“Who Ordered that??” I. Rabi

Other particles . . .

Strong force mediator – pi meson, or “pion”; other mediators?

Neutrino – electron and muon types (at least)

Are we done yet? How do we know?

Splitting the “particles”

Electrons, muons have no structure: these are basic particles (with the tau particle)

Neutrons and protons do have structure: they must have “parts”

Murray Gell–Mann “quarks”

“Three quarks for Muster Mark”

Well, really only two at first: up and down

Proton = 2 up + 1 down

Neutron = 1 up + 2 down

Kaons and Sigmas: “Strange” quarks

Quarks and Leptons and Bosons, Oh My!

What do we have now?

6 quarks, 6 leptons; with antiparticles

4 mediators (one per force)

Higgs field?

Why do we have all this stuff??

Only need two quarks, an electron, and the electron neutrino to make up all of matter.

New theories

How far have we come?