"All these things being considered, it seems probable to me that God in the beginning formed matter in solid, massy, hard, impenetrable, moveable particles of such sizes and figures, and with such other properties, and in such proportion to space, as most conduced to the end for which he formed them; and that these primitive particles being solids, are incomparably harder than any porous bodies compounded of them; even so very hard, as never to wear or break in pieces; no ordinary power being able to divide what God himself made in the first creation. While the particles continue entire, they may compose bodies of one and the same nature and texture in all ages: but should they wear away, or break in pieces, the nature of things depending on them would be changed. Water and earth, composed of old worn particles and fragments of particles, would not be of the same nature and texture now, with water and earth composed of entire particles in the beginning. And there, that nature may be lasting, the changes of corporal things are placed only in the various separations and new associations and motions of these permanent particles."
Isaac Newton - Optics



Nuclear and Particle Physics

Particle Physics is the discovery and measurement of the fundamental constituents and their basic interactions.

Particle Physics is not all of physics.
Þ Complex systems require new concepts,
                              e.g. Superconductivity

Particle Physicists try to ignore multibody systems.

Nuclear Physics is the study of the simplest complex systems constructed from the fundamental constituents.



The Particle Physics Universe

Constituent point fermions



interacting via forces mediated by vector bosons
W+, W-, Z0
as a consequence of gauge symmetries

SU(3)Colour(strong) x SU(2)weak x U(1)em


Unresolved questions:



Nuclear physics

* What can you make from quarks and leptons?

* What happens when the things you make fall apart?



 Conservation Laws

If nothing is conserved, then nothing can be described.


Conserved quantities, Symmetry Principles, Invariants

(Conserved quantities always correspond to some symmetry, but not always vice versa. We usually try to formulate physics in terms of relativistic invariants.)


Momentum (p) and Energy (E)
qµ = [(Ef -Ei)/c, pf -pi] and s = E2-p2 }
Angular momentum (
Electric charge (Q), colour (r,b,g), weak isospin (T3)
Baryon number (B), Lepton number (L)
Lepton generation number (Le , Lµ , Lt)
Spin-statistics relation, CPT
cross sections (s)
proper lifetimes (t), decay widths (G), branching ratios (B.R.)  


Quark generation number (1,2,3), Isospin (I)
Parity (
P), Time reversal (T), Charge conjugation (C, CP)




The number of fundamental units and the dimensions of any physical quantity are arbitrary. There are, however, several common conventions.

   SI: metre - kilogram - second - ampere (+ kelvin - mole - candela)

   Gaussian: centimetre - gram - second    (Fcoulomb = q1q2/r2)

   High Energy Physics: eV (or second or metre)
(Fcoulomb = q1q2a/r2, e=1, c=1, =1)
a = e2/(4pe0 c) = 1/137.035989(61) }


We convert between units using conversion constants:

24 hours/day
2.54 cm/inch
2.2 pounds/kg
1 esu/(cm3g/s2)1/2    
2997924580 esu/C    from (q2/r2)Gaussian = (q2/4pe0r2)SI
299792458 m/s    (c)
6.5821220(20)x10-16 eV/s-1    (=h/2p)
1.60217733(49)x10-19 C/e
1.60217733(49) x10-19 J/eV