Forces of
Nature
What are we made of ?
The Strong Nuclear Force
The strong nuclear force is
described by a theory that is
similar to electromagnetism…
except that the fields carry
(colour) charge…..
This difference changes the
way in which the vacuum is
polarized so that…
Confinement
You can never pull hard enough to
liberate a quark from a proton…
The QCD Vacuum
Every so often quantum effects create a quark anti-quark pair.
The attractive force is so strong that
binding energy >> mass energy
The vacuum has lower energy if it fills itself with quark antiquark pairs!
The vacuum is really full of quark anti-quark pairs with a density
15
3
like that of an atomic nucleus (10 grams/cm ) !!
The Proton Mass
The quark pairs are responsible for the proton’s mass
Interaction
energy provides
proton mass
Neutrinos
Gravity
The problem of understanding planetary motion
Descartes (1636) had a model
of fluid vortices
It didn’t match the observations!
Newton (1687) proposed a universal law of gravity
2
F= GmM/r
Which acted instantaneously at a distance on planets in an empty
space – it worked!
Relativistic Space-Time
Newton’s gravity can’t be the whole truth… instantaneous action at a
distance is forbidden….
General Relativity describes gravity in a new way
Particles travel by the shortest path in a space curved by
masses
Space-time is like a rubber sheet that can be bent
Note: only the surface exists!
Note: change to gravity and F=ma sets gravit. mass = inertial mass
Gravitational Waves
A very heavy mass, like a star, distorts the space time
sheet if it oscillates or collides with something…
The energy loss from this emission has
been seen for a pair of orbiting neutron
stars
Searches are now on to see these
very weak waves directly at LIGO