FUNDAMENTAL PARTICLES AND
PROCESSES!
Exact theories of three of
the four fundamental forces exist, in terms of exchange of
virtual “vector bosons”. One for the electromagnetic force,
three for the weak force and eight for the strong force. The
electromagnetic boson, the photon, couples to charge. The weak
bosons, W± and Z0, couple to weak
charge, and the strong bosons (gluons) couple to color.
Colors: red, green and blue.
Anticolors: yellow [anti-blue], cyan [anti-red] and magenta
[anti-green]. Quarks carry a color, while gluons carry a color
and an anticolor. Color couples to gluons, so not only can
quarks emit and absorb gluons, gluons themselves can also emit
and absorb gluons! Color cannot exist except inside
hadrons. In the external world, all objects must be “white”
(colorless). Hence quarks and antiquarks cannot be pulled out
of hadrons, and gluons cannot cross empty space from one
hadron to another!
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The
fundamental point particles of which the universe is made are
two quarks and the electron. However, in addition to
these up and down quarks, there are four other quarks,
strange, charmed, top and bottom. And in addition to the
electron, there are five other leptons, the muon, the tauon,
and three neutrinos! There is at least one other
fundamental pointlike particle of which nothing is known, the
so-called dark-matter particle.
Color cannot exist
outside of a “quark-gluon” plasma such as existed in the
early universe at the age of a millionth of a second, or
inside the proton and neutron today. So since gluons carry
color, protons and neutrons cannot interact by exchanging
gluons, they have to exchange virtual, colorless
quark-antiquark pairs! The lowest-mass mesons
involved are the so-called pi-mesons. That's why the
strong force appears to be so weak when it acts between a
proton and neutron, but appears to be infinitely strong
when it acts between two quarks!
The force between quarks becomes constant
at large distances, so that the work required to pull a
quark, or any other colored object, out of a bound system
is infinite. Color is absolutely confined.
Inside a proton or
neutron things are as complex as they can get.
Empty space, the
vacuum, is also as complicated as it can get!!
Effective field theory
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String theory
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The standard model
of particles and fields is obviously incomplete. It does
not include gravity, and does not include the two major
components of the universe, Dark Matter and Dark Energy.
At the present time, there are no clues from experiment as
to what needs to be done to generalize the approach
further. Any day now, some discovery could be made at the
Large
Hadron Collider, which would point out the way our
descriptions need to go to become still more general.
A POSSIBLE HINT FOR
THE FUTURE.
The Standard Model has
been dazzlingly successful, but it only describes about 5%
of the universe. Nearly 27% of the universe consists
of Dark Matter, individual particles with large mass(?)
but interacting (presumably) only gravitationally and
weakly. And perhaps 68% of the universe is composed
of an energy field in the vacuum of space itself, an
intrinsic property of space... Dark Energy. Dark
Matter can be observed indirectly by gravitational
microlensing, and there is hope of detecting it on earth,
or making it in the LHC. Dark Energy is observed
indirectly only, by causing increasing acceleration of
more and more distant objects... but this effect is
difficult to measure accurately... and our state of
knowledge may change drastically in the near future.
What about gravity? There
are two main efforts to obtain a quantum theory of
gravity. One is String Theory, which automatically
contains a string excitation that is a spin-2 graviton.
However, there is no experimental evidence whatsoever that
string theory has anything to do with reality. The other
approach is Loop Quantum Gravity, which quantizes
space-time itself, so that “instead of having fields in
space-time, you have fields in a field.” There is no
experimental evidence so far that loop quantum gravity is
correct.
The Early Universe!
Large Hadron Collider!
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