Not
only have we found sub atomic particles but we also now know there is 'anti-matter'.
Anti-matter was predicted by Paul Dirac(English physicist - despite the
name!) in 1928.
He solved the equations for electron orbitals in the atom
and proposed negative energy states for electrons.
A simple example of
how he came to this conclusion is by asking ourselves,
'What is the root of 4?'
A root can produce two possible solutions +2 or -2
In 1932 Carl Anderson found experimental evidence for one in a cloud chamber (we study
those next year).
Anti-matter is the
complement to matter - it has the opposite characteristics.
Characteristics of particles are given by quantum numbers (for
charge, baryon number, strangeness etc.) - anti-particles have the opposite
sign for each one when compared to the matter particle's characteristic
quantum numbers.
Remember:
You can
have anti-matter - but there is no such thing as anti-energy!
The
rest mass of a particle is the same as the rest mass of an anti-particle - you don't have negative mass..
The
charge, baryon number and strangeness of a particle is the opposite
of the charge, baryon number and strangeness of an anti-particle.
Annihilation
An
anti-electron is a positron β+.
This
anti-particle is positive and has the same mass as an electron.
If a positron and electron
meet they annihilate one another - poof! and their combined mass (2me)
is converted to electromagnetic energy (in accordance with the Einstein
equation (E = mc2) ).
The energies are calculated
in terms of electron volts (eV) The eV is a very small unit of energy
- used a lot in nuclear calculations.
You need to be able
to convert from one to the other.
Remember at GCSE
you learned that:
E
= Q V
(joule) = (coulomb)
(volt)
So, a joule could
be thought of as a 'coulomb volt'
Similarly, if we
don't use a full coulomb of charge, but only the charge on an electron
'e'
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A simple example of
how he came to this conclusion is by asking ourselves, 
You can
have anti-matter - but there is no such thing as anti-energy!
