9. Symmetry and antimatter
A consequence of special relativity is that mass is a form of energy :
e = mc2. You don't need a special conservation law for mass.
In theory all the mass of a piece of matter can transform itself in energy
and viceversa the energy contained in radiation (light) can transform itself
in matter with mass. I.e. matter transforms in radiation. But, if you look
at how things really work, you find a peculiar asymmetry : in fact a particle
of big mass can transform itself only in (stable) particles of lesser mass but
the transformation in radiation only is impossible or forbidden as physicists
say, since the properties of matter are different from properties of radiation.
Then Dirac made an astonishing hypothesis : that in addition to matter, antimatter exists whose properties are such that when it fuses with matter the result
is pure radiation. Well antimatter exists and is currently produced
in particle accellerators! So now we have a complete symmetry:
matter + antimatter = radiation .
The most fascinating thing about antimatter is that you have also antiatoms,
antimolecules etc...In principle nothing forbids the existence of antiworlds with aliens made by antimatter. If a spaceship from such antiworld arrives
on Earth it will explode producing something similar to the blow-up of many
atomic bombs.
For this reason we are almost sure that the Universe contains very little
antimatter, the only exception being antineutrinos.The antineutrino
interacts so little with matter that can cross the entire Earth without
annihilating itself.So,antineutrinos are the only antimatter present in abundance everywhere around us. Each of us,through antineutrinos, can experiment
a constant rain of antimatter particles crossing his body.
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