20
R. N. Mohapatra
Just as the positron appeared as the anti-particle of electron, the same would
happen for each particle that we know since we can apply the theory of
relativity to all known particles when they move very fast. Thus was born
the concept of anti-matter. It is interesting that a simple mathematical sign
ambiguity led to a ground breaking concept of a whole new world of particles
in physics, i.e. all matter is accompanied by anti-matter. When matter and
anti-matter meet, they destroy each other and give a burst of light, carrying
the same energy as the total mass of matter and anti-matter particle together.
The anti-particle of a proton is called an anti-proton and similarly for each
particle. There also appeared a new class of particles which are their own antiparticles. For example, the photon is its own anti-particle. We come back to
this question when we discuss the mass of the neutrino.
There is also another profound implication of the energy formula of theory
of relativity: if a particle has mass, it can move at any speed less than the speed
of light, whereas if it has no mass, it can move only at the speed of light, a
realization that did not exist before the theory of relativity came along. This
will play a significant role as we try to understand the mass of the neutrino
and its implications for new physics.