8. Symmetry and Einstein's special relativity
Among other big contributions to science, Einstein was the creator of
two theories that have both the name of relativity and are
both deeply related to symmetry.
The easiest of the two is the special relativity.
This is based on the well known fact(Galileo remarked it first) that an
experiment or a machine works in the same way if it is still or
in a rectilinear uniform motion(car going with uniform speed on a straight
way).
Lorenz found that this simple symmetry principle must be corrected
since nothing can go more quickly than light. Einstein developed it
completely discovering that only massless objects can go at light
speed (and they are forced to go always at this speed). For normal
objects as speed approaches the light's speed, a series of
phenomena appear that make more and more difficult the accelleration:the mass
will increase,the size along the motion will decrease and the time will
slow down.So the accellerating twin coming back on Earth will find the
brother dead.All this has been verified with particles in accellerators
that get heavier and heavier as they are accellerated and ,if they decay,they will do this more slowly.
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