Someone watching a car
accelerate toward light speed
would see something
very strange.
It would seem as though the
car itself were getting shorter
and that time for the person
in the car was slowing down.
However, you wouldn't
see these effects
until the car began to
approach the speed of light.
At 90% of the speed of light
the car would appear to shrink
to 44% of its usual length.
This thought experiment
answered Einstein's
old question
about what he would see
if he traveled along
with a beam of light.
He simply couldn't
make the trip
for at the speed of light,
length would contract to zero
and time would stop.