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.