Narrator: 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.