Many people often think that they have a very clever idea
for violating the fundamental physical law
that nothing in the Universe can go faster than the speed of light.
Suppose Adam’s spaceship accelerates to a
speed just slightly less than the speed of light.
Then, once the spaceship reaches this speed, Adam will walk forward.
The idea is that the speed of the spaceship
plus Adam’s walking speed will exceed the speed of light.
However, from Sarah’s perspective outside the spaceship,
time inside the spaceship is moving very slowly.
Hence, Sarah will see Adam walking very slowly.
If the spaceship moves even faster, then from Sarah’s perspective,
time inside the spaceship will move even slower,
and Adam’s walking speed will decrease even more.
If the ship’s speed equals the speed of light,
Sarah will see time inside the spaceship stop completely,
and she will see Adam’s walking speed decrease to zero.
Therefore, Sarah will always see Adam moving slower than the speed of light.
The same thing is true if Adam tries to throw a ball forward out of the spaceship.
As the spaceship approaches the speed of light,
Sarah will the speed with which Adam moves his arms
to throw the ball approach close to zero.
Therefore, Sarah will always see the ball moving
at slightly less than the speed of light.
From Adam’s perspective, his spaceship was standing still the entire time,
and his ball therefore never even got close to the speed of light.
Einstein’s Theory of Relativity has therefore not been violated,
from either Sarah’s perspective, or from Adam’s perspective.
More information about Einstein’s Theory of Relativity
is available in the other videos on this channel.