OK. Everything so far makes sense. Let's move on to the speed of light for a
In 1887 two American scientists performed a now-famous experiment. The
experiment seemed to show that the speed of light was independent of motion. In
other words, that light always travelled at the same speed: 186,000 miles per
second. It didn't matter if the source of the light was moving or if the
observer was moving.
There was another indication that the speed of light was constant, too—one
that Einstein found especially difficult to ignore. James Clerk Maxwell, the
mind behind electromagnetic theory, had developed equations that described the
nature of electricity, magnetism, and even light. These equations, the
predictions of which were confirmed by experiment, by the way, implied that
light always travelled at the same speed.
Which brings us to the next question...
Again, you're on a train. This time, though, the train is moving much faster—at half the speed of light, or 93,000 mps (miles per second). And instead of
throwing a ball, you turn on a flashlight.
Question: How fast is the light travelling relative to the observer standing alongside the tracks?