That's the funny thing.

Say you go with a train that is at 90% of the light speed. You have a laser gun. You shoot it in the direction of the train. You would assume that - just like with shooting a ball or a bullet - that the light will escape your laser gun very slowly. At 10% of the speed of light.

That is not what is happening. The light will still travel at 100% light speed, even for you it will appear like the light is going at 190% light speed. What the heck, that is not possible is it?

It's not. For someone on the outside, light still goes at 100% light speed. In fact for any observer, light always goes at 100% light speed. You cannot catch up with light by just going fast enough after it.

This is all possible because light has no mass. That's relativity folks.

As a matter of fact, what we often hear - "nothing can travel quicker than the speed of light", is merely a consequence of one big assumption: The assumption that any observer will see light travel at the same speed - the speed of light.