# Please explain me this relativistic occurrence [duplicate]

So, for example, we have the planet, a spaceship (cylinder shaped) and a ball in it (spaceship is like transparent so we can see the ball). We are on the planet looking at the ship. The spaceship moves the speed of light and the ball with it. But what if the ball was moving, for example, 50000 km/h in the ship? It should still be moving the speed of light to us, but would it go through the ship?

In Special Relativity you have the Lorentz factor $$\gamma(v)=1\big/{\sqrt{1-\tfrac{v^2}{c^2}}}$$ which describes the transformation from the quantities as measured in one reference frame to those measured in another reference frame moving at speed $v$ with respect to the other. As you can see, if $v=c$ the factor $\gamma(v)$ turns out to be ${1\over 0}$ (or infinity, if you prefer) and you can't perform any transformation between this two frames.