Bla, it's almost correct, but...

You can travel at the speed of light only if you don't have mass (so only particles with no mass like photons) because at the speed of light time doesn't pass, and mass became *infinite*. You should use infinite energy to reach the speed of light, obviously impossible...

(I think that no-mass particle, in vacuum, can *only* travel at the speed of light because they need no energy to reach it. Correct me if I'm wrong)

But even if you go at the 99.9999 % at the speed of light you cannot notice anything different on the ship because the time (from the outside) is 99.9999 % slower. If you measure the speed of light you'll find it travels at 300'000 km/s, that is impossible, as I already said.

E.g. The ship is going at 299'999'999 m/s (1 m/s less than the speed of light, approximated at 300'000 km/s).

You start to run and, *according to you*, you are going at 5 m/s. So it should be 300'000'004 m/s, more than the speed of light. What happens then? The time on the ship *according to an observer* is really really small. With your time you are running at 5 m/s but for an observer to (e.g.) 0.00001 m/s (always less than 1). Your second is much much *longer*.

To reach that 1 m/s you should run at 300'000 km/s according to *your* time, relative to the ship.

Hope it's clearer...