Let’s see it this way, for suppose you are in a train which is moving with the speed of light, and now you want to see your image on a mirror “inside” the train, and as we know, to see our image in a mirror the light must fall on us and then reflect on on to the mirror, only then an image is formed on the mirror.
And as we supposed, we are in a train with the speed of light, so relatively the speed of reflected light and the train is in the same direction and it is zero, so we cannot see our image on the mirror, and this violates the theory of relativity, we must see our image on the mirror. And it is possible when the speed of light in the outside frame of referance is twice the speed of light!!! this is impossible. How can the speed of light from outside is twice?
So to be able to see our image in the mirror, The conclusions of Einstein were, in this case the train should contract in the direction it is moving and the time inside the train should slow down compared to the time outside the train.
So, nothing can move faster than light, at that speed the length becomes zero, time would stop and the mass becomes Infinite.
The only viable way of breaking the light barrier may be through General Relativity and with space time. It looks like moving faster than light but it is actually not moving faster than light.
->The Big Bang itself expanded much faster than the speed of light. But this only means that “nothing can go faster than light”, as we are in the same Universe.
-> If you wave a flashlight across the moon, then, its image can travel faster than light speed (since the beam of light is going from one part of the Universe to another part on the opposite side, which is, in principle, many light years away). Well…. this seems to move faster than light but, it is actually not, it is just travelling faster than light relatively.