Not all scientists think, that the speed of light is the top speed. Everybody, who looks at the equiations for a few minutes can see, that there is a possibility of particles whith an imaginary mass, which travel always at a speed faster than light. They are called tachyons.
Whole books exist on thios matter.
When a particle is accelerated by means of any force and it approaches the speed of light, it becomes more and more massive. When it approache the speed of light and more force is applied, it does not really speed up, but just becomes more massive. This is not a theory from the ivery twoer, but it is observed in the large particle accelerators. If it would be possible to move faster than the speed of licht, it would be possible to move vackwards in time. This is just a simple consequence of the equiations of relativity.