This is arguably a corollary to the Heisenberg Uncertainty Principle.
We can't know the universal speed limit, as anything faster than c (the speed of light) would be unobservable to us, but that doesn't necessitate that it can't exist.
This idea flies in the face of a paramount premise in Einstein's Theory of Special Relativity, wherein he asserts that nothing can travel faster than the speed of light, as light isn't so much a particle or wave, but a phenomenon indicative of how the universe works. This tenet was since debunked as the speed of light did, in fact, turn out to be variable when it was shone through different materials (gasses, glass, and the nucleus of certain exotic atoms), and when effected by gravity as in the case of Gravitational Lensing, which was initially thought to be proof of the Theory of General Relativity.
| 
