Question

Nothing travels faster than light.


True


False

Answer 1

True — with important caveats.

In special relativity, the speed of light in vacuum (c ≈ 3.0×10^8 m/s) is the ultimate speed limit for anything that carries mass or transmits information. Accelerating a massive object to c would require infinite energy, and no signal can be used to send information faster than c.

Apparent exceptions exist but do not violate that statement:
- Light travels slower than c in a medium; particles can exceed the local light speed in a medium and produce Cherenkov radiation, but they still move slower than c in vacuum.
- Phase or group velocities in certain media can exceed c, but they do not carry information superluminally.
- Quantum entanglement produces instantaneous correlations, but it cannot be used to send information faster than c.
- In cosmology, distant galaxies can recede faster than c because space itself expands, but this is not a signal propagating through space faster than c.

So the practical, physical rule is: nothing that can carry information or mass travels faster than light in vacuum.