Question: How fast is the speed of light?

Reka Nagy answered on 11 Nov 2016:

Depends on what it’s travelling in – if it’s travelling in vacuum, it goes really fast (faster than anything else that we know of!), at 300,000,000 meters per second.

If it’s travelling in something else, such as water or glass, it goes more slowly as it collides with atoms and molecules present in these materials. Still pretty fast, though, about three quarters of its speed in vacuum.