To anyone reading this now and thinking, “299,792,458 m/s is the speed of light!”: stairlane’s comment originally gave 299,456,352 m/s as the speed of light. Unfortunately they’ve since edited it to the correct value, thus ruining a very good exchange
Right, and that's a definition. Modern SI works by defining constants, so then when scientists figure out a way to measure more exactly they're actually refining our understanding of the SI units, the numbers (such as the speed of light in metres per second) never change any more, so that's convenient.