Question: Is there any way of knowing the exact speed of light?

Edward Bovill answered on 20 Mar 2013:

Scientists have been studying the speed of light since 490BC, when a Greek philosopher Empedocles claimed that light had a finite speed. The speed of light has been measured by many different scientists since then, but the exact speed of light in a vacuum has now been measured to be 299,792.458 meters per second. The length of a meter is actually defined as the distance travelled by light in 1/299 792 458 of a second!