This is because as fast as light is -- moving at the speed of light -- it isn't instantaneous: at 299,792.458 kilometers per second (186,282 miles per second), it requires that length of time to ...

Ripples in spacetime are what gravitational waves are, and they travel through space at the speed of...[+] light in all directions. Although the constants of electromagnetism never appear in the ...

If you want the instantaneous speed according to the definition 2, that would also be 20 m/s. It's all about definitions. Suppose we want to have a discussion about gardening.

measure instantaneous speed of object at two points (point A and point B) on route; measure time for object to travel between point A and point B ...