I didn't lie
I suspect Kaol seeded some filler posts earlier just for this point in the day.

Speed is relative. You have to define your speed against some physical body. There's no such thing as absolute speed. That's all there is to it. And as you approach light speeds, it all screws up.

The speed of light, c, is constant, no matter what you measure it against. So on earth, we can measure c as 3 x 10^8 m/s relative to the earth. But, using my earlier example, the person on the rocket travelling away from earth at 1000m/s would also measure c as the same speed. As would the person on the spaceship travelling at 500m/s. That's where it all becomes difficult and unintuitive.
( K2k6 has a proper job these days, Tue 22 Jul 2008, 16:25, Reply)