I know frequency and energy vary in photon. I also know that mass is the same as energy, which relates to Einsteins famous equation. What I want to know first is, can energy exist without mass? Some energy being transported somewhere for e.g. without no mass. So, the real question is, if you send a photon to travel somewhere doesn't matter which color it will travel all until it reaches some kind of surface, then it can be absorbed or bounced. Still, that photon wouldn't be lost if it traveled either 5000km or 1000000000000Gm's. Perhaps it could reduce it's energy, and acquire another color, but it wouldn't stop moving. How is this possible? Doesn't it constantly have to spend energy to move with its velocity? I know distance is contracted when you reach the speed of light so PERHAPS it relates to something of this. But I can't find a way to link up the 2. If you do, please reply :D P.S. I simply love thinking about this stuff and getting answers for it.