[Coda]

Originally Posted by Potironette

Oh wow, light is strange! I wonder why it happens that regardless of relativity, everyone sees it as 1.0c faster than themselves?

That's Einsteinian relativity instead of Newtonian relativity. The shortest description I can give you is that the speed of light is really better described as the speed of time, that is, a measurement of the relationship between time and space. If it sounds confusing that's because it is and I don't know if I can make it intuitive.

Uh, but if lightbeamA were racing lightbeamB would lightbeamA see lightbeamB as going 1.0c faster.

Answering this fully gets pretty deep into relativity and I'm not sure I can satisfactorily answer it without going overboard -- and then THAT risks being too confusing.

At the core of it, though, is that you can't consider things from a photon's perspective. The math breaks down; trying to set up that frame of reference ends up quite literally dividing by zero.

You might have heard about time dilation -- the faster you go, the slower time appears to pass for everyone else. When you hit the speed of light, the universe stops experiencing time at all from your perspective; if you COULD look through a photon's eyes, you'd see yourself crossing the entire universe without any time having passed at all. You couldn't see another photon moving because there would be no time for the photon to move in: your velocity formula of (change in position) / (change in time) ends up with a zero on the bottom.

And why Newton's first law doesn't work is because even without another force acting on it, the light travels 1.0c faster?

It's not so much that Newton's first law doesn't work so much as it is that it doesn't apply. The law has a big "if" in it. At normal scales you can simplify that condition to "no net force" but the more formal statement of the law is "in an inertial reference frame" and light doesn't have one of those, for the above reason.

Err, so the Earth rotates around every day and around the time the skies turn pink/orange at the place, the place is further away from the sun. And because it is further away the sunlight has to go through more air stuffs to reach the person's eyes at that place. And because there is more sky, the blue's already been scattered a lot further away, now what's left to be scattered to reach the person is the red/orange light? And so those reach the person's eyes?

You got it.

But if that's so then why is it that during nighttime the sky is more bluish than reddish?

Because the Earth itself is in the way. Only the light that gets scattered the most can reach you, because anything taking a more direct path is busy shining on the daytime side of the planet.