Relatively speaking
Here's something that has always bothered me about the theory of relativity:
Say there's a spaceship traveling at half the speed of light, or 0.5c. They turn on their headlights. From the perspective of the astronauts on the spaceship, the light should be leaving those headlights at the speed of light, 186,000 miles/second, right? Assuming this is a very bright light, a planet 186,000 miles ahead will be struck by light exactly one second after the ship turned on its headlights.
Well, what about the people on a different planet watching this spaceship pass them by at 0.5c? How fast do they observe the light leaving the headlights of the spaceship? The speed of light is supposed to be a constant c, no more and no less. But the light is leaving the headlights at c and these headlights are attached to a ship travelling at 0.5c, therefore isn't the light travelling at 1.5c? And isn't this not allowed?
What am I missing here? It's thoughts like this that keep me up at night.
good god.
All motion is relative. There is no right answer. How cares anyway? Spaceships are gay.
If the second planet was also 1 light second away, they would also see the light suddenly appear in 1 second. The first planet would see the light getting bluer and bluer, while the second planet would see the light get bluer and then redder as the spaceship passed it by. The physics guys say that the speed of the light emitter just changes the wavelength--scrunching it up if it's approaching and stretching it out if it's leaving.
However, the people on the fist planet would only see the light for 2 seconds, cause then the spaceship would smack into them!
Guy at telescope: "What the hell is th..."