hypothetical. someone is traveling at almost the speed of light. they then turn on a flash light. i understand that how all observers to this will see the light move at a constant, the speed of light. that's based on relativity and frames of reference.
what i dont understand, if an observer sees someone almost going at the speed of light, wouldn't the light have to appear to be going faster than light speed given the person moving and the light being emitted are in fact moving at different speeds?
is it possible to appear to be moving at faster than light speed even if that's not in fact true?
Imagine you have a ship [S] that is traveling at half the speed of light that sends out a beam of light ——->
On the ship after 1 second you see this:
<—————-> (1ls)
[S]—————>
So the light has travelled 1 light second away from the ship.
If you’re on the ground watching the ship. In 1 second, you see this:
<——————->
[S]———>
You see the ship has moved 1/2 a light second, and the light has only travelled 1/2 a light second away from the ship. (The light has travelled 1 light second total)
That’s so weird? How can the speed of light travel the same distance away from observers 1ls?
Imagine the ship has a huge clock on the side, and you have your own clock on the ground what would you see on the clocks..
0.5S
Ground clock: 1s
<——————-><——————->
[S]——————>
1s
Ground clock: 2s
The ships clock ticks slower so that when the clock has ticked to 1 second you will see the light 1light second away from the ship, even then the light has travelled 2 light seconds from your perspective, and take 2s to reach there.
Imagine if the ship is travelling even faster.
<——————-><——————->
[S]—>
0.2s
In this case the ship has travelled almost 2 light second, the light is only a tiny amount in front of the ship: but according to the ships clock, only a fraction of a second has passed.