The Speed of Light is the same for all observers.

[Pants]

I'm just trying to get my head around this. How is the speed of light constant for all observers? Can someone help me out using this realistic example?

Say that someone has a torch (a bright one) on earth. We have two observers, Ship 1 and Ship 2.

Ship 1 blasts off at 0.8c... A few hours later:
Ship 2 blasts off at 0.9c in the same direction.

At the same time Ship 2 is passing Ship 1, the torch is flashed. For both ships to observe the same speed of light, surely the light would have to reach them at the same time?

But it wouldn't, ship 1 would see the light sooner, as by this time Ship 2 would be long gone...?

It's constant if we're observing from earth, and it makes sense that it would reach Ship 1 first. But how is it constant from the perspective of the ships?

 

[Pants]

as ship 2 is going faster, the passage of time for him is slower relative to ship 1

So both ships perceive the same passage of time at the instant of the torch flash.

Christ that's going to be even harder for me to get my head around!

Edit: So if you actually had a stopwatch on both ships, they would record the same amount of time has passed before they saw the torch light. But if you had a stopwatch recording the same thing from earth you would record that the light got the Ship 1 first, then record a later time for Ship 2. That makes my head hurt.