Quote:
Originally Posted by sjastro
Hello Alex.
The best way to explain this is with a thought experiment.
Suppose I'm driving in my car and I turn my headlights on. You're at a location a few kilometers down the road. The photons from my headlights reach you after a time t= d/c where d is the distance from you when I turned my headlights on and c is the speed of light.
Suppose there are other observers at various locations along the road. They receive the photons after t1=d1/c, t2= d2/c, t3= d3/c etc.
Note that all observers will measure the speed of the photon as c which is independant of the speed of my car as I approach the observers.
Since my car is travelling very much slower than c each observer will note that I turn my headlights on followed by a period of elapsed time when I drive past their locations. The elapsed time is t(1)= d1/u, t(2)=d2/u, t(3)=d3/u etc where u is the speed of my car.
This order of events is consistant with each observer.
Now let's suppose I defy SR and my car is now travelling at u=c. I turn my headlights on. What happens now. Both the car and the photons arrive at the same time for each observer. Each observer will claim I turned my headlights on at the instant I passed their location despite the fact that each observer is in a different location.
At the speed of light all events become simultaneous.
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Hi everyone, I love this stuff.
Steven could I ask for some further clarification please?
I understand your statement, however, if t1, t2 and t3 above are measureable in your first example with the slow moving car, wouldn't the three observers simply claim that you turned your headlights on at a different time? (observer 1 @t1, ob2 @t2, and so on). I realise that you actually turned them on once only, but isn't that what relativity is all about? Everyone will have different measurements of such experiments because their measurements are relative to their position in time-space? This includes your own perceptions of when you turned the lights on.
Please bare with me, and correct me if I'm wrong as I am only just learning all this stuff. My statements are mearly how I understand GR, and SR, and I would love some further guidance where this is concerned.