Speed Of Light and stimilation

1. Aug 20, 2005

Spin_Network

On a par with Einsteins "riding-along-on-a-lightbeam", if I was travelling at the front of a beam of light, and I shone a Laser in the direction of travel, will the Laserbeam work?

Do Laser's travel well?

2. Aug 20, 2005

gurkhawarhorse

i think it would work perfectly well and if u could measure the speed of laser beam it would be travelling at c of course.
gurkha

3. Aug 20, 2005

HallsofIvy

gurkhawarhorse's point is that if you were "traveling at the front of a beam of light" and sent a beam of light from a laser (or flashlight for that matter), you would see it moving ahead of you at c, because, in your frame of reference you are stationary.

Someone in another frame of reference, however, would see you moving at the speed of light and see no light shining in front of you- he would see the light from your laser moving at the same speed as you and so not "shining in front of you".

I, personally, would feel a lot better about that if you were moving at 99.9% the speed of light, relative to the observer. In that case, again, you would see the light from your laser moving away from you with speed c. The observer, as you go flying by, would also see that light moving away from him at speed c, because everyone, in any frame of reference, sees light moving at speed c.

Specifically, if you have speed v (0.999c here but could be anything less than c) and you send a beam of light ahead of you, the observer, relative to whom you are moving at speed c would see the beam of light as having speed
$$\frac{v+c}{1+\frac{vc}{c^2}}=\frac{v+c}{1+\frac{v}{c}}=$$
$$c\frac{v+c}{v+c}= c$$.