Shining a laser out of a train - What does the stationary

[mycotheology]

Lets say its the future your camera has an insanely fast shutter speed. You're standing on the ground watching a train travel past at just under the speed of light and the train driver is shining a laser pointer out the front window. With your insanely fast reflexes you take a take a picture of the train (or better yet you record a video). Would you see the laser light slowly moving ahead of the train, or would you see the laser beam traveling ahead of the train at full speed? If its the latter, I'm mighty confused because I can't see how you would record normal light speed for the laser beam, rather than light speed + the speed of the train.

If its the former then I think I'm starting to get my head around special relativity.

 

[jtbell]

You "see" the light as traveling at speed c. If the train is traveling at 0.99c for the sake of argument, then from your point of view, the separation between the train and the light pulse increases at the rate of 0.01c.

From the point of view of someone on the train, the light pulse recedes at speed c.

 

[mycotheology]

Ah right, so the stationary observer sees the light travel ahead of the train at 0.01c, that's what I needed to know, thanks a lot.

 

[phinds]

Ah right, so the stationary observer sees the light travel ahead of the train at 0.01c, that's what I needed to know, thanks a lot.

Just keep in mind that that is a somewhat dangerous way of looking at things from the point of view of understanding physics. What the observer sees is light moving at c. The speed of the emitting object is irrelevant.

 

[sardar]

I can provide an explanation for this scenario based on the principles of special relativity. According to the theory of relativity, the speed of light is constant and the same for all observers, regardless of their relative motion. This means that the speed of light is always measured to be the same, regardless of the motion of the source or the observer.

In this scenario, the train is traveling at near the speed of light, while the laser beam is also traveling at the speed of light. This means that from the perspective of an observer on the ground, the laser beam would appear to move at the speed of light, with no additional velocity due to the train's motion. This is because the speed of light is already the maximum possible speed, and cannot be added to by the motion of the train.

So, in the recorded video, the laser beam would appear to be traveling at the speed of light, with no additional velocity due to the train's motion. This may seem counterintuitive, but it is a fundamental principle of special relativity.

In conclusion, from the perspective of an observer on the ground, the laser beam would appear to move at the speed of light, regardless of the motion of the train. This is due to the constant speed of light and the principles of special relativity.