I am not physics student so please pardon me if this sounds silly because I might be mixing irrelevant things here and I am not even getting how to ask my question.
My main question is, does light travels at the same speed irrespective of from where/who/how the light is created/generated (assuming light travelling in vacuum)? Meaning, the light coming from a candle or a beam from a lazer gun or a sun rays or light coming from any other star takes same time to travel from Point A to Point B? Does energy and force what caused that light to be generated has any impact on how fast they move?
When I think of moving of photons my basic physics knowledge which I learnt in childhood tells me that for moving anything some force has to be applied and speed and distance of the object depends on how much force is applied. I am hoping its same for the photons too. In that case what I wonder is the light from a match stick, lighter, torch, lazer, sun or any bigger and larger star is same? They will be same unless all applies same force to the photon.
Best Answer
Yes. Inertia is resistance to change in motion. It doesn't take much effort to get a skateboard moving, or to stop it moving. But it takes a lot of effort to get a locomotive moving, or to stop it moving. That's because the locomotive is more massive. And as Einstein said, the mass of a body is a measure of its energy content. The relationship between mass and energy is given by E=mc² where c is the speed of light. Hence inertia has something to do with the speed of light. Maybe not much, but you did say anything to do with.
Edited:
Yes, in that light doesn't overtake light. Because of the particular wave nature of light. The wave speed doesn't vary like it does for waves in the ocean. But note things like the Shapiro Delay article on Wikipedia where you can read that "the speed of a light wave depends on the strength of the gravitational potential along its path".
Yes. All the light travels at the same speed between A and B in vacuum. This isn't quite true in say glass or water, hence prisms and rainbows. But there are no rainbows associated with gravitational lensing.
No. The speed depends on the properties of space, see Wikipedia where you can read that the speed c with which electromagnetic waves (such as light) propagate through the vacuum is related to the electric constant ε0 and the magnetic constant μ0 by the equation $c={\frac {1}{\sqrt {\varepsilon _{0}\mu _{0}}}}$.
It isn't. You can't push a photon to make it go faster or slower. That's because the photon has an E=hf wave nature. It isn't a body like a locomotive is a body. However it does offer resistance to change of motion, and you can accelerate a photon in the vector sense via Compton scattering:
That's because it has a non-zero "inertial mass". Which is why Einstein said "if the theory corresponds to the facts, radiation conveys inertia between the emitting and absorbing bodies". Note though that inertial mass is better thought of as a measure of energy. The the meaning of the word mass has changed over the decades such that it's nowadays assumed to mean rest mass. A radiating body loses mass, and the absorbing body gains it. But the photon isn't at rest and you can't slow it down, so rest mass doesn't apply.
The light consists of photons of difference frequencies, and there may be differences in the polarization, but other than that I can't think of any other differences.