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that would not happen in reality... an observer moving in the frame of reference of a photon

Consider a thought experiment that would not happen in reality. Consider an observer moving in the frame of reference of a photon moving away from a gravitational source. Firstly would the observer detect the change in the nature of the wave of the photon and the resulting change in energy as it travels away? Would the wave of the mass of observer change in such a way that the change in the photon would be undetectable to them?

Quote from: jeffreyHConsider a thought experiment that would not happen in reality. Consider an observer moving in the frame of reference of a photon moving away from a gravitational source. Firstly would the observer detect the change in the nature of the wave of the photon and the resulting change in energy as it travels away? Would the wave of the mass of observer change in such a way that the change in the photon would be undetectable to them?The reason they can't happen in reality is the same reason that your question cannot be answered. E.g. I assume that you're not asking us to forget the laws of physics in order to answer your question, correct? If so then you're asking us to suppose that something has happened which the laws of physics prohibit, i.e. being at rest in the rest frame of light. If we did that then we'd be violating the law of physics stating that the speed of light is invariant and we'd also be violating Maxwell's equations. If, instead, you're asking us what happens under certain circumstances, and supposing the laws of physics are invalid, then you can in fact make up any answer that you'd like to since one is just as likely to be correct as another when you're making up the laws of physics as you go along.

Leading on from this impossibility we can question whether light has any mass, although not rest mass. To accelerate a mass to light speed we say that we need infinite energy. If this is so then how can we say a photon has any mass?

Is there a mass limit so infinitesimally small that when increased relativistically it will not require infinite energy to move it at light speed? Is this the photon mass?

Quote from: jeffreyHLeading on from this impossibility we can question whether light has any mass, although not rest mass. To accelerate a mass to light speed we say that we need infinite energy. If this is so then how can we say a photon has any mass?Because photons are "born" moving at the speed of light so no work is done on them to accelerate them. In fact work cannot even be done on a photon in an inertial frame of reference.

Quote from: jeffreyHIs there a mass limit so infinitesimally small that when increased relativistically it will not require infinite energy to move it at light speed? Is this the photon mass?No. The photon mass is the mass a photon has by virtue of its momentum. i.e. m = p/v = p/c.

And of course in order to do work on the photon would require the force to be in the photon's frame of reference. []

So how do we determine the momentum with zero rest mass?

We know v in advance but m would need to be determined. In order to determine p we need m.

Jeffrey, if you ask a question just to prove that you didn't really meant to ask it? what exactly did you think you were doing there? Setting up a 'honey trap'?

Now take a look at what Pete has said and then read the section Momentum of the Photon here:...sorry, you cannot view external links. To see them, please REGISTER or LOGINFrom this you will see why Pete has used E/c and why he is right. Pete often gets jumped on for his attempts to put people on the right track. Often by those he is trying to help. Well he is right here isn't he? Without people such as Pete, Clifford, Evan and JP this site would be full of nonsense. Let's try and learn something we might all benefit.