A bit confused with the massless nature of photons

[Johnny5]

No they don't. Light speed © is a constant in all frames. It doesn't matter which frame you sit in' date=' light always travels at c and is therefore not at rest. Thus there can be no rest frame for light. (Assuming they don't have mass.)

 

I suggest you read my post before commenting on it.[/quote']

 

Severian, you are making a mistake. Photons do have rest frames, and their speed in their own rest frame is of course zero. The rest frame of a particle is a three dimensional rectangular coordinate system, with the particle situated at the origin, in which the particle is permanently at rest regardless of whether or not that particle is being subjected to any external forces. In other words, in the rest frame of a particle, the speed of the particle is always zero, no matter where the particle goes. The frame is permanently "attached" to the particle.

 

And the fundamental postulate of the special theory of relativity is not that the speed of light is c in all frames, but that its speed is c in any reference frames in which Maxwell's equations are true. <--- that much is of course correct, because it is a tautology. The question is are there any reference frames in which Maxwell's equations are true. Special theory says, "yes there are reference frames in which Maxwell's equations are true, and those frames are the inertial frames.

 

Regards

[ans]

what I'm unsure of is if [math]m=m_o.\gamma[/math] and if the rest mass of a photon = 0, then relativistic mass=0?

Also when considering a photon, v=c, the relativistic formula doesn't make sense.

ie [math]\gamma = \frac {1}{\sqrt{c^2-v^2}}[/math]

[Severian]

Severian' date=' you are making a mistake.

[/quote']

 

I know what a rest frame is, thanks. The only way that a photon can have a rest frame is if it is slowed down in a medium (e.g. water). But that is not what we are meaning by 'photon' in this context.

 

And the fundamental postulate of the special theory of relativity is not that the speed of light is c in all frames, but that its speed is c in any reference frames in which Maxwell's equations are true.

 

Maxwell's equations are never true because they are classical. However, QM aside for a moment, Maxwell's equations are true in all inertial frames (in the classical sense) because they can be written in a covariant way ([math] \partial_{\mu} F^{\mu \nu}=0[/math]). This doesn't change by including gravity (although one should then add gravitational interactions too of course), so Maxwell's equations are true in all frames.

 

There is an easy way to settle this. Imagine a frame S, where the the photon is travelling at speed c. Let us denot your photon rest frame as S'. Please give me a Lorentz transformation which transforms from S to S'. You will find that the time axis become parallel to the direction of the photon's flight and therefore S' is not a valid reference frame.

 

Edit: One could I suppose argue that light is stationary at the event horizon of a black hole, but this is a limiting case, and not really applicable.

 

Edit: I even found a paper on Maxwell's equations in non-inertial frames: http://ej.iop.org/links/q79/ju4Vl9q47pptrQXkOP059A/jav23i22p5169.pdf