The strange world of Phil the photon

[Q-reeus]

I know I am really late, but this isn't true. Remember we derived the length contraction and time dilation under the assumption that were were not massless! taking the limit as your mass goes to zero or your speed goes to c, logically does not imply that you turn into light. it important to remember how these amazing results came about...from original assumptions, hold onto them.

A little amazed you picked up on that point! It's standard position that one can never be in the frame of a photon. Think of the absurdities - photon wavelength is infinite, while the rest of the universe has zero length and has aged infinitely.

 

[Q-reeus]

This is really the thrust of your query, isn't it?: If we have a bunch of photons, arranged in a particular way, where is their gravity (or stress-energy tensor) located?

Not exactly. There are now two related issues:
1: Photon count vs classical field amplitude.
My money is on the 1-2-3 'semi-classical accounting procedure' given prior - direct proportionality applies. It fundamentally conflicts with the relation implied by QFT - field amplitude going as the square root of photon count. Can't see any way to reconcile.
EDIT: Just realized that for a free-space dipole antenna, the radiation field drops off such that QFT relation holds. Dropping this point for now - a puzzle.

2: As per two frequency laser beam setup there is this question of what constitutes beam effective mass. Making the usual assumption object mass >> laser beam 'mass', clearly the net angle of beam deflection by nearby massive object is purely a spacetime curvature 'diffraction' effect indifferent to beam energy density. By contrast gravitational action of beam on mass should be directly proportional to the beam energy density and thus a function of beat phase. Bare in mind that modern laser frequency stability can be around 1 part in 10¹⁵ (http://congrex.nl/ICSO/Papers/TPosters/FCXNL-10A02-1987002-1-ACEF_ICSO_PAPER.pdf" ). Meaning at optical frequencies one could readily achieve beat wavelengths many thousands of kilometers long - many orders of magnitude larger than the size of a typical setup. So quantum uncertainty surely plays no significant role here. Action vs reaction holds here if the beat envelope is much larger than the significant gravitational range of the object, or at such times it is symmetrically disposed wrt object. Otherwise there may well be a temporal imbalance, although averaging out to zero over a full beat cycle.

The short answer is that nobody knows.
I don't have a good long answer. Quantum mechanics is a castle in the air looking for a foundation. The uncertainty principle is enough; if you don't know where something is, you don't know how the very space, upon which you build your quantum mechanics is shaped. If you can't define the shape of the space upon which you base your theory, your theory is suspect. So theorists get by with presuming spacetime is flat and well behaved and call it Lorentz invariant as if this is enough.

Thanks for that frank assessment!

 

[Q-reeus]

Issue 1 in thread #37 has become deeply problematic, but the conflict now is between what should be equivalent analysis - time and space evolution of EM fields within: an energized cavity resonator, and that of fields propagating away from an antenna source. The assumption of linear amplitude gain with time in a resonant cavity is well established; eg.
http://www.jpier.org/PIER/pier78/15.07090605.Wen.pdf", sections 5.2, 5.3, fig's. 6, 9, 10. It is definitely not a 'square root' relation. Nevertheless if the free-space antenna picture was hit upon first, this thread would likely never have started.

Issue 2, originally proposed to show that phase matters despite a quirky indifference for photon addition, is now also in limbo. Even the fluctuations in net force balance are not inherently gravitational in nature. The same thing will show up for propagation through a bent waveguide, or even a straight waveguide. It simply shows the vital influence of phase, and just how 'phase insensitive' photons become 'phase sensitive' in an aggregate situation (EM wave) remains for me a mystery without any simple explanation.

 

[Dale]

You may want to start a new thread in the QM forum. This doesn't seem to be very related to SR or GR now that your 2 key issues are not about gravitation. You probably will get better responses if the right people see it.

 

[Q-reeus]

You may want to start a new thread in the QM forum. This doesn't seem to be very related to SR or GR now that your 2 key issues are not about gravitation. You probably will get better responses if the right people see it.

Agreed - will give that some thought. Just wasn't evident at the start of what, apart from a few helpful inputs about the strangeness of photon addition, has mainly been a self discovery exercise.

 

[Dale]

Yes, and at the beginning with the discussion of gravitational interactions the fit here was not bad at all, I don't think that was a mistake. I just think a new set of eyes will be better for the remainder of the question in the way that it has since evolved.