Re: [Phys-L] foundations of physics: Galilean relativity

[Moses Fayngold <moshfarlan@yahoo.com>]

     On Monday, October 5, 2015 1:46 PM, Jeffrey Schnick <JSchnick@Anselm.Edu> wrote:
   
> ...If I understand them correctly, John and Moses both think that the acceleration of the photon is the same as that >which a particle at the original position of the photon would experience meaning that as the photon gets farther >and farther from the planet, the photon's acceleration remains constant at its original value in its original direction.  >That makes no sense to me.

  To me, too. I've never said that  "...as the photon gets farther and farther from the planet, the photon's acceleration remains constant at its original value in its original direction". Nor did I mean it. We all must be very careful about numerous conditions and assumptions (especially unspoken ones!) accompanying our argument. I do think that acceleration of the photon in the gravity field is the same as that of any other particle at the same time and location. Therefore I think that acceleration of the photon pair right after the e-p annihilation is exactly the same as that of the initial pair, provided that the separation between its members had been negligible.  Only under the latter condition can we equate individual accelerations to that of the CM. This is what I meant (but had not explicitly formulated) in my previous argument. This statement about the discussed event at specified location in spacetime remains true and is experimentally manifest as deviations of the born photons' trajectories from their initially horizontal and strictly opposite directions. My second point was that already this initial deviation creates the corresponding transverse components of velocity (turns the photons' directions through a small angle), and as a result, their CM in 2Y will definitely be sufficiently far displaced from its initial position, even without any subsequent acceleration (which will indeed be increasingly negligent).     Unfortunately, I cannot say exactly how far does it make "sufficiently far". It critically depends on numerous conditions, including the size of the planet. But on conceptual level, I think the following example must be true: Suppose it would take 1s for the initial e-p pair to fall onto the surface of the planet if there were no annihilation. Annihilation with horizontal momenta of the produced photons would save the system from hitting the surface (or from crossing the Schwarzschild sphere in case of a black hole). But I think that 2Y after the event the CM of the photon pair must be far on the opposite side of the planet, even though the pair's CM would surely have no noticeable acceleration. But it would still have the initial transverse velocity acquired during the first 1s of the process.   Moses Fayngold,NJIT       _______________________________________________
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