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→Bending of light in Newtonian gravity
:[[User:AugustO|AugustO]] 02:45, 26 June 2012 (EDT)
:[[User:AugustO|AugustO]] 02:45, 26 June 2012 (EDT)
::Yeah, I've heard of that. But the photon has zero mass. [[User:AndyFrankinson|AndyFrankinson]] 20:20, 26 June 2012 (EDT)
::Yeah, I've heard of that. But the photon has zero mass. [[User:AndyFrankinson|AndyFrankinson]] 20:20, 26 June 2012 (EDT)
:::Newtonian physics doesn't know about zero-mass particles, hence it doesn't make a unique prediction. One possible interpretation is to say "zero mass -> zero gravitational force -> no bending". Another interpretation is to take the mathematical limit of the equations for ''m''->0. Since ''ma = GMm/r<sup>2</sup>'', the mass of the photon cancels and you get ''a = GM/r<sup>2</sup>'', even in the limiting case ''m=''0. This leads to bending by half the amount as predicted by relativity (and observed). --[[User:FrederickT3|FrederickT3]] 22:47, 26 June 2012 (EDT)