Q-reeus No, I am talking about a longer path due to the path's curvature, caused by the effects of mass. Every curved path through spacetime is longer than a direct geometrical path, thus every curve gives longer transit times. And those curves are caused by mass. Two identical photons emitted similtaineously from the same source will have a delay between their arrival times if one passes a large mass closer than the other passes, simply because the closer path is more curved. That effect is well known in Relativity, I'm pretty sure that's what Shapiro is chasing. It seems, from the cite, that the effect is so minute it is in the noise, the Wiki article had a plea for an actual cosmologist to revue the article and, as I said, I will be waiting to go further than that on such speculative and unconfirmed data. If there is a single exception to light always travelling at lightspeed we would have seen photons travelling at less than lightspeed in a vacuum, that simply has not happened(believe me, it would be front page news). I do not accept Shapiro's work or paper as being valid, it has no experimental confirmation. Again, no one has ever measured lightspeed in vacuum in or from any frame as being slower than that in any other frame in vacuum. GrumpyPlease Register or Log in to view the hidden image!