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Originally posted by TallTroll:
True, the Pair Formation Threshold is only 1.022 MeV, but note that this only makes it POSSIBLE for a high-energy photon to decay. An interaction with matter is required to trigger the decay.
Cool, I wasn't aware of that detail.
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you can see that you need a VERY clean acceleration chamber for any significant chance of a photon surviving the trip.
But how does one "accelerate" (actually, add energy to) a photon directly once it has been emitted, without having it interact with matter? The only thing I can think of offhand would be by dropping it down an intense gravity well, and it seems somewhat perverse to contemplate sending a photon into a black hole in order to boost it to the energy level necessary for it to turn into a black hole.
I suppose you could also accelerate _yourself_ to near lightspeed, so that the photons you encounter along the way will appear to be so intensely blueshifted that they turn into super-high-energy gamma rays from your frame of reference, but I suspect it will be hard to report what you observe afterward.
I just dabble in this stuff, though, so if I've made any further oversights I will renounce my skepticism gracefully.