"Robert J. Bradbury" <firstname.lastname@example.org> writes:
> The question is, when does the
> energy density become high enough to effect that the "fabric"
> of space/time/energy/mass enough to effect the progagation?
The mass of the energy is E/c^2, so it starts to have a noticeable gravitational pull as GE/c^2 becomes noticeable. As the energy goes up to the Planck energy density 1e28 g/cm light is definitely going to be behaving according to the superposition principle, the stream will have become associated with so much space-time curvatures that things turn weird. I guess it would be self-focussing, as a beam would have a radial pull inwards.
As for pair production, the limit is when h nu = 2 m_e c^2. Much, much lower. But it requires some field or particle in the vicinity to absorb some momentum to occur. I guess that beyond this frequency, a beam would quickly scatter into positron-electron pairs and scattered gamma rays.
It is probably easier to make black holes by compressing matter than using lasers.
Anders Sandberg Towards Ascension! email@example.com http://www.nada.kth.se/~asa/GCS/M/S/O d++ -p+ c++++ !l u+ e++ m++ s+/+ n--- h+/* f+ g+ w++ t+ r+ !y