2 photons with energies of at least 0.511 MeV are crossing the same spot at the same time - there is 1.22 MeV energy in a point, enough to create electron and positron pair. Will it happen? If yes, isn't it a nice way to create antimatter, or at least anti-electrons? If it doesn't, then one could potentially store the energy of, for example, 1Kg in space smaller than an atom and there would be no mass. It could even be much much more energy, possibly infinite. Even if its for tiniest of time scale, still - either one could relatively easy create anti-matter, or ,potentianally, store +- infinite amounts of energy in a single point (or something close to a point) without any mass created ... OR?