(I am no native speaker...corrections are very welcome!) * The photon is the only thing in the univers, which is able to travel with lightspeed. At lightspeed time stands still from photons point of view. How can the photon change its properties (energy, frequency) then, since any process takes time? * E=mc^2 states the equivalence of energy and matter and we proofed that correct -- with the atom bomb. But is there a way to convert energy back to matter, as Einsteins formula also implies ?