Howdy, I'm no physicist, but I am a scientist by trade and some basic physics questions always bug me because I don't have any bases of understanding of the concepts. I apologize if these questions seem a bit abstract: Suppose an event occurs that causes the emission of EM radiation (for example, a transition in an electron's energy state that causes a photon to be released to satisfy conservation of energy). 1) What is the driving force for the propagation of this energy? Is it simply by conservation of momentum that it will continue to propagate even in the absence of a medium? If you, by some convention, assign a momentum to any EM radiation to explain its propagation -- then don't you also have to say that work must be done to move the radiation through any distance in space? 2) Related to the above scenario, when EM radiation propagates through space, is there any efficiency loss as the energy travels? If you assume that it performs no work on its surroundings, then I would also guess you'd have to conclude that it is perfectly efficient in that no loss of energy occurs no matter what distance the radiation travels. This seems like quite an odd thing to me!