A homework question is asking for a diagram illustrating a photon becoming a electron-positron pair (please don't post an image as it's homework). Looking through the internet there seems to be some disagreement as to whether a single photon can create an electron-positron pair: "Show that a single photon cannot produce an electron-positron pair, but needs additional matter or light quanta." "For example you've got a 5MeV photon, so you think that there is plenty of energy to make e − e + pair. Now you make a boost along the direction of the photon momentum with v=0.99c and you get a 0.35MeV photon. That is not enough even for one electron. " so a photon would have to have a massive amount of energy, but is it even possible? if not why is this diagram on wiki? http://upload.wikimedia.org/wikipedia/commons/a/a5/Pair_Production.png i could just draw that diagram but if it's not a realistic possibility then would like to put in a comment as such. Thanks for any comments / ideas on this.