I accept that what I write below will be unpopular and argued with vehemently, however I think it should be considered with an open mind and recognised for the sense that it has. Originally the concept of an expanding universe (and therefore by extrapolation the concept of the Big Bang that must have initiated it) all came from the simple observation of a red-shift in most observed galaxies, with the Doppler shift increasing as the distance to the observed galaxy increased. This lead to the logical deduction (at the time) that the over-all entity was expanding... and must therefore have started from a single point at some point in the past - ie: Big Bang. Why then is it that we find it easier to come up with increasingly complicated theories that have culminated in the most recent puzzle - dark energy - rather than explore the possibility that photons lose (or convert) energy as they travel. As it lost energy - for whatever reason, but surely one that must be as easily or more easily described than the workings of dark energy - it would red-shift. Giving the appearance of distant galaxies moving away from us. And as light traveled through even greater distances of space it would lose still more energy, red shifting still further, and giving the appearance of more distant galaxies traveling away from us even faster than those closer to us. Which, of course, would give the over-all appearance of the entire structure expanding away from us when in fact it was just an illusion.