read analogy here: http://cmb.physics.wisc.edu/tutorial/hubble.html Less like an explosion and more like raisins baking in raisin bread. No matter from which raisin you look, all other raisins appear to be moving away. the question: The universe is the very boundary of space time, so it isn't expanding into anything or is it? It is just expanding. What does the "dough" in the analogy expand into?