| > before the big bang the whole observable universe was contained in a small sphere and then it started to expand We have no evidence of any time when the universe was not expanding. At the earliest times we have evidence of, the universe was already expanding (extremely rapidly--much, much, much more rapidly than it is now). At those times, our observable universe was indeed contained in a very small volume. > suppose I point a laser beam to the space and by chance this laser beam never finds any kind of matter in its way, where is this laser going to? Since the universe is spatially infinite in our best current model, the laser beam will just keep on going forever. > To an infinite void? According to our best current model, no, the laser beam will never stop passing by matter, of approximately the same average density as the matter we can see. > Is it correct to say that stars radiate energy to the infinite then? Yes, as long as you recognize that "the infinite" never becomes a "void". |
I didn't understand this part, why would the laser beam would never stop passing by matter? Because of the metric expansion of the universe? Isn't it reasonable to assume that there is a skirt of the universe where matter keeps expanding into nothingness?