Alternative theories to the big bang? Hey all, are there any theories out there on the origins (or infinite existence of) the universe beside the big bang that actually adhere to current scientific knowledge and fact?
 A: It depends in part on how much you encompass within the term "big bang." There is virtually complete consensus among astrophysicists that the Universe is expanding, that it used to be much hotter and denser, and that various observed effects such as the microwave background radiation are artifacts of that hot dense period. If that's what you mean by "the big bang," then I'd say there are no viable alternatives at present.
But if you think that the term "big bang" encompasses more than that, and especially if you think that it refers to a theory that describes the actual origin of the Universe itself, then the answer is that there are lots of alternatives. We think that we know quite a bit about what the Universe was doing over a wide range of times "after $t=0$," but we have absolutely no idea what happened "at $t=0$." I'm using scare quotes here because in fact we have no idea whether "at $t=0$" is even a meaningful thing to talk about!
For instance, there are some models in which, in some sense, times going back to $t=-\infty$ existed ("eternal inflation" being an example). There are others in which there really is a beginning at a finite time in the past. In the somewhat odd terminology of cosmology, we often refer to all of these theories as "big bang models," because they all involve evolution from a hot dense early stage, even though they're quite different when it comes to the nature or existence of the actual beginning.
