To me, the BB is just the best guess we have, at the moment, based on our observations.
That is what
any theory IS. There's no "
just".
What did you think a theory was?
Primarily, the CMB, based on an expanding cosmos. As Steve points out, it is not the solid based proven science (such as evolution, still questioned by religious nuts) that so many assume it is.
There is no such thing as "solid based proven" in science. Proof is for mathematics and alcoholic drinks.
What observations are there that suggest that the current consensus amongst cosmologists is wrong?
Lots of people say utterly stupid shit like "It is theory, not fact" or "It is not proven", as though these were insightful revelations that give us
carte blanche to place any wild speculation we like on an equal footing, rather than being statements of the obvious that serve only to highlight the speaker's lack of understanding of science as an epistemology.
You can find someone who will say these things about almost any well publicised theory (certainly including evolution); Almost invariably this is an effort to promote religious and/or new age "woo" that cannot stand on its own merits.
An hypothesis is a guess about how reality might be. An hypothesis that has been refined and tested very thoroughly is a theory. No theory is ever "proven", only "not yet disproven". That applies equally to evolution, quantum field theory, the big bang, and general relativity. All are subject to tweaks as new data become available. Some are certain to be wrong in interesting ways (we know this because QFT and GR are not compatible, so one or both
must be wrong in extreme conditions, despite being very accurate in more ordinary circumstances).
Newton's theory of universal gravitation is similarly wrong in extreme conditions; That doesn't, however, make it less insane to believe in trancendental levitation, or that rocks sometimes fall up. It remains useful, despite being "wrong", because it's not very wrong - in fact, it's barely wrong at all.
Ironically, the mistaken idea that a theory is either right (proven, invaluable, and infallible), or wrong (disproven and totally worthless) is a hangover from the C19th "clockwork universe" ideas that stem from total faith in Issac Newton's theories and laws; And from the human desire for order and certainty.
Reality is, however, under no obligation to be easy to comprehend, nor to be simple to model with perfect accuracy. And the last century and a quarter of physics have shown that it is neither.
Which is not even close to saying that "anything goes", or that some Internet crackpot has a similar standing for his wild-assed speculations and (often already disproven) nonsense, to the standing of the consensus of experts who have actually bothered to learn the state of the art before attempting to improve upon it.
Learning science is hard, because it's
not about learning what current theory says, but rather is about learning what has been shown to be impossible, and how, and why. And there's a LOT of impossible stuff. And scientists are not allowed to just take other scientists word for anything* (although inevitably they do so as a shortcut, and often that comes back to bite tnem).
People prefer the lazy approach of instead just memorizing rules and laws, as they would if studying religion or law; And it is this lazy approach that is often mistaken for science, not least because up until the end of High School, that's what most people are (wrongly) told science is. But it ain't.
* Well, obviously it's "allowed", but when they do it, they're no longer practicing science, but are practicing faith - which we all know to be a very serious character flaw, but (sadly) life's not long enough for universal skepicism.
