You don't need to "believe in it"--there's no leap of faith needed--it works well, and unless some as yet fantastic empirical data gets revealed, it's not going to need major tweaking.
(In my best sotto voce I will happily admit that evolution does not help us at all in grasping how life came to be, and that the cell theory's weakness is that it cannot explain the original cell.)
Meanwhile, kids get drilled on the Big Bang Theory with little complaint in these parts, a model which purports to explain the origins of our universe (or at least everything since after the first 30 seconds, when the universe got to be a few millimeters in diameter, which, of course, makes no sense without a reference).
Look in a textbook and read about it--about 14 billion years ago or so (give or take a billion here or there), the universe was a singularity, a point. Something happened--and space started to expand, to exist.
Too many times I have seen this pictured as an explosion--the event is being viewed from the outside by the illustrator. The textbook I've used the past three years has a picture of an explosion among the stars:
The big bang theory says that 12 to 15 billion years ago, an event called the big bang sent matter in all directions. This matter eventually formed the galaxies and planets.(Holt Science and Technology: Physical Science, 2006, p. 21)
Big problem--there was no outside, there were no directions-- at least according to the model. So who is looking at the "explosion"? God?
The model too often gets oversimplified, taught by folks with insufficient understanding (and I put myself in that category), and as a result we create myths instead of a scientific model.
When viewed this way, the Big Bang model becomes a religious one. Yes, I know the picture is just to help students imagine the event, and yes, I know that the textbooks are not pushing the God thing, but the result is the same. It's bad science.
What do I do? I hedge.
If we accept that the universe is expanding (and we do little in class to show this is so), then it makes sense to think that the universe was "smaller" or "more dense" in the past.
And that's as far as I can take it with "low level" freshmen, without getting into religious (by my understanding) grounds. My kids may leave 9th grade knowing a little less about the common scientific myths we thrust on 14 year old children in our schools, but I think they might have a better grasp on what science means.
I am a science teacher--I teach science.
The artwork is from NASA.