Recently I went to a planetarium with a group and the subject came up that Mormons do not believe in the Big Bang theory. Is that true and if it is why?
I think there’s some misunderstandings in play here. The first is what exactly Mormons believe. For the most part, there is silence on the creation of the universe. The scriptures in Genesis that deal with the creation are narrowed in scope by modern revelation. The Lord told His prophet that He created many worlds, “but only an account of this earth, and the inhabitants thereof, give I unto you” (Moses 1:35). So the account in the Old Testament, and even the additional accounts revealed to other prophets, deal only with the creation of this earth, not the galaxy, or even the universe. Admittedly, there is a passing reference to the stars being created, so that does lend credence to God creating the entire universe at this time, but I don’t think that means what traditional Christians take it to mean.
A tradition has arisen among Christianity that almighty God, being the Uncreated Creator, or First Cause, must have omnipotently created the entire universe out of nothing. This is termed ex nihilo, meaning “out of nothing”. Frankly, it doesn’t have a lot of scriptural support, except perhaps from a particular definition of the English word create. It is not the way the ancients understood the scriptures. Joseph Smith taught:
“You ask the learned doctors why they say the world was made out of nothing, and they will answer, ‘Doesn’t the Bible say he created the world?’ And they infer, from the word create, that it must have been made out of nothing. Now, the word create came from the word baurau, which does not mean to create out of nothing; it means to organize; the same as a man would organize materials and build a ship. Hence we infer that God had materials to organize the world out of chaos—chaotic matter, which is element, and in which dwells all the glory. Element had an existence from the time He had. The pure principles of element are principles which can never be destroyed; they may be organized and re-organized, but not destroyed. They had no beginning and can have no end” (King Follett Sermon, see the April and May Ensign.
So Mormons as a whole don’t tend to believe that God created the universe out of nothing, but we do tend to believe that God did create it. With traditional Christianity, we continue to maintain the omnipotence of God and His unchanging eternal nature.
The other misunderstanding here is what exactly the Big Bang is. The Big Bang is a model that describes the expansion of the universe, much like if you saw an inflating balloon you could take some key measurements and extrapolate what it looked like before it started inflating. With the Big Bang, the timeline for the expanding universe has been mathematically traced back to what the conditions were like when t=0, at the very start. In other words, the model reverses the expansion of the universe until everything – all the matter and all the energy and everything that comprises the universe – is collapsed down to a single, finite point – called a singularity. As time approaches 0, the universe is so dense that most of the laws we accept may not even apply anymore(!), so beyond that is a bit of a mathematical guess.
The key takeaway from this is that the Big Bang theory does not have the universe exploding out from nothing. All the matter and energy already existed. All models that I’m aware of that track t<0 continue to maintain the total sum of energy and matter. (The principle two that I’m familiar with are that the universe is in a cycle of expanding and collapsing; and another that simply has the singularity existing in a questionably unstable state. Again, the challenge for modeling it is that we aren’t sure what physical laws still apply, so we aren’t sure what a steady state would look like). So the scientific community does not have any sort of ex nihilo model for the origin of the universe.
So, to turn things on its head, there is nothing in the Big Bang theory that disagrees with Mormonism, but the theory is at odds with traditional Christianity unless the ex nihilo creation occurred before the singularity.