Of course a christian can believe that the big bang theory. In fact it fits perfectly into the christian world view. God created the world at some point (boom), and then it was...
The only reason why a christian would not believe the big bang theory is because he takes Genesis literally. But taking Genesis literally is nonsense, for many reasons including the following: The Genesis actually contains 2, not one creation story, with a different order of creation. Which one is to be taken literally? Answer: obviously none. Genesis talks about God's relation to us and our relation to Him. It does not even try to be a historic or scientific text...
