The cosmological argument is an argument based on the idea that all things must have a cause and that the fundamental first cause must relay back to something all-powerful that exists outside of this universe.
"Nothing cannot create something" This statement is a not only a fundamental to the argument of cause and effect, but logic also, as if it is untrue, then ‘nothing’ is indifferentiable to ‘something’.
Just as a painting demands the existence of a painter, our world and universe demand a first cause or designer. The theory of a big bang as the origin of our universe does not deny the necessity of something existing prior to the explosion—there would be no explosive reaction if nothing existed.
It would appear logical to conclude that something inside the universe cannot have caused the beginning of our universe, just as it is logical to conclude that a character in a book yet to be written cannot write the book that they’re going to be in. The "chain of causes" must go back to a cause outside of the universe. In the example of the book, this would be the writer—someone who has the power to create a story and its characters by utilising their ability to write. We can extend this idea to God, a first cause who can utilise His abilities to bring about His will.
As God is timeless, spaceless, and immaterial by definition, He can exist outside of our universe and serve as what the ancient Greek philosopher Aristotle defined as the "prime mover"—the original source of motion in our world.
Science reinforces this need for a "prime mover" as fundamental laws such as the first law of thermodynamics rely on the fact that energy can only be transferred, not created or destroyed. This also extends to the Newtonian laws of motion, where the first law states that an object at rest will remain at rest unless acted on by an external force.
The only way we can avoid a "first cause" scenario is if everything is an infinite regress. This would be impossible, however, as if there were no starting point, we would not exist now. There must therefore be a first cause, and that cause must be outside of our universe—this must be God.