re: Do you accept the notion of the Big Bang as the origin of our universe?

We perceive a series of efficient causes of things in the world.

Nothing exists prior to itself.

Therefore nothing [in the world of things we perceive] is the efficient cause of itself.

If a previous efficient cause does not exist, neither does the thing that results (the effect).

Therefore if the first thing in a series does not exist, nothing in the series exists.

If the series of efficient causes extends ad infinitum into the past, for then there would be no things existing now.

That is plainly false (i.e., there are things existing now that came about through efficient causes).

Therefore efficient causes do not extend ad infinitum into the past.

Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God.

Aquinas