I am posting this here because religious arguments apply, with God as the outside influence, but one could just as well posit that something happened before the Big Bang, or Creation, if you prefer without theism.
I find folks often argue the start of our universe as if it were a closed system: big bang forward to now. (Who says it even has to be now forward? Who is to say there might be Langolier like beings who live the time stream differently, even repairing the timeline between our "seconds?") Three ways (at least) to discuss this would be something happened before, God is the outside influence and/or the universe is not all there is and whatever else there is has at least some effect on our universe. A mix of these three and more is welcome, of course.
A closed system cannot survive, and I suspect would not have survived as long as ours. Admittedly, from our perspective, there's a lot here to keep it going a long time from OUR perspective, so maybe it is closed... though I suspect not.