This question just popped up on Yahoo! Answers:
"How do you think the universe came into existing?
I want your own theories/ideals about how the universe was created within absolutely noting?I know we may never know.. its fun to think about it. Your ideals on anything like this whether it be how planets were made, life, space or anything like that I would like to hear it. so please and thank you for your time"
This is my answer:
"There is overwhelming evidence that our Universe was contained within a tiny, extremely energetic point around 13 billion years ago. Therefore, we can say with confidence that a "Big Bang" happened, in the sense that we know that our Universe expanded extremely rapidly from that point. After that, the reasons for the formation of stars and planets are very well understood (basically gravity), and the cause of life is fairly well understood (if the laws of chemistry applying across ten thousand billion billion planetary systems over billions of years did not lead to the formation of life, it would be pretty surprising).
"However, there is still the rather significant question of what caused the existence of that tiny point of massive energy that became our Universe? There are various theories such as the "Big Bounce" or a series of "bubble universes" within a greater "multiverse", but all are highly speculative and rather unsatisfactory since they leave open the question "but what caused that?"
"One answer can almost certainly be ruled out - God. There are no meaningful reasons to believe in a god other than (arguably) the existence of our Universe. But if we believe that "God" is the cause of the Universe, we have achieved nothing since we are left with the question "but what caused God?" and we are back to square one. In fact, we would be left asking why we bothered suggesting God in the first place since it explains nothing and only adds pointless complication.
"Some people may answer that God is causeless. However, that argument is self-defeating. If something can be causeless then, by definition, the Universe could exist without cause. Using the philosophical argument known as Ockham's Razor, we would then conclude that the Universe just came into existence for no reason and your original question would become meaningless - pretty unsatisfactory, I think you will agree! We would also conclude that there is no longer ANY reason to believe in God and could dimiss his existence for the same reasons that we do not believe in fairies or Darth Vader. So whichever way we look at it, God is a pretty useless explanation.
"I think a far more likely answer to your question is that even within a void, there is some essential 'thing' that makes the existence of Universes like ours either a necessity or at least a possibility. If either of those scenarios is correct, then there is no longer a mystery and we are simply left to work out the precise details (the "how" of your question). Regarding what such a 'thing' might be, I would assume it would be some law of mathematics or logic. However, I appreciate that someone could respond to that with "but why do mathematics and logic exist and why are they the way that they are?" Well I'm sorry, but no one knows the answer to that yet. I expect that given enough time our species will work it out one day, or maybe we will make contact with a more advanced species that can explain it to us."
I'm up against some intellectual giants (sample: "I think that somehow the Universe is the aftermath of erosion/decay/death of something that we will never understand") but I'm hopeful of getting that treasured 'Best Answer' prize.