the big bang occured 13.75 billion years ago. since then the universe has been expanding outwards. therefore there is an edge to the observable universe. it’s 1^26 (that’s 1 with 26 zeros after it) meters in every direction.
We don’t know much about what’s beyond that as we can observe it. THere are theories that are universe is one of many universe where the collective is known as the multiverse!
Since the universe has been expanding outwardly since the big bang, a question remains that is largely unanswered (unless I am not keeping up to date with modern physics). At least when i was studying physics, scientists were unsure whether the universe would keep on expanding like a large balloon for ever, or if it would stop and just stay at one size, or whether it would start to contract again. If it contracts back in, then eventually it would collapse all the matter (stars and planets) into a tiny tiny dot which would probably cause a huge explosion and big bang 2 would start it all off again.
A really interesting philosophical question is whether life would start again in big bang 2?
I suppose Christianity is one of the first to talk about the world ending in the “2nd coming”. It is not necessarily a bad thing in this case as the “2nd coming” offers the hope of eternal life. St. John at Patmos in the Book of the Revelation wrote about what will precede the 2nd coming. That was around 90 AD.
More people or relegions, even before Christianity, have come up with theories or prophesies about the world ending. I suppose everything that has a “start” should also have a “finish” (?)