Onifre writes:
What is meant by "spacetime" is a description of the geometry of the universe, ie. Minkowski spacetime. That is finite in size down to Plank scale.
This had an origin, the Big Bang.
I believe the Big Bang Theory explains events that occur after T>0 but does not in itself explain the cause or origin of the spacetime itself.
The origin/cause of the Big Bang is still being hypothesized though Hawkings predicts that our universe, the spacetime we exist in, did not have an origin meaining the concept of time itself cannot have a first cause. Cause and effect are concepts dependent on the concept of time and therefore time is unbounded i.e. it has no one point of origin, as Hawkings predicts. Therefore it makes no sense to say that spacetime had a beginning.
There are other hypothesis/theories that state that our universe (not all of spacetime) had other types of origins i.e. spawned off from other universes (multi-world theory), is part of a large omniverse (the brane), is infinite progression of expansion and collapsing spacetime continuum, etc, or a combination of the above. As we digger deeper into reality we reveal many of these theories are interrelated and have hidden truths that apply.
Just to add another perspective albeit a layman's perspective based on some very limited amount of knowledge.
Edited by DevilsAdvocate, : No reason given.
One of the saddest lessons of history is this: If we've been bamboozled long enough, we tend to reject any evidence of the bamboozle. We're no longer interested in finding out the truth. The bamboozle has captured us. It is simply too painful to acknowledge -- even to ourselves -- that we've been so credulous. - Carl Sagan, The Fine Art of Baloney Detection
"You can't convince a believer of anything; for their belief is not based on evidence, it's based on a deep seated need to believe." - Carl Sagan
"It is far better to grasp the Universe as it really is than to persist in delusion, however satisfying and reassuring." - Carl Sagan, The Demon-Haunted World