Multiple universes
Is our observable universe one of many? The "Multiverse" is a term for a proposed group of universes — perhaps many, perhaps an infinite number — of which our universe is only one.
So what, frankly?
We have no answer without going outside the Universe, but the mere possibility of the Multiverse is of interest to people who do not believe in a Creator, because it gives an answer to the "Fine Tuning Problem"[1] i.e. that the Universe appears to be fine-tuned for life, as if God had made it for life, including humans. To the theist who says something like "the Universe is perfectly made for us: it must have had God to make it" the atheist can reply "that's only our universe!"
Creationist approaches to the Multiverse
There is a long history of debate about whether the apparent fine tuning of our Universe implies a Creator, but if a divine Creator exists that is clearly a good explanation for it. A Creator who could make our Universe could make others, so in that sense it is a non-question. However Christians, including Christadelphians, often insist that there can only be one Jesus Christ, Son of God.