One way to look at such a reality is in terms of a story.
Stories (except for creation stories) rarely begin at the very beginning. A story exists in its own universe, but occupies only part of it. James Joyce's Ulysses uses 265,000 words to cover a single day (June 16, 1904), but it is assumed that Leopold Bloom existed before the beginning of the story. The book covers a small region (Dublin) of its universe, but it is assumed the universe spreads out in all directions.
Likewise, our lives do not begin at the start of creation, and they visit only a small portion of the universe we believe exists.
Even though we can only "know" the present moment, we can speculate about the past - even the time before our own stories began. We can use clues from the present to reconstruct what we think happened.
For a long time, physicists assumed the universe had a "steady state" - that is, the universe had always been much as it is, with stars and planets coming into being and ending their existence.
Edwin Hubble suggested the data pointed to a moment when all matter and energy was in one incredibly small space, and the universe expanded from that.
If we accept this "backstory" to the universe in which our stories are told, there is indeed a beginning to the great story of the universe - a point at which all matter, energy, and time itself came into being. There is no "before" here - this is the absolute beginning of the story, which can have no before, no prequel.
For some physicists, this beginning is sufficient. Stephen Hawking says there is no need for a creator here - not of time, of space, of matter, or energy, or of physical laws.
Other physicists search for a cause of this, and many settle on God as first cause.
But if we're looking at this as a story, we ought to at least consider the possibility of an author.
This post is part of a series on Prodigal Creation.