About my previous post, here is an analogy to help understand when I explain that Genesis 1:1 "In the beginning" refers to God's creation of time itself as a precursor and prelude to creating matter and energy.
Suppose you are the only person on an unpopulated continent that stretches for thousands of miles in all directions, and you decide to plant a garden and build a house. You are a perfectionist, though, and not a slob, plus you understand that the garden must be of the highest quality since someday others will depend on it.
(Remember, this is an analogy and not a fantasy and science fiction "hint" about "aliens.")
Thus, in order to architect your garden and house, you survey the land and select the location. You place a pole into the ground from which you will make all your measurements.
That pole is "the beginning." That is how a human can understand God's need to create "time" (the understanding of and ability to experience a sequence of events).
Thus, God's first creation IS the "first day." What God creates during the first day is actually secondary after the reality that God first had to create a system by which both inert and organic matter (life) can be comprised of matter and energy, which are snapshots of sequential activities that allow existence, growth and change.
So just as the analogy person sets the pole and all his measurements will build off of that pole, God sets the pole of establishing a beginning of time, and all subsequent events, such as the creation and growth of the universe, are measured off of that pole.
Someone could one day study the analogy person's process of building the garden and home, tracing it back to the placement of the first "pole." But that process would give no additional insight into how the person did their surveying or indeed where the analogy person even came from. That can only be obtained by actually asking the analogy person.
Thus, astrophysicists and other scientists can only trace matter, energy and time back to the "beginning of time." This, however, gives no insight into God and "where God comes from" himself, and only gives further glory to God's creative power. Scientists can only trace back to the placement of the "first pole" (the first moment of the Big Bang), which is the beginning of "time," but scientists know no further about God than what everyone, including the "uneducated" faithful, know from God's own explanation to them in the scriptures.
I hope you find this analogy helpful to understanding.