To demonstrate that God does not exist and is not the best explanation for the existence of the universe, many skeptics have asserted that the universe could be infinitely old. By infinite, they mean the universe has been around for forever. If it is true that the universe has been around for an infinite amount of time, there is no need for God to create the universe from nothing, as Genesis 1 states. But, if the universe is not infinite, the best explanation for the existence of the universe is God.
First, philosophically, I believe the notion that the unversed has been around for an eternal amount of time has many problems. It seems that an actually infinite number of things existing in the real world is impossible due to the absurdities which would take place. To illustrate, I’ll use a thought experiment. 1)Suppose you have a book with an infinite number of blank pages. 2) You, being a prolific writer, want to fill all of the pages. 3) You are given 13.4 billion years to finish writing in the book. 4) On top of this, you finished one page every year. Could you finish the book? No, you couldn’t. While you’ve amassed 13.4 billion pages, in 13.4 billion years, you’re still left with an infinite number of pages to finish. What if you had an infinite amount of time to finish the book, could you finish it? No matter how hard you try, you couldn’t finish the book. Even though you have an infinite amount of time, there will always be one more page to fill.
Now, what if we replace the last page of the book with today’s date, October 21, 2019? If the universe has been around for an infinite amount of time, could we ever arrive at “today” October 21, 2019? I don’t think so, because, like the infinite number of blank pages in the book, there will always be a day before October 21, 2019. Yet, we all acknowledge today is October 21, 2019. This means, that there hasn’t been an infinite amount of days before today and therefore, the universe cannot be eternal. If the universe is not eternal, then it must have a beginning. Thus, an actual infinite number of days does not exist.
Second, I believe the existence of an eternal universe has scientific problems as well, without appealing to “because the Bible tells me so.” In 2003 Arvin Borde, Allan Guth, and Alexander Vilenkin published a paper addressing, in essence, this very question. The BGV theorem, as it is called, showed that any universe which has been, on average, expanding throughout its history, must have a beginning. Vilenkin states,
A remarkable thing about this theorem is its sweeping generality. We made no assumptions about the material content of the universe. We did not even assume that gravity is described by Einstein’s equations. So, if Einstein’s gravity requires some modification, our conclusions would still hold.
Thus, even with any future modifications to what we currently know about the universe, BGV theorem holds—the universe must have a beginning. If it has a beginning, it is not infinitely old.
Vilenkin, a religious agnostic stated,
It is said that an argument is what convinces reasonable men and a proof is what it takes to convince even an unreasonable man. With the proof now in place, cosmologist can no longer hide behind the possibility of a past-eternal universe. There is no escape: they have to face the problem of a cosmic beginning.
While there may not be a literal "infinity war" going on, atheist who believe the universe is past eternal, definitely have an infinity problem.
 Alexander Vilenkin, Many Worlds in One: The Search for Other Universes. (New York: Hill and Wang, 2003), 174 (a synopsis).
 Ibid., 175.