I just finished listening to the audiobook A Universe from Nothing: Why There Is Something Rather Than Nothing by Lawrence M. Krauss. As you might expect, the book does not live up to its title in full but it does give some depth to a number of science concepts that have been floating around in popular culture. If you like the video How Far Can We Go? Limits of Humanity and want to know more, read this book.
One of the ideas touched upon very briefly in the book is that the Universe could have always been. By the term Universe here, I mean whatever pre-existed and gave rise to the Big Bang, our current phase of existence, and whatever comes after. I define the term Eternal Universe to mean a universe that goes on forever without an end and always was without a beginning.
I once attended a debate where a speaker gave the following argument in an attempt to make the concept of an Eternal Universe that always was seem absurd. He asked rhetorically, "If time never had a beginning but goes back to negative infinity, how would you ever get to now?" I was disappointed that his opponent did not respond to this flourish but instead stuck to prepared arguments.
Here is how I would have responded. Imagine that you are where you are now in some point in space. You can imagine that this space extends from where you are out to an infinite distance in all directions. Pick a direction and call that positive infinity. Point in the opposite direction and call this negative infinity.
Imagine that I now ask you rhetorically, "If space never had a beginning but goes back to negative infinity, how would you ever get to here?" You might easily reply, "I did not have to travel from negative infinity to get to here because I always was here". The debater was relying upon the fact that most of his audience was used to thinking of time as something that flows forward in just one direction rather than something that is in all directions.