Who knows? If space can be infinite, why can't time be infinite as well? We don't know, and we will never fully understand how the universe works. We may understand more, but never all of them. Human knowledge is finite, so we will never understand infinite things. That's it ...
If the universe is infinite in all dimensions and has always existed, then it has no conceivable beginning. If it started and expanded infinitely then it has a central point of outward expansion, if we can detect where the universe is expanding to relative to our position in the universe we can then determine where the central point is and thus determine the center/origin point of the universe. This, of course, is assuming the universe is spherical. If the universe has always existed there is no origin point and may or may not be infinite. If the universe is finite and has always existed, we cannot assume anything, there are too many variables such as if it has changed size or shape. If we eliminate the variables and assume the universe is finite and has always existed and was, is, and always will be immutable, it is safe to assume that the universe itself is its own origin point, since it has never changed and is of a finite size. This is all quite mathematical rather than philosophical, and you probably preferred philosophical but I have already typed it and I’m not going back.
Think about it, if you went to the end of the universe, and shot an arrow, and it went on and on, but then it hit some type of wall, so, you would stand on the end of that and shoot again, and again, and again. The arrow would keep on going no matter what. Even if there was, and end, or not, the universe is stil infinate
Haven't scientists proven that the universe as we know it is expanding? If so, how could it be expanding if it always existed? (I need more words to fill up this response so I'm just going to type until we get down to zero words left. Okay...Three, two, one, YAY!!!)