Well, in some sort they are. Time is just an other dimension of the universe.
Aside from the fact that you can't prove there was a "big bang" (only accept the incumbent theoretical framework of a subset of astrophysicists), there is more.
Ohh, but there is plenty of evidence that there was a big bang: the red shift of galaxies or the cosmic background radiation.
Even if you accept the "big bang" premise, you can't prove that there haven't been other "big bang" events, perhaps separated by hundreds of billions of years, and by regions of emptiness many times the size of our universe.
I don't know whether there are other universes besides this one or not but if there are any terms like "separated by hundreds of billions of years, and by regions of emptiness many times the size of our universe" just don't make sense.
I suggest you contact Physicist if you want to know more about this or you may read some of his older posts where he debunks this "before the big bang" idea.
Then let me explain. Our universe is theorized to be roughly fifteen billion years old. It is theorized to be expanding, and at an increasing rate of volumetric enclosure, like a balloon. This leaves two possibilities--that it will either continue this way indefinitely, or it won't. If the former is true, it implies that there is absolute void beyond the current boundary of our universe, into which our universe expands. If you don't admit this, then it is impossible to meaningfully say that our universe is expanding--at all.
It also implies, if you argue for indefinite expansion, that there is an infinite supply of this void. This void is the emptiness I allude to above, and it provides ample housing for as many universes as you care to define, and as large as you care to make them. This addresses the first of your things that "don't make sense". The fact is, if our universe is expanding, then by definition there are regions of void where it currently isn't, but which our universe will expand to occupy in the future.
If there is an infinite supply of void for this (or any) universe to occupy, then by definition, there could exist another universe, or many other universes, separated by gigantic expanses of void, so extensive that no two universes would intersect, even a quadrillion years after the genesis of any of them (intersection of universes is not out of the question, of course, but we'll leave that aside for now).
If, on the other hand, our universe will stop expanding at some point, say 20 billion years from now, then a further set of possibilities come to the fore. Our universe could remain that maximum size forever, shrink somewhat, shrink completely back to the speck from whence it theoretically came and disappear into oblivion, resume growth at some point for reasons unknown, oscillate between the maximum size and some other size...the possibilities are endless.
For the sake of argument, let's go with the "universe shrinks back to a speck and disappears into oblivion" argument for now. Total elapsed time, 35 billion years of expansion, 35 billion years of contraction back to oblivion, 70 billion years total elapsed time from the "big bang" that hatched it.
Then what? Does our hypothetical "speck" lie dormant in the void, ready to explode back into existence for no reason whatever, just like last time? No, you say? Why not? It did it once, why not again, 23 billion years after contraction back to a nothing. Come now, why, precisely isn't this possible? What factor prevents this, what great cosmic governor to ensure that one, and only one occurrence of that "big bang" trick occurs, ever. What's the matter, is this nature thing a one trick pony?
Oh, and the bigger problem. If, as postulated by the "big bangers", there simply was nothing prior to the "big bang"--no time, no space, no anything, just void, that presents an even bigger conundrum, doesn't it. Infinite void, with nothing in it, is the ultimate stable state. There is no reason whatever, absent God, for that state to change--ever. It is the ultimate equilibrium. Yet, the evolutionists and arrogant (subset of) astrophysicists would have you believe that some manifest destiny, something literally outside of nature, caused nothing to transition into something.
Either that, or you must argue that the nature of nature is to create something out of nothing. A neat trick indeed, and one can scarcely imagine something so supernatural as that. At the very least, you'd expect nature to be capable of repeating the trick.
As your for your Physicist friend, bring him on. He'll be in for the philosophical ride of his life.