Think of it this way... the universe is endless if you think we are the only creatures that’s rather naive
the mathematical probability we are alone in this universe is pretty much zero.
There are approximately 200 billion stars just in our Milky Way galaxy alone. Each star could theoretically have a full solar system
Also, they predict at least 100 billion galaxies in our universe and the universe is ever expanding.
While contemplating the overall size of the universe and all that is out and it making me feel the size of a single electron in my pinkie roe compared to the size of our planet and what is the meaning of life and what is all out there peering down at u
Size is the key here. Even if there is other intelligent life in the universe, it is incredibly unlikely that we or any others would ever bump into one and other. The phrase the universe is expanding doesn't mean it is adding galaxies. It means the galaxies that exist are getting farther apart.
In any event, the notion that other life is a mathematical certainty, or even a likelihood, is currently not provable. We don't have enough examples of it to understand it. Until we do the idea that "well there are a lot of stars, so there must be life on at least one of the planets that likely surround them is, at best, an unfounded guess, and, more accurately, wishful thinking.