Which part exactly? The fact that there is life in the universe is a statistical certainty..
Not a "statisical certainty" if you study astrobiology. Astrobiologists themselves are all over the map on that one. But that's irrelevant, I think it's very likely there is life outside of Earth, quite possibly intelligent life, but.....
the fact that something may have/are visiting this planet is within the realm of possibility due to that
The issue is that you can't conflate the possibility of life in the universe with the possibility of life visiting us because the very immensity you're using to insist on life in the universe simultaneously makes it almost impossible for that life to visit us.
First off, you can almost completely discount that any being outside our galaxy will ever visit us. This is both due to the sheer distance to the closest galaxy (2,500,000 light years - even light would take MILLIONS of years to reach us from even the very very closest one) as well as the sheer number of stars in their own galaxy. So with that fact alone, you reduced the # of potential star systems with life by a factor of a trillion. Only 0.0000000001% of stars in the universe are within our galaxy.
Second, even in our own galaxy, we are 25,000 light years away from the center. Sure, there are 100 billion stars in the Milky Way, but ~99.99% of those are over 1000 light years away from us. So consider that the first long-distance radio broadcasts were made in the late 1800s, that means that a star 1000 light years away wouldn't receive that signal until the 2800s, and even if they can fly at the speed of light, wouldn't get back here until the 3800s at the earliest. And an additional problem you run into - even if those civilizations started exploring the universe before we sent out radio signals, why would they have reached us? Wouldn't they have thousands upon thousands or millions upon millions of closer stars to explore and develop first? Why would they have skipped the 10,000 stars closest to themselves in order to randomly manage to make it to us?
If you close it down to within 100 light years of Earth, you get a reasonable 500 or so stars. Just 500 stars are within ONE HUNDRED light years of us, which is still an insane distance. And now that you're down to 500 stars, are you still sure it is a "statistical certainty" that one of them has developed life, and not just life but intelligent life, and not just intelligent life but interstellar-travelling life, and not just interstellar-travelling life but interstellar-travelling life on the exact same time frame as us (not going extinct 100 million years ago or arising 100 million years later) and travelling to our exact location?
Once you get to within 20 light years of Earth, you're down to about 100 stars. Spread out over a 5 billion year old time frame, it's just not that likely that one of those 100 stars has developed interstellar life on the exact same timeframe as our narrow existence. We're a tiny blip in our planet's history and we could unalive ourselves before too much longer.
All of those star numbers can be plugged into the Drake Equation (
), which you can learn more about by looking up than I have time to share here. But suffice it to say that, while the correct values for the drake equation are unknown, there's a high probabilty that some of them are very small numbers, and thus reducing your R from "the number of stars in the Milky Way" to "The number of stars within X light years" seriously reduces your chances of getting an N larger than 0.5.
My confidence that alien life forms have not visited Earth, beyond just the physical improbability of travelling such immense distances and the relatively few stars within close range of Earth, is mostly based on:
1. The complete, utter lack of serious evidence for any such visit
2. The extreme difficulty that humans have keeping secrets of any serious import, which makes a conspiracy to hide all evidence extremely unlikely
3. The unlikeliness that any one government or secret para-government body could control all knowledge of such visits
4. The complete lack of NHI-derived signals we've detected, which suggests that no one within the range has been sending anything out via radio signal or any other detectable signal....which suggests to me that it is unlikely that interstellar travel and communication is occurring in any serious way anywhere near us.
Like I said above I'm open to the possibility that aliens will LATER visit us. But it seems very unlikely to happen in my lifetime for the reasons I gave above.