We now know that exoplanets and the conditions for life abound in the universe. Where the conditions for life abound, the null hypothesis ought to be that life abounds. In discussions of alien life and intelligence, we are often biased by earlier states of knowledge about the universe and our position in it. When we first started digging up dinosaur bones, we came up with fantastical notions of creatures to explain these artifacts that were mysterious to us. Notions that fit into our existing worldview, drawn from folk knowledge and cultural history. Once archeologists started studying the bones carefully, they gave us stories more fantastical than we could have ever imagined in the framework of our folk knowledge. I suspect the same will turn out to be true of UAPs.
For example, UAP stories are often ridiculed on the premise that intelligent alien life would not bother to come all this way just to hide out in the ocean. That's our folk knowledge of aliens: they like to travel, are eager to make contact with other life forms and are capable of doing so. But the elusive behaviour of UAPs is exactly what we would expect from an "unmanned" scientific probe. The home planet would be dozens or hundreds of light years away, so the craft would need to be completely autonomous in the absence of any communication system. Where does an autonomous probe go to look for signs of life? Oceans.
Very very big and very very old. Take the probability of an intelligent being evolving, multiply that by the probability of it being on a planet that had vast amounts of practically free energy stored from the last great extinction and figured out how to use it, multiply that by the probability of them not running out of that energy until they can develop new sources (without destroying each other in the process), then multiply that by the probability of them figuring out space travel, multiply that by the probability that they are within reach of us with that technology, multiply that by the probability that they care enough to come over here, and finally multiply that by the probability that this occurs within the 2000 years or so when we aren't too ignorant to appreciate it.
With vastness comes separation. The more vast it is the more likely there is life elsewhere, and the less likely its in travel rangeor would be able to identify life on earth.
The possible shapes of life are much bigger than the universe.
The chances of intelligent life existing outside Earth are lower than the chance of that same intelligent life speaking flawless Swedish. We might as well send some Europop records to space as signals to aliens.
"Intelligence" is a human invention created by humans to describe humanity. It only applies to humans and human-like beings.
Trees and crabs and birds appeared very recently in the timeline of life on Earth and will probably get extinct eons before shrimp or tardigrades know what happened.
Life is likely plentiful in the Universe. Earth-like life is almost certainly unique.
Intelligent life might happen on every 10,000th planet or it might only happen in every 10,000th universe.
As long as we know of only one occurrence of intelligent life we have no clue of the probability. And human intuition on what's right doesn't help us here.
We still have only one data point for life and one data point for intelligence.
It's absurd to claim intelligent life doesn't exist, as we know it does on Earth. And it's absurd to claim any level of probability for other intelligent life until we have one more data point.
> We still have only one data point for life and one data point for intelligence.
Don't we have many points for both? There are ~8.7 million species on the planet. What we only have one data point for is a planet that contains life and intelligence.
Regarding oceans, I want to add that the overwhelming majority of our land is in the northern hemisphere. Add the speed of light time lag, and anyone starting with a southern perspective will see a water-world with no technosignature whatsoever.
If one were to send a probe, one could wisely plan on purpose to land it in the ocean, deploy submersibles with flight technology and have them just go around and lay low.
They would hide, lay low and their aerodynamic performance might simply be their idea of a modest, basic platform. They would otherwise be wholly unprepared to make contact or perform in air to air combat.
For example, UAP stories are often ridiculed on the premise that intelligent alien life would not bother to come all this way just to hide out in the ocean. That's our folk knowledge of aliens: they like to travel, are eager to make contact with other life forms and are capable of doing so. But the elusive behaviour of UAPs is exactly what we would expect from an "unmanned" scientific probe. The home planet would be dozens or hundreds of light years away, so the craft would need to be completely autonomous in the absence of any communication system. Where does an autonomous probe go to look for signs of life? Oceans.