There can be forms of life in universe which we may not even understand.
For example - Think of yourself an ant living next to a river. The ant would have no prospective or understand of what is going on in the river and all the fish inside it.
The difference between ants and humans being that humans can invent ways to understand what is going on in the river. If there's something out there and it is discoverable in principle, there's a good chance we'll discover it someday.
This. We think we can see clearly with our senses and command the world at will, and we can, compared to ants. But what would an ant thinking about a river it's observing be like? Ok tbh idk if an ant is best expample, lets just assume its able to think to the level I'm describing. So the ant is looking at the river, what does it see? Most likely just a bunch of shimmering stuff, just randomness. Maybe it notices there are patterns but, it likely has a hard time even determining that what is in front of it has the same stuff that it finds on grass in the mornings. The thing is, the ant can't really see anything clearly. What it does know, and can see clearly is navigation of its tunnels and working with the other ants.
Unlike ants, we can use our rationality to go beyond our senses. Instead of looking at rivers we look at space, planets around stars light years away.
And that's all true before you even get to the fact that it looks like we are on the cusp of some really breathtaking ways of augmenting our intelligence.
> There can be forms of life in universe which we may not even understand.
If you're looking for X and have no idea what this X is, then you won't be able to find. Thus, they probably only look for what's familiar or defined as "life form".
> The odds seem pretty good that we will find extraterrestrial life, someday.
I know I have an unpopular opinion here, but I just don't see it happening. It seems like wishful thinking to expect to find life extraterrestrial life. Of course, I'd love to find out I'm wrong. But what is the observable data to suggest otherwise?
The prevalence of planets around other suns. The exchange of physical material between planets. The recent visit by an extra-solar asteroid, which if it had been involved in a collision could have ended up in part on our planets.
The frequency of protein and DNA precursors in ordinary organic chemistry.
I think of the early history of our own planet. Sun and shade, heat and cold, tides causing wet and dry in phases unsynchronized with the other effect. A tiny random chemistry lab on every grain of sand on every beach for a billion years. What are the odds that life wouldn't happen? A more interesting statistic in my view.
I guess finding that instance of life would go a long way to proving that it's just a statistical probability. I'm just a doubter by nature. I sometimes wonder what people's motivations are for looking for the things they do. The Universe is so endlessly fascinating, there's so many questions we don't even know to ask yet.
I think it depends on what "someday" means to you. Within our lifetimes? Almost certainly not. Within 100 generations? Still, probably not. But "eventually"? I could see that being likely, if:
* humanity doesn't extinguish it's own flame
* there isn't some freak, inescapable, immitigable cosmic occurrence before we've gotten out of our own solar system
* we develop technology for near-lightspeed or FTL travel
If the above were true, I think the only thing that would stop us from finding non-Earth-origin life some time before the heat death of the universe would be if there is actually no other life out there, which I think is unlikely.
However... I do think that there's basically 0.0% chance of finding extraterrestrial life in the deserts of Earth, excepting in the case that the spontaneous generation of simple life is exceedingly common. But, I guess determining how common that might be is one of the goals of the search.
You need to account for the fact that we really haven't been able to do much searching on any other planet. Mars looks very promising as far as once having harbored life. Even though we don't have conclusive evidence to say so, if you forced scientists to bet their life's savings one way or the other, the vast majority of them would probably bet Mars did harbor life at some point. You'd probably find a non trivial number of them also betting it currently harbors life.
You're definitely right that, we haven't been able to. It seems we have guesses based on assumptions based on peripheral observations. Like I said, I would love to find out that there is, but I haven't seen anything that has convinced me that it's only a matter of time until we do.
The odds will vary greatly depending on whether we mean any life (microbial or unicellular life seems most likely), or complex, let alone sentient life.
Technically the term encompasses the former too, but all too often people seem to equate it with the latter.
Personally I am more convinced by the "rare Earth" hypothesis too, and I don't believe humanity will discover complex alien life ever thorough its existence. Obviously I understand why this point of view gets the boos.
For example - Think of yourself an ant living next to a river. The ant would have no prospective or understand of what is going on in the river and all the fish inside it.