By sheer probability, when you think about how outrageously large space is, it's unlikely there aren't other lifeforms out there, including sentient ones capable of using tools and stuff.
The problem is, that what people want aliens to be like is conveniently bipedal and preferably humanoid, conveniently able to breathe an atmosphere with roughly the same composition as ours, and to live comfortably at the same atmospheric pressure, temperature range and gravity, and also to conveniently also communicate by manipulating sound, ideally with their mouths. This is the part that people might feel let down by.
Again, by sheer probability because space is enormous, there could well be species that could hang out in a room with and learn to speak the language of a human... but most aliens would be hard to hang out with, because they might take the form of a 20 foot long jellyfish that communicates through flashing pulses of ultraviolet light down its tentacles and lives in water on a planet entirely covered in it.
Is there life of ANY kind in different galaxies? Space large, probability, yada yada yada yadda! There could very well be life of some kind in our own solar system.
Intelligent life, though? Hard to say. I have to ask myself just how common intelligent life is. Is it normal that it took earth 4 billion years to evolve an intelligent species, or is that unusually long? For all we know, intelligent life could be very common, and we're just a statistical out liar. I don't think that's the case, but how can we know?
And same goes for just plain complex, multi-cellular life. What is the real probability of it ever occurring? Is earth the norm, is earth odd, or is it a statistical outlier? And in what way?
Then again... space large and stuff.
For me, I wouldn't write it off. The obvious reason sentient creatures are rare is because it's REALLY damn hard to make a functional planet. Like first, there's the placement of the Earth near its sun... THEN there's how far the moon needs to be. What SIZE the moon needs to be... etc. etc. The fact that they call our area the "Goldilocks Zone" makes a lot of sense when you consider these factors. All that said, this is why I also wouldn't write-off the fact that we COULD be alone as sentient species. I'm still shocked a race as crazy as humanity has even managed to live THIS far. Even when we started off as walking fish. Maybe there WERE sentient species but they all died (or they're all Octopi). Who knows, but what I will say is that humans should seriously focus on their own planet.
A little off-topic, but something interesting happened to William Shatner, a person who's obsessed with this kinda stuff, where after Bezos took him to space he just had the biggest existential crisis ever. He went from "Ah, the miracles of space! I wonder what lies beyond!" to "I COULDN'T SEE ANY STARS! ALL I COULD SEE IS A BIG, BLACK VOID! Locusts are going to feast upon my flesh one day! The poor will wear my clothes once I'm dead. What is legacy?!? Oh... Earth really is all we got!!!"
Meanwhile Bezos, being the sociopath he is, is like "YIPEE! WE DID IT!" (seriously dude thinks space is the only place for people to go).
This interview made me respect Shatner as a person. Yeah, Earth is all we got and we should be thankful that we exist.
I think it would be the height of human vanity to say that there is only life one place in the universe, and that this is it. Billions of galaxies, trillions of stars, an untold number of planets & moons... to think that Earth is the only place with life is borderline preposterous.
Now, do I believe it's been here? No. Do I believe we'll ever go there, if we even discover other life bearing planets at all? No. The sheer distances involved make it impractical to even communicate between solar systems, much less travel between them. Even if we could somehow design a space ship that could travel at Warp Factor 10 (and survive the experience), that is only 1000 times the speed of light (C). That sounds pretty fast, but when you consider that the farthest galaxy from us is 32 billion light years away (that means that traveling at C it would take 32 billion years to get there. Traveling at Warp 10 (1000C) would take you 32 million light years to get there). I realize that is the farthest away galaxy, but even still the nearest galaxy 179,000 light years away, or 179 years at Warp 10.
Now, consider communications. Even traveling at the speed of light it would take 179,000 years for a radio signal to reach that galaxy. Add another 179,000 years for the signal from their reply to get back to us and you're looking at one boring phone call.
It's just too far.
There are so many variables that have to be just right for intelligent life to happen. Little things like a moon, as large as ours compared to the planet, to stabilize our spin and allow us to have seasons. Not only where we are in the solar system (the usual thing people talk about like liquid water) but where we are in the galaxy. Too close to the center, you will be bathed in radiation. Life that started to process the CO in the air to make O2. Having a star that is stable, non-binary. Those are actually super rare. Having a large planet like Jupiter to clean our system of loose objects. Having an abundant supply of water. And these are just the things to start the process. As of now we don't know if life starts easy or is a 1 in a million thing. An even bigger hurdle is to go from a single cell to multicell organism. Science really has zero idea if that's easy or a 1 in a billion chance. As far we know it happened once here. This is just to get the ball rolling.
Another problem people don't talk about is for a massive amount of time in the age of the universe, you can't have life. Until the first stars formed, then exploded, there was no heavy elements. Then they have to form stars again and make solar systems. So a large time span of the universe, literally nothing past hydrogen, helium, and a tiny amount of lithium existed.
Finally we come to the size of the universe. Here is the scary part scientist don't like. An infinite universe. If it's infinite, there are infinite intelligent being out there. There is an infinite number of YOU out there. No matter how small the chance of a perfect copy of you is, add infinite to the other side of the equation, the result is an infinite number of it happening. When you look at the galaxy and life, there is so many factors, that I am agnostic on the question.
I believe there might be some other form of life in the galaxy. It just feels so weird for me to imagine that life was only able to develop here on planet Earth, so I'm fairly convinced there has to be something else beyond, something we can't notice just yet. Now, do I think it's an intelligent and socialized specimen? Not necessarily. It might be anything, even just plants or insects.