The probability of no other intelligent life other than ours is near zero. The reason most question it is because we are relatively unintelligent, given we can’t even exit our solar system, and also see anything clearly in the next closest system.
The fact that there are habitable planets out there gives us hope that we will find extraterrestrial life, perhaps intelligent, but to assert that there must be life out there is speculation. To say that those who question whether there's extraterrestrial intelligence is pure arrogance.
We're not so sure on that score:
https://siberiantimes.com/science/casestudy/features/f0100-s...
I've read this thought experiment somewhere -- imagine, you're locked in a cell and are given a set of lockpics, and you are told you have to pick the lock of the door and get out, or in 1 minute a neurotoxin is released that will kill you.
You have no idea how to pick locks, but you try anyway and you manage to open the lock in 10 seconds.
You are asked how tough do you think the lock was?
You reply "it was really easy, I have no idea how to do it, yet I did it in 10 seconds, easy!".
What you don't know is there were also another 1 trillion cells and you're the lone survivor -- the lock was incredibly hard to pick, with a 1 in a trillion chance of success, but to you, the survivor, without external information it seemed really easy, you were just incredibly lucky.
What's even crazier to think about is the sequence of events that happened before humans appeared on Earth. Perhaps humans wouldn't have appeared if dinosaurs hadn't gone 'extinct' the way they did. It was also not guaranteed that our species would survive as long as we did - we have some evidence that we've come close to extinction before. Furthermore, it took a very long time for civilization to appear and even with civilization around, we weren't really advancing significantly before the industrial revolution. Yet what was vital for the industrial revolution? A cheap, plentiful, and easy to use source of energy - fossil fuels. The reason we have so much fossil fuel is because nothing could break down dead trees for millions of years, so they were buried instead. That eventually formed into various fossil fuels.
The sequence of events that led humanity to the point where we could start exploring our solar system is crazy. Take plentiful fossil fuels out of the mix and modern society wouldn't exist.
We're not looking for just intelligent life. We're looking for intelligent life that has got to at least a similar level of development as us. I don't think that's something guaranteed at all for intelligent life. Perhaps there are dozens, thousands, millions of planets, where intelligent life evolved, for every planet like ours, where intelligent life got to the point we did.
Or there could've been life nearby that went extinct the minute we began fashioning our own tools out of stone and metals.
There could've been whole wars fought in space with the winners/losers going extinct before we were ever even formed through evolution.
Would be nice if we can ever explore all of the universe and figure out all those secrets, and see the archaeology of other races, but I don't know if we'll ever get there. Would be amazing if we did, to only find out that we are the only sapient species. How rare a thing that would be that we're the only ones to make it past the great filter.
I think it's odd we don't see more synthetic ai type signs of life out there, at least.
I think if we do kill ourselves we might have AI before then to at least broadcast to the universe that we were here.
1. ET life formed and vanished so quickly that they didn't even get to the stage where they generate electromagnetic signals.
2. ET life formed and got to generate EM waves, but:
- they're either too far from us that we haven't detected those waves yet;
- they only recently got to this stage and the signals they produce have not reached us yet;
- or both.
3. ET life formed way sooner than we did; figured out how to generate EM waves, and then vanished entirely. So, any signals of their civilization they must have sent out there have already reached earth, but before we began listening for such signals.
4. Then again, since there are practically infinite number of planets with habitable conditions for ET life, statistically speaking, we must have already received a signal from at least one of them.
Which leads me to this:
5. ET life doesn't exist, because the universe as we know it is most probably a simulation inside a computer and the computational resources can only render so many different objects at a time. (This is serious stuff, researchers have already proposed methods for verifying this: https://www.washington.edu/news/2012/12/10/do-we-live-in-a-c...).
Looking at our own universe, building a simulator for it inside itself looks like a non starter. We’re even detecting gravity waves from black hole collisions billions of light years away, that's how detailed the simulation would have to be. There’s no way to build a simulator with that level of detailed fidelity of a universe in that same universe. Imagine designing a computer chip to run a simulation of itself. Yes we run low fidelity weather simulations, but to simulate outcomes in our universe at a general level like that you wouldn’t need to simulate consciousness. In the same way that we don't think superintelligent AI would necessarily need to be conscious, the actors in a history simulation wouldn't need to be either. Our universe is too detailed to be a statistical simulation and too complex to be an accurate simulation. The parameters don’t make sense.
That only really leaves the possibility that the simulator is running in a dramatically more complex universe, so simulating ours would be relatively easy. But then, there would be almost infinitely many less complex universes they could simulate, why choose ours? The more complex the universe running the simulator(s), the more lower complexity universes there are available to simulate. As the number and complexity of universes available to run simulators goes up, the number of lower complexity universes (and the complexity of them) that it's possible for them to simulate also goes up, so the probability they will bother with ours probably stays steady at a very low prior.
Or maybe this is an example
The smartest human in history, with all the encouragement in the world, couldn't invent agriculture or ironworking from scratch if they were born a hunter-gatherer. Innovation means building on the work of hundreds of generations of the best and brightest. That can't happen if you don't regularly interact with other people. Every genius octopus is starting from a blank slate.
Perhaps somewhere near an underwater volcano there is a technologically advanced octopus city waiting to be found?
Like Octlantis, but hotter, and with steel (“Cuttlefisheffield“?):
https://www.theguardian.com/environment/shortcuts/2017/sep/1...
I think it would be more arrogant to assume that we're somehow special or unique in what is an incredibly massive universe where we exist as mote of dust upon a mote of dust. Right now, humanity is in the stage of tossing messages in a bottle into an unimaginably vast ocean, while using a hastily built telescope attempting to see over the horizon.
This isn't to discount the incredible efforts of those people exploring the cosmos, but rather that to demonstrate just what we're working with.
We simply don't know yet!
We have a good estimate for how many worlds there are out there, but without the probability for life to exist, it could just be we are the only planet in the entire universe that holds life/intelligent life.