I love thinking about this, I’d argue it’s as much a philosophical question as it is scientific.
It seems unimaginable to me that the only life in the universe is on Earth. The numbers already discussed here are to unimaginably large for it to be conceivable that this is the sole planet life has appeared on. It’s the nature of that potential life that is most intriguing to me. If results like those from JWST this week are confirmed, the universe must surely be teeming with life. But that would tell us nothing about the intelligence elsewhere. Once life arises somewhere is it then inevitable that, given enough time, intelligent life will develop? Or is that the bit that is vanishingly rare? Or are there intelligent life forms all across the galaxy and beyond, but they have no chance of developing an understanding their place in the wider cosmos, and will never even dream of leaving their own planet?
My feeling is that intelligence is fairly common, and a significant number of those life forms reach a level to where humanity is at now, but intelligence at that level is considerably more fleeting. From that, the chance of two separate space faring civilisations ever becoming aware of each other, let alone meeting, would seem extremely unlikely. Assuming evolution works similarly universe wide it seems the things that have made us successful here are likely needed elsewhere. Unfortunately the aggression and violence of humans has significantly contributed to get us to the point where we are now, and our use of technology now has great destructive potential in its own right. From weapons, climate change, pandemics, and possibly AI, we have a lot of things of our own making that could be our downfall. And despite the billions of year of Earth to this point, it’s only the last hundred years or so we’ve been leaking radio telltales of our technologically advanced civilisation, with those signals reaching a few dozen stars. Assuming a similar pattern elsewhere, how long do these visible signs last before something, be it an asteroid hit or created by life itself, puts an end to these beacons? I wouldn’t fancy a bet that humans will be here in a thousand years time, let alone a million years. Even a million years would still be only 0.0002% of the age of Earth. The odds of another 0.0002% overlapping with us and reaching out? Not great I’d imagine.
The other argument against intelligent life being common I quite like is that the universe just isn’t old enough yet, we may be among the first. Clearly evolution itself needs a long time, but the conditions to even get to that point need time as well. It takes a few generations of stars to seed the galaxy with the abundances of elements we’re made of, and a long time for those to condense out and eventually become a planet that life can begin doing its thing on.
Sorry for the long post, it’s something I love to consider very much!
Tldr; Life might be common, it might be rare, it might take ages, it might wipe itself out if an asteroid doesn’t beat it to it, and we have no idea whatsoever.