Probing Planets in Extragalactic Galaxies Using Quasar Microlensing
arxiv.org
arxiv.org
Maybe the laws of physics and mortality will prevent us from meeting them, let proving their existence, but in such an ultimate vastness where we know that life does exist, life must exist.
I don’t get Fermi though. If you take the inconceivably large problem space that is “life finding other life in the universe” and cross it with the infinitesimally small amount of space-time we’ve occupied actively looking for other life, how is not having found other life yet a paradox?
It is possible we are first. The Copernican principle, to my eyes, is taking a bit of a beating lately anyhow. It was a fine heuristic for a while, but many people seem to have forgotten it is only a heuristic that seemed to work for a while and not an actual law of the universe. So maybe we are that unique. But it is worth pointing out that would itself be a significant sea change in the current philosophy dominant in science.
It could be that others have come and gone but never quite made it to space. Cave paintings go back 40,000 years. I'd say that displays a level of intelligence. Yet there was a significant period of time until we managed to develop agriculture (30,000 years), or writing (37,000 years).
At lot can happen during that time. In fact during these years humans could have died out many times, succumbed to the changing climate or disease.
But considering all this, you have to take into account that the universe consists of upwards of 2 trillion galaxies, at least as far as we can see. That's a lot of potential. But if we can never make contact, does it even matter if its there or not?
An advanced species would mostly broadcast on purpose only, which indeed, raise other concerns.
There was a similar theory (well more a science magazine one) than Fermi paradox to explain there is no other planet in the universe. Until we started to know what to look for and suddenly they appeared everywhere.
Fermi paradox is at the same time clever at the same time you wonder if you are actually doing something akin "There is 0 chance you can throw 1000 dice and produce to produce a positive integer number", just because you look at a specific sequence and indeed that exact sequence is statistically impossible to exist randomly.
Bacteria, plants, insects, and even some animals can all live in a human city and not realise their environment is artificial. The city is conceptually invisible to them, and interactions with it will appear random, or at least extremely unpredictable.
Recognisable interspecies intelligence may be a question of relative cognitive ability, not of physical presence.
Even assuming that there was a large civilization out there that communicated via EM across interstellar distances, they'd almost certainly use point to point lasers to keep the SNR usable.
It doesn't take hypothesizing all that many low probability events for the creation of life, or intelligent life, before you get to numbers like "less than one per galaxy", and it isn't all that far from a logarithmic perspective to get to "less than one per universe".
So it is indeed the case that our ignorance is such that we can't simply look up at the universe and go "it has to be teeming with life!", because we do not yet know that the probability of life is not in fact orders of magnitude smaller than the observable universe. We don't know that it isn't teeming with life either, but that's where you get into the Fermi paradox and the Great Filter arguments.
If you believe it, then it makes you wonder at what point in our development are we going to be able to see the cones for ourselves and then wonder about them? We now have two probes that have gone extra-solar and perhaps soon we'll have rocketry to send something toward Alpha Centauri.
My personal favorite theory for your question of 'when?' is that it actually has nothing to do with reaching a physical point in our universe. Instead, we make some advance that either A) allows us to perceive another dimension/energy that we couldn't before, or B) raises our consciousness to a level to match what should be the tons of aliens in space.
Always fun to think about!
If life evolved on a planet a billion years before earth, why haven't they colonized the galaxy?
Kurzgesagt recently published a video covering the idea of the "Great Filter".[1] The idea is that there must be something (some "filter") preventing life from colonizing their galaxy.
[0]: https://en.wikipedia.org/wiki/Self-replicating_spacecraft
Maybe the challenge of producing a thing capable of going interstellar distances and foraging the resources it needs to create copies of itself is only short distance (in time) away from our present capabilities but maybe it is vastly far away or impossible. Given we definitely don't know how to do this now, we basically can't say which it is.
That's like saying "life on extraterrestrial earths."
So the paper is saying there there probably aren't more than 2000 planets per star? That seems like a pretty large upper-bound.