Radio waves take time to travel; there could be many civilisations out there whose signals haven't had time to reach us.
If that's the case, we're just the first intelligent civilisation to evolve in our immediate vicinity.
It's far more likely that signal-emitting life is so rare (or short-lived) so that they are separated by distances where their signals weaken to undetectability, than that we are the one fantastically lucky star to be the first among a hundred billion.
Star Trek showing all the rival civilizations exploring the galaxy at the same time makes no sense at all. It's far more likely that civilizations would arise separated by time of millions or billions of years, than that they would all be concentrated within a few centuries. (Trek does hint strongly that the explanation is panspermia, that life was seeded everywhere at the same time to account for the time-concentrated development.)
What we don't know is what makes signal-emitting civilizations cease to do so. But (if we aren't the fantastically unlikely first one) either something must, or they're so far apart that signals can't be detected between them.
The universe is approximately 13.8 billion years old. Primates evolved only six million years ago. So let's be charitable and say it took only 13 billion years for a lifeform capable of transmitting radio waves to evolve.
Unless I'm missing something, if we're listening for ETs, we would only have visibility into a sphere with a radius around 1/45th the radius of what is out there?
My point is, if the Universe is such that it takes a minimum of, say, 10 billion years for planetary conditions to make evolution possible and evolution to wind up at intelligent life, then there could be hundreds or thousands of civilisations out there, at this very moment, whose earliest signals won't reach us for millions of years.
Primates evolved six million years ago here. There are plenty of stars [...] older than our sun [...] where they could have
I, embarrassingly, have a crackpot theory where G isn't a constant. I'll spare HN; it would make me sound like a moron.
A hypothetical civilisation may well have emerged with a head start of five billion years – a span of time sufficiently vast to allow for profound advancement, assuming favourable conditions and uninterrupted development.
However, I find the oft-repeated assertion – that alien civilisations have likely annihilated themselves due to traits as tediously predictable as short-sightedness, internal strife or some anthropocentric parody of self-sabotage – to be both intellectually lazy and philosophically barren. such a narrative reveals far more about the limitations of the human imagination than it does about the potential trajectories of alien life.
A more measured and plausible explanation lies not in self-inflicted extinction, but in the nature of the galaxy itself. Five or more billion years ago, the Milky Way could have been a significantly less hospitable environment – more unstable, more violent, and subject to higher stellar activity. One must also consider the precariousness of location: the galactic core, unlike the relative quietude of our outer spiral arm, is a congested and perilous stellar thoroughfare, far less conducive to the emergence and persistence of complex life.
To default to the notion of civilisational self-destruction is to betray a lack of imagination – or worse, a projection of our own inadequacies onto the cosmos.
It's at least 4b years old on earth, that's not "relatively recently"
We've been technologically capable for less than 200 years, that's nothing in the grand scheme of things.
We could have just missed them by a few millions years and we would have no ideas at all. There might be 10 ancient Egypt tier civilisations out there right now that might develop radio tech by the time we're extinct or back to low tech.
As Lynn Margulis would say the chimps aren't the main show. Intelligence maybe an over rated and very buggy feature of Life. And the bugs get amplified as the minds interact with each other and group size increases.
The philosophers have talked about the bugs for a long time (see Plato's chariot, Hobbes passion vs reason, Freuds id-ego-superego, Kahnemann's system 1 vs system 2, Haidt's Elephant Rider). The mind needs stories to handle the bugs. And there is no dearth of stories on Earth to keep the 3 inch chimp brain occupied forever.
We should look for those.
If there were no eukaryotes, there'd likely be no way of getting past the energy per gene ceiling that constrains the other two domains of life.