given the age of the Universe and the relatively short time it would take for an advanced civilization to spread across the Milky Way Galaxy (650,000 years, by Hart’s estimate), Earth should have been visited by an extraterrestrial civilization (ETC) by now.
It took humans 30,000 years to cross the Atlantic. Using modem propolsion systems, it takes us two years to get to Mars and 40 to reach the edge of the solar system. This seems like an extremely generous estimate considering the Milky Way has a 50,000 light year radius.
I'm as bullish about extraterrestrial life as anyone, and I think a fuller survey of even just the current Solar System has potential. But I have no idea how you get a full galactic survey in so short a time, given what we know about the soft limits on speed of travel and communication.
By Tipler’s refined estimate, an ETC would be able to explore the entire galaxy in “less than 300 million years.”
That definitely feels like it's more in the ballpark. But, again, it presumes a certain amount of steady cartography by the hypothetical fleet of Von Neuman probes.
There's a Sci-fi series called The Bobverse that explores the idea of a sentiment fleet of Von Neumans exploring the galaxy, and the various trial and tribulations involved. One point it discusses is that even with a saturation of probes, you don't get real time communication. So even in a hypothetical universe where alien life did exist and survey earth, what are they odds they'd be watching us at the moment of our development. What would an alien AI be looking for and what would it do when it was discovered?
We could still be too primitive to bare noticing. Or we could be living in between blinks of an alien camera that only reports back every 1000 years.
As we look out at the cosmos, we could be looking at things we don't understand. After all, what does a star surrounded by a Dyson Sphere look like to a telescope that is searching for glimmers of light, heat, and gravity? SETI is operating purely on conjecture. That's assuming alien civilizations are even capable of creating these hypothetical superstructures. Or that the structures would function as we intuit.
At some level, I have to question if we know what we're looking for. Because so much of this feels like we're searching for humans deep in space. Perhaps the reason we can't find aliens is that they are simply... too alien.
My personal take is that there’s some kind of anthropomorphic fallacy in thinking life should tend towards “civilization”.
Life will tend towards reproductive success and it seems entirely plausible to me that reproductive success doesn’t at all imply the use of radio waves.
The dinosaurs were a very intelligent life form that never tended towards civilization and some of their bird ancestors can be smarter than most mammals etc. Expecting the trait of civilization to emerge seems unfounded and against available evidence.
Space travel seems impossible. I realize you can back of the envelope it in a way that makes it seem within grasp but there’s no economic benefit in colonizing another star and only some marginal mining benefit in even visiting the nearby planets so I don’t think it will ever happen.
My theory is that if any ETI exists, our species is under quarantine until we have either grown up or burned ourselves out. They will have seen violent, self-destructive beings in the past and know it is dangerous to let them spread and destroy peaceful society. If they can travel between the stars, they would have to be able to communicate to keep cohesion, this communication could very well include the warning "Avoid this system, there are killer apes on that planet".
Or avoid the vampires, werewolves, and zombies that are constantly around based on the intercepted documentaries.
Well the vampires are on the nightly news reports about Wall Street, and zombies are shown in attendance at every tRump rally... so yeah the ETs would certainly know they are quite prevalent here. Don't see as many werewolves in the news, but they interview a shit ton of ghouls.
The commenter who identified that we're now able to eliminate radiowave-broadcast communications, via lasers ( & fiberoptics, etc ), is spot-on.
There is another angle, though.
Imagine a simplified-model of civilization...
a batch of 7 newborn-babies, instead of hundreds of genetically-distinct populations in Africa...
those 7 babies live in "eden".
they learn that they can consume everything they want, that doesn't harm them.
they learn that they have to be somewhat self-moderating, because others fight them when one crowds the other, too much.
etc.
they move away from each-other, & some lose their skin-pigment, others change it...
an empire forms, in-which industry is the rule ( the Roman empire ).
Now a momentum is set in-place, that is making the sequence of the Industrial-Revolutions inevitable...
at the time of the Roman Empire, the children are, say, 11yo.
at the time of the Industrial Revolutions, they are in puberty, their brains forced into chaos, & ALL sorts of new force-multiplying technologies landing in their hands...
So, what is The Great Filter?
What happens when it is unconscious-toddler-mind, or unconscious-adolescent-who-never-got-challenged, who has all the world-snuffing technologies that we now have, but who has the global-responsiblity-level of .. drunk & drugged narcissistic children...
Say you have 7 kids going into The Great Filter, representing the whole populations-sea of our world...
Say only 1 of them survives The Great Filter...
Are they going to be CAREFUL in what they do, technologically, from then on??
Obviously.
I don't expect more than about 1.5% of this planet's population to survive this century's TANTRUM/POGROM that has narcissism-roots, politics-roots, religion-roots, food-insecurity-roots ( like total collapse of the terrestrial & marine food-webs, later this century ), etc.
Will the remnant who survive this century, if any do, be as careless with technology as we currently are??
How could they be?
If The Great Filter is an automatic force-growing-up consequence of EVERY world-overwhelming-species, who mixes accommodated-immaturity with ecosphere-destroying technology, then whatever portion of worlds who reach The Great Filter have survivors of it, .. it'd be inherent in the survivors' experience that they have been made careful.
Same as you don't find incapable-of-self-discipline in career-military-officers, you don't find our murderous carelessness/ideological-rabies in any survivor of The Great Filter:
Universe automatically force-extinguishes populations who won't grow up, who gain the technological-leverage that we've gained.
So, silence depicts a lack-of-carelessness AND an absence-of-need to be throwing-away-energy through radiowave broadcast, both.
When combined, galactic silence makes much fundamental sense.
We're in our species' "puberty" stage, and haven't survived our force-growing-up Great Filter, yet.
If we do, well, then finding others who also did, will make sense.
If we won't, .. then our epitaph will be that we wouldn't grow-up, at ANY cost.
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