This has the same issue I have with any theory where the great filter is a technology that evolves roughly contemporaneously with spaceflight (like atomic weapons): It’s just not probable that _every_ civilisation would destroy themselves before being multi planetary. By virtue of the events being so close, some civilisations would escape destruction if only through dumb luck.
Personally I think the lack of visible galactic civilisations is more plausibly explained by a combination of life being rare (and probably brought to Earth via panspermia after billions of years of evolution elsewhere) and both multicellular and sentient life also being rare.
> Personally I think the lack of visible galactic civilisations is more plausibly explained by a combination of life being rare (and probably brought to Earth via panspermia after billions of years of evolution elsewhere) and both multicellular and sentient life also being rare.
Besides these facts, space is big and the timescales of evolution are long.
Let's say there's a planet with advanced multicellular life just a dozen light years away. They're roughly the same development level as us with a post-atomic/semiconductor level of technology. We could not currently detect them unless they were beaming an extremely directional radio signal at us (accounting for proper motion between our star systems). We're not going to pick up their TV signals, those will fade below the cosmic background by about Saturn's orbit. Even high powered AM radio won't be coherent past Pluto. The odds a powerful military or weather radar beam crosses our section of their sky to be detectable by us are extremely low.
We might be able to detect spectra of industrial pollutants or biomarkers if that system is oriented such the planet transits its host star.
That assumes there's a project with the funding and appropriate telescopes to do the looking.
Space is big and terrestrial planet hunting is under-funded. It would take a lot of luck to see intelligent life next door. Postulating super AI or handwavy explanations for not finding aliens everywhere is silly. The boring answer is space is huge and aliens are almost impossible to see in the best case. We'd be very lucky to see ourselves from Alpha Centauri even knowing where to look.
> I think the lack of visible galactic civilisations is more plausibly explained by a combination of life being rare (and probably brought to Earth via panspermia after billions of years of evolution elsewhere) and both multicellular and sentient life also being rare.
I always put this out here when this sort of topic comes up, but it’s certainly possible that given life itself is apparently rare, and intelligent life is definitely rarer still…that we could be among the first and most advanced so far.
We make the assumption that there must be others and far more advanced, but all we know about life so far would indicate that intelligent life on the one place where we know it exists took nearly 4B forms of life to produce that 1 form that can apparently even conceptualize that there may be others out there…and…it apparently took over a third of the age of the universe for us to get as far as we have.
Atomic weapons emerged slightly before the first craft to leave the Earth’s atmosphere, but we’re still nowhere near interstellar travel. On the other hand, the difficulty of space travel is largely a function of the escape velocity, which is dependent on the gravitational pull of your planet and solar system (both of which are variable).
One issue with your claim though is that once you have interstellar flight, you certainly have weapons of mass destruction. Even crashing a coke-can sized meteor into the Earth at 1% of the speed of light would cause major destruction.
It also feels like there's one pretty damn critical building block of modern society and space travel that would be galactically rare: hydrocarbon fuel.
If we didn't have oil, coal, etc in the insane quantities we have it in, we'd be nothing. It singularly enables global transportation, which has enabled global information sharing, which enables everything else. Its critical in the production of plastic, which is the most important material humanity has developed, period. Its the only way we know how to get into space. Its unlikely that planet-scale deployments of renewable tech like wind & solar would be possible without oil; to enable the manufacturing, mining, deployment, and tertiary required systems like batteries.
If we had evolved in the first hundred-million-year phase of life on the planet, there would have been no significant life before us to rot underground for a few hundred million years to make the hydrocarbons we use today. Or, there would have been so little that the reservoirs of it would be used up after a few decades or a century of burning it in lamps (every planet gets dark!), before the intelligent life realizes its true value (propulsion and plastic).
Another totally unrelated aspect of the problem I think about: Take the IQ spectrum, split in half at 100, and kill all the humans on the >100 side. The humans that are left (<100) would be very unlikely to leave the planet's surface in their lifetimes, and because genetics are a big factor in inherent intelligence, their ability to get to space has been delayed possibly indefinitely.
Put this another way: Space travel is on the razor's edge of our intelligence capacity. And its not enough to have a three standard deviation genius come along every couple generations; that's just a Galileo being born in the 1500s, they'll discover and document things for sure. But it takes many highly intelligent, motivated, and enabled (see: Oil) people to unlock space flight, computing, nuclear power, etc. Its easy to imagine even a human civilization that sits with a median IQ of what we'd say is 60-70, and they literally never pursue these kinds of high technology. But you can get really far with 60-70 IQ. You get nearly all of the evolutionary advantages a 100+ IQ person would have, you can make hunting traps, outsmart prey, you can farm, even smith and mine minerals; but you probably aren't sending rockets into orbit.
My take is: The universe and even our galaxy is probably surprisingly full of bronze-age era civilizations; and they've probably been that way for centuries. The Great Filter is most probably a combination of Ultra-High Quantities of Hydrocarbon Fuel, plus widespread median Academic-level Intelligence.
I find it delusional to think we're close in any way to being multiplanetary. Mars hardly has an atmosphere and you can't survive outside a pressurized environment. You could build a base there but not a city, not even considering the amount of people need to have a self sufficient community and the amount of resources needed to transport what's needed to jumpstart it.
Personally I think the lack of visible galactic civilisations is more plausibly explained by a combination of life being rare (and probably brought to Earth via panspermia after billions of years of evolution elsewhere) and both multicellular and sentient life also being rare.