Galactic Settlement and the Fermi Paradox
m.nautil.us
m.nautil.us
That's somewhat of a wild assumption. What's a "spacefaring species"? Are we one since we've built a few ships and went to the moon?
Have they solved problems that might be intractable, like being able to travel anywhere remotely far in anything else than a "generation ship"?
Have they found the power to deploy those ships, and the materials (and amounts required of them) to withstand the radiation of space, incoming meteors and space debris over decades of flying, while still being able to propel their spaceships out of their gravity?
And why would those settlements even be able to survive in space, going out on some remote systems, and not knowing what they'll find there, and what exactly their Earth-like planets will provide them?
>William Newman and Carl Sagan later wrote a major rebuttal to Hart’s work, in which they argued that the timescales to populate the entire galaxy could be quite long. In particular, they noted that the colonization fronts Hart described through the Milky Way might move much more slowly than the speed of the colonization ships if their population growth rates were so low that they only needed to spread to nearby stars very rarely. They also argued that being a long-lived civilization is inconsistent with being a rapidly-expanding one, so any species bent on settling the galaxy would not last long enough to succeed. In other words, they reasoned that the galaxy could be filled with both short-lived rapidly expanding civilizations that don’t get very far and long-lived slowly expanding civilizations that haven’t gotten very far—either way, it’s not surprising that we have not been visited.
That sounds much more logical!
It may just be that such a developmental landmark is a prerequisite of a civilization reaching interplanetary scale and it may even be a great filter.
We are the only intelligent more-or-less spacefaring species that we are aware of and if we can't do it why would we think other hypothetical intelligent spacefaring species can do it.
Are you just questioning the Von Neumann machine aspect or the entire feasibility of sending a basic dumb probe out to another star for a fly-by?
Not necessarily. I think you underestimate how much of space is space and how little of it is anything else... and that most of that "anything else" is dark matter. Only ~4% of the mass energy of the entire universe is matter.
It seems more likely than not to me that any arbitrary path through interstellar space would never pass near anything larger than a grain of dust.
https://wiki.evageeks.org/First_Ancestral_Race
(Though I suppose two probes would have to accidentally land on the same planet to lead to that outcome.)
Part of the Fermi paradox they skipped in this article is the idea of a Great Filter which prevents life from evolving or creating a space faring culture. The assumption is that we're past the filtering event, but it's entirely possible that we haven't reached it and in some unknown future our race will cease to exist.
Imagine a technology which would allow a single insane being to destroy the entire planet, or at least all intelligent life. We're not too far off from that point now if you consider modern political power. If that point of technological advancement is inevitably discovered prior to the technology required to become a space-faring race.
The idea of an individual or small team of scientists creating a world-threatening virus or triggering nuclear war is not that far outside our current state of affairs. Interstellar space travel is likely at least 100 years in the future.
It seems more logical to assume that the universe appears empty to us because we are the only organisms like ourselves, and that other life forms exist in ways that are simply incomprehensible to us at the current level of scientific understanding.
Edit: To use a metaphor I’ve just thought of (and think works): many people assume that meeting extraterrestrial life will be akin to Europeans landing in the New World. It’s more likely that it will be akin to the discovery of the atom.
In fact I'd be very suspicious if recognisable alien life appeared and knocked on our door, because it would literally be so astronomically unlikely I'd be skeptical about taking it at face value.
But I've never seen any sign the people involved in SETI are doing this with blinders trying to find bipedal creatures with a mouth that breathes oxygen and are about 1-2 meters tall.
The assumption always seems to be that experience as we perceive it now is some sort of default, objective one. It’s far more likely that we are simply locked into a very narrow viewpoint. The scales are simply so large that we are unable to comprehend them in any meaningful way.
Carbon can form more molecules than all the other elements combined, so it makes sense that complex chemical "elements" are heavily based on it.
In fact if you compare most common elements in universe[1] and most common elements in human body[2] they are mostly the same (different order)
1: https://en.wikipedia.org/wiki/Abundance_of_the_chemical_elem... 2: https://en.wikipedia.org/wiki/Composition_of_the_human_body
As well, carbon chemistry is rich under earth conditions (temperature and pressure wise). We simply don't know for others.
Even if we assume that the vast majority of life forms are undetectable/incomprehensible, there is still no good explanation for why Earth would be the only place suitable for life forms similar to us.
Among the many steps necessary to evolve life as we know it, which one could only happen here?
So the paradox is still there.
And this just assuming a single civilization, while as you said: there could be more worlds with life similar to ours that there are grains of sand on Earth. So where is everyone?
So now imagine a civilization similar to us but slightly older, not only would this civilization's signals have reached all parts of our galaxy, but those signals would likely be much stronger than we have produced in the last 100 years. It would also be possible for a civilization a few hundred millions years older than us to send probes to every star of the galaxy by now.
1. There is still no good explanation _that we know of_. We don't even know if we are the only life forms in existence or not: none of the observations made so far support the latter, but do not disprove it either. So we can't prove or disprove _any_ hypothesis about extraterrestrial life.
2. "Suitable for life similar to us" and "suitable for life to spontaneously appear" are two very different things. And we still don't know enough about either.
We may say today that interstellar travel is impossible, but tomorrow we may find a solution.
We may say today that we are alone, only to be visited by intelligent aliens somewhere in the next millennia.
We may never be visited by anyone or visit anyone, but the universe may be full of intelligent life.
We simply cannot compute anything for such a problem, with so many unknowns.
- Richard Dawkins, The Selfish Gene, 1976
Dawkins talking about the first sentence, about 1980:
"...that was no metaphor. I believe it is the literal truth, provided certain key words are defined in the particular ways favoured by biologists. Of course it is a hard truth to swallow at first gulp. As Dr Christopher Evans has remarked, "This horrendous concept - the total prostitution of all animal life, including Man and all his airs and graces, to the blind purposiveness of these minute virus-like substances - is so desperately at odds with almost every other view that Man has of himself, that Dawkins’ book has received a bleak reception in many quarters. Nevertheless his argument is virtually irrefutable" ...
Self assembling replicators from some civilization should have colonized and cataloged every star system over billion year time scales.
It's inconceivable that no intelligent space faring civilization would have thought to do this.
There are too many stars and too many close enough galaxies that could contain life. If they've been spacefaring for even ten thousand years longer than us then they're almost certainly able to monitor us without our ability to detect it.
But if we're doomed to a great filter in the near future, like nuclear war, then it still doesn't mean we're alone. It just means that out there in the sky there are others kinda like us. Searching for meaning before hitting a technological explosion of one kind or another that wipes us out. But just because we don't have contact doesn't mean we're alone, even if we're only present in each others respective imaginations.
What if the ROI of space colonization even at multi-decade or multi-century timescales is negative? Then why would anyone do it?
What if they just feel like exploring, and gaining knowledge, and seeing things no one else has ever seen?
It's entirely conceivable that every space faring civilization which has tried has failed simply because the odds are so stacked against success, even once, at every step along that process. Just because the math is simple, doesn't mean the application is simple.
Hell, we don't even know what the odds are of becoming a space faring civilization to being with, and it doesn't seem axiomatic that every such civilization would even want to seed the galaxy with self-assembling replicators to begin with.
1. Expansionist civilizations that encounter one another reliably obliterate one another. Non-expansionists don't spread out.
2. Advanced civilizations have no need for goldielocks-zone planets. Where mass is needed, Kuiper-belt objects are more convenient sources. The notion of Dyson spheres seems especially silly: even extreme primitives would have confined fusion power, and have no need to rely on primitive, diffuse stellar radiation.
Both could be true, along with others not listed.