Such a mechanism would make complex life even more rare in the universe. Better this solution to the Fermi paradox than that sentient species tend to destroy themselves with technology.
I've always seen a problem with the idea of the great filter: why do we think the filter is one thing or one discrete barrier?
Why couldn't there be a very large number of low-probability filters and/or a continuous probability of failure spread across billions of years? Add them all up and the cumulative effect would be the same as a single great filter, but there would not be one single primary hurdle that needs to be cleared.
This and the Fermi paradox itself are really just speculations. We have only one data point, which makes it impossible to say anything definitive.
If we find abundant ET life, it's evidence we're fucked, since at least one filter is in front of us. Only by having little or no ET within cosmological distances would the possibility remain open there's no GF ahead of us.
Please explain because i would intuit the opposite. The less life's we see, the less likely that life survives to/through technological ages that would allow them to talk to us. If we see abundant life the it must be very easy to survive, thus less filters
If life is abundant, there must have been something to prevent it from spreading, now or in the distant past. The fact that we evolved in an apparently empty universe, rather than in one that's been totally colonized, implies something stops this from happening. This thing is called the Great Filter, and it's apparently extremely effective.
If the GF is in front of us, in a universe with lots of ETI, our chances of evading it are extremely small. After all, no one else has; why would we be so special?
Nick Bostrum has called detection of ETI, or even complex ET life, the worst news mankind would ever receive. It would be a death sentence for our future.
Space is called space for a reason. I feel like even scientifically knowledgeable people have a hard time wrapping their heads around just how much space is out there.
Signals diminish with the square of distance. SETI would never hear anything from other stars unless it was broadcast with insanely high transmit power or was directed right at us (and still very powerful). Nobody would do that unless they knew someone was here actively listening.
So for example, to reach the Centauri system (the nearest star) with a signal as powerful as the signal Voyager sends to Earth would require a transmit power of over 100 megawatts at a minimum. That's just the nearest star. It gets exponentially harder as you go further out. For more distant stars you're talking gigawatts or terawatts or beyond.
Even barring concerns about attracting attention, why dedicate that kind of resources to operate an interstellar border blaster if you don't even have a reason to think anyone's listening, and if you won't get a reply for hundreds or thousands of years?
This is not making a point you think it's making. If SETI is problematic, success becomes even more depressing, since it implies even more non-communicating civilizations out there (and, presumably, existing densely in the past as well). So why wasn't Earth colonized eons ago?
Why would it be? It’s full of corrosive oxygen and biomass that would be a biohazard to anything carbon based and organic. It’s habitable to us because we evolved here but it might be toxic hell to something else.
If you are going to sterilize Earth you might as well just terraform something dead. This isn’t even getting into the ethical questions, just looking at practicality.
If you’ve got the technology to come here, well, you might as well terraform something dead. We almost have the technology to terraform Mars (albeit over thousands of years) and it seems easier to do and possibly faster than interstellar flight.
Building giant space station habitats is also easier than interstellar flight. Uploading brains to machines, which would allow settlement of almost anywhere, is probably easier than interstellar flight. AGI is probably easier than interstellar flight.
In fact interstellar flight is so hard it might rarely be attempted anywhere by anyone unless there’s a forcing function like one’s star becoming unstable or some other cosmic scale calamity. Solar systems are huge and contain vast amounts of resources.
Why would a colonizing civilization have to choose between these options? If it experiences relentless growth, it would occupy everything. If it has grown to occupy some locations around a large number of stars, that's enormous growth from its initial system. Why would this growth stop? Instead, I'd expect it to fully exploit all the resources in all the systems reached. The solar system would look very different from what it looks like. There would be no asteroid belt; there would be a space colony belt.
They could be galaxies that have been fully colonized, but searches for them have turned up nothing. Specifically: if by "fully colonized" we mean fully exploiting the energy resources of the galaxy, this would show up in the spectrum of emitted radiation, with energy being emitted as waste heat instead of starlight. Infrared surveys put the fraction of such fully colonized galaxies at less than 1 in 100,000, and consistent with none at all.
Expanding is a significant use of resources. It requires consistent dedication over very long timeframes to succeed. Just look at how long it's taking to even have a permanent presence (not even close to a self-sustaining colony) on the Moon, which is one light-second away.
That’s one reason I’m skeptical of ultra-grabby hyper-expansionist aliens. Human cultures have become less obsessively expansionist as they’ve become more educated and advanced, with rare and usually transient exceptions.
Imperialism usually burns out after a while as the cost begins to exceed the benefit.
I could see a universe of mostly steady state civilizations that experience occasional bouts of expansionism or the sending of things like the Nauvoo from The Expanse. But those are transient events. This would greatly increase the time required for the galaxy to become saturated with life as per Fermi paradox models. It might happen eventually, meaning if we wait long enough some alien Mormons might show up. (The Expanse reference.)
Then consider that intelligence is probably a recent (on cosmic time scales) phenomenon due to metallicity. Previous generations of stars and planets probably lack the mineral diversity to support complex intelligent life.
There will be strong selection for expansionist cultures and species. As long as the universe is mostly unoccupied, expansion means increasing your share of the total population. Relatively static cultures will simply become irrelevant compared to their expansionist competitors. The experience on Earth recently is in the context of a world where all places that can be occupied (at the current tech level) have been.
The selection effect will operate at the biological level as well. Currently on Earth birth rates are declining. Modern civilization is acting like a kind of pesticide. But like any pesticide, it's going to select for resistance. This will likely mean more people will have an increased desire to have children. Selecting for this may take a while, but on the time scales involved in this thread it would happen very quickly.
In the long term, all societies in which selection is allowed to operate will push up against limits and be in states of Malthusian equilibrium. To counter this would require an unreasonable uniformity of control across time and space. All ET species, at all points in their history once they can undertake colonization, will have to exert rigid control on their societies and biology. Any defections from this uniformity will explode exponentially and overwhelm those who are not controlled.
You can have abundant life that is functionally isolated by physics, or said differently, by the degree of technological and societal advancement required to traverse the space between.
Great distances and inherent speed limits seem like a decent way to accomplish that.
I think it's clear that interstellar travel, while not trivial, should be possible for a civilization just a bit more advanced than our own. The energy or material resources required for interstellar colonization are very small compared to the resources available. It doesn't even require relativistic speeds, although reaching (say) 0.01 c doesn't require outrageous engineering, just a large spacecraft and lots of hydrogen bombs.
Now, perhaps it's universally true that civilizations don't advance much beyond where we currently are, or don't persist for sufficiently long for interstellar colonization to be successful. These would also be very depressing outcomes if they are imposed on us by the GF.
Interstellar colonization is more difficult than it's commonly imagined. To build a colony ship you need the same resources you'd need to build a large habitat. There would be economic pressure to build habitats that'd compete with the building of colony ships.
When a colony ship arrives to a new planet, it'll need to bootstrap a full industrial chain before it can build its own colony ships to expand to other systems. It's reasonable to assume there would be little incentive for that before the colony starts to require off-planet resources on their own system, and, therefore, has a compelling reason to build a space economy. For us, this would easily be in the thousands of years even if no terraforming is needed, and let's not even consider we'd need a consistent multi-century planning to get there. Precursor missions with automated in-situ resource collection and storage would allow colonists to arrive to a fully built and stocked colony, which would save some time. Existing biospheres might present issues of toxicity and biological risks: you really don't want to grow up on a (Dune's) Rossak (even if it grants you superpowers).
So, let's say Earth manages to establish 10 successful extra-solar colonies over 5 thousand years. It'll be at least a good couple thousand years until those successful colonies can each establish 10 others and raise the number to 100 worlds. If we manage to diligently expand at that exponential ration, we'll soon bump into other intelligent space-faring species that also share this commitment to reproduce.
And what motivates the continued expansion? Exhaustion of resources, if that is it, means that decay immediately eats into your reproduction and it isn’t a proliferation, but at best a continuous parasitic migration.
I don’t think that is clear at all. I think it reflects a massive gap in understanding of how difficult it is to do anything with humans for more than a generation.
I think the rare Earth hypotheses get it backward, it all looks unlikely when you only have one data point. I think that complex life finds a way and it all looks like a six cushion bank shot in retrospect.
