If another intelligent alien civilization exists, it will almost certainly expand rapidly into the rest of the universe. Even if 99.999% of the individuals don't want to leave their home world, the remaining 0.001% that does will expand and multiply. But it's reasonably likely humans are the only intelligent life in the observable universe.
You're assuming a lot with this post.
- Aliens have the human tendency to multiply to fill (and then exceed) any natural constraints
- Aliens have any interest in leaving their planet
- It's possible to meaningfully compare human intelligence with alien intelligence
- Alien life is possible for us to identify
Bad assumptions lead to poor results. As far as aliens go, we don't have remotely enough evidence (of anything) to be able to draw any kinds of conclusions.
"Multiplying and filling" is not merely a human tendency; it's one intrinsic to all life. Anything that didn't bother to maximally create copies of itself in its environment went extinct long ago. Whatever life emerges anywhere else will be subject to the same competitive constraint to replicate or die. The one credible counter-argument to this assertion I have come across is this and you are right that we don't know if that is highly likely outcome in the evolution of civilizations. I suspect not, given that we are very far from that state now and that we are not so technologically far from being able to fill the galaxy with von Neumann probes. Given that the singleton is a very specific outcome that must be absolute in its realization to prevent galactic colonization, I favor the view that it is rather unlikely.
I agree with you that most life we know on Earth tends to multiply to fill natural constraints. Humans are the only life that tends to multiply and then exceed those natural constraints though that hasn't already wiped itself out. That creates in us a need to abandon our world and seek life elsewhere. A form of life that lives within natural constraints would not have this same need, and thus not be driven to explore space.
Humans do not exceed natural constraints because humans are "universal explainers" for which the only natural constraints are the laws of physics. Regarding your hypothetical form of life, that sounds as if it is essentially the singleton possibility I pointed out: a civilization where any stray desire by an individual that runs counter to the civilization's goal of complete stasis is everywhere and always suppressed. I agree it is a possibility but what I find less plausible is that such a state could be eternally stable.
On the question of identifying alien life, if we constrain our imaginations to our current understanding of physics, the 2nd Law of Thermodynamics suggests that this will not be the case (assuming the replication-is-inevitable hypothesis is also correct). There is just no way to hide the heat-correlates of an energy-intensive galactic civilization that we know of.
Again, you're making a lot of assumptions here.
Humans don't even have a good working definition of life. Is fire alive? It grows, metabolizes, excretes waste, goes through many stages of change, and finally dies. Why aren't viruses alive? Given that we can't define what we're looking for, what makes you think we'll know it when we find it?
What if a creature has an extremely slow metabolism? It moves slower than a glacier, in inches every thousand years. It reproduces every hundred million years or so. How would we identify and recognize such a creature?
You're assuming that energy usage is in a form that we know. You're also assuming that energy use is an indicator of intelligence. So many assumptions. . .
Well, I'm a bit of a panpsychist on Tuesdays and Thursdays so I agree that a totally satisfactory definition of "life"--and our ability to clearly identify
subjects of experience--are difficult tasks.
Of course, we could sit here all day thinking up possible creatures that would confound our abilities to recognize them as such, but then I would find it interesting that they would have exotic qualities of precisely the sort that make them difficult to recognize (yes, I know about the Dark Forest hypothesis which would be an argument for why this might be the case). Regardless, our best estimates and uncertainty of parameters within the Fermi Equation suggest the odds of another civilization existing anywhere in our proximity is not particularly high, so going to extraordinary lengths to stay hidden seems pointless given our best current knowledge.
On the other assumptions, yes, I pointed out that my commentary was based on our present understanding of physics. If we want to imagine what our future knowledge in physics will or won't allow, we are going to be here a while. Maybe the
neutral chi zeptino interacts with the
axion malaka field to produce
hapson excitations in the
air chrysalis, and the aliens have all uploaded their minds to its phase-space?
The result is the view that non-expanding technological society would need either an absolutely powerful top-down enforcement of this rule and/or be (unchangeably!) in the mind parameter-space such that all of its members never elect to become replicators.
Now you're making assumptions about the organization of an (apparently authoritarian) alien society. But we don't even know that intelligent life on other worlds would organize into a society. Humans only do that because we're evolved from pack animals (apes).
So . . . many . . . assumptions.
I'm not making an assumption here; rather, I'm pointing out the sort of features a non-expanding civilization would necessarily have to maintain its stasis. The critical feature is eternal stasis, which could be achieved either via top-down or bottom-up mechanisms.
As a biologist I need to chime in and point out that not all forms of life on Earth are predisposed to "multiply and fill" their available niche. Many organisms have environmental feedback mechanisms that reduce or halt growth and reproduction when a resource begins to become limiting. As noted, humans and some other organisms do not have such biological constraints.
Yet even within human society we seem to be hitting an inflection point, where wealthy societies are (by and large) not reproducing faster than replacement (i.e. the birthrate for most countries in the G20 are slowing, and many are at or below the level necessary to maintain the same population without immigration). Countries like Canada, Japan, the USA, Germany, Spain, UK etc are all at or under this threshold already.
Given the economic expansion we've witnessed in the last 50 years and its negative correlation on birthrates, one could imagine that Earth will hit a maximum population number sometime in the next half-century, and then (possibly) slowly decline in the 2100s. In fact the most effective way of stopping global population grwoth (if that was our goal) very well could be to raise the income standards of the the several dozen mostly African and Asian countries where birthrates are still >>3/woman.
It's entirely conjecture whether ET lifeforms would share our human train of "multiply and fill".
All it takes is one sub-group to maintain a high fertility rate and it doesn't matter what most of rest of the world does. Maybe
everyone will be Amish in 200 years. There are some reasons to doubt this in the specific case of the Amish as pointed out in that analysis (and 200 year forecasts are silly)--but then pick any other possible sub-group that might counter the overall trend of declining global birth-rates, and maybe
they will populate the world.
Re: feedback mechanisms, yes, some bacteria will actively prevent overpopulating a limited volume through such mechanisms. I would suggest this presents just a modest correction to the assertion that all life on earth maximally replicates. For humans, the feedback mechanism is not biological or genetic (at least directly); it has much more to do with what people believe and desire. As alluded to in the Amish example, some sub-groups desire different things which give rise to different birth rates. An ideology that results in higher birth-rates will, in the long run, replace any that favors lower ones. All that is required is enough variation in the society with respect to ideology that sub-groups with a more aggressive replication-goal are likely to exist. A society without (expressed) ideological variation brings us back to the singleton as a possible preventative measure to exponential replication and expansion.
