I suppose I am not the typical blogger when I say, "I covered that topic 14 years ago, so I don't need to cover it again, right?"
Recently the question of the existence of alien intelligence has come to my attention again. It's a sensational topic. People have been discussing it continuously, I'm sure, but it comes to me anew as part of my scanning for suitable YouTube videos to watch.
These are the links to the posts I made 14 years ago:
http://bartfusn.blogspot.com/2008/06/aliens-are-bountiful-but-unreachable.html
http://bartfusn.blogspot.com/2008/09/failure-to-detect-aliens-does-not-mean.html
None of my views have changed, but I will add a new analysis. Some people may find it boring. (Oh, no! I will lose viewers and advertising revenue!)
Wikipedia includes an article on "The Fermi Paradox", which is essentially: If earth isn't special in some way, there should be lots of other intelligent civilizations in the galaxy. Yet, we have not detected any, let alone had any of them come visit us. How can this be?
First I'll give my answer, which is basically: "You can't get there from here." Most likely the resources and technology needed to colonize a single other world are too great and beyond the capabilities of EVERY ONE of the millions of civilizations.
But if we get past that step, we realize that colonizing the galaxy requires an expanding population growth of colonized planets. Some of the time a colonized planet has to colonize two or more others. If civilizations can expand at most for a small distance around their origins, and habitable planets are as sparse as we suspect, that is why we haven't met any aliens. I'll abbreviate "You can't get there from here" with the shorter "TOO FAR".
I think all of the other explanations are unsatisfactory (except for the Zoo Hypothesis). Here I focus on the Wikipedia article's list of hypothetical explanations.
https://en.wikipedia.org/wiki/Fermi_paradox#Hypothetical_explanations_for_the_paradox
Earth is special: extraterrestrial intelligence is rare or nonexistent. This is hubris. As scientists look, they find planets around stars, stars of the right types, and planets of the right size and composition, the right distance from their stars. Given our current detection capabilities, everything they would expect to find in support of life elsewhere they have found.
The key question for the others is not, "Is this a possibility?"or "Is this pretty likely?" but rather, "Is this so certain that it would prevent ALL of the millions of civilizations from reaching us?" Some of them are about time limits on these other civilizations. Others are about their being too alien. Others are about why they don't communicate with us. But all are consistent with the resolution of the paradox being that there are alien civilizations (likely millions), but we haven't detected any of them.
A. Global catastrophic risk. ALL?
B. Intelligent alien species have not developed advanced technologies. TOO FAR. If millions of species have been at this for a long time and none has developed the right technologies, chances become very high that there is some limitation beyond cleverness, that is a barrier to all societies. ALL? and TOO FAR mix.
(I switch here from using letters for possibilities to numbers).
As an overall concept (specific examples below) some complex set of psychological or sociological forces will limit or destroy civilizations. None of these have the aura of inevitability. ALL?
1. It is in the nature of intelligent life to destroy itself. ALL?
2. It is in the nature of intelligent life to destroy others. ALL?
3. Civilizations only broadcast detectable signals for a brief period of time. ALL?
4. Alien life may be too alien. (This becomes a version of "earth is special", if ALL of the millions of species are so terribly alien. The electromagnetic spectrum and the presence of physical bodies seem pretty basic). ALL?
5. Colonization is not the cosmic norm. ALL?
6. Alien species may have only settled part of the galaxy. TOO FAR. With so many species having the opportunity for so long, why would they stop halfway?
7. Alien species may not live on planets. ALL? RELEVANT?
8. Alien species may isolate themselves from the outside world. ALL?
9. Lack of resources needed to physically spread throughout the galaxy. TOO FAR. Some few individual planets may be brimming with resources, but that's just one small step on being able to spread.
10. It is cheaper to transfer information than explore physically. IRRELEVANT, or a variant of "too alien".
11. Humans have not listened properly. IRRELEVANT.
12. Humans have not listened long enough. IRRELEVANT.
13. Intelligent life may be too far away. TOO FAR. Treated more fully in other points.
14. Intelligence may exist hidden from view. IRRELEVANT.
15. Everyone is listening but no one is communicating. ALL?
16. Communication is dangerous. ALL?
17. Earth is deliberately avoided. The "zoo" hypothesis. Interesting. In a class by itself!
I am proposing that ALL of the millions of civilizations have failed at colonization. That's a high bar to meet, that even with some highly unlikely mix of favorable circumstances, not a single one of millions has succeeded at an arbitrarily expanding colonization.
Here is a brief rundown of what is required to have an expanding population of of colonization.
A huge spacecraft must be constructed. Life must be maintained for thousands of years if the spacecraft goes near the speed of light, millions if it doesn't. Long-term stasis might be one option, but it is entirely possible that NO form of intelligent life can survive and thrive after long-term stasis -- space has dangerous objects and dangerous rays. Otherwise, the society with its usual cycle of life and death must function aboard the spacecraft for those thousands or millions of years.
The spacecraft has to stop when it reaches its destination. The energy to set it off from the home planet can be assembled locally, but the energy to stop has to be carried with the spacecraft, and it is huge. Additional energy in similar quantities is required for course corrections, if the aliens detect from their spacehip that there is a more promising place to visit.
Aiming difficulties. Before setting out on this voyage, the colonists have to know where they are going. Perhaps their techniques will let them verify that there is a world which matches their own environment rather closely, and that is not already occupied by a civilization that would not welcome them. But for an expanding pattern of colonization, far more is required: The planet has to have support for a sizable population, lots of heavy industry, and large, accessible quantities of many minerals to construct at least one new colony ship. Suppose for instance aliens with needs like humans detect a planet with a band like our arctic tundra around the equator and glaciers elsewhere. Perhaps colonists could eke out a living, but not build a large industrial base.
Note also that when scientists make estimates of planets that could host life, they mean life that evolved for local conditions. Some other organism that evolved on another planet may have far more specific requirements for their own survival.
There has to be a net gain. Some of the time, a planet has to have at least TWO successful colonizations for this to be an expanding process. If we allow for some of the colonization efforts being failures, we need to replace them and still have a net growth.
Some have proposed a robotic colonization instead of one with living organisms. This does solve some of the problems, for instance relaxing environmental requirements. Our robots on earth are more and more capable with time. But that does not mean that there is no limit to what they can achieve even in the best of circumstances with millions of civilizations trying. A robot needs to quickly find materials allowing it to replicate itself, which are on earth mined from ores and then processed, at great expense. Then they must build a large industrial base, then construct two or more huge spaceships and launch them -- that is indeed a lot of work. What's more, most engineering systems advance by trial and error, getting feedback from earlier attempts to perfect later ones. But if the robot goes a thousand light years away and is even capable of sending information back, the time between one version and the next one improved based on experience is no less than 2,000 years.
I am not a skillful web searcher, but it seems there are far more articles on how robotic probes could proliferate than the immense difficulties. Perhaps this is akin to how conspiracy theories get huge press, and the debunkers write the facts but don't recycle them endlessly.
I have written ALL? In front of most of the proposed limitations, and so I am hesitant to write ALL! In front of this one. But to me it looks like the engineering challenges cannot be overcome by some rare local favorable circumstances, even with millions of civilizations trying.
For us to be surprised that we have not met any aliens, we have to be confident that some civilization somewhere can solve the "TOO FAR" problem to reach over very large expanses of space. The assertion that not a single one can solve that problem seems to me far more likely than any other explanation.
When I think about colonization efforts, I imagine a map of the universe with widely scattered islands of intelligent life. Most are single planets. Here and there just possibly colonization might have happened, proceeding to a small handful of nearby stars, or even merged togther. They form little bubbles. But the bubbles are way too far apart to meet each other reliably, let alone expand to cover the entire galaxy.
This seems by far the most plausible explanation for why we have met no aliens. Earth is not special, so there have been millions of other civilizations throughout our galaxy and others. However, not a single one of those millions can create a colonization effort that can grow arbitrarily large, and thus come into contact with us.
The second most likely explanation is the "Zoo Hypothesis", but that's an explanation for another day.
None of others seems remotely plausible to me.
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