Over the years, I’ve done a lot of posts speculating about alien civilizations. My take is generally that while extraterrestrial life may be prevalent in the universe, complex life is rare, and intelligent civilization producing life is profoundly rare.
This seems evident from our own history, where simple life appears to have started as soon as it could on Earth, but complex life took billions years to get off the ground and needed numerous prerequisite developments. A civilization producing species only evolved once among 8.7 million different species, and required a highly improbable sequence of events.
There’s also the Fermi paradox, which asks if alien civilizations are common, then where is everyone? Taken together, it leads to the profoundly rare conclusion. That means our nearest neighboring civilization is likely very far away, far enough that there hasn’t been enough time for them to reach us yet, likely hundreds of millions or even billions of light years away.
This means it’s possible that, due to the expansion of the universe, we may never get a chance to meet them. If we do, it will likely be some distant vanguard of human expansion into the universe, or our AI progeny, that eventually meets their vanguard or AI progeny, probably millions or billions of years in the future.
It turns out Robin Hanson thinks along similar lines, although in far more detail. Scott Aaronson did a post this weekend on Hanson’s theory about alien civilizations, which Hanson himself has detailed in a series of blog posts. His estimate of the distance to our nearest neighbor is one to four billion light years. I don’t fully understand how he narrows it down to that range, but it seems plausible enough.
Hanson discusses the idea of a “grabby civilization” (GC), one that is aggressively expansionist and appropriates resources in the universe for its purposes. This is in contrast to other quieter civilizations that may be in harmony with nature or something and not be very noticeable. But a GC should be very noticeable, building Dyson swarms around the majority of stars in galaxies, making those galaxies less visible, except in the infrared range, or perhaps other megaprojects we haven’t conceived of.
We don’t see signs of a GC (at least not conclusive ones). But Hanson points out that the light of their alterations may not have reached us yet. Depending on how fast such a civilization can spread, that light may not reach us too far ahead of the civilization itself. In other words, there is both an expanding sphere of influence for the GC, and an expanding sphere of detection. A GC able to expand at near the speed of light may not have a sphere of detection much bigger than its sphere of influence.
Of course, this is on cosmological time scales. A civilization expanding from an origin a billion light years away, that expands at 99% the speed of light, would still have its effects visible to us 10 million years before they arrived. But it would mean they had already appropriated everything in that direction.
Hansen thinks a more likely scenario is, assuming we don’t destroy ourselves, we become a GC ourselves and start expanding. This brings us back to the scenario I mentioned above, where our vanguard meets theirs, half a billion years from now on Hanson’s estimate. My assumption had always been that it would be a surprise event for the two vanguards, but if Hanson is right, they should see each other approaching in advance through their visible effects.
It’s worth noting that expansion throughout the universe would likely not be straightforward, but would often involve following cosmic filaments around intergalactic voids. We might imagine humanity’s vanguard splitting from each other in many directions, and then meeting again on the other side of a void. But hundreds of millions of years could have passed in the interim. How different might the factions have become over that period? Those factions might be almost as alien to each other as anything else they might meet in the universe.
In both cases, you have to wonder what happens when two GCs, or even two factions of the same GC, meet like that. It might be natural selection on a cosmological scale. Even if some encounters are friendly, it’s not hard to imagine many of them won’t be. And it’s not like either side would be able to coordinate a consistent policy across disparate meeting points since all communications could only happen at the speed of light.
Hanson also notes that the time span for expansion is limited. The local Virgo supercluster is expected to become causally separated from the rest of the universe by 150 billion years from now. Eventually, the local group will itself become isolated from the rest of Virgo. We’ll be able to see the rest of the universe for trillions of years, but the light will only be from the first 150 billions years or so. In other words, we might eventually see the effects of many more civilizations than we ever have the chance to meet.
Hanson imagines different civilizations sending out information about themselves into the wider universe. Some may try sending information physically, all in an attempt to tell their story to a wider universe, while there’s still time.
Once the various islands of the universe have become isolated from each other, there remains a long future, as everyone watches the rest of the universe become increasingly more red shifted, and bizarrely, time dilated. A long time to review the stories they may have received. In later ages, the idea that there was once a wider universe could become the stuff of distant legend.
Of course, all of this assumes this type of expansion is possible. Or if possible, that it’s possible fast enough for civilizations to come into contact with each other. It might be the expansion is possible, but only practical at 5% of the speed of light, which might put us back into the mode of never encountering each other. Although it shouldn’t prevent us from seeing their effects.
What do you think of Hanson’s idea of grabby civilizations? Should we become one as a defensive precaution? Or hunker down as a quiet one and hope for the best? I’m usually dismissive of the idea of Earth as a backwater in our galaxy, but on an intergalactic scale, the local group actually is a backwater. Maybe we shouldn’t call attention to ourselves?