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posted by janrinok on Sunday January 19 2020, @12:31PM   Printer-friendly

Galactic Settlement and the Fermi Paradox:

A spacefaring species could easily settle the entire Milky Way given billions of years. Yet the fact is that there is no obvious one in our solar system right now. The supposed inconsistency between these statements is the Fermi Paradox, named for the Nobel Prize-winning physicist who supposedly first formulated it. In a trenchant formulation of the Fermi Paradox, American astrophysicist Michael H. Hart called the lack of extraterrestrial beings or artifacts on Earth today "Fact A." He showed that most objections to his conclusion—that a spacefaring civilization could have crossed the galaxy by now—stem from either a lack of appreciation for the timescales involved (it takes a small extrapolation from present human technology to get interstellar ships, and even slow ships can star-hop across our galaxy in less time than the galaxy's age) or else the dubious assumption that all members of all extraterrestrial species will avoid colonizing behaviors forever (an example of what I've called the monocultural fallacy).

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.

Being a long-lived civilization is inconsistent with being a rapidly-expanding one.

In a 2014 paper on the topic, my colleagues and I rebutted many of these claims. In particular, we argued that one should not conflate the population growth in a single settlement with that of all settlements. There is no reason to suppose that population growth, resource depletion, or overcrowding drives the creation of new settlements, or that a small, sustainable settlement would never launch a new settlement ship. One can easily imagine a rapidly expanding network of small sustainable settlements (indeed, the first human migrations across the globe likely looked a lot like this).

Another factor affects Newman and Sagan's numbers on timescales and colonization-front speeds. Most of the prior work on this topic exploits percolation models, in which ships move about on a static two-dimensional substrate of stars. In these models, a star launching settlement ships can quickly settle all of the nearby stars, limiting the number of stars it can settle. But real stars move in three dimensions, meaning that they can carry their orbiting settlements throughout the galaxy, and that a settlement will always have fresh new stars to settle if it waits long enough.

Jonathan Carroll-Nellenback, at the University of Rochester with Adam Frank, not long ago finished work, with Caleb Scharf and me, on analytic and numerical models for how a realistic settlement front would behave in a real gas of stars, one characteristic of the galactic disk at our distance from the galactic center. The big advances here are a few:

Carroll-Nellenback validated an analytic formalism for settlement expansion fronts with numerical models for a realistic gas of stars. He accounted for finite settlement lifetimes, the idea that only a small fraction of stars will be settle-able, and explored the limits of very slow and infrequent settlement ships. He also explored a range of settlement behaviors to see how galactic settlement fronts depend on them.

The idea that not all stars are settle-able is important to keep in mind. Adam Frank calls this the Aurora effect, after the Kim Stanley Robinson novel in which a system is "habitable, but not settle-able."

A very interesting read.


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  • (Score: 0) by Anonymous Coward on Sunday January 19 2020, @07:53PM (3 children)

    by Anonymous Coward on Sunday January 19 2020, @07:53PM (#945441)

    There's a much better explanation in my opinion: pleasure. Few people take on children as a feeling of a public responsibility. Most do so either accidentally or because their biological clock kicks in and you face this overwhelming desire to have a child. I'm sure some fools also get into thinking it'd be fun and entertaining. To annihilate humankind all you need to is to create something that's sufficiently more pleasurable than the motivations and innate drives that push us to have children. Alternatively, develop drugs that enable people to suppress these urges.

    I think these are vastly more likely than us nuking ourselves to death because pleasure is actively, enthusiastically, and voluntarily spread. Death and destruction is something folks tend to try to avoid. Your underground military bases or bomb shelters can save you from a nuke. But nothing can save you from enjoying yourself to point of letting yourself fade into nothingness while failing to reproduce.

  • (Score: 1) by khallow on Monday January 20 2020, @05:59AM (2 children)

    by khallow (3766) Subscriber Badge on Monday January 20 2020, @05:59AM (#945685) Journal

    But nothing can save you from enjoying yourself to point of letting yourself fade into nothingness while failing to reproduce.

    I can think of a number of ways that can happen. Such as being unable to feel such pleasure. Or wiring the pleasure so that it reinforces the reproduction instincts rather than the other way around. Or using robotics that to birth and rear the children without distracted human involvement.

    • (Score: 0) by Anonymous Coward on Monday January 20 2020, @12:44PM (1 child)

      by Anonymous Coward on Monday January 20 2020, @12:44PM (#945767)

      Pleasure, like pain, is probably a universal. It's little more than an evolutionary trick to push an organism towards good outcomes. Something that can never feel pleasure would have difficulty ever choosing the correct action. And similarly one that cannot feel pain would have difficulties avoiding bad outcomes. Any species that evolves such sensory devices would be many orders of magnitude more successful than any other species.

      It's only once you reach a certain level of cognition that you suddenly learn how to game the system to the point that we can actively and purposefully make things that feel good yet provide extremely negative outcomes. For instance this is also why I doubt there will ever be a species with perfect memory. Imagine we had perfectly crystal clear memories of events alongside all sensory perceptions. It's likely we'd end up dying off as a species as we sit around memory-bating to the most pleasant moments. Directly analogous to how we may end up killing ourselves off with artificially generated pleasure.

      The big argument against this is natural selection. Those that are capable of putting interests aside of mere pleasure would end up having a tremendous evolutionary come reproductive advantage that would gradually spread to everybody. Yet the reason I think this argument is weak is because of the timeline this will happen in. Reaching 'max pleasure' will likely be an event that goes 0 to max in a matter of a few decades. It could even, in theory, happen within our lives. And so evolutionary mechanics would not have time to kick in. On the other hand one might argue it will be a slow progression. Perhaps we've already begun it with the development of practically endless delicious food. Those that indulge grow fat, die young, and more frequently fail to reproduce or produce defective offspring. Those that don't, thrive. I have no idea how to even begin to weight the probabilities. It's complex.

      • (Score: 1) by khallow on Monday January 20 2020, @02:42PM

        by khallow (3766) Subscriber Badge on Monday January 20 2020, @02:42PM (#945833) Journal
        All the solutions I pointed to can be implemented in zero generations too.