Reading Notes

The Great Filter - Are We Almost Past It? Robin Hanson

  • Fermi Paradox - by the Drake Equation, life should be abundant in the universe
    • There are lots of stars
    • Many of those stars are sun-like
    • There are lots of planets
    • Many of those planets are presumably earthlike (even though we can’t detect them yet)
    • So where is everyone? Why have we not discovered any form of life outside of Earth?
    • More to the point, why hasn’t an extraterrestrial civilization colonized Earth?
    • If interstellar travel is possible (even at slow sublight speeds), there’s still plenty of room in geological timescales for interstellar civilization to spread
  • The Fermi Paradox must force us to revise one or more of our standard views in biology, astronomy, physics or the social sciences
  • These revisions suggest that humanity ought to be much more wary of future disasters
  • Life will colonize
    • So far, on Earth, life has evolved to fill every viable ecological niche that it can find
    • Newly opened frontiers don’t stay sterile for long
    • Life seems to have a “dispersal phase”, and sexual mixing and mutations encourage exploration of new “technologies”
    • Moreover, humanity, overall has expanded to fill geographic and economic niches
      • Even when a particular human civilization fails to expand, other civilizations expand to fill in the gap
    • Thus we should expect when interstellar space travel is possible, some of our descendants will try to colonize the other planets in the solar system, and then other stars
    • We should expect this as long as society allows certain members to have and act on alternative views
    • A million years is a cosmologically short time scale, yet even very low rates of population growth will overwhelm the fundamental limits of negentropy in that time
    • Evolutionary pressure should encourage a maximum economically feasible growth rate, as those who do not explore are outcompeted by those who do, and discover fresh resources
  • The Data Point
    • There is at least a 1/1000 chance over the next ten million years that humanity’s descendants will reach an “explosive point” where human civilization expands outwards at near light-speed
    • This explosion will fill most every available niche containing usable resources
    • Moreover, this explosion would be detectable - colonization would disturb the natural state of of the place that it colonizes
    • If advanced life forms had colonized our planet, we would have known by now
    • If advanced life forms had restructured our solar system, we would have known by now
    • If advanced life forms had left the Sun alone (nature preserve theory), but had colonized nearby stars, we would have known by now
    • But our local stellar neighborhood doesn’t look like it’s been colonized
    • This suggests that no prior civilization has reached the “explosive point” and started expanding rapidly
  • The Great Filter
    • Best guess evolutionary path to an explosion that leads to colonization of the visible universe: # Right star system # Self-reproducing molecules (RNA, DNA, or something similiar) # Simple (e.g. prokaryotic) life # Complex (e.g. eukaryotic) life # Sexual reproduction # Multi-cellular life # Tool-using animals # Current human civilization # Colonization explosion
    • The Great Silence implies that one or more of these steps are much more improbable than we have reason to believe
    • The fact that our universe isn’t already full of life implies that it’s very hard for life to arise
  • Someone’s story is wrong
    • Biologists have worked hard to show that evolutionary steps aren’t especially improbable
    • Plausible models show how RNA turns into cellular life, how cellular life becomes more complicated, how intelligence evolves, and how intelligence leads to tool use and scenario generation
    • Similarly, technological optimists have taken standard economic trends and our understanding of evolutionary processes to show that if we can colonize the solar system, we can colonize the galaxy within a short period of time after that
    • Colonization of the solar system is already possible with current technology - the barriers are economic
    • However, the one data point described above - the fact that the universe has not already been colonized shows that at least one of the models described above is wrong
    • Life is either more rare than we think, or complex life is more rare than we think, or intelligence is more rare than we think, or it’s a lot harder for species to escape their home planet/solar system than we think
  • It Matters Who’s Wrong
    • Is the Great Filter in our past (i.e. we’ve already passed through it and we have no further obstacles towards becoming a universe-spanning life form) or is it in our future, in which case we should worry?
    • If the Great Filter is in our future, we should seek out Filter scenarios and take steps to prevent or mitigate them
  • Reconsidering Biology
    • Many biologists do expect a large filter between dead matter and intelligent tool using life
    • Complain that astronomers who estimate Drake Equation terms don’t understand biology
    • Say that tool use has only arisen once in the fossil record (i.e. humans)
    • How do we evaluate this possibility?
      • Distinguish between “discrete” and “trial-and-error” evolutionary steps
      • Discrete steps have to succeed within a specific time window
      • Trial-and-error steps are search across a mostly flat fitness landscape - failure today doesn’t affect the chances for success tomorrow
      • Main Great Filter implications all concern “trial-and-error” steps
      • “Hard step” candidates
        • Origin of life
        • Complex life (0-8 steps)
        • Sexual reproduction (2-3 steps)
        • Society (2 steps)
        • Cradle (1 step)
        • Possible language step (1 step)
      • Overall, 7-9 hard steps in biology
      • Step duration doesn’t necessarily correspond to how difficult the step is - was the transition easier to surmount than expected, or was it a hard step that you got lucky on?
    • 2 more hard steps outside of biology
      • Getting the right sort of planet
      • Civilization destroying itself
    • Panspermia
      • If life originated outside the Solar System, then that would allow for many more trial-and-error steps to have taken place
      • Allows steps prior to single-celled life to be less probable, but makes up for it by allowing single-celled life to spread from place to place
    • SETI evidence
      • If SETI finds radio signals from extraterrestrial intelligences, then this would also help us pin down our biological expectations
      • Would actually be bad news - would indicate that Great Filter is in our future, since there are other species that have reached our level of technology but not spread
  • Reconsidering Astrophysics
    • Fast space travel between stars and galaxies could be much more difficult than it looks
    • The universe might be smaller than it looks (unusual topology), which, in turn would imply that the universe is younger than it looks
    • It might be easy to create “baby universes” with unlimited mass and negentropy - the process for which prevents civilizations from expanding to colonize
    • Alternatively, maybe the universe is alive, but we just don’t see it
      • Large scale engineering may be impossible, which would mean that civilizations could not affect the spectra of stars
      • Best use of stellar resources preserves the spectrum of a star
      • Advanced life colonizes “dark matter”
  • Rethinking Social Theories
    • Humanity will either destroy itself or lose its propensity to expand
    • Galaxy is populated by “stable, ethical and spiritual civilizations”
    • Civilizations would have to follow this path with a nearly 100% reliability
    • From what we know of social science and history, this seems really really unlikely
    • More pessimistic social scenarios:
      • Nuclear war: would have to take place prior to dispersal across Solar System
      • Ecological failure: would have to take place prior to humanity transcending biology either through machine intelligence or uploads
      • Social collapse
        • Easter Island (though, wasn’t that actually an ecological failure?)
    • Zoo/common zoo theories
      • First expanding civilization had a strong preservationist intent
      • Preserved majority of space as “nature preserves”
      • However
        • Preservationist instinct would have to not affect the competitive viability of that initial civilization
        • Civilization would have to invest resources in preventing “poaching” (i.e. stopping other civilizations from colonizing under its nose)
  • Conclusion
    • To support optimism about the future, we must find especially improbable past evolutionary steps
    • Possible hard evolutionary steps: life, complexity, sex, society, cradle and language
    • Great Filter can be explained if the expected time averaged logarithmically to 30 billion years for each of those steps
    • If only 1% of stars can support life, then with that expected value, we would expect no other life to have colonized the universe
    • We must be careful to avoid a “God of the Gaps” approach, where we say the Great Filter is whatever we haven’t yet eliminated
    • Candidates for the Great Filter must have an exceedingly small probability of success
    • If we can’t find the Great Filter in our past, we must fear it in our future

Where Are They - Why I Hope the Search for Extraterrestrial Life Finds Nothing - Nick Bostrom

  • Bostrom hopes we find no life on Mars
  • The more complex the life, the more pessimistic he is
  • SETI has been going for ~50 years, and has come up with nothing
  • We have every reason to believe (from exoplanet surveys) that our solar system is not distinguished, and that Earth isn’t a special or rare planet
  • So where is everyone? Why haven’t we detected life? Why haven’t we been visited by extraterrestrial life?
  • There must be a Great Filter somewhere which prevents life from expanding
  • This filter must be exceedingly powerful - out of billions and billions of germination points, not once does life expand past a single planet
  • Where might this filter be located?
    • It’s either in our past or in our future
    • Past
      • Some extremely improbable step in the sequence of events by which an Earth-like planet gives rise to intelligent life
      • Maybe we shouldn’t take evolution of intelligence for granted?
      • Maybe we shouldn’t take evolution of life for granted?
        • We have not successfully replicated abiogenesis in the lab
        • The emergence of life took hundreds of millions of years after the cooling of the Earth - points to abiogenesis being an enormously low probability event
      • Candidates for evolutionarily improbable events have to share the following criteria:
        • Has to have only occurred once - if it happened more than once, the probability is too high for it to be a Great Filter
        • Took a long time to occur even after its evolutionary prerequisites were in place - needed many local random recombinations, or several improbable mutations all occurring at the same time
      • Possibilities:
        • Original emergence of life
        • Prokaryote to eukaryote transition
        • Multi-cellular organisms
        • Sexual reproduction
    • Future:
      • There is some improbability that prevents almost all technological civilizations at our level of technology from progressing to the point where they engage in large-scale space colonization
      • It’s highly probable that if there were interstellar life, we would have encountered it by now
        • Von Neumann Probes
        • Even traveling at 1% of the speed of light, Von Neumann probes can colonize the galaxy in 20 million years (relatively short by cosmological timescales)
        • Moreover, life on Earth exhibits a strong tendency to spread where-ever it can - we should expect the same for interstellar life
        • If going to space is cheap, we should expect civiliations to go to space - most resources are off-world
      • So why don’t we see anyone out there?
        • Destructive tendencies common to virtually all technologically advanced civilizations
          • Even complete civilizational collapse that stops technological progress for hundreds of thousands of years at a time would not be enough to form a Great Filter
          • Any civilization-scale disaster would have to be a global cataclysm - X-Risk
            • Nuclear war fought with enormous stockpiles
            • Genetically engineered infection
            • Environmental disaster
            • Asteroid impact
            • Wars or terrorist acts committed with powerful superweapons
            • AGI with destructive goals
            • High-energy physics experiments
            • Permanent totalitarian regime protected by mind control and surveillance
          • For an X-Risk to be a Great Filter, it would have to apply to not just humanity, but virtually all civilizations and species capable of technology
            • For this reason, asteroid impacts and natural disasters are unlikely to be Great Filters - you’d have to posit that all civilizations would fall victim to these before being able to escape their homeworlds
            • The best candidate is a technological discovery - something that almost all civilizations discover, and something whose discovery leads almost certainly to disaster
  • So what does all this have to do with finding life on Mars?
    • The more advanced life we find on Mars, the lower the probability that the Great Filter is in our past
    • Conversely, if we find that Mars had (has) all the ingredients for life, but no life, we can have greater confidence that the Great Filter is in our past - that Earth is past the Great Filter merely by virtue of developing life
    • Of course, there’s nothing stating that there has to be only one Great Filter - the evolution of life might be exceedingly improbable, and it might be exceedingly difficult for species to escape their home planets

Don’t Fear The Filter - Scott Alexander

  • The Great Filter is not garden-variety X-Risk: Great Filters have to kill of all or almost all civilizations, not just human civilizations
  • The Great Filter is not unfriendly AI: if anything, UFAI would be easier to observe than a “normal” civilization
    • The best studied class of UFAI is paperclip maximizers
    • We haven’t seen a sphere of the visible universe tuned to some optimal criteria, expanding at a significant fraction of the speed of light
  • The Great Filter is not transcendence
    • It takes just one match to start a conflagration
    • It takes just one species to colonize a galaxy
    • Literally every species would have to turn into hippies in order for transcendence to be a viable Great Filter
  • The Great Filter is not alien exterminators
    • If there is already a civilization out there, that we haven’t detected, watching us, it already knows about Earth
    • We shouldn’t worry about sending radio messages because the fact that Earth hasn’t been scorched into a sterile ball of rock means that whoever is out there is okay with us, at some level
    • Moreover, if they’ve got a billion year head start on us, it means that they had space travel when Earth had… single celled micro-organisms – there’s no realistic way for us to threaten them
  • So we shouldn’t worry about the Great Filter because it’s unlikely there’s anything we can do about it