Reading Notes
- 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
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
- 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
- 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