Our sun appears to be a typical star: unremarkable in age, composition, galactic orbit, or even in its possession of many planets. Billions of other stars in the milky way have similar general parameters and orbits that place them in the galactic habitable zone. Extrapolations of recent expolanet surveys reveal that most stars have planets, removing yet another potential unique dimension for a great filter in the past.
According to Google, there are 20 billion earth like planets in the Galaxy.
A paradox indicates a flaw in our reasoning or our knowledge, which upon resolution, may cause some large update in our beliefs.
Ideally we could resolve this through massive multiscale monte carlo computer simulations to approximate Solonomoff Induction on our current observational data. If we survive and create superintelligence, we will probably do just that.
In the meantime, we are limited to constrained simulations, fermi estimates, and other shortcuts to approximate the ideal bayesian inference.
While there is still obvious uncertainty concerning the likelihood of the series of transitions along the path from the formation of an earth-like planet around a sol-like star up to an early tech civilization, the general direction of the recent evidence flow favours a strong Mediocrity Principle.
Here are a few highlight developments from the last few decades relating to an early filter:
- The time window between formation of earth and earliest life has been narrowed to a brief interval. Panspermia has also gained ground, with some recent complexity arguments favoring a common origin of life at 9 billion yrs ago.
- Discovery of various extremophiles indicate life is robust to a wider range of environments than the norm on earth today.
- Advances in neuroscience and studies of animal intelligence lead to the conclusion that the human brain is not nearly as unique as once thought. It is just an ordinary scaled up primate brain, with a cortex enlarged to 4x the size of a chimpanzee. Elephants and some cetaceans have similar cortical neuron counts to the chimpanzee, and demonstrate similar or greater levels of intelligence in terms of rituals, problem solving, tool use, communication, and even understanding rudimentary human language. Elephants, cetaceans, and primates are widely separated lineages, indicating robustness and inevitability in the evolution of intelligence.
When modelling the future development of civilization, we must recognize that the future is a vast cloud of uncertainty compared to the past. The best approach is to focus on the most key general features of future postbiological civilizations, categorize the full space of models, and then update on our observations to determine what ranges of the parameter space are excluded and which regions remain open.
An abridged taxonomy of future civilization trajectories :
Civilization is wiped out due to an existential catastrophe that sterilizes the planet sufficient enough to kill most large multicellular organisms, essentially resetting the evolutionary clock by a billion years. Given the potential dangers of nanotech/AI/nuclear weapons - and then aliens, I believe this possibility is significant - ie in the 1% to 50% range.
This is the old-skool sci-fi scenario. Humans or our biological descendants expand into space. AI is developed but limited to human intelligence, like CP30. No or limited uploading.
This leads eventually to slow colonization, terraforming, perhaps eventually dyson spheres etc.
This scenario is almost not worth mentioning: prior < 1%. Unfortunately SETI in current form is till predicated on a world model that assigns a high prior to these futures.
PostBiological Warm-tech AI Civilization:
This is Kurzweil/Moravec's sci-fi scenario. Humans become postbiological, merging with AI through uploading. We become a computational civilization that then spreads out some fraction of the speed of light to turn the galaxy into computronium. This particular scenario is based on the assumption that energy is a key constraint, and that civilizations are essentially stellavores which harvest the energy of stars.
One of the very few reasonable assumptions we can make about any superintelligent postbiological civilization is that higher intelligence involves increased computational efficiency. Advanced civs will upgrade into physical configurations that maximize computation capabilities given the local resources.
Thus to understand the physical form of future civs, we need to understand the physical limits of computation.
One key constraint is the Landauer Limit, which states that the erasure (or cloning) of one bit of information requires a minimum of kTln2 joules. At room temperature (293 K), this corresponds to a minimum of 0.017 eV to erase one bit. Minimum is however the keyword here, as according to the principle, the probability of the erasure succeeding is only 50% at the limit. Reliable erasure requires some multiple of the minimal expenditure - a reasonable estimate being about 100kT or 1eV as the minimum for bit erasures at today's levels of reliability.
Now, the second key consideration is that Landauer's Limit does not include the cost of interconnect, which is already now dominating the energy cost in modern computing. Just moving bits around dissipates energy.
Moore's Law is approaching its asymptotic end in a decade or so due to these hard physical energy constraints and the related miniaturization limits.
I assign a prior to the warm-tech scenario that is about the same as my estimate of the probability that the more advanced cold-tech (reversible quantum computing, described next) is impossible: < 10%.
From Warm-tech to Cold-tech
There is a way forward to vastly increased energy efficiency, but it requires reversible computing (to increase the ratio of computations per bit erasures), and full superconducting to reduce the interconnect loss down to near zero.
The path to enormously more powerful computational systems necessarily involves transitioning to very low temperatures, and the lower the better, for several key reasons:
- There is the obvious immediate gain that one gets from lowering the cost of bit erasures: a bit erasure at room temperature costs 100 times more than a bit erasure at the cosmic background temperature, and a hundred thousand times more than an erasure at 0.01K (the current achievable limit for large objects)
- Low temperatures are required for most superconducting materials regardless.
- The delicate coherence required for practical quantum computation requires or works best at ultra low temperatures.
Assuming large scale quantum computing is possible, then the ultimate computer is thus a reversible massively entangled quantum device operating at absolute zero. Unfortunately, such a device would be delicate to a degree that is hard to imagine - even a single misplaced high energy particle could cause enormous damage.
Stellar Escape Trajectories
The Great Game
If two civs both discover each other's locations around the same time, then MAD (mutually assured destruction) dynamics takeover and cooperation has stronger benefits. The vast distances involve suggest that one sided discoveries are more likely.
Spheres of Influence
Conditioning on our Observational Data
Observational Selection Effects
All advanced civs will have strong instrumental reasons to employ deep simulations to understand and model developmental trajectories for the galaxy as a whole and for civilizations in particular. A very likely consequence is the production of large numbers of simulated conscious observers, ala the Simulation Argument. Universes with the more advanced low temperature reversible/quantum computing civilizations will tend to produce many more simulated observer moments and are thus intrinsically more likely than one would otherwise expect - perhaps massively so.
We estimate that there may be up to ∼ 10^5 compact objects in the mass range 10^−8 to 10^−2M⊙per main sequence star that are unbound to a host star in the Galaxy. We refer to these objects asnomads; in the literature a subset of these are sometimes called free-floating or rogue planets.
Although the error range is still large, it appears that free floating planets outnumber planets bound to stars, and perhaps by a rather large margin.
Assuming the galaxy is colonized: It could be that rogue planets form naturally outside of stars and then are colonized. It could be they form around stars and then are ejected naturally (and colonized). Artificial ejection - even if true - may be a rare event. Or not. But at least a few of these options could potentially be differentiated with future observations - for example if we find an interesting discrepancy in the rogue planet distribution predicted by simulations (which obviously do not yet include aliens!) and actual observations.
Also: if rogue planets outnumber stars by a large margin, then it follows that rogue planet flybys are more common in proportion.
SETI to date allows us to exclude some regions of the parameter space for alien civs, but the regions excluded correspond to low prior probability models anyway, based on the postbiological perspective on the future of life. The most interesting regions of the parameter space probably involve advanced stealthy aliens in the form of small compact cold objects floating in the interstellar medium.
The upcoming WFIST telescope should shed more light on dark matter and enhance our microlensing detection abilities significantly. Sadly, it's planned launch date isn't until 2024. Space development is slow.