From: Phillip Huggan (email@example.com)
Date: Tue Jul 19 2005 - 14:26:49 MDT
10^11 and 10^11 are the figures for the # of stars and galaxies in the universe. Ignoring earlier 1st generation stars which tend to be very metal poor, and marginal brown dwarf star surfaces and radioactive asteroid cores, there are ten planets in each stellar system capable of facilitating the emergence of life. Of these sites, 80% are in rod or disc shaped galaxies too metal poor, and 75% of these are in the outer galactic arms too metal poor or in galaxy cores with too many nearby stars exploding or perturbing planetary orbits. 5X10^20 is cut by needing a sun optimally sized so as not to tidally lock its earth, or to burn up its fuel too quickly; the sun also needs not to be part of a double or triple star system which form the majority of all systems, so down to 10^19. Exo-earth needs a stable orbit. All of the planets discovered to date outside our system are giants of highly eliptical orbits. The habitable zone of a star which yields liquid water slowly moves outwards
and only leaves room for one planet, so now 10^18. Life needs a gas giant in a stable orbit to sweep away asteroids (10^17), the latter in abundance in the early stages of a systems formation combined with a moving habitable star yield a few billion years window for life to evolve, about what life on earth took. Not enough time for multiple chances at evolution. Earth needs to be earth-sized; Mars can't hold an atmosphere and anything bigger screws with the crust composition for plate-tectonics (10^16). Now a biggie: the moon. It prevents earth from tidally locking to the sun, stablizes the earth's tilt (giving it a hope in hell of escaping a permanent ice-age), impacted earth at a near-perfect angle to give earth its optimal tilt, and helped out by providing tides to wean ocean life to land, and added some heavier elements to earth upon impact. Down to 10^12 (1/100 correct collision angle for 1/10 Mars-sized body hitting earth 10% of the time). 10% more water accumulating on
earth results in no land surfaces, too little water prevents ocean currents from fighting tendency to ice-age. Now at 10^11. Plate tectonics allow the formation of continental shelves which accumulate silica and limestone essential for atmospherically feedbacking earth out of permanent ice-ages. Figure 10% of earth shaped bodies undergo plate tectonics; no other bodies in the solar system do (10^10). Too much carbon in the crust composition yields runaway global warming (Venus), too little yields few opportunities for prokaryotic life and IR fossil-fuels to form (10^9).
Now many feedbacks are in play and it becomes much harder to estimate the odds of getting to 2005 AD earth. 1st and maybe even 2nd generation stars do possess large quantities of supernovae heavy element debris. The first one or two billion years in a solar system's formation are too asteroid rich to facilitate life (and the star is "angry"), and life on earth languished around for over a billion years in the single-celled state before hitting multi-celled status. The suggests any post-singularity civilizations out there are not billions of years ahead of us... Life evolves in response to near extinction level events which alter the environment. Too big an asteroid or super-volcano and a species goes extinct. To small an event, and life goes on as usual. To reach the Cambrian explosion after which point there is enough diversity for biological feedback mechanisms to eventually thaw ice-ages, requires passing through 7 or so (# pulled out of midair) almost extinction events
which don't kill off the key biosphere species in question, but do cause it to mutate to its earth-friendly form. I'll say say each of these event has a probability of wiping out the climate modifier plankton or whatever, just less than half of the time. So there go two more orders of magnitude to reach a somewhat stable carbon/silicate/oxygen cycle which gives us a break from ice-ages once in a while (10^7). Too much oxygen in the stablilized atmosphere leads to runaway plant fires every few decades, too little and animals can't breathe or harness fire (2X10^6). Doesn't seem too hard to go from ooze on the beach to apes with opposable thumbs, language, fire... something killed all but 2000 of our descendents off, so it is not inevitable (10^5). Once life gets smart enough to hunt, they tend to hunt all the useful animals to extinction. Without the ox or the cow, the economics for an industrial revolution isn't there. Maybe pigs and chickens and sheep could facilitate this,
but probably not. There are very few animals which have the natural temperament to be domesticated, and have been around humans long enough to learn to "trust" them enough for domestication without being hunted to extinction. In addition, there are only a dozen plants which are really economically useful for agriculture. This requires a large east-west swath of landmass. Even China would not have been able to hit IR without the introduction of species from this critical Eurasian territory, before the next ice-age. So as a people populates a world from origin, they have to achieve domestication of animals before they become skilled hunters. This sweet spot on the geography and agriculture time-line combined with the favourable existence of plant and animal species only happens 1/1000 of the time (10^2) before the next ice-age. The other 999 times ruin the emergence of civilization for all subsequent post-iceage periods for many hundreds of millions of years (2 more chances
for each planet in the future before the habitable ring moves outwards a a star warms, so up to 60). An IR requires the lack of an imperial body monopolizing tech competition. This seems to be a function of hostile geographies (mountains in europe, but still farming facilitated by ) along with no military hedgmony achieved despite the obvious military applications yielded by a newfound scientific spirit. That that this all occurs near such a large east-west swath of land which still previously facilitated north-south animal migration is 1/60 (1 planet makes it to 19th century earth). Making it through nukes and pandemics (we're still not out of danger for the latter): 1/10 (one in ten). Harnessing MM and AGI and any time-travelling UFAIs: 1/10? (one in a hundred?). All the smaller probability factors not listed 1/100 (one in ten thousand).
About half of all GUTs predict cosmic strings. There are usually only a dozen or two of these in existence, but an AGI might find a way to harness these or naturally occuring worm-holes. The math above shows that we may just be optimally positioned to reach MM/AGI before many of our own parrallel universes, and certainly before ETs, and thus monopolizing time-travel, if it is possible in the universe. The hundreds of millions of light-years that our own super-cluster encompasses is sterile. Our primary threats are MM tyrannies, MM arms races, MM enabled technologies, and AGIs of an unfriendly nature, not aliens.
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