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手把手估算银河系可探测文明. Sal Khan 创建




I've talked a bunch about the Drake Equation or our own version of the Drake Equation that starts with that with the number of stars in the galaxy but I haven't given it a shot yet I haven't tried my own attempt at thinking about how many detectable civilizations there are so let's actually do that here so let's just assume let's just assume that there are 100 billion stars one hundred billion stars so that's my first term right over there let's say that one fourth let's say that one fourth will develop planets will develop planets and let's say of the solar systems that develop planets on average on average let's say that point that they develop on an average of point one planets capable of sustaining life or really that you'll have one planet for every ten of these solar systems with planets that's just my assumption there I don't know if that's right now let's multiply that times the fraction of these planets capable of sustaining life that actually will get life and I don't know what that is but I hinted in previous videos that life is one of those things that it seems like if you have all the right ingredients it's so robust that you have life at these underwater volcanoes you have bacteria that can process all sorts of weird things so let's say that that probability is pretty high let's say that that is 50% or half of the planets that are capable of getting life actually do have life I would guess that that might even be higher but once again just guess now we have to think about of the life what fraction becomes intelligent what becomes intelligent over some point in the history well I'll say it's a tenth a tenth of all you know maybe if the asteroids didn't kill the dinosaurs it wouldn't have happened on earth who knows or maybe we would just have some very intelligent dinosaurs around we don't know so and maybe there are other forms of intelligent life even on our own planet that we haven't fully appreciated dolphins are good are good candidates some people believe that octopuses have the because they have such flexible arms there's a theory that they could develop eventually in the ability to kind of one day if they if their brains mature and all of the rest make tools the same way primitive primates eventually we're able to have larger brain sizes and actually manipulate things to make tools so who knows I don't want to get into all of that so there's a 1 in 10 chance that you get intelligent life and then assuming that intelligent life shows up what fraction is going to become detectable I don't know I don't know whether dolphins will ever communicate via radio or not so let's just say that that is I don't know let's say that that is another another 1 in 10 chance or I'll put a 0.1 0.1 and then we have to multiply it times the detectable life of the civilization on average once again huge assumptions being here but the detectable life of a civilization let me just put it at ten thousand years ten thousand years either they destroy themselves or they get beyond that type of radio type communication electromagnetic type communication maybe they start doing all sorts of weird wacky things probably it won't take you ten thousand years to even progress it that it might take you less time but let's just do this just for the sake of fun and then the lifespan of your average star that's probably one of the things that we have the best sense of so on average let's put it at ten billion years ten billion years so let's calculate all of this let's get my handy ti-85 out and so we're going to have a hundred billion that's one times ten to the ninth sorry that's not one that's a hundred times ten to the ninth so let me clear it or you could have one times ten to the eleventh that is a hundred billion times 0.25 times 0.1 times 0.1 times 0.5 times 0.5 times 0.1 again times 0.1 times 0.1 again times 0.1 times 10,000 divided by ten billion so times so times 10,000 one two three divided by ten billion so that's one e ten one times ten to the tenth power one with ten zero so let's see what we get we get twelve point five which is kind of a neat but you know these are heavily dependent on this so I we're saying if we given these assumptions there should be 12.5 detectable civilizations detectable civilizations in our in our galaxy right now so the question is why aren't we detecting it maybe they're radio signals maybe there are electromagnetic waves are getting to us but we don't we can't differentiate it from noise right now and that's what the whole SETI project is all about of trying to try to keep track of all of this information that that all of this these radio waves and electromagnetic waves that are coming from outer space towards Earth and seeing if any of them actually have any non noise signal that actually looked like they're being generated by some type of intelligent civilization so maybe we're getting them and we're just not detecting them or maybe something else is at play maybe we've overestimated one of these maybe there is a lot of life but maybe they're not using electromagnetic waves to communicate maybe that's some type of primitive way of communicating maybe they start doing telepathy or something crazy or they start using some type of quantum thing that allows them to communicate more directly without having to wait for the speed of light you know that is a very slow way to communicate it and it is a slow way frankly if you're trying to communicate across solar systems and stars and planets or even across galaxies one can imagine so maybe maybe we're just kind of in a transition state of communication that electromagnetic waves radio and all the rest is just a transition state maybe in a hundred years we'll figure out another better way that's not detectable in our traditional ways maybe we're being bombarded with another type of communication mechanism that we're just not ready to perceive yet who knows but it's just a fun thought experiment to say that hey given these assumptions there should be at least couple of civilizations or a handful of civilizations that we might be able to detect