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Detectable civilizations in our galaxy 4

Taking a shot at estimating the number of detectable civilizations. Created by Sal Khan.

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  • blobby green style avatar for user Rick Gardner
    The equation does not factor for the chance that an intelligent life form could colonize another planet in another solar system. Let's say 1 in a million. Then you would have to estimate the average number of planets colonized by such a life form.
    (9 votes)
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    • orange juice squid orange style avatar for user davidlamm
      Colonizing a planet or two wouldn't affect these numbers by much, assuming these civilizations colonized planets close to their stars. The real issue at hand is if a civilization continues to expand into space at the same rate we have done on earth. Check out the Fermi Paradox to learn more about this fascinating question.
      (4 votes)
  • leaf red style avatar for user Joseph Hemmingson
    What if a non-intelligent for of life develops some form of detectable technology? Could we eliminate one variable from the drake equation?
    (3 votes)
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    • leafers ultimate style avatar for user Boris Stanchev
      Well, that would be rather strange since anything that develops detectable technology would have to be intelligent by our definition.

      However, we need to be open minded about one thing. Maybe there is a form of life out there that naturally communicates using radio waves, but that didn't necessarily developed any technology. It could be that such communication is innate to the biology of such life forms. But what would make such a form of communication travel interstellar distances? That would require a pretty powerful transmitter that's unlikely to come about through natural selection. So I find it very hard to imagine any form of life that has technology that's detectable to us on earth that isn't intelligent.

      It's same to assume that any life that has developed technology would have to be intelligent.
      (12 votes)
  • leaf green style avatar for user Nicholas
    Is it safe to assume that these other hypothetical civilizations are equally distributed through out the galaxy or are there areas that would have a higher probability of harboring intelligent life?
    (5 votes)
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    • piceratops ultimate style avatar for user AegonTargaryen
      Well, the center of the galaxy is filled with deadly radiation because of the large amount of massive stars. The outer reaches of the galaxy don't have as much heavy elements as other areas and planets are less likely to form. Life is unlikely to form within 5 light years of a massive star as its radiation would sterilize planets even in other solar systems. The sun happens to sit in the area that we would predict life to come from. If you are looking for life, look for stars midway from the center and far away from massive stars.
      (8 votes)
  • aqualine ultimate style avatar for user Tanishq
    So is it possible for another planet be searching for other planets as well but not using electromagnetic waves?
    (5 votes)
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    • boggle blue style avatar for user Davin V Jones
      The only other force that acts at a significant distance, that we are aware of, is gravity. It is possible they could use that, but unlikely as gravity is a much weaker force than the electromagnetic force and therefore would require much more effort to utilize for communication.
      There is another property of the quantum world, which we are currently exploring, called quantum entanglement in which entangled particles can 'communicate' their properties instantly at even great distances instantly, which would even be faster than the speed of light. We still don't fully understand this though and if it is possible to even use this property for communication. But it is possible a more advanced civilization has figured this out.
      (5 votes)
  • blobby green style avatar for user webtweakers
    There are some other factors that influence this calculation that have not been taken into account, or at least lower the probability of some of the factors that are used. For example: the tides caused the moon contributed to the birth of life. Without it, evolution might have been slower. Also Jupiter saves the inner planets from bombardments. It's almost likely that a similar solar configuration is required for life to sustain for longer periods of time to be able to become intelligent.
    (6 votes)
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  • aqualine ultimate style avatar for user Jorge Daniel Garcia
    How likely would intelligent life develop underwater? Could there be intelligent beings as intelligent or more intelligent than humans that would only live under water? Would their communications, electromagnetic or otherwise, be detectable?
    (4 votes)
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    • purple pi purple style avatar for user voyagerst
      A major problem with a purely underwater civilization is this: water and electricity do not mix, therefore an underwater civilization would have no means of using the electricity so central to our lives. So, although it is possible, I think it would be less likely for an intelligent species that lives underwater to create advanced technology with which they could broadcast into space and communicate than it would be for a terrestrial species.
      (1 vote)
  • male robot hal style avatar for user TSearcy
    What are the odds of two species on a single planet simultaneously developing intelligence to the point of detecting/transmitting signals from/to another planet? Here on earth, we speculate about the intelligence of other species, but our dominance of the planet has very likely prevented any other species from evolving intelligence to the same degree. Is it fair to assume that each planet that harbors life will have only a single "intelligent" species?
    (3 votes)
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  • mr pink red style avatar for user Jorge Garcia
    It seems to me that Sal's statement that f-sub-l (the 4th term) must be fairly large because life is "robust" and adaptable to all kinds of rugged environments is logically flawed.

    Our assumption is that life evolved only once. So it is irrelevant how good life - once evolved - is at filling niches. Even if it fills every available square foot of earth... life still only evolved once... in one place. And the question is not whether a planet is able to SUPPORT life (which we can guess is fairly easy), but whether it is able to EVOLVE life from not-life (which... we have no way to guess).

    But here is an example of the logical flaw. Sal's sweeping statement is like saying that any given place on any road on earth's surface is fairly likely to be a car factory, based on the observation that on almost every place in every road on earth (from the highest to the lowest, from the longest to the shortest, from the smoothest to the bumpiest) we find cars.

    The fact that something can easily occupy a space is in no way correlated (I think) with whether that space can spawn such an object. Spawning being a radically different activity from "being found there".
    (5 votes)
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  • leaf grey style avatar for user Jimby99
    what makes life considered intelligent?
    (3 votes)
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  • aqualine ultimate style avatar for user samwolfenstein
    Would the 1936 Olympics be the first thing that aliens could detect?
    (1 vote)
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Video transcript

I've talked a bunch about the Drake equation, or our own version of the Drake equation that starts 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 that there are 100 billion stars. 100 billion stars. So that's my first term right over there. Let's say that 1/4 will develop planets. And let's say of the solar systems that develop planets, on average let's say that they develop an average of 0.1 planets capable of sustaining life. Or really, that you'll have one planet for every 10 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. And you have life it these underwater volcanoes, you have bacteria that can process all sorts of weird things. So let's say that probability is pretty high. Let's say that is 50%, or half of the plans that are capable of getting life actually do have life. I would guess that that might even be higher. But once again, just a 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-- maybe if the asteroids didn't kill the dinosaurs, it wouldn't have happened on Earth. Who knows? Or maybe we'd just have some very intelligent dinosaurs around. We don't know. And maybe there's other forms of intelligent life even on our own planet that we haven't fully appreciated. Dolphins are a good candidate. Some people believe that octopuses, because they have such flexible arms, there's a theory that they could develop eventually the ability to kind one day, if their brains mature, and all of the rest, make tools the same way primitive primates eventually were 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 is-- I don't know. Let's say that is another 1 in 10 chance, or I'll say 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 10,000 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 10,000 years to even progress it. That 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 10 billion years, 10 billion years. So let's calculate all of this. Let's get my handy TI-85 out. And so we're going to have 100 billion. That's 1 times 10 to the 9th. Sorry, that's 100 times 10 to the ninth. So let me clear it. Or you could have 1 times 10 to the 11th. That is 100 billion times 0.25 times 0.1 times .05 times 0.1 again, times 0.1 again, times 10,000 divided by 10 billion. So times 10,000, 1, 2, 3, divided by 10 billion. So that's one 1e10. 1 times 10 to the 10th power. 1 with 10 zeroes. So let's see what we get. We get 12.5, which is kind of a neat number, but these are heavily dependent on this. So we're saying if given these assumptions, there should be 12.5 detectable civilizations in our galaxy right now. So the question is, why aren't we detecting it? Maybe their radio signals, maybe their electromagnetic waves are getting to us, but we can't differentiate it from noise right now. And that's what the whole SETI project's all about, of trying to keep track of all this information, all of 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 look 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 a 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. That is a very slow way to communicate. 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 could imagine. So maybe we're just kind of at a transition state of communication, that electromagnetic waves, radio and all the rest is just a transition state. Maybe in 100 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 a couple of civilizations, or a handful of civilizations that we might be able to detect.