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Video transcript
In the last video on the Drake equation we tried out some numbers we just made some assumptions that seemed reasonable at least to me and we got that there should be 12.5 detectable civilizations in the Milky Way Galaxy and I've talked about a bunch of reasons about why we are not detecting them but I left out one of the most obvious reasons that we are not detecting them and it was rightfully pointed out in the comments below that video and thats just the signal might be too weak if theres 12.5 if there's on the order of 10, 11, 12 detectable civilizations in our galaxy they could be quite far from us this isn't the Milky Way but this is a galaxy that probably doesn't look too different from our Milky Way we could obviously never get this vantage point of our galaxy well at least not for a while not unless we can travel quite far away from it but lets say we are over here you could imagine if the ten civilizations or the twelve civilizations are here, one, two, three, four there's probably a lot more at the center actually because that's where our density is higher so let me put it here so one, two, three, four, five, six, seven eight, nine, ten, eleven, twelve the closest of them might be tens of thousands of light years away from us and there might be a lot of stuff in between all sorts of crazy things happening stars exploding all sorts of signals that we are receiving and it might just be that the signals from those civilizations are too weak to reach us or that there is too much interference from all of the other craziness that's happening around the galaxy there's also these other reasons that I've talked about in the last video maybe they've gone beyond using radio as a form of communication and thats why.. or they never used it to begin with and that's why we don't even see them ever using it or they used if for a very short period a kind of transition period and maybe in a hundred years we'll discover the next best thing the other idea behind why we're probably or maybe why we might not be able to detect civilizations is that well there might be a lot fewer than ten when I did the Drake equation right over here I just made a bunch of assumptions none of these seemed crazy but I assumed a reality where you didn't have these kind of cataclysmic events in the galaxy at regular intervals but we know there are cataclysmic events that happen in our galaxy in other galaxies the one we know the most about although there are all sorts of things that we don't know much about are gamma ray bursts and these are still kind of trying to be understood GAMMA RAY BURSTS and you can watch the video on quasars those are essentially of highly energetic rays being released when all this material is being kind of absorbed into super massive black holes at the centers of galaxies that tend to be very very very often billions of light years away and gamma rays are one of the things that get emitted from those but you can also have gamma ray bursts within galaxies we believe maybe certain types of stars when they collapse into black holes you have this burst of gamma rays there might be certain kinds of neutron stars with the right properties that might every now and then release gamma rays and the view is is that if there is a civilization that is within a few thousand light years near one of these gamma ray bursts and its in wrong place its kind of in the path of the burst then its a good chance that those civilizations will be completely wiped out that those planets will become sterilized because there is so much radiation coming out from that gamma ray there's even some theories that some of the extinction events that have happened in Earth's history we are not talking about the dinosaurs we are talking about billions of years ago maybe a billion years ago or two billion years ago that these might have been caused by relatively local gamma ray bursts the theory is that these might hit earth on the order of once every billion years and if you think about the galaxy as a whole we're kind of in.. our solar system is orbiting the galaxy its kind of a nice distance from the center of the galaxy the closer you get into the center the higher densities of stars you have so you can imagine if earth gets hit with one of these gamma rays bursts every couple of billion years you can imagine something closer the center of the galaxy gets hit with these gamma ray bursts much much much more frequently just because there is more activity there there are more stars that are closer by more stars that are aging more stars that might be collapsing into black holes so the simple answer is we don't know there could be a thousand civilizations out there and we're not sophisticated enough to notice them just yet or there might be very very few because all of this craziness that happens in the galaxy or who knows there might be none although I find that kind of... that's not too exciting so I try not to think about that one