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In the last video on the Drake equation

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we tried out some numbers

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we just made some assumptions

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that seemed reasonable at least to me

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and we got that there should be 12.5

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detectable civilizations in the Milky Way Galaxy

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and I've talked about a bunch of reasons

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about why we are not detecting them

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but I left out one of the most obvious reasons

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that we are not detecting them

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and it was rightfully pointed out in the comments

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bellow that video

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and thats just the signal might be too weak

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if theres 12.5

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if there's on the order of 10, 11, 12 detectable

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civilizations in our galaxy

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they could be quite far from us

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this isn't the Milky Way

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but this is a galaxy that probably doesn't look

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too different from our Milky Way

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we could obviously never get this vantage point

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of our galaxy

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well at least not for a while

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not unless we can travel quite far away from it

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but lets say we are over here

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you could imagine if the ten civilizations

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or the twelve civilizations are

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here, one, two, three, four

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there's probably a lot more at the center actually

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because that's where our density is higher

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so let me put it here

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so one, two, three, four, five, six, seven

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eight, nine, ten, eleven, twelve

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the closest of them might be

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tens of thousands of light years away from us

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and there might be a lot of stuff in between

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all sorts of crazy things happening

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stars exploding

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all sorts of signals that we are receiving

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and it might just be

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that the signals from those civilizations

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are too weak to reach us

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or that there is too much interference

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from all of the other craziness

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that's happening around the galaxy

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there's also these other reasons

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that I've talked about in the last video

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maybe they've gone beyond

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using radio as a form of communication

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and thats why..

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or they never used it to begin with

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and that's why we don't even see them

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ever using it

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or they used if for a very short period

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a kind of transition period

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and maybe in a hundred years we'll discover the next best thing

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the other idea behind why we're probably

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or maybe why we might not be able to detect civilizations

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is that

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well there might be a lot fewer than ten

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when I did the Drake equation right over here

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I just made a bunch of assumptions

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none of these seemed crazy

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but I assumed a reality

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where you didn't have these kind of cataclysmic events

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in the galaxy at regular intervals

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but we know there are cataclysmic events

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that happen in our galaxy

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in other galaxies

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the one we know the most about

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although there are all sorts of things that we

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don't know much about

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are gamma ray bursts

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and these are still kind of trying to be understood

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GAMMA RAY BURSTS

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and you can watch the video on quasars

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those are essentially of highly energetic rays

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being released when all this material

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is being kind of absorbed into super massive black holes

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at the centers of galaxies

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that tend to be very very very often

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billions of light years away

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and gamma rays are one of the things that get emitted from those

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but you can also have gamma ray bursts within galaxies

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we believe maybe certain types of stars when they collapse

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into black holes

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you have this burst of gamma rays

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there might be certain kinds of neutron stars

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with the right properties that might every now and then

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release gamma rays

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and the view is

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is that if there is a civilization

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that is within a few thousand light years

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near one of these gamma ray bursts

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and its in wrong place

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its kind of in the path of the burst

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then its a good chance that those civilizations will

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be completely wiped out

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that those planets will become sterilized

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because there is so much radiation

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coming out from that gamma ray

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there's even some theories

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that some of the extinction events that have happened in Earth's history

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we are not talking about the dinosaurs

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we are talking about billions of years ago

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maybe a billion years ago

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or two billion years ago

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that these might have been caused by

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relatively local gamma ray bursts

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the theory is that these might hit earth

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on the order of once every billion years

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and if you think about the galaxy as a whole

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we're kind of in..

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our solar system is orbiting the galaxy

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its kind of a nice distance from the center of the galaxy

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the closer you get into the center

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the higher densities of stars you have

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so you can imagine if earth gets hit with

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one of these gamma rays bursts

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every couple of billion years

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you can imagine something closer the center of the galaxy

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gets hit with these gamma ray bursts

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much much much more frequently

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just because there is more activity there

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there are more stars that are closer by

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more stars that are aging

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more stars that might be collapsing into black holes

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so the simple answer is we don't know

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there could be a thousand civilizations out there

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and we're not sophisticated enough to notice them just yet

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or there might be very very few

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because all of this craziness that happens

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in the galaxy

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or who knows there might be none

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although I find that kind of...

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that's not too exciting

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so I try not to think about that one