1 00:00:00,425 --> 00:00:08,636 It's estimated that our galaxy, the Milky Way, has 100 to 400 billion stars, 2 00:00:08,636 --> 00:00:12,029 and when you hear a number like that the obvious question is: 3 00:00:12,029 --> 00:00:15,944 Are there civilizations on planets that are orbiting any of these stars 4 00:00:15,944 --> 00:00:20,241 and maybe even more interesting question is can we detect any of those civilizations? 5 00:00:20,241 --> 00:00:24,379 Have they gotten to the level of technological progress like us, 6 00:00:24,379 --> 00:00:27,662 that they are emitting electromagnetic waves into space 7 00:00:27,662 --> 00:00:30,287 and other civilization like ours can detect and say, 8 00:00:30,287 --> 00:00:36,954 "Hey, there is someone else out there watching television or using radio or whatever else they might be doing." 9 00:00:36,954 --> 00:00:39,933 So, what I want to do with this video is not answer that question. 10 00:00:39,933 --> 00:00:41,938 That's a big open question, we don't know the answer. 11 00:00:41,938 --> 00:00:45,508 We don't have anywhere near enough information to definitively answer that question, 12 00:00:45,508 --> 00:00:49,502 but I want to do is come up with a framework for at least thinking about that question, 13 00:00:49,502 --> 00:00:51,236 a way of actually estimating 14 00:00:51,236 --> 00:00:56,929 how many detectable civilizations there are in just our galaxy, 15 00:00:56,929 --> 00:01:00,918 and there is a formula, that you may or may not have heard of, 16 00:01:00,918 --> 00:01:02,959 called the Drake Equation. 17 00:01:02,959 --> 00:01:04,379 and what we are going to do is independently 18 00:01:04,379 --> 00:01:08,000 derive our own version of the Drake Equation. 19 00:01:08,000 --> 00:01:09,831 It's going to be slightly different, 20 00:01:09,831 --> 00:01:11,554 but it is the same thought process 21 00:01:11,554 --> 00:01:14,425 and in the future video, I'm going to maybe reconcile 22 00:01:14,425 --> 00:01:17,425 what we come up with, with the Drake Equation, 23 00:01:17,425 --> 00:01:20,338 and just so you know Drake equation is named for Frank Drake, 24 00:01:20,338 --> 00:01:23,810 who is a Professor at University of California Santa Cruz. 25 00:01:23,810 --> 00:01:27,021 He first, kind of put some structure around this problem, 26 00:01:27,021 --> 00:01:29,790 that's why the formula or the equation has his name, 27 00:01:29,790 --> 00:01:32,364 but the equation is not an equation you can apply 28 00:01:32,364 --> 00:01:35,523 on a daily basis and get results that you can use to build things, 29 00:01:35,523 --> 00:01:40,871 but what it's, it's the structures of our thinking around this question of 30 00:01:40,871 --> 00:01:46,041 How many detectable civilizations are there in our galaxy? 31 00:01:46,041 --> 00:01:50,067 And to answer this question, I am going to start little bit differently than Frank Drake did 32 00:01:50,067 --> 00:01:53,498 He starts with the number of new stars that're born each year, 33 00:01:53,498 --> 00:01:56,282 we will see that our definitions are actually pretty close to each other 34 00:01:56,282 --> 00:02:00,856 what I want to do, is start with the total number of stars, 35 00:02:00,856 --> 00:02:03,902 So, we are trying to come up with is, 36 00:02:03,902 --> 00:02:07,825 I will call it 'N' and this is number of detectable civilizations, 37 00:02:07,825 --> 00:02:20,256 number of detectable civilizations in the Milky Way, in our galaxy. 38 00:02:20,256 --> 00:02:25,867 and once again, there could be civilizations, looking back in the star field right over here 39 00:02:25,867 --> 00:02:30,179 this star right over here, maybe it has a planet that is in the right place 40 00:02:30,179 --> 00:02:33,579 that has liquid water and maybe there is intelligent life on that planet, 41 00:02:33,579 --> 00:02:37,000 but they might not be detectable, 42 00:02:37,000 --> 00:02:42,375 because, they aren't technologically advanced enough that they are using electromagnetic radiation 43 00:02:42,375 --> 00:02:45,215 or maybe they just figured out some other way to communicate 44 00:02:45,215 --> 00:02:49,768 or maybe they are beyond using electromagnetic radiation, you know, radio waves and all the rest to communicate 45 00:02:49,768 --> 00:02:53,415 so we will never be able to detect them. 46 00:02:53,415 --> 00:02:57,215 We are talking about civilizations like ours that are, to some degree, 47 00:02:57,215 --> 00:03:00,605 using technology not too different than our own. 48 00:03:00,605 --> 00:03:03,698 That's what we mean by 'detectable', 49 00:03:03,698 --> 00:03:06,021 so let's think about that little bit. 50 00:03:06,021 --> 00:03:11,200 I like to start with just the total number of stars in our solar system. 51 00:03:11,769 --> 00:03:15,667 So let's just start with, I will call it, N*, 52 00:03:15,667 --> 00:03:33,000 so this is the number of stars in our galaxy, and our best guess, I said is this's going to be 100-400 billion stars. 53 00:03:33,000 --> 00:03:35,815 We don't even know how many there are, some of them are undetectable, 54 00:03:35,815 --> 00:03:38,271 and the center of our galaxy is just a big blur to us 55 00:03:38,271 --> 00:03:40,646 we don't even know what's on the other side of that, 56 00:03:40,646 --> 00:03:44,267 e can't even see all the stars that are packed into the center, 57 00:03:44,267 --> 00:03:49,200 so this is our best guess, 100-400 billion stars. 58 00:03:49,200 --> 00:03:54,113 Now obviously, there is going to be subset of those stars that even have planets. 59 00:03:54,113 --> 00:03:56,954 So, let's multiply the times that subset; so lets multiply 60 00:03:56,954 --> 00:03:59,615 times the frequency of having a planet. 61 00:03:59,615 --> 00:04:04,067 If you are a star, this is the percent chance or the frequency or 62 00:04:04,067 --> 00:04:08,010 of the fraction of these stars that have planets (f sub p) 63 00:04:08,010 --> 00:04:17,485 so, I'll write this way "fractions that have planets", 64 00:04:17,485 --> 00:04:21,575 So, if this is a hundred billion, let's say I am making a guess here 65 00:04:21,575 --> 00:04:23,138 and we are learning more about this everyday, 66 00:04:23,138 --> 00:04:27,387 there are all these discoveries of 'exoplanets'- planets outside our solar systems, 67 00:04:27,387 --> 00:04:29,098 maybe this is one fourth. 68 00:04:29,098 --> 00:04:33,102 Then you could say, well that means there are 100 billion times one fourth, 69 00:04:33,102 --> 00:04:37,148 that means there are 25 billion stars that have planets around them. 70 00:04:37,148 --> 00:04:40,036 But that's still not enough to go to civilizations. 71 00:04:40,036 --> 00:04:43,646 We also need to think about planets, there could be a planet like Jupiter, 72 00:04:43,646 --> 00:04:49,205 and we don't know how life as we know it can survive on a planet like Jupiter or Neptune or Mercury. 73 00:04:49,205 --> 00:04:52,267 It has to have planets that are good for sustaining life. 74 00:04:52,267 --> 00:04:55,938 Preferably have a rocky core, liquid water on the outside, 75 00:04:55,938 --> 00:04:58,538 that's what we think are the ingredients we need for life, 76 00:04:58,538 --> 00:05:02,021 maybe we are just not being creative enough, that's what we know as life is being. 77 00:05:02,021 --> 00:05:12,744 So, let's multiply this times the average number of life sustaining or planets that could sustain life on them. 78 00:05:12,744 --> 00:05:15,129 So we don't necessarily know that they are going to have life, 79 00:05:15,129 --> 00:05:17,344 but they seem like they are just the right distance from the star, 80 00:05:17,344 --> 00:05:23,708 not too hot, not too cold. They have the right amount of gravity, water, all the other stuff, 81 00:05:23,708 --> 00:05:26,762 and we still don't know what this means, 82 00:05:26,762 --> 00:05:44,662 but this means average number, so given a number of solar systems with planets, what's the average number of planets capable of sustaining life, 83 00:05:44,662 --> 00:05:46,225 and once again, you don't know this answer. 84 00:05:46,225 --> 00:05:53,308 maybe it is 0.1, it's probably less than 1. 85 00:05:53,308 --> 00:05:56,025 Therefore any given solar system that has planets, 86 00:05:56,025 --> 00:05:59,621 the average number capable of sustaining life maybe its 0.1 maybe it's more than 1, I don't know. 87 00:05:59,621 --> 00:06:02,667 We don't know the exact answer here, but I will throw an answer in, 88 00:06:02,667 --> 00:06:05,846 I 'll throw out a guess, maybe it is 0.1. 89 00:06:05,846 --> 00:06:10,902 And here the fraction that has planets (f sub p), i don't know, i will throw that out as, 90 00:06:10,902 --> 00:06:15,277 and once again I am making up these numbers, we really don't know the right answers, this is one-fourth. 91 00:06:15,277 --> 00:06:18,185 But if we were to multiply this out we would have 92 00:06:18,185 --> 00:06:25,185 the average number of planets in our solar system that are capable of sustaining life 93 00:06:25,185 --> 00:06:30,067 that are around stars that have planets and these planets are capable of sustaining life. 94 00:06:30,067 --> 00:06:43,533 Now, n sub p will give us the total number of planets in our galaxy capable of sustaining life. 95 00:06:43,533 --> 00:06:48,533 Now, just because you have liquid water and right temperature and all the other rest of the ingredients 96 00:06:48,533 --> 00:06:52,333 doesn't mean that you will actually have life happening on your planet. 97 00:06:52,333 --> 00:06:58,733 So let's multiply that times the fraction that actually generate life (f sub l) 98 00:06:58,733 --> 00:07:03,267 So f sub p is the fraction that actually have life 99 00:07:03,267 --> 00:07:04,600 and this is actually a very , we dont know this answer, so this is the fraction 100 00:07:04,600 --> 00:07:10,867 that have life on them 101 00:07:10,867 --> 00:07:13,800 And this is a really big open question 102 00:07:13,800 --> 00:07:16,067 maybe if you have the ingredients, maybe every planet has life 103 00:07:16,067 --> 00:07:21,000 maybe it is a frequent thing that's happening in our galaxy and frankly our universe 104 00:07:21,000 --> 00:07:23,267 or maybe it's a very infrequent thing 105 00:07:23,267 --> 00:07:26,467 maybe it's just the right kind of freak set of circumstances that just have to happen 106 00:07:26,467 --> 00:07:30,267 i will throw out a number, just for the sake of having a number 107 00:07:30,267 --> 00:07:32,933 maybe it is one out of every ten planets 108 00:07:32,933 --> 00:07:36,600 that have all the right ingredients for life actually do generate life. 109 00:07:36,600 --> 00:07:39,867 My personal guess is probably higher than that given that 110 00:07:39,867 --> 00:07:44,400 life seems life seems such a robust and flexible thing we have seen in all sort of weird circumstances. 111 00:07:44,400 --> 00:07:48,333 Actually let me make it higher number than that so let me make it one half (0.5) 112 00:07:48,333 --> 00:07:52,800 assuming that we have all of the ingredients. 113 00:07:52,800 --> 00:07:53,800 So this should tell us essentially 114 00:07:53,800 --> 00:08:00,384 how many planets in our galaxy have had life on them at some point 115 00:08:00,384 --> 00:08:04,600 in those planets' lives. 116 00:08:04,600 --> 00:08:10,200 The life might have come and gone 117 00:08:10,200 --> 00:08:12,600 maybe destroyed itself through nuclear war. 118 00:08:12,600 --> 00:08:16,800 But this would tell us the number of planets in our galaxy 119 00:08:16,800 --> 00:08:20,933 that had life at at least one point in their history. 120 00:08:20,933 --> 00:08:24,133 Now we care about civilizations, about intelligent life.. 121 00:08:24,133 --> 00:08:33,667 So maybe if the asteroid never hit earth... 122 00:08:33,667 --> 00:08:38,000 the dinosaurs would have never evolved to the point of generating 123 00:08:38,000 --> 00:08:41,867 radios and tvs and telephones and all the rest.. 124 00:08:41,867 --> 00:08:44,067 and so it is kind of a freak circumstance 125 00:08:44,067 --> 00:08:47,800 that because they were destroyed these gaps in the ecosystem developed 126 00:08:47,800 --> 00:08:49,792 so we could emerge and and be intelligent and 127 00:08:49,792 --> 00:08:51,018 do all these crazy things 128 00:08:51,018 --> 00:08:52,410 like make YouTube videos and all the rest. 129 00:08:52,410 --> 00:08:55,623 So, let's multiply this times the fraction 130 00:08:55,623 --> 00:08:56,792 if you get all of this, the fraction 131 00:08:56,792 --> 00:08:59,908 that actually end up having intelligent life 132 00:08:59,908 --> 00:09:05,942 and maybe this fraction is, 133 00:09:05,942 --> 00:09:15,338 to a number of 1/10, then probably 134 00:09:15,338 --> 00:09:17,008 in the next video I'll calculate it all. 135 00:09:17,008 --> 00:09:19,227 Now this is very important to realise 136 00:09:19,227 --> 00:09:22,374 because once again, you could have life 137 00:09:22,374 --> 00:09:25,637 these are all examples of life right over here 138 00:09:25,637 --> 00:09:27,797 This is actually life on Earth, on our planet 139 00:09:27,797 --> 00:09:29,377 even though this looks quite alien 140 00:09:29,377 --> 00:09:32,236 this is a weeble, kind of looked at from very close-up, 141 00:09:32,236 --> 00:09:35,226 but there is all sorts of forms of life 142 00:09:35,226 --> 00:09:37,963 many of which we probably can't even begin to imagine 143 00:09:37,963 --> 00:09:41,975 but what we care is that if intelligent life 144 00:09:41,975 --> 00:09:44,158 starts to emerge on the planet 145 00:09:44,158 --> 00:09:46,526 because only intelligent life has a chance, 146 00:09:46,526 --> 00:09:49,943 we believe of being able to eventually communicate in ways 147 00:09:49,943 --> 00:09:53,342 that are detectable by us. 148 00:09:53,342 --> 00:09:55,152 Now I said intelligent life, but 149 00:09:55,152 --> 00:09:57,577 maybe not all intelligent life will eventually 150 00:09:57,577 --> 00:10:00,704 get to the technological sophistication, where 151 00:10:00,704 --> 00:10:05,719 they will be using radio waves, electro-magnetic radiation to communicate with each other 152 00:10:05,719 --> 00:10:08,542 maybe we might have stagnated at this stage 153 00:10:08,542 --> 00:10:11,253 if nothing of the right things didn't happen.. 154 00:10:11,253 --> 00:10:15,385 So what we need to do now, is multiply this 155 00:10:15,385 --> 00:10:19,600 so right here, we would have the number of planets 156 00:10:19,600 --> 00:10:25,376 in our galaxy that have had intelligent life on them at some point in their history 157 00:10:25,376 --> 00:10:28,943 maybe not at a time that coincides with ours, 158 00:10:28,943 --> 00:10:34,235 but what we wanna do is bring it down even more to the percentage that get to the point 159 00:10:34,235 --> 00:10:38,527 that they can develop technology that allows us to detect them. 160 00:10:38,527 --> 00:10:47,044 So, let me multiply times the fraction that are, I'll put a 'C' here, 161 00:10:47,044 --> 00:10:49,976 'C' for, maybe they're using communication; 'C' for communications 162 00:10:49,976 --> 00:10:53,627 that allow us to detect them. 163 00:10:56,703 --> 00:10:56,703 So this is detectable, the fraction that are detectable. 164 00:10:57,734 --> 00:11:02,840 Now you might think that we're done, this will give you the Total Number of Civilizations, or life-forms 165 00:11:02,840 --> 00:11:11,125 in our Galaxies or the planets that have life forms that developed detectable technologies at some point 166 00:11:11,125 --> 00:11:19,206 in their history.. Now it would be nice if civilizations be not born and die 167 00:11:19,206 --> 00:11:22,895 but the reality is, they do die. They might destroy themselves or whatever, 168 00:11:22,895 --> 00:11:26,960 and they might exist for only a small period of time for the history of that planet 169 00:11:26,960 --> 00:11:28,891 or the history of that Solar System. 170 00:11:28,891 --> 00:11:35,659 So in order to make it the number of civilizations that are in existance now 171 00:11:35,659 --> 00:11:39,902 and I'll clarify what "now" means in the next video because really if we are 172 00:11:39,902 --> 00:11:43,192 detecting something from a star that's 10,000 lightyears away 173 00:11:43,192 --> 00:11:45,892 our "now" means we are just receiving their signals 174 00:11:45,892 --> 00:11:50,527 so, they released the signals 10,000 years ago. 175 00:11:50,527 --> 00:11:54,453 But what I want to do is get to know what is the fraction of these whose signals 176 00:11:54,453 --> 00:11:57,658 are reaching us right now. 177 00:11:57,658 --> 00:12:02,688 and here, I'll say what's the average lifespan of a civilization 178 00:12:02,688 --> 00:12:06,342 I'll put that "L", who knows what is, maybe 10,000 years 179 00:12:06,342 --> 00:12:15,022 so civilization lifespan as going to be that over the life of the star 180 00:12:15,022 --> 00:12:22,145 So, I'll put a 'T' here, for the average lifespan for the star, 181 00:12:22,145 --> 00:12:24,410 and I could say the average lifespan for the planet, 182 00:12:24,410 --> 00:12:26,703 or whatever, but we're assuming once our star 183 00:12:26,703 --> 00:12:29,888 supernovas, you're not going to have a chance for 184 00:12:29,888 --> 00:12:33,258 life on Earth to develop anymore. 185 00:12:33,258 --> 00:12:35,542 So, maybe this thing appears ten thousand years 186 00:12:35,542 --> 00:12:39,219 and this down here is maybe 10 billion years. 187 00:12:39,219 --> 00:12:42,043 and if you were to multilply this out, you should get 188 00:12:42,043 --> 00:12:46,676 the number of detectable civilizations in our galaxy right now. 189 00:12:46,676 --> 00:12:49,109 I'll leave you there, and next we'll discuss it a little bit 190 00:12:49,109 --> 00:12:54,911 more, and reconcile it with the more famous version of Drake's equation, 191 00:12:54,911 --> 00:12:58,145 and I'll also try and talk about this little piece of bit, 192 00:12:58,145 --> 00:13:00,222 because I think it might be a little confusing, and 193 00:13:00,222 --> 00:13:03,000 I'll try to diagram that out a little bit more..