WEBVTT - Great Filter 0:00:00.520 --> 0:00:04.440 What exactly does figuring out if aliens exist have to 0:00:04.519 --> 0:00:07.680 do with the end of the world. Well, it turns 0:00:07.720 --> 0:00:10.360 out that the odd emptiness that we find in the 0:00:10.440 --> 0:00:13.840 universe can give us clues about what may have gone 0:00:13.840 --> 0:00:17.440 on or didn't go on before we humans came along. 0:00:18.440 --> 0:00:22.480 Did something bad happen? And if so, might it happen 0:00:22.520 --> 0:00:26.279 to us two? Looking around for signs of whether we're 0:00:26.320 --> 0:00:29.760 the only intelligent life to have ever evolved can help 0:00:29.800 --> 0:00:33.720 answer those questions. And when you look at it, the 0:00:33.840 --> 0:00:38.080 universe does seem amazingly large for Earth to be the 0:00:38.200 --> 0:00:42.199 only planet with life on it. Consider it like this. 0:00:43.440 --> 0:00:47.040 Let's say that you're a photon, a tiny packet of light, 0:00:47.680 --> 0:00:50.400 and one day you had the wherewithal this set out 0:00:50.440 --> 0:00:54.320 to travel across the universe. You would find that, perhaps 0:00:54.320 --> 0:00:57.120 to your great surprise, such a trip would take you 0:00:57.200 --> 0:01:02.640 around fifty billion years. Yes, you, light, which can travel 0:01:02.680 --> 0:01:05.640 at the speed of light, would take fifty billion years 0:01:05.640 --> 0:01:07.960 to cross from one side of the universe to the other. 0:01:08.680 --> 0:01:10.720 At least that's how long it would appear to take 0:01:10.760 --> 0:01:14.520 you to as humans. And this is just the observable universe. 0:01:14.720 --> 0:01:16.760 The amount of the universe that light like you has 0:01:16.760 --> 0:01:19.960 had time to travel across since the Big Bang. Within 0:01:20.000 --> 0:01:23.399 that vast space, there are anywhere from one billion to 0:01:23.600 --> 0:01:27.760 two trillion galaxies by our current causes, at least of 0:01:27.800 --> 0:01:30.040 which our own Milky Way is on the larger side 0:01:30.080 --> 0:01:33.199 of the spectrum. There are larger but there are also 0:01:33.240 --> 0:01:36.600 a lot of smaller ones too. Within these billions or 0:01:36.640 --> 0:01:41.160 trillions of galaxies are billions and billions and billions of stars, 0:01:41.319 --> 0:01:45.920 and probably exponentially more planets. The total number of planets 0:01:45.920 --> 0:01:48.880 and stars in our universe, the total number of places 0:01:48.880 --> 0:01:53.480 for life to exist, is mind bogglingly large. And so 0:01:53.600 --> 0:01:57.040 you packet of light or wavelength, depending on your mood, 0:01:57.600 --> 0:02:00.320 might think to yourself, as you traveled across the verse 0:02:00.360 --> 0:02:03.040 and saw that the Earth is the only planet that 0:02:03.240 --> 0:02:05.920 is home to intelligent life. Out of the attend to 0:02:05.960 --> 0:02:08.600 the who knows what power planets that could host life, 0:02:09.360 --> 0:02:12.360 You might think to yourself, in your little photon voice, 0:02:13.080 --> 0:02:18.320 what waste are we alone in the universe? And if 0:02:18.360 --> 0:02:21.400 we are alone, why? These are the questions at the 0:02:21.400 --> 0:02:24.360 heart of the Fermi paradox, and they continue to nag 0:02:24.400 --> 0:02:27.480 at us. The answer is plainly obvious if you look 0:02:27.520 --> 0:02:30.160 at it, but it depends on how you look at it. 0:02:30.840 --> 0:02:33.639 With the Fermi paradox, the same thing can look very 0:02:33.639 --> 0:02:36.480 different to any two people. And it's not just the 0:02:36.520 --> 0:02:41.400 paradox itself. Even the evidence is equally ambiguous. It's all 0:02:41.440 --> 0:02:45.000 like one big contradem words that have two meanings that 0:02:45.040 --> 0:02:48.440 are the opposite of one another, like how weather can 0:02:48.480 --> 0:02:51.880 mean both to wear away and to withstand something. The 0:02:51.919 --> 0:02:54.560 size of our empty universe can mean that we are 0:02:54.600 --> 0:02:59.240 both alone or one of many. Another example of this 0:02:59.400 --> 0:03:03.680 ambiguity is the very presence of life on Earth, something 0:03:03.680 --> 0:03:05.600 that people who believe that we're not alone in the 0:03:05.680 --> 0:03:08.440 universe point to. His evidence is that life here on 0:03:08.480 --> 0:03:11.239 Earth seems to have emerged the first chance that it had. 0:03:12.280 --> 0:03:15.919 The famous astronomer and science writer Carl Sagan was one 0:03:15.960 --> 0:03:18.720 of those people. He was an optimist when it came 0:03:18.760 --> 0:03:22.560 to the family paradox. He believed that life was out there, 0:03:22.800 --> 0:03:26.560 we just hadn't found it yet. Sagan pointed to evidence 0:03:26.560 --> 0:03:29.280 from the fossil record that here on Earth life began 0:03:29.320 --> 0:03:32.880 as early as five hundred million years after the Earth form. 0:03:32.960 --> 0:03:35.840 It was almost like it was waiting to emerge, and 0:03:35.920 --> 0:03:38.960 since it emerged quickly here on Earth, it stands to 0:03:39.000 --> 0:03:42.040 reason that life should emerge wherever it gets the chance, 0:03:42.200 --> 0:03:45.880 anywhere in our universe. When you take into account the 0:03:45.920 --> 0:03:48.480 idea that there are perhaps three hundred billion stars in 0:03:48.520 --> 0:03:51.960 the Milky Way alone, even if some small fraction of 0:03:52.000 --> 0:03:55.280 those have habitable planets that could host life, then we 0:03:55.320 --> 0:03:58.680 should expect to encounter it sometime soon as we spread 0:03:58.680 --> 0:04:02.600 out to explore the country side around planet Earth. But 0:04:02.640 --> 0:04:04.960 there's a problem with basing our view of the rest 0:04:05.040 --> 0:04:08.600 of the universe on our own existence. The idea that 0:04:08.640 --> 0:04:11.560 we can gain insight into our universe from our existence 0:04:11.640 --> 0:04:15.120 is called the anthropic principle, and it's vulnerable to a 0:04:15.200 --> 0:04:20.080 logical fallacy called selection bias. Being the only intelligent life 0:04:20.080 --> 0:04:22.840 in the universe, we're the only data point in our 0:04:22.920 --> 0:04:26.360 data set, and so we tend to skew the results 0:04:26.360 --> 0:04:29.440 a little bit. It's hard to resist the temptation of 0:04:29.520 --> 0:04:33.320 cherry picking the data when there's only one cherry. Yes, 0:04:33.360 --> 0:04:37.159 of course, life can arise. Our very existence proves that fact. 0:04:37.600 --> 0:04:40.200 But what it does not prove is that the emergence 0:04:40.200 --> 0:04:44.680 of intelligent life or any life, really is easy or inevitable. 0:04:45.440 --> 0:04:48.839 What if, instead, life emerging in our universe is really, 0:04:49.320 --> 0:04:55.400 really really hard. Perhaps the existence of living, breathing, intelligent 0:04:55.480 --> 0:04:58.120 things here on Earth doesn't show the emergence of life 0:04:58.160 --> 0:05:01.600 is inevitable. Perhaps as shows that it was the singularly 0:05:01.680 --> 0:05:05.320 most unlikely event in the history of our entire universe. 0:05:11.400 --> 0:05:13.720 If you could crack open a strand of your DNA 0:05:14.200 --> 0:05:17.839 and read the pairs of adenine, guanine, cite of scene 0:05:17.880 --> 0:05:21.159 and dimin the ones and zeros of your genetic code, 0:05:21.800 --> 0:05:24.800 you would find a history of life on Earth written 0:05:24.839 --> 0:05:28.480 into it. Not only does your DNA contain the blueprints 0:05:28.520 --> 0:05:31.120 for making a full version of you, but if you 0:05:31.160 --> 0:05:33.920 look at it correctly, it also bears the marks of 0:05:33.920 --> 0:05:37.360 those who have come before you. You'll find your parents genes, 0:05:37.440 --> 0:05:40.080 of course, and their parents. But as you go further 0:05:40.160 --> 0:05:43.200 back in time, you'll also find the contributions of all 0:05:43.200 --> 0:05:46.520 of the animals in bacteria that ever reproduced along the 0:05:46.600 --> 0:05:49.800 last several billion years to form a connected chain of 0:05:49.839 --> 0:05:54.120 life that eventually led to you. But you'll find that 0:05:54.160 --> 0:05:56.320 you run into a wall the further you go back. 0:05:57.200 --> 0:05:59.520 There's a point beyond which we can no longer read 0:05:59.560 --> 0:06:03.080 the taves of our DNA. It ends right before we 0:06:03.120 --> 0:06:05.240 get to the emergence of life here on Earth the 0:06:05.360 --> 0:06:08.760 very beginning. That is to say, no one is sure 0:06:09.279 --> 0:06:14.680 how life began as it stands now, the general consensus 0:06:14.680 --> 0:06:19.200 among sciences the concept of a biogenesis, that life emerged 0:06:19.240 --> 0:06:23.400 from nothing nothing living anyway, let's go back to the 0:06:23.480 --> 0:06:27.680 early Earth. About five million years after it formed, the 0:06:27.720 --> 0:06:31.040 surfaces just begun to cool enough that solid clay ground 0:06:31.040 --> 0:06:33.440 has begun to form, and with the cooling off, the 0:06:33.560 --> 0:06:37.360 muggy atmosphere cooled as well, condensing in the rain that 0:06:37.480 --> 0:06:40.200 began to collect in pools which would become the peatree 0:06:40.279 --> 0:06:44.120 dishes where life took its first steps. But to get 0:06:44.200 --> 0:06:48.680 from here to life, something extremely unlikely had to happen. 0:06:49.600 --> 0:06:54.520 Plain old, lifeless molecules had to spontaneously arrange themselves into 0:06:54.560 --> 0:06:58.920 new forms that became the building blocks of life. At 0:06:58.960 --> 0:07:01.560 this point, there was nothing but raw materials on Earth, 0:07:01.880 --> 0:07:04.560 and we have to get from here to living organisms. 0:07:05.400 --> 0:07:08.320 That means that not only do you have a functioning organism, 0:07:08.400 --> 0:07:10.960 it has to carry with it the encoded instructions to 0:07:11.000 --> 0:07:13.440 make a copy of itself, and some way to read 0:07:13.440 --> 0:07:16.840 those instructions and actually make that copy. It's like the 0:07:16.920 --> 0:07:20.080 idea of putting some plastic pellets and metal shavings into 0:07:20.080 --> 0:07:23.360 a bucket and expecting an autonomous three D printer to 0:07:23.440 --> 0:07:27.480 form from it, or more to the point, it would 0:07:27.520 --> 0:07:31.200 be like the idea of rotting meat growing maggots. For 0:07:31.240 --> 0:07:34.040 a long time, humans thought that this kind of thing 0:07:34.240 --> 0:07:38.720 spontaneous generation, was how some life arose. Prior to when 0:07:38.760 --> 0:07:41.960 science took up the mantle of explaining our universe, people 0:07:42.000 --> 0:07:45.200 relied on their everyday observations to explain occurrence is like 0:07:45.240 --> 0:07:48.600 maggots growing on rotting meat, seeming to appear out of nowhere. 0:07:49.440 --> 0:07:52.000 It seemed just as likely as anything that maggots could 0:07:52.040 --> 0:07:56.559 spontaneously generate, or baby mice from grain, which was another 0:07:56.600 --> 0:08:00.200 common folk belief. But eventually scientists figured out a way 0:08:00.200 --> 0:08:03.560 to disprove this idea, which really gained support when we 0:08:03.600 --> 0:08:07.480 realized that tiny, unseen life lived around us everywhere and 0:08:07.480 --> 0:08:08.960 that it had a hand in a lot of the 0:08:09.040 --> 0:08:13.120 things that we saw. Germ theory was developed and the 0:08:13.200 --> 0:08:17.920 concept of spontaneous generation was abandoned. That is until the 0:08:18.000 --> 0:08:22.040 nineteen fifties, when researchers started working hard on figuring out 0:08:22.160 --> 0:08:26.200 how life on Earth might have come about. Spontaneous generation 0:08:26.520 --> 0:08:32.400 made an unexpected comeback. A biogenesis holds that quadrillions upon 0:08:32.520 --> 0:08:36.480 quintillions of simple molecules present in Earth's early atmosphere and 0:08:36.559 --> 0:08:40.880 oceans randomly configured themselves into a mind bending number of 0:08:40.920 --> 0:08:45.600 different combinations. Some of these abominably large number of combinations 0:08:45.600 --> 0:08:49.600 happen to create useful complex molecules like amino acids, which 0:08:49.600 --> 0:08:53.640 are the precursors for proteins. Now, it's one thing to 0:08:53.720 --> 0:08:58.320 form simple molecules to randomly combined to form more complex molecules, 0:08:58.360 --> 0:09:01.280 but there is still the issue of replication. Ship If 0:09:01.320 --> 0:09:04.120 those molecules don't make a younger copy of themselves, that 0:09:04.240 --> 0:09:07.880 innovative chemical chain is broken and the new molecule loses 0:09:07.920 --> 0:09:10.160 the chance to continue to evolve in a new and 0:09:10.240 --> 0:09:13.840 even more complex things. And this is the point where 0:09:13.840 --> 0:09:17.760 science is currently stuck. Somehow, they say, some of those 0:09:17.800 --> 0:09:21.760 molecules managed to form a stable string of nuclear times, 0:09:21.800 --> 0:09:25.760 probably r N, a ribonucleic acid which is capable of 0:09:25.760 --> 0:09:30.040 doing two very important things. It can encode information in 0:09:30.080 --> 0:09:33.319 its nuclear tide chain, and it can also transcribe those 0:09:33.360 --> 0:09:36.880 nuclear tides to produce proteins. And once you have proteins, 0:09:37.200 --> 0:09:39.600 you can do all sorts of things that supports life. 0:09:40.800 --> 0:09:45.320 Back in two organic chemists Stanley Miller and Herald Urray 0:09:45.640 --> 0:09:48.199 saw it to show that this was possible by recreating 0:09:48.200 --> 0:09:51.680 the conditions of earlier Earth. In a flask. They simulated 0:09:51.720 --> 0:09:54.400 a primitive ocean and built an atmosphere out of the 0:09:54.480 --> 0:09:57.000 gases thought back in the fifties to have been present 0:09:57.000 --> 0:10:00.040 on Earth soon after it formed. They mimicked why in 0:10:00.280 --> 0:10:03.800 storms with the flickering electrical current, and when Miller inspected 0:10:03.800 --> 0:10:07.520 the broth that resulted, he found that nineteen amino acids 0:10:07.520 --> 0:10:12.640 and amans, the precursors to proteins, had assembled spontaneously. It 0:10:12.679 --> 0:10:15.520 seems that Miller had shown that when the conditions were right, 0:10:15.880 --> 0:10:20.480 the foundations for life would arise. But lately the idea 0:10:20.559 --> 0:10:25.680 that a biogenesis just happened randomly is falling out of favor. Instead, 0:10:26.000 --> 0:10:28.640 some scientists have begun to suspect that there is some 0:10:28.760 --> 0:10:32.400 set of organizing principles that serves as a driving force 0:10:32.520 --> 0:10:35.920 for life to emerge. Just like how gravity will draw 0:10:35.960 --> 0:10:39.520 a ball downhill, or how magnets will always repel or 0:10:39.559 --> 0:10:42.640 attract one another when they're close together, there is some 0:10:42.760 --> 0:10:46.839 fundamental governing force of nature that causes life to assemble 0:10:47.120 --> 0:10:51.120 along predictable lines. We just haven't figured out what that 0:10:51.200 --> 0:10:54.800 force or those lines are yet. This is a pretty 0:10:54.840 --> 0:10:57.599 surprising idea if you think of it. One of the 0:10:57.679 --> 0:11:00.720 laws of the universe, the second law of therm mom dynamics, 0:11:01.120 --> 0:11:05.840 is that things tend towards disorder, not order. The idea that, 0:11:05.840 --> 0:11:09.120 when presented with the right conditions, dead molecules in the 0:11:09.240 --> 0:11:13.120 universe will organize themselves into something living and breathing runs 0:11:13.320 --> 0:11:16.959 totally counter to that, and this new view also includes 0:11:17.000 --> 0:11:21.360 evolutionary biology as one stretch of these organizing principles of life. 0:11:22.280 --> 0:11:26.280 So the idea is that molecules arrange themselves into self replicating, 0:11:26.520 --> 0:11:31.480 metabolizing parts that form increasingly complex beings that eventually include 0:11:31.480 --> 0:11:35.079 you and me, which makes you wonder what the end 0:11:35.120 --> 0:11:55.240 point is. To some people, the idea that life arose 0:11:55.320 --> 0:11:59.160 from simple dead molecules that just happened to randomly assemble 0:11:59.240 --> 0:12:03.560 themselves in the living things is just too unlikely to accept, 0:12:04.520 --> 0:12:07.160 And even if we do accept that this is precisely 0:12:07.240 --> 0:12:10.120 how life arose on Earth, the idea that it could 0:12:10.160 --> 0:12:14.920 ever happen again anywhere else is too improbable. That virtually 0:12:15.000 --> 0:12:19.360 proves that we humans are alone in the universe. One 0:12:19.400 --> 0:12:22.960 issue people raise is time. They say that Earth just 0:12:23.040 --> 0:12:25.600 simply hasn't been around long enough for all of that 0:12:26.000 --> 0:12:30.040 random chemical trial and error to have taken place. The 0:12:30.120 --> 0:12:34.840 idea that life organizes along some unknown universal principles definitely 0:12:34.840 --> 0:12:38.079 addresses that idea of time, and so does pant spermia. 0:12:38.840 --> 0:12:42.440 Pant Spermia is a concept from astrobiology, and it says 0:12:42.520 --> 0:12:45.120 that the seeds of life are all over the universe 0:12:45.160 --> 0:12:48.719 in abundance everywhere. They can be found on board asteroids 0:12:48.720 --> 0:12:51.920 and other celestial objects, and that these seeds of life 0:12:51.920 --> 0:12:56.760 are constantly bombarding planets all over the universe. If the 0:12:56.800 --> 0:12:59.520 conditions on the planet happen to be right, well, then 0:12:59.559 --> 0:13:02.280 those sea needs of life will germinate and grow into 0:13:02.480 --> 0:13:06.920 something new and living. This certainly addresses the issue of time. 0:13:07.600 --> 0:13:10.280 Life could have evolved elsewhere in the universe, which is 0:13:10.320 --> 0:13:13.080 billions of years older than Earth, and then spread to 0:13:13.120 --> 0:13:17.520 our planet aboard an asteroid. We've recently found that some 0:13:17.600 --> 0:13:21.000 chemical precursors to life can be found on celestial objects 0:13:21.000 --> 0:13:23.920 like asteroids, and that they're able to survive re entry 0:13:24.000 --> 0:13:26.960 into an atmosphere, which can get pretty hot. This is 0:13:27.000 --> 0:13:30.080 important because it's widely accepted that an atmosphere is a 0:13:30.120 --> 0:13:34.400 precondition for life to emerge. If you take pants bermia, 0:13:34.520 --> 0:13:36.800 and you take the recent view that life follows some 0:13:36.960 --> 0:13:40.800 organizing principles as immutable as the laws of physics, then 0:13:40.840 --> 0:13:43.920 you arrive at a conclusion that Earth is just another 0:13:43.960 --> 0:13:46.640 place that happened to have the right conditions when a 0:13:46.760 --> 0:13:50.160 rock bearing the precursors to life landed around four billion 0:13:50.240 --> 0:13:54.520 years ago. In this view, then of course life is 0:13:54.559 --> 0:13:58.400 abundant in the universe. But then we find ourselves right 0:13:58.440 --> 0:14:03.160 back to where we started. Where is everybody? Perhaps the 0:14:03.200 --> 0:14:06.400 best answer to that comes not from an astrobiologist or 0:14:06.440 --> 0:14:11.160 an astronomer, but from an economist named Robin Hansen, who 0:14:11.200 --> 0:14:15.520 proposed that there must be something, some incredibly difficult step 0:14:15.720 --> 0:14:18.480 between the point where dead matter forms life and the 0:14:18.520 --> 0:14:23.240 point where intelligent life becomes a galactically colonizing civilization that 0:14:23.360 --> 0:14:27.760 no species has ever been able to overcome. He calls 0:14:27.760 --> 0:14:30.760 it the great filter. Every piece of matter in the 0:14:30.800 --> 0:14:32.640 universe is the sort of thing that could have started 0:14:32.640 --> 0:14:37.600 that process, started life, and then advanced life, etcetera. But 0:14:38.760 --> 0:14:41.440 so far nothing out there has done that. So the 0:14:41.480 --> 0:14:45.280 great filter is whatever is in the way, whatever makes 0:14:45.280 --> 0:14:48.120 it hard for any one piece of ordinary dead matter 0:14:48.280 --> 0:14:52.720 to produce expanding, lasting life. There's surely a countless number 0:14:52.720 --> 0:14:55.200 of steps along the path from dead matter to the 0:14:55.240 --> 0:14:59.360 emergence of a galactically visible civilization. But the Great Filter 0:14:59.480 --> 0:15:02.800 high Path says, supposes that a handful of them are really, 0:15:03.320 --> 0:15:06.640 really hard, and that one of them in particular must 0:15:06.680 --> 0:15:10.000 be so hard that is thus far prevented any life 0:15:10.200 --> 0:15:15.960 from reaching galactic proportions. This is Oxford University philosopher Toby 0:15:16.160 --> 0:15:19.040 ord if there were a hundred pieces you needed to 0:15:19.040 --> 0:15:21.640 get into the right order in order to create something 0:15:21.800 --> 0:15:26.280 that obeyed natural selection and and was it the basic 0:15:26.400 --> 0:15:31.080 level needed to actually bootstrap up towards complex life, then 0:15:31.080 --> 0:15:34.600 there are a hundred factorial ways you could arrange those pieces. 0:15:34.600 --> 0:15:37.200 That's that's more than uh tends to the power of 0:15:37.240 --> 0:15:40.240 a hundred different possibilities. And then it just turns out 0:15:40.320 --> 0:15:43.160 you need an incredibly rare event to get there. The 0:15:43.200 --> 0:15:46.960 Great Filter offers two possible solutions to the question posed 0:15:46.960 --> 0:15:52.520 by the Fermi paradox. Whereas everybody everybody never existed, or 0:15:52.600 --> 0:15:57.040 everybody is dead, if the Great Filter is in our past, 0:15:57.440 --> 0:16:00.040 it says pretty strongly that we are the first and 0:16:00.240 --> 0:16:04.880 only intelligent life that exists in the universe. If that's true, 0:16:05.360 --> 0:16:09.000 then by the Great Filter, there is something, some step, 0:16:09.360 --> 0:16:12.320 some right of passage you could call it, that has 0:16:12.360 --> 0:16:16.080 prevented every other life from reaching the point that we're at. 0:16:17.360 --> 0:16:19.640 And if that's the case, then we are the only 0:16:19.680 --> 0:16:23.880 life to have made it through the Great Filter. That 0:16:23.960 --> 0:16:27.080 means that we can be optimistic about our future. We 0:16:27.200 --> 0:16:29.480 made it through that right of passage that has kept 0:16:29.520 --> 0:16:33.240 every other attempt at life from evolving. It means our big, 0:16:33.360 --> 0:16:37.000 vast universe isn't wasted on us. It's just waiting there 0:16:37.040 --> 0:16:40.400 for us to use it, and guilt free too. Since 0:16:40.560 --> 0:16:43.040 no one else is around to use it, we have 0:16:43.120 --> 0:16:46.600 a responsibility to put it to use. You could even say. 0:16:47.360 --> 0:16:51.160 But there's another possibility to the Great Filter too. It 0:16:51.200 --> 0:16:56.320 may also lie just ahead in our future. Maybe intelligent 0:16:56.360 --> 0:16:58.920 life is a dime a dozen in the universe. But 0:16:59.000 --> 0:17:02.800 the reason we don't see other civilizations is because they've 0:17:02.840 --> 0:17:07.280 all died off. And if all of those intelligent civilizations 0:17:07.320 --> 0:17:11.679 all died before any any of them could make it 0:17:11.720 --> 0:17:14.400 off of their home planet and spread throughout the universe, 0:17:15.240 --> 0:17:17.840 the Great Filter is a big red flag for us. 0:17:19.440 --> 0:17:21.399 It tells us that we should expect to meet the 0:17:21.440 --> 0:17:25.920 same fate that every other intelligent life has. The Great 0:17:25.960 --> 0:17:29.000 Filter will spell the end of the world for us too. 0:17:30.600 --> 0:17:33.120 To answer the question of whether we face imminent doom 0:17:33.240 --> 0:17:36.159 or not, we have to look at the evolution of life, 0:17:36.800 --> 0:17:39.240 and to do that we have no choice but to 0:17:39.320 --> 0:17:41.920 turn to the one place where we know life evolved. 0:17:42.840 --> 0:17:45.320 At the risk of falling victim to the selection bias, 0:17:45.800 --> 0:17:49.840 we have to look to Earth for clues. We've already 0:17:49.840 --> 0:17:53.200 talked about how utterly improbable the origin of life appears 0:17:53.200 --> 0:17:56.359 to have been, but it's probably best to start looking 0:17:56.520 --> 0:18:02.560 even further back than that. If life emerged on Earth, 0:18:02.640 --> 0:18:05.240 that means that the conditions were right for life on Earth. 0:18:05.720 --> 0:18:08.520 That's the one day to point we have ipso fact, though, 0:18:09.200 --> 0:18:11.440 so the best way to find out what conditions life 0:18:11.440 --> 0:18:14.320 requires is to look at the conditions of our planet. 0:18:15.040 --> 0:18:19.240 And it turns out that Earth has some spectacularly peculiar 0:18:19.320 --> 0:18:24.040 characteristics that make it ripe for life. So peculiar, in fact, 0:18:24.480 --> 0:18:27.000 that a pair of researchers named Peter Ward and Donald 0:18:27.000 --> 0:18:29.680 Brownlee rolled all of them up into what they call 0:18:29.720 --> 0:18:32.880 the rare Earth hypothesis. It's just what it sounds like 0:18:33.280 --> 0:18:36.679 when you add up all of its peculiarities. Earth is 0:18:36.720 --> 0:18:41.120 not like other planets. First, Earth happened to form around 0:18:41.119 --> 0:18:43.640 the right kind of star. Our son is a main 0:18:43.720 --> 0:18:47.040 sequence star, which means it produces light and heat by 0:18:47.080 --> 0:18:51.560 fusing hydrogen into helium. Main Sequence stars aren't rare. They 0:18:51.600 --> 0:18:54.680 make up about nine of stars. But our Son also 0:18:54.720 --> 0:18:57.359 happened to be of the right size too. It's not 0:18:57.480 --> 0:18:59.520 so large that it will use up its fuel in 0:18:59.600 --> 0:19:03.000 just a few billion years. That means that the Sun's slow, 0:19:03.080 --> 0:19:05.720 steady burn would go on long enough to give life 0:19:05.760 --> 0:19:09.119 time to develop. The Sun also isn't too small to 0:19:09.160 --> 0:19:12.960 support life either. It is you could say, just right 0:19:13.040 --> 0:19:16.280 for life. Our Sun has also placed in a really 0:19:16.320 --> 0:19:19.440 great spot in our galaxy. We happen to be located 0:19:19.440 --> 0:19:21.679 out in the country, in a bit of a backwater 0:19:21.760 --> 0:19:24.400 when it comes to the Milky Way, about twenty eight 0:19:24.440 --> 0:19:27.480 thousand light years from the galactic center, in a galaxy 0:19:27.520 --> 0:19:31.920 that's one thousand light years across. For decades, study presumed 0:19:31.920 --> 0:19:33.880 that the center of the galaxy would be the most 0:19:33.920 --> 0:19:37.000 happening spot. That's where the most stars tend to be, 0:19:37.359 --> 0:19:42.080 and more stars would be more potentially habitable planets. Civilizations 0:19:42.119 --> 0:19:44.440 that arose in the center might even be in contact 0:19:44.480 --> 0:19:47.560 with one another, forming something of a galactic urban area. 0:19:48.760 --> 0:19:51.679 But recently it's become clear that the galactic center might 0:19:51.680 --> 0:19:55.200 not be so flourishing. After all. There are more stars, sure, 0:19:55.800 --> 0:19:58.960 but more stars also means that there are more collapsing stars, 0:19:59.359 --> 0:20:01.840 which release bursts of energy that can burn away the 0:20:01.880 --> 0:20:05.680 atmosphere of any planets in the vicinity, So the galactic 0:20:05.720 --> 0:20:08.680 center might actually be less of a bustling urban area 0:20:09.000 --> 0:20:13.280 and more like sterile and dead. Our Sun is pretty 0:20:13.320 --> 0:20:15.760 far away from the galactic center, way out past the 0:20:15.800 --> 0:20:19.600 suburbs where nothing much happens. In other words, that's good 0:20:19.720 --> 0:20:21.879 for life on Earth because it means that it cuts 0:20:21.920 --> 0:20:25.280 down on the number of sterilization events as life developed 0:20:25.280 --> 0:20:28.520 over Earth's history, giving it a good chance of succeeding. 0:20:29.600 --> 0:20:32.119 And Earth just so happens to be located within the 0:20:32.160 --> 0:20:35.040 Sun's goldilocks zone that I mentioned in the last episode. 0:20:35.760 --> 0:20:37.680 If it was a little nearer the Sun and about 0:20:37.680 --> 0:20:40.359 one and a half million kilometers closer, it would be 0:20:40.400 --> 0:20:44.200 too hot to support life, and much further away Earth 0:20:44.240 --> 0:20:47.320 would be too cold for it. It also turns out 0:20:47.400 --> 0:20:50.320 that where Earth is positioned in the Solar System is 0:20:50.400 --> 0:20:54.280 hugely important to giving life a fighting chance. Earth is 0:20:54.320 --> 0:20:57.280 the third rock from the Sun, with five others between 0:20:57.400 --> 0:20:59.920 us and the rest of the galaxy. Six if the 0:21:00.080 --> 0:21:02.720 math that suggests there's a planet nine out there turns 0:21:02.720 --> 0:21:05.600 out to be correct, or if you continue to count 0:21:05.600 --> 0:21:09.240 hapless Pluto, the Sun and the planets in our Solar 0:21:09.280 --> 0:21:12.760 System formed from a massive cloud of cosmic dust, that 0:21:12.920 --> 0:21:15.080 same stuff that might have blown up so many alien 0:21:15.119 --> 0:21:18.960 pilots traveling between the stars. We still aren't quite sure 0:21:18.960 --> 0:21:23.320 exactly how the planets formed. One model astoundingly suggested that 0:21:23.320 --> 0:21:25.919 they could have formed in as little as a thousand years, 0:21:26.720 --> 0:21:28.919 but the birth of the Solar System was likely a 0:21:28.920 --> 0:21:31.280 free for all grab of the elements that make up 0:21:31.320 --> 0:21:36.240 the planets today. Initially, astronomers presumed that the planets formed 0:21:36.280 --> 0:21:39.480 in their current arrangement, but lately it's become clear that 0:21:39.480 --> 0:21:42.639 that probably wasn't the case. The planets may have actually 0:21:42.680 --> 0:21:45.960 moved around and migrated from one spot to another in 0:21:46.000 --> 0:21:49.040 the early life of the Solar System before settling into 0:21:49.080 --> 0:21:52.800 the arrangement that we see them in today. If that's correct, 0:21:53.119 --> 0:21:56.520 then we were astoundingly lucky that Jupiter ended up where 0:21:56.520 --> 0:22:04.880 it didn't. Jupiter is a gas giant made up largely 0:22:04.920 --> 0:22:07.520 of hydrogen and helium with a metal and ice core. 0:22:07.920 --> 0:22:10.520 It's like a Sun that never started burning because it 0:22:10.600 --> 0:22:13.399 lacked the mass needed for gravity to kick start fusion. 0:22:14.280 --> 0:22:20.520 But Jupiter is massive, truly, you could fit around within it. 0:22:20.520 --> 0:22:23.840 It's the most massive planet in our Solar System, and 0:22:23.880 --> 0:22:26.760 because of its mass and its position between Earth and 0:22:26.760 --> 0:22:30.800 the chaos of the interstellar space outside of our Solar System, 0:22:31.000 --> 0:22:34.240 Jupiter acts as a huge defensive guard for our planet. 0:22:34.800 --> 0:22:37.919 When asteroids or comets or other flotsam and jetsam bent 0:22:38.000 --> 0:22:42.600 on destruction in oer our Solar System, Jupiter's extraordinary gravitational 0:22:42.680 --> 0:22:46.200 pull draws them into its orbit and slingshots them out 0:22:46.320 --> 0:22:49.880 back into space. Without Jupiter to run interference for Earth, 0:22:50.480 --> 0:22:53.400 it would have a steady diet of life ending bombardments 0:22:53.440 --> 0:22:59.520 from space. So thanks Jupiter. This is astronomer Donald brown Lee. 0:23:00.040 --> 0:23:01.520 He's one of the guys who came up with the 0:23:01.600 --> 0:23:08.600 rare Earth hypothesis. Jupers are actually pretty rare uh planets 0:23:09.480 --> 0:23:13.359 and um uh so uh in terms of rare Earth. 0:23:13.440 --> 0:23:16.040 You know whether it was juper is good or bad. 0:23:16.200 --> 0:23:20.520 Typical planet as systems probably don't have jupers. Our moon, too, 0:23:20.560 --> 0:23:23.399 seems to have played a number of factors and fostering 0:23:23.440 --> 0:23:28.080 life on Earth. Our moon's pretty unusual itself as far 0:23:28.119 --> 0:23:30.960 as moons go. It's enormous. It's about one point to 0:23:31.160 --> 0:23:33.880 percent the mass of the Earth and doesn't sound like much. 0:23:34.200 --> 0:23:37.240 But other planets moons like Phobos and Demos, which or 0:23:37.240 --> 0:23:40.880 a bit Mars, are closer to asteroids in size. Our 0:23:40.960 --> 0:23:44.320 moon more resembles a small planet, and because it's so big, 0:23:44.600 --> 0:23:48.120 it has some very peculiar effects on Earth. For one, 0:23:48.160 --> 0:23:52.120 it stabilizes our planet. The Earth doesn't sit upright as 0:23:52.119 --> 0:23:55.480 it spins around on its axis. It's tilted actually at 0:23:55.480 --> 0:23:59.159 about a twenty three degree angle. Because of this tilt, 0:23:59.280 --> 0:24:03.359 we have seas which create predictable variations in the temperature 0:24:03.440 --> 0:24:05.800 of regions on Earth over the course of the year. 0:24:06.920 --> 0:24:09.639 So when you think about the difference between winter and summer, 0:24:09.960 --> 0:24:12.359 you get a good idea how much variation a tilt 0:24:12.400 --> 0:24:15.199 can create. And add more of an angle to the 0:24:15.240 --> 0:24:18.280 tilt and the Earth and the temperature variations would become 0:24:18.320 --> 0:24:21.840 more severe. Since during winter or hemisphere would be further 0:24:21.880 --> 0:24:24.440 away than it is now from the Sun and much 0:24:24.480 --> 0:24:27.720