1 00:00:00,000 --> 00:00:24,820 Good afternoon. It's an honor to be here with you today. We live in an era where the dominant 2 00:00:24,820 --> 00:00:32,760 scientific worldview is based on materialism and metaphysics that holds aspects of this 3 00:00:32,760 --> 00:00:40,840 physical world such as matter and energy as self-existent. From the physical universe and 4 00:00:40,840 --> 00:00:48,220 its laws, this view claims, we can explain everything we see and everything we experience. 5 00:00:48,220 --> 00:00:54,320 The material universe is sufficient to explain the nature of all that exists and if that 6 00:00:54,320 --> 00:01:00,960 is true, then in the words of the late Stephen Hawking, science can explain the universe 7 00:01:00,960 --> 00:01:08,160 without the need for a creator. This or some version of this view is very common in our 8 00:01:08,160 --> 00:01:16,220 day, particularly in academic circles. Yet this view leaves many questions unanswered. 9 00:01:16,220 --> 00:01:23,220 For example, what is the nature of consciousness? What is the origin of morality? Does it even 10 00:01:23,220 --> 00:01:32,820 exist? What about love or mercy? Are these illusions? Are they simply electrochemical impulses? Did 11 00:01:32,820 --> 00:01:40,280 they simply arise as encoded reactionary patterns in our brains through evolution? If so, are 12 00:01:40,280 --> 00:01:48,380 moral principles simply reducible to mathematics and statistics? And finally, given these questions, 13 00:01:48,380 --> 00:01:55,380 a proponent of materialism lived their life consistently with their worldview? While these profound 14 00:01:55,380 --> 00:02:04,060 questions remain unanswered, materialists use ancillary arguments in support of their view. One such 15 00:02:04,060 --> 00:02:10,140 argument that I want to examine here is the appeal to mediocrity, sometimes called the Copernican 16 00:02:10,140 --> 00:02:20,620 Principle. To explain what I mean, consider the story of the Pale Blue Dot. In his book, The Pale 17 00:02:20,620 --> 00:02:28,220 Blue Dot, the late astronomer Carl Sagan recounts an event that occurred in the course of NASA's 18 00:02:28,220 --> 00:02:38,140 Voyager 1 mission. In 1990, 12 years after the launch of Voyager 1, the spacecraft had left the outer planets of the 19 00:02:38,140 --> 00:02:47,180 solar system. And on February 14th, it was commanded to turn around and take a family portrait of the 20 00:02:47,180 --> 00:02:54,380 planets in the solar system it was leaving forever behind. When the images were transmitted back, NASA 21 00:02:54,380 --> 00:03:02,140 scientists and engineers were having difficulty finding the Earth. Eventually, they found it as a pale blue dot 22 00:03:02,140 --> 00:03:08,540 near a shaft of light that was entering the camera, reflecting from some point on the spacecraft. 23 00:03:09,180 --> 00:03:14,940 And about this picture, Carl Sagan had this to say. Because of the reflection of sunlight, 24 00:03:15,900 --> 00:03:21,580 the Earth seems to be sitting in a beam of light as if there was some special significance to this small 25 00:03:21,580 --> 00:03:30,220 world. But it's just an accident of geometry and optics. Our posturings, our imagined self-importance, 26 00:03:30,220 --> 00:03:36,620 the illusion that we hold some privileged position in the universe are challenged by this point of pale 27 00:03:36,620 --> 00:03:44,780 light. Our planet is a lonely speck in the great enveloping cosmic dark. As you can sense here, 28 00:03:45,420 --> 00:03:50,620 this is actually not a scientific statement, but a philosophical, actually a theological one. 29 00:03:51,740 --> 00:03:56,140 But the claim is not supported by all the science that we've learned over the last few hundred years, 30 00:03:56,140 --> 00:04:02,460 in fact. In this talk, I would like to examine the assertions of this so-called Copernican principle 31 00:04:03,900 --> 00:04:09,660 in the light of modern science, and in particularly my field, which is extrasolar planets or exoplanets. 32 00:04:11,100 --> 00:04:15,660 Before we discuss exoplanets, let's take a brief historical look. 33 00:04:17,500 --> 00:04:23,980 It was Aristotle who, 2400 years ago, argued for a geocentric model of the universe. 34 00:04:23,980 --> 00:04:31,020 He envisaged the concentric set of crystalline spheres in which the heavenly bodies resided. 35 00:04:31,820 --> 00:04:39,100 Most nearby was the moon, then Venus, actually Mercury, then Venus and Mars, and then Jupiter and 36 00:04:39,100 --> 00:04:46,300 Saturn. Further out were the firmament, which are the stars, and these were all sent into motion by a 37 00:04:46,300 --> 00:04:53,580 prime mover. Aristotle said reason and common experience confirmed this view and no one doubted it. 38 00:04:53,980 --> 00:05:00,220 But there was problems with this simple view. One was the retrograde motion of the planets. 39 00:05:00,860 --> 00:05:06,700 For example, if you look in the night sky, look at Mars, which comes near us every two years. It 40 00:05:06,700 --> 00:05:11,500 comes to a point called opposition, which is the point on the sky opposite to the direction of the 41 00:05:11,500 --> 00:05:16,940 sun at that time. And if you watch its location relative to the background stars, you would notice 42 00:05:16,940 --> 00:05:22,540 a retrograde motion. Over the course of a few months, you see the planet moving one direction, 43 00:05:23,180 --> 00:05:28,300 then backwards, and then forward again in the same direction relative to the stars. 44 00:05:28,940 --> 00:05:34,060 This was difficult to explain in the basic geocentric view of Aristotle. 45 00:05:35,340 --> 00:05:40,780 500 years after Aristotle, in his great work called the Almagest, 46 00:05:40,780 --> 00:05:48,460 Ptolemy provided an explanation. He agreed with Aristotle that the perfect heavenly bodies have 47 00:05:48,460 --> 00:05:54,620 to have perfect motion, which meant they were going in circles. But the planets are actually 48 00:05:54,620 --> 00:05:59,980 traveling in smaller circles called epicycles, and the epicycles are centered on something he called 49 00:05:59,980 --> 00:06:07,980 deferreds, which in turn are centered on the earth. In this way, the planets can have retrograde motion. 50 00:06:08,780 --> 00:06:13,820 By setting the diameters and rotation rates just right, Ptolemy was able to make very accurate 51 00:06:13,820 --> 00:06:22,460 predictions of the locations of the planets. So good, in fact, that for the next 14 centuries, there was no rival to this picture. 52 00:06:22,460 --> 00:06:26,460 It wasn't until the 16th century 53 00:06:26,460 --> 00:06:35,100 that a serious alternative was proposed. And here it was Nicholas Copernicus, who in his own magnificent work, 54 00:06:35,100 --> 00:06:39,100 called On the Revolutions of the Heavenly Bodies, 55 00:06:39,100 --> 00:06:47,180 detailed a much more elegant system, the sun-centered or heliocentric system. The earth, he suggested, 56 00:06:47,180 --> 00:06:52,140 was not the center of the universe, and the heavenly bodies do not all revolve around the central point. 57 00:06:53,100 --> 00:07:00,620 With these and a few other axioms, he was able to explain the same observations more elegantly and simply. 58 00:07:02,380 --> 00:07:08,700 But it goes on further. In the 20th century, it was the astronomer Harlow Shapley of Harvard University 59 00:07:08,700 --> 00:07:16,460 who discovered that the sun is not at the center of our galaxy, which is called the Milky Way. 60 00:07:17,020 --> 00:07:20,060 He did this by measuring the locations of globular clusters 61 00:07:21,420 --> 00:07:28,220 on the sky, including their distances. Globular clusters are many galaxies with hundreds of thousands of stars. 62 00:07:30,540 --> 00:07:37,180 Shapley noticed that they're orbiting an area of our galaxy that is many thousands of light years from us. 63 00:07:37,900 --> 00:07:46,460 So he famously concluded, the solar system is off-center, that means we are off-center, and consequently man is too. 64 00:07:48,220 --> 00:07:55,020 So you see this pattern. Copernicus showed us that the earth is not at the center of the solar system. 65 00:07:55,900 --> 00:08:00,380 Then Shapley showed us that the sun is not at the center of the galaxy. 66 00:08:00,380 --> 00:08:08,860 And later, though I didn't mention it earlier, Edwin Hubble discovered that the Milky Way is only one of hundreds of billions of galaxies. 67 00:08:10,060 --> 00:08:13,580 Pointing to these observations, this so-called Copernican principle 68 00:08:13,580 --> 00:08:24,460 seems to show us that man does not hold a central position in the universe, and by extension, it must be true that we are not here for a purpose. 69 00:08:25,100 --> 00:08:32,140 The claim seems to be well supported when I express it as I just did, but the claim gets some of the history wrong. 70 00:08:32,140 --> 00:08:39,660 For example, neither Copernicus nor Galileo would consider Earth's removal from the center a demotion. 71 00:08:40,620 --> 00:08:48,020 But also, the claim actually completely misses much of what we've learned in the last century about habitable planets. 72 00:08:48,020 --> 00:08:53,460 These are planets where life could at least survive if placed there. 73 00:08:54,500 --> 00:08:59,540 So now, we consider the question, what is a habitable planet? 74 00:09:00,420 --> 00:09:02,340 What do we need for a habitable planet? 75 00:09:02,900 --> 00:09:13,700 There are many requirements, but at a minimum, a habitable planet must be a terrestrial planet that support complex carbon and water-based life. 76 00:09:13,700 --> 00:09:18,500 It needs to be a planet in what is called the circumstellar habitable zone. 77 00:09:19,540 --> 00:09:24,340 And finally, it needs to be a planetary system in the galactic habitable zone. 78 00:09:26,020 --> 00:09:35,380 The first requirement, mainly that it should be a terrestrial planet, meaning a rocky planet, is already limiting. 79 00:09:35,940 --> 00:09:39,780 This is because much of the matter in the universe consists of hydrogen and helium. 80 00:09:39,780 --> 00:09:47,280 It takes complex processes in the stars to generate the heavy elements that make up a planet that is rocky, like the Earth. 81 00:09:48,500 --> 00:09:52,080 Beyond being rocky, however, it must also have water. 82 00:09:52,580 --> 00:09:55,140 And these are just minimum conditions. 83 00:09:56,380 --> 00:09:58,580 There is also the location of the planet. 84 00:09:59,780 --> 00:10:04,260 Their circumstellar habitable zone is defined as that region around the star 85 00:10:04,260 --> 00:10:09,740 where water could be liquid at some part of a rocky planet that is situated there. 86 00:10:10,860 --> 00:10:15,320 Since the surface heat of a planet is from the sunlight it absorbs, 87 00:10:15,720 --> 00:10:19,620 around a cold star, the habitable zone is close in. 88 00:10:20,220 --> 00:10:23,440 While around a hot star, it has to be further out. 89 00:10:23,440 --> 00:10:28,860 If a planet is located closer to its host star than the inner edge of the habitable zone, 90 00:10:29,340 --> 00:10:36,360 a runaway greenhouse effect will raise its temperatures, 91 00:10:36,960 --> 00:10:42,800 causing the water to evaporate into the atmosphere and be carried away by the solar wind, 92 00:10:42,900 --> 00:10:44,340 making the planet dehydrated. 93 00:10:45,620 --> 00:10:47,980 At the other extreme of the habitable zone, 94 00:10:47,980 --> 00:10:52,700 there will be precipitation in terms of ice and snow, 95 00:10:52,920 --> 00:10:57,360 and that will make the planet absorb less of the starlight and become colder still. 96 00:10:58,120 --> 00:11:01,120 And this leads to an uninhabitable snowball planet. 97 00:11:01,820 --> 00:11:05,680 In our solar system, only the Earth is inside the habitable zone. 98 00:11:06,540 --> 00:11:09,300 So the planet has to be the right distance from the star. 99 00:11:10,760 --> 00:11:12,080 As for the star, 100 00:11:13,080 --> 00:11:16,340 are all stars equally suitable? 101 00:11:16,340 --> 00:11:18,700 It turns out the answer is no. 102 00:11:19,580 --> 00:11:24,020 Many astronomy textbooks refer to our sun as an average star. 103 00:11:24,660 --> 00:11:27,080 This is true only in a limited sense. 104 00:11:27,780 --> 00:11:30,820 There are certainly stars that are more hot than our star, 105 00:11:30,940 --> 00:11:35,000 and there are stars that are cooler than our star, than our sun. 106 00:11:35,980 --> 00:11:41,260 But the sun is actually within the 10% most massive stars in the Milky Way. 107 00:11:41,260 --> 00:11:46,120 And in fact, stars that are much more massive than the sun 108 00:11:46,120 --> 00:11:50,440 are actually too unstable to be producing habitable zones. 109 00:11:51,640 --> 00:11:54,400 And then stars that are less massive than our star 110 00:11:54,400 --> 00:11:57,760 have habitable zones that are cooler, 111 00:11:58,000 --> 00:12:00,420 so they have habitable zones that are closer in, 112 00:12:01,280 --> 00:12:03,940 requiring that close, tight-in habitable zone. 113 00:12:03,940 --> 00:12:07,640 But then when a planet gets that close to a star, 114 00:12:09,040 --> 00:12:11,680 it suffers from an effect called tidal locking. 115 00:12:12,280 --> 00:12:15,400 So for the cool stars, the tidal locking problem occurs. 116 00:12:16,000 --> 00:12:18,600 The spin of the planet becomes equal in duration 117 00:12:18,600 --> 00:12:20,340 with its orbital period, 118 00:12:20,520 --> 00:12:21,280 and as a result, 119 00:12:21,760 --> 00:12:25,180 one side of the planet becomes permanently day, 120 00:12:25,620 --> 00:12:28,100 while the other side becomes permanently night. 121 00:12:28,100 --> 00:12:30,860 The day side becomes hot, 122 00:12:31,340 --> 00:12:33,720 and the moisture is transported to the other side, 123 00:12:34,660 --> 00:12:37,840 where it snows down and stays permanently frozen. 124 00:12:39,200 --> 00:12:41,760 Tidally locked planets are poor choices for life. 125 00:12:42,480 --> 00:12:46,420 Cool stars also have more frequent, life-threatening events, 126 00:12:46,560 --> 00:12:49,120 these bursts called coronal mass ejections. 127 00:12:49,920 --> 00:12:52,760 In the end, only 4% of the stars 128 00:12:52,760 --> 00:12:55,860 are main-sequence G stars, like our sun. 129 00:12:55,860 --> 00:13:01,260 And then what about the location of the star within the galaxy? 130 00:13:01,920 --> 00:13:06,300 To get heavy elements from which a rocky planet can form, 131 00:13:06,720 --> 00:13:09,160 you have to be closer to the center of the galaxy. 132 00:13:10,020 --> 00:13:11,900 On the other hand, if you get too close, 133 00:13:12,300 --> 00:13:15,200 life-threatening events like supernovae become more frequent, 134 00:13:15,980 --> 00:13:18,500 as supernovae can sterilize life 135 00:13:18,500 --> 00:13:20,240 within many light years around it. 136 00:13:20,980 --> 00:13:23,120 These are more frequent not only near the center, 137 00:13:23,260 --> 00:13:24,980 but also within the spiral arms. 138 00:13:24,980 --> 00:13:27,920 So the planetary system, to stay safe, 139 00:13:28,000 --> 00:13:30,440 needs to be at the right radius 140 00:13:30,440 --> 00:13:32,720 from the center of the galaxy. 141 00:13:33,380 --> 00:13:35,780 Not too far, not too close, 142 00:13:35,900 --> 00:13:37,320 and not within a spiral arm. 143 00:13:38,260 --> 00:13:40,020 And what about the galaxy itself? 144 00:13:40,840 --> 00:13:43,740 Here, too, we find ourselves in a privileged place. 145 00:13:44,500 --> 00:13:46,140 Our galaxy, the Milky Way, 146 00:13:46,840 --> 00:13:51,160 is among the 3% most massive galaxies 147 00:13:51,160 --> 00:13:53,720 in the nearby universe. 148 00:13:54,660 --> 00:13:56,620 Because it was so massive, 149 00:13:56,620 --> 00:14:00,500 it was able to accumulate heavy elements more quickly, 150 00:14:01,460 --> 00:14:04,060 and planet formation started here earlier, 151 00:14:04,600 --> 00:14:06,660 in the Milky Way. 152 00:14:08,240 --> 00:14:10,520 Almost two-thirds of the age of the universe 153 00:14:10,520 --> 00:14:14,020 had gone by by the time there was enough material 154 00:14:14,020 --> 00:14:16,480 that a planet like the Earth could be formed. 155 00:14:16,480 --> 00:14:18,080 So there was a brief window. 156 00:14:19,520 --> 00:14:22,360 There are, in fact, many parameters 157 00:14:22,360 --> 00:14:24,300 that we could discuss. 158 00:14:24,440 --> 00:14:25,560 The list is very long. 159 00:14:26,360 --> 00:14:28,740 Very briefly, at least we need a planet 160 00:14:28,740 --> 00:14:29,840 with a magnetosphere. 161 00:14:30,720 --> 00:14:32,500 Our magnetosphere on the Earth 162 00:14:32,500 --> 00:14:34,220 protects us from the cosmic rays 163 00:14:34,220 --> 00:14:36,000 and occasional solar bursts 164 00:14:36,000 --> 00:14:39,160 that would otherwise dehydrate our atmosphere. 165 00:14:39,880 --> 00:14:41,180 We need a large moon. 166 00:14:41,180 --> 00:14:44,420 The Earth's moon is unusually large 167 00:14:44,420 --> 00:14:46,120 relative to the Earth's size. 168 00:14:46,880 --> 00:14:49,120 This is important because our massive moon 169 00:14:49,120 --> 00:14:52,580 stabilizes the axial tilt of the Earth's rotation. 170 00:14:53,700 --> 00:14:56,500 And that helps to stabilize our climate. 171 00:14:57,660 --> 00:15:00,200 To support large living beings like animals 172 00:15:00,200 --> 00:15:02,220 and like us humans, 173 00:15:02,700 --> 00:15:05,460 a planet needs to have high enough oxygen content. 174 00:15:06,380 --> 00:15:08,160 But then if it has too much oxygen, 175 00:15:08,700 --> 00:15:10,600 there will be rapid fire growth. 176 00:15:10,600 --> 00:15:13,300 So there needs to be a neutral gas as well 177 00:15:13,300 --> 00:15:15,160 to avoid devastating fires. 178 00:15:16,580 --> 00:15:19,260 Our oxygen-nitrogen-dominated atmosphere 179 00:15:19,260 --> 00:15:21,200 is perfect balance of these requirements. 180 00:15:22,140 --> 00:15:24,460 Finally, the Earth's planetary neighbors 181 00:15:24,460 --> 00:15:26,940 play important roles. 182 00:15:27,820 --> 00:15:30,580 Jupiter, the largest planet in our solar system, 183 00:15:30,680 --> 00:15:32,820 has 300 times the mass of the Earth. 184 00:15:33,380 --> 00:15:35,140 It has a near circular orbit 185 00:15:35,140 --> 00:15:39,060 and orbits five times farther from the Sun 186 00:15:39,060 --> 00:15:40,180 than the Earth. 187 00:15:40,720 --> 00:15:42,700 This combination of being massive 188 00:15:42,700 --> 00:15:45,680 and having a large circular orbit 189 00:15:45,680 --> 00:15:49,180 makes Jupiter a benevolent agent 190 00:15:49,180 --> 00:15:50,220 in the solar system, 191 00:15:51,040 --> 00:15:52,540 absorbing to itself, 192 00:15:52,680 --> 00:15:55,440 like a massive vacuum cleaner, 193 00:15:56,640 --> 00:15:58,000 comets and asteroids 194 00:15:58,000 --> 00:16:00,440 that could potentially threaten life on the Earth. 195 00:16:00,920 --> 00:16:02,840 Many of these eventually crash 196 00:16:02,840 --> 00:16:04,860 into Jupiter and Saturn. 197 00:16:06,000 --> 00:16:08,680 We now move from theory to experiment. 198 00:16:09,120 --> 00:16:10,520 Over the last two decades, 199 00:16:11,340 --> 00:16:13,840 there has been many discoveries 200 00:16:13,840 --> 00:16:15,120 of exoplanets, 201 00:16:15,240 --> 00:16:16,500 planets around other stars. 202 00:16:16,860 --> 00:16:18,120 What have we learned from them? 203 00:16:18,740 --> 00:16:19,860 First, very briefly, 204 00:16:20,380 --> 00:16:21,860 I'd like to point out 205 00:16:21,860 --> 00:16:22,980 some of the techniques. 206 00:16:23,640 --> 00:16:25,440 In the first very important technique 207 00:16:25,440 --> 00:16:26,860 called radial velocity, 208 00:16:27,480 --> 00:16:29,660 the planet is not detected directly, 209 00:16:29,660 --> 00:16:31,720 but the wobble of the star 210 00:16:31,720 --> 00:16:33,900 in reaction to the pull of the planet 211 00:16:33,900 --> 00:16:36,180 is detected from the red and blue shifts 212 00:16:36,180 --> 00:16:37,980 of the star's spectrum. 213 00:16:39,220 --> 00:16:41,240 Another highly successful technique 214 00:16:41,240 --> 00:16:42,100 called transit 215 00:16:42,100 --> 00:16:45,200 looks for the very small drop in the light 216 00:16:45,200 --> 00:16:48,720 from a star when a planet transits, 217 00:16:49,200 --> 00:16:51,400 when the planet comes in front of the star. 218 00:16:53,420 --> 00:16:55,740 A third one that is special to me 219 00:16:55,740 --> 00:16:57,800 because this is the area in which I work 220 00:16:57,800 --> 00:17:00,700 is one of direct imaging 221 00:17:00,700 --> 00:17:02,260 where a technique is used 222 00:17:02,260 --> 00:17:05,840 to actually image the planetary system directly. 223 00:17:06,440 --> 00:17:08,680 Here you see a montage of many years 224 00:17:08,680 --> 00:17:11,200 of images of an exosystem 225 00:17:11,200 --> 00:17:12,800 and the planets growing around that. 226 00:17:15,240 --> 00:17:17,240 Now, what have we learned from these? 227 00:17:17,440 --> 00:17:19,360 From the radial velocity measurements, 228 00:17:20,040 --> 00:17:22,240 we've discovered one important lesson 229 00:17:22,240 --> 00:17:25,180 that Jupiters, like our Jupiter, 230 00:17:25,440 --> 00:17:26,440 are very uncommon. 231 00:17:27,640 --> 00:17:29,340 Most gas giant planets, 232 00:17:29,460 --> 00:17:30,480 and Jupiter and Saturn 233 00:17:30,480 --> 00:17:32,560 are examples of gas giant planets, 234 00:17:33,060 --> 00:17:35,860 have elliptical rather than circular orbits, 235 00:17:35,980 --> 00:17:36,680 it turns out. 236 00:17:37,560 --> 00:17:39,580 Over time, the elliptical orbit 237 00:17:39,580 --> 00:17:42,100 means they migrate towards the star, 238 00:17:42,580 --> 00:17:45,960 eventually settling from an elliptical orbit 239 00:17:45,960 --> 00:17:47,180 to a circular orbit 240 00:17:47,180 --> 00:17:48,820 very tightly around the star. 241 00:17:48,820 --> 00:17:50,480 Along the way, 242 00:17:50,940 --> 00:17:54,820 they can knock off other planets 243 00:17:54,820 --> 00:17:55,800 in the solar system. 244 00:17:55,940 --> 00:17:57,800 They are very dangerous when they do that. 245 00:17:58,260 --> 00:18:00,520 These kinds of planets are called hot Jupiters, 246 00:18:00,720 --> 00:18:01,960 and they're very dangerous. 247 00:18:05,300 --> 00:18:06,700 The other technique 248 00:18:06,700 --> 00:18:08,340 was the transit technique, 249 00:18:08,760 --> 00:18:10,660 and it has also provided us 250 00:18:10,660 --> 00:18:12,580 a picture of thousands 251 00:18:12,580 --> 00:18:14,160 of other planetary systems. 252 00:18:15,000 --> 00:18:17,140 But here, too, the results show 253 00:18:17,140 --> 00:18:19,080 that in the great majority 254 00:18:19,080 --> 00:18:21,460 of the planets discovered, 255 00:18:21,760 --> 00:18:23,680 they are closer to their host star 256 00:18:23,680 --> 00:18:26,060 than even our innermost planet, Mercury. 257 00:18:27,260 --> 00:18:28,460 So our solar system, 258 00:18:28,560 --> 00:18:29,420 by that comparison, 259 00:18:29,680 --> 00:18:31,140 is exceedingly unusual. 260 00:18:32,540 --> 00:18:34,580 So we see a large number of conditions 261 00:18:34,580 --> 00:18:37,660 are necessary for a life-hospitable planet. 262 00:18:38,360 --> 00:18:39,660 And when we look at the universe, 263 00:18:39,800 --> 00:18:41,500 we see that the usual condition, 264 00:18:42,080 --> 00:18:43,340 the usual situation, 265 00:18:43,340 --> 00:18:44,900 is that these conditions 266 00:18:44,900 --> 00:18:47,120 are not all present at the same time. 267 00:18:47,880 --> 00:18:48,820 In fact, one can make 268 00:18:48,820 --> 00:18:50,120 a statistical estimate 269 00:18:50,120 --> 00:18:51,560 of the expected rate 270 00:18:51,560 --> 00:18:52,920 following the approach 271 00:18:52,920 --> 00:18:55,060 of Frank Drake from the 60s, 272 00:18:55,520 --> 00:18:57,540 where he used a very simple calculation, 273 00:18:58,100 --> 00:18:58,860 and he estimated 274 00:18:58,860 --> 00:19:00,820 the number of planets in the Milky Way 275 00:19:00,820 --> 00:19:02,860 that could host advanced life, 276 00:19:02,940 --> 00:19:05,060 such as they could give us a radio signal. 277 00:19:06,020 --> 00:19:07,760 Considering a few conditions, 278 00:19:07,880 --> 00:19:09,880 he estimated that there should be 279 00:19:09,880 --> 00:19:11,460 on the order of a few million 280 00:19:11,460 --> 00:19:13,440 planetary systems in our galaxy 281 00:19:13,440 --> 00:19:15,220 that could send us a signal. 282 00:19:16,380 --> 00:19:17,900 But half a century later, 283 00:19:18,040 --> 00:19:19,740 the list of conditions 284 00:19:19,740 --> 00:19:21,360 are actually quite a bit more. 285 00:19:21,980 --> 00:19:23,280 And when you actually do 286 00:19:23,280 --> 00:19:25,080 the same type of calculation now, 287 00:19:25,180 --> 00:19:26,960 you expect much less than 288 00:19:26,960 --> 00:19:29,000 one in 10,000 Milky Ways 289 00:19:29,000 --> 00:19:30,200 where you could expect 290 00:19:30,200 --> 00:19:31,780 to see a planet like the Earth. 291 00:19:34,140 --> 00:19:35,800 So this isn't up to now. 292 00:19:35,900 --> 00:19:37,200 It's been an argument to say 293 00:19:37,200 --> 00:19:39,440 that the Earth is a very rare planet. 294 00:19:39,440 --> 00:19:43,260 But there is a yet more profound aspect 295 00:19:43,260 --> 00:19:44,680 to our existence here, 296 00:19:44,800 --> 00:19:45,940 and this is a notion 297 00:19:45,940 --> 00:19:47,220 of what is called 298 00:19:47,220 --> 00:19:48,340 the privileged planet. 299 00:19:48,840 --> 00:19:51,600 And this was first pointed out 300 00:19:51,600 --> 00:19:53,180 by astronomer Guillermo Gonzalez 301 00:19:53,180 --> 00:19:54,760 and philosopher Jay Richards. 302 00:19:55,460 --> 00:19:56,640 And their point was 303 00:19:56,640 --> 00:19:57,860 that the requirements 304 00:19:57,860 --> 00:19:59,100 for habitability 305 00:19:59,100 --> 00:20:01,480 appear to overall be coinciding 306 00:20:01,480 --> 00:20:02,660 with the requirements 307 00:20:02,660 --> 00:20:03,660 for discovery. 308 00:20:04,260 --> 00:20:04,900 That is, 309 00:20:04,960 --> 00:20:06,060 the same conditions 310 00:20:06,060 --> 00:20:08,760 that a planet should be habitable 311 00:20:08,760 --> 00:20:09,660 are all together 312 00:20:09,660 --> 00:20:11,100 what we would need 313 00:20:11,100 --> 00:20:12,800 for that habitable planet 314 00:20:12,800 --> 00:20:13,540 to be a place 315 00:20:13,540 --> 00:20:14,640 where intelligent beings 316 00:20:14,640 --> 00:20:15,280 could study 317 00:20:15,280 --> 00:20:16,860 and learn about the universe. 318 00:20:17,760 --> 00:20:18,880 An example of this 319 00:20:18,880 --> 00:20:19,620 that is beautiful 320 00:20:19,620 --> 00:20:21,000 is the example 321 00:20:21,000 --> 00:20:22,420 of the perfect eclipse. 322 00:20:23,100 --> 00:20:23,800 Did you know 323 00:20:23,800 --> 00:20:24,760 that the Earth, 324 00:20:25,420 --> 00:20:27,000 from the Earth's point of view, 325 00:20:27,140 --> 00:20:28,200 the moon on the sky 326 00:20:28,200 --> 00:20:29,740 and the sun on the sky 327 00:20:29,740 --> 00:20:31,500 are exactly the same diameter? 328 00:20:32,040 --> 00:20:32,920 And as a result, 329 00:20:33,060 --> 00:20:34,540 the Earth is the only place 330 00:20:34,540 --> 00:20:35,300 where we can have 331 00:20:35,300 --> 00:20:35,920 what is called 332 00:20:35,920 --> 00:20:37,520 perfect eclipses. 333 00:20:37,520 --> 00:20:39,220 If the moon was 334 00:20:39,220 --> 00:20:40,240 a little bit closer, 335 00:20:40,740 --> 00:20:41,500 it would not cover 336 00:20:41,500 --> 00:20:42,440 enough of the sun. 337 00:20:42,880 --> 00:20:44,240 If it was a little bit farther, 338 00:20:45,040 --> 00:20:45,940 if it was a little closer, 339 00:20:46,040 --> 00:20:47,000 it would cover too much 340 00:20:47,000 --> 00:20:48,040 and if it was a little farther, 341 00:20:48,160 --> 00:20:48,740 it would not cover 342 00:20:48,740 --> 00:20:49,500 enough of the sun. 343 00:20:50,000 --> 00:20:50,780 As it is, 344 00:20:50,860 --> 00:20:52,340 we have perfect eclipses 345 00:20:52,340 --> 00:20:53,640 and we can study 346 00:20:53,640 --> 00:20:54,800 aspects of the sun 347 00:20:54,800 --> 00:20:55,600 that were otherwise 348 00:20:55,600 --> 00:20:56,740 unavailable to us. 349 00:20:57,240 --> 00:20:57,820 For example, 350 00:20:58,000 --> 00:20:58,600 historically, 351 00:20:59,080 --> 00:21:00,240 it was from observing 352 00:21:00,240 --> 00:21:03,060 the spectra of the atmosphere 353 00:21:03,060 --> 00:21:03,860 of the sun 354 00:21:03,860 --> 00:21:05,640 during a perfect eclipse 355 00:21:05,640 --> 00:21:07,780 that astronomers first discovered 356 00:21:07,780 --> 00:21:08,920 that the sun 357 00:21:08,920 --> 00:21:10,280 is a hot ball of gas. 358 00:21:10,820 --> 00:21:11,980 It also enabled them 359 00:21:11,980 --> 00:21:13,220 to know 360 00:21:13,220 --> 00:21:14,880 what elements are present 361 00:21:14,880 --> 00:21:15,640 in the sun. 362 00:21:16,060 --> 00:21:16,680 This, in turn, 363 00:21:16,800 --> 00:21:17,560 opened the door 364 00:21:17,560 --> 00:21:19,200 for studying other stars. 365 00:21:19,980 --> 00:21:21,500 It was also during an eclipse 366 00:21:21,500 --> 00:21:23,580 that Einstein's theory 367 00:21:23,580 --> 00:21:24,260 of gravity, 368 00:21:24,580 --> 00:21:26,160 which eventually told us 369 00:21:26,160 --> 00:21:26,940 about the beginning 370 00:21:26,940 --> 00:21:27,780 of the universe, 371 00:21:28,920 --> 00:21:31,140 was put to its most famous test. 372 00:21:31,140 --> 00:21:32,680 The sun's mass 373 00:21:32,680 --> 00:21:33,760 bends the light 374 00:21:33,760 --> 00:21:34,760 from distant stars 375 00:21:34,760 --> 00:21:35,700 but the bending 376 00:21:35,700 --> 00:21:36,540 is so small 377 00:21:36,540 --> 00:21:37,480 that only stars 378 00:21:37,480 --> 00:21:39,340 seen very near the sun 379 00:21:39,340 --> 00:21:40,120 show an effect. 380 00:21:40,400 --> 00:21:41,440 But you can only see 381 00:21:41,440 --> 00:21:41,960 this effect 382 00:21:41,960 --> 00:21:43,240 during a perfect eclipse. 383 00:21:46,300 --> 00:21:48,400 Many of the other factors 384 00:21:48,400 --> 00:21:50,240 also facilitate discovery. 385 00:21:51,240 --> 00:21:51,860 But we're not, 386 00:21:52,020 --> 00:21:52,820 because we're not 387 00:21:52,820 --> 00:21:54,020 at the center of the galaxy, 388 00:21:55,360 --> 00:21:57,380 our night sky is dark. 389 00:21:57,480 --> 00:21:58,140 It's not bright. 390 00:21:58,220 --> 00:21:59,480 We can actually do astronomy. 391 00:21:59,480 --> 00:22:01,120 We also, remember, 392 00:22:01,260 --> 00:22:01,960 we said we need 393 00:22:01,960 --> 00:22:03,540 an oxygen-nitrogen atmosphere. 394 00:22:03,940 --> 00:22:05,340 Well, that's a clear atmosphere. 395 00:22:05,940 --> 00:22:06,800 By comparison, 396 00:22:07,340 --> 00:22:09,360 Venus has a carbon dioxide atmosphere 397 00:22:09,360 --> 00:22:10,120 which is opaque. 398 00:22:10,300 --> 00:22:11,280 You couldn't do astronomy 399 00:22:11,280 --> 00:22:12,320 from Venus. 400 00:22:13,600 --> 00:22:15,560 It's also 400 degrees Celsius 401 00:22:15,560 --> 00:22:16,680 on the surface of Venus. 402 00:22:17,020 --> 00:22:18,300 So it's not a good platform. 403 00:22:19,180 --> 00:22:20,520 The list of interconnected 404 00:22:20,520 --> 00:22:22,820 requirements for habitability 405 00:22:22,820 --> 00:22:24,540 and discovery is long. 406 00:22:25,100 --> 00:22:26,120 But the picture by now 407 00:22:26,120 --> 00:22:26,860 should be clear. 408 00:22:27,620 --> 00:22:28,500 There is abundant 409 00:22:28,500 --> 00:22:29,460 solid evidence 410 00:22:29,460 --> 00:22:31,240 that the world is designed 411 00:22:31,240 --> 00:22:33,080 and that we can infer 412 00:22:33,080 --> 00:22:34,520 as well 413 00:22:34,520 --> 00:22:35,780 that God wants us 414 00:22:35,780 --> 00:22:37,360 to study this world 415 00:22:37,360 --> 00:22:39,380 and to see its design 416 00:22:39,380 --> 00:22:40,680 and to realize 417 00:22:40,680 --> 00:22:42,340 the glory of its creator. 418 00:22:43,180 --> 00:22:44,440 So far from being 419 00:22:44,440 --> 00:22:46,460 a mere pale blue dot, 420 00:22:46,920 --> 00:22:48,160 our planet is not only 421 00:22:48,160 --> 00:22:49,540 made for supporting life, 422 00:22:49,880 --> 00:22:51,440 but it was also made 423 00:22:51,440 --> 00:22:52,660 to support the world. 424 00:22:52,660 --> 00:22:53,220 Thank you. 425 00:22:53,220 --> 00:22:53,280 Thank you. 426 00:22:53,280 --> 00:22:53,440 Thank you.