WEBVTT 00:00.000 --> 00:13.100 For example, the Earth's axial tilt, the angle of Earth's axis to the ecliptic, have very 00:13.100 --> 00:14.600 precise numbers. 00:14.600 --> 00:17.880 The universe is full of such specific values. 00:17.880 --> 00:20.720 Can you inform us about the fine-tuning in the universe? 00:20.720 --> 00:27.440 Yeah, when it comes to fine-tuning, there is sort of two levels of fine-tuning we want 00:27.440 --> 00:29.740 to make a distinction about. 00:29.740 --> 00:36.000 The first level of fine-tuning is we can ask the question, why do the laws of physics have 00:36.000 --> 00:37.860 to have the constants that they have? 00:37.860 --> 00:44.500 For example, the speed of light is 300 million, 3 times 10 to the 8 meters per second. 00:44.500 --> 00:49.080 So we can ask the question, okay, it had to be some value, maybe it would have been 2, 00:49.080 --> 00:52.060 you know, it could have been 2 times 10 to the 8 meters per second. 00:52.060 --> 00:58.560 Maybe it could have been 4, and is it, you know, we just happen to have 3, is that maybe 00:58.560 --> 01:00.240 not very special. 01:00.240 --> 01:02.120 It turns out it is special. 01:02.120 --> 01:08.040 It turns out you cannot deviate from 3 times 10 to the 8 meters per second very far before 01:08.040 --> 01:14.820 the conditions for life in the universe are not favorable. 01:14.820 --> 01:15.820 That is one example. 01:15.820 --> 01:18.180 The gravitational constant is another one. 01:18.180 --> 01:25.560 If the gravitational constant is too strong or too weak, it has very big effect on the formation 01:25.560 --> 01:27.400 of planets. 01:27.400 --> 01:33.660 There are forces inside the nucleus, the strong nuclear force and the weak nuclear force. 01:33.660 --> 01:38.360 Those forces, those parameters are also fine tuned. 01:38.360 --> 01:48.900 The sun is powered by a nuclear process where hydrogen and helium and beryllium and carbon 01:48.900 --> 01:54.240 and oxygen are formed in a few theories of nuclear interactions. 01:54.240 --> 01:58.820 It turns out that these energy levels are well connected, well matched to each other to make 01:58.820 --> 01:59.820 this happen. 01:59.820 --> 02:04.360 If they were just a little bit different, there would be no production of oxygen, for example, 02:04.360 --> 02:06.980 or very little production of oxygen. 02:06.980 --> 02:13.760 And so what we find is that the universe is very fine tuned in terms of the constants of 02:13.760 --> 02:14.760 nature. 02:14.760 --> 02:21.220 Those things that are expected to be the same all over the universe, but the value itself 02:21.220 --> 02:23.700 is a very special value. 02:23.700 --> 02:27.380 And the value is conducive to life in the universe. 02:27.380 --> 02:32.400 And that's the fine tuning of the parameters of the universe. 02:32.400 --> 02:39.500 But even in a universe that is so spectacularly fine tuned, as ours seems to be, extremely fine 02:39.500 --> 02:44.880 tuned, even when you have this kind of a universe, you can ask the question, how easy is it? 02:44.880 --> 02:50.460 How expected is it to have a planet like the Earth in this kind of universe? 02:50.460 --> 02:54.580 Can you be talking about, well, what are the processes that produce a planet? 02:54.580 --> 02:56.840 You know, there is a protoplanetary disk. 02:56.840 --> 03:00.340 There is a, you know, aggregation of materials. 03:00.340 --> 03:02.340 There is the formation of the planet. 03:02.340 --> 03:10.020 There is the bombardment that occurs because of the material in the universe, in the protoplanetary 03:10.020 --> 03:11.020 disk. 03:11.020 --> 03:13.620 Then there is the stellar formation that is going on. 03:13.620 --> 03:15.820 What kind of star are you forming? 03:15.820 --> 03:20.820 And it turns out that those conditions are also rare. 03:20.820 --> 03:27.500 In other words, even if you have a very friendly universe like ours, exceedingly well designed 03:27.500 --> 03:33.540 universe as ours, even then, when you ask the question, the laws that are operating in 03:33.540 --> 03:38.560 this universe, would they easily produce many, many Earths? 03:38.560 --> 03:42.460 Like if we go to the next star, are we going to find another Earth? 03:42.460 --> 03:46.800 Well, we have a very good understanding now of what are the conditions and what does it 03:46.800 --> 03:49.300 mean when we say an Earth? 03:49.300 --> 03:52.760 First we want a terrestrial planet, for example. 03:52.760 --> 03:57.220 In our own solar system, the Earth is a terrestrial planet, meaning it has rock, it's rocky. 03:57.220 --> 04:00.060 It has water, but it has rocks. 04:00.060 --> 04:03.320 But if I go to Jupiter, it's not that kind of a planet. 04:03.320 --> 04:09.380 If I go, you know, if you arrive at Jupiter, it is just a gas and the pressure builds up very 04:09.380 --> 04:14.480 rapidly as you descend into the gas, completely unfriendly to life. 04:14.480 --> 04:18.940 So you need a terrestrial planet, you need water, but you don't want too much water because 04:18.940 --> 04:24.980 you have to have those interfaces between land and water where the water thickness is 04:24.980 --> 04:36.640 small enough that there is a combination of moisture and sunlight that penetrates the water to keep 04:36.640 --> 04:37.820 the warm waters. 04:37.820 --> 04:43.320 That much of the food production in the sea occurs in the places where water is touching 04:43.320 --> 04:44.320 the land. 04:44.320 --> 04:49.320 When you go really deep, there's not enough sunlight in the deep to produce abundant life, 04:49.320 --> 04:51.100 essentially. 04:51.100 --> 04:56.220 And then you can ask, you know, what does it take to have a climate that is stable? 04:56.220 --> 05:02.740 And the Earth's axial tilt gives us the seasons, but it also is an axial tilt that is not doing 05:02.740 --> 05:05.200 this as we go around. 05:05.200 --> 05:07.680 This is not the case for our planetary neighbors. 05:07.680 --> 05:11.860 Mars, for example, does not have a stable axial tilt. 05:11.860 --> 05:14.580 Where does this axial tilt stability come from? 05:14.580 --> 05:17.980 We have this very large moon relative to the Earth. 05:17.980 --> 05:24.820 Our moon is actually part of our, the Earth-Moon system is actually part of a system that is 05:24.820 --> 05:29.520 really designed to keep us having a stable climate. 05:29.520 --> 05:31.440 So the moon is doing multiple things for us. 05:31.440 --> 05:33.320 It's not just there randomly. 05:33.320 --> 05:35.140 It has a job. 05:35.140 --> 05:36.860 We can talk about Jupiter. 05:36.860 --> 05:43.120 Jupiter has a job relative to the Earth, and the job is that Jupiter's mass is so high 05:43.120 --> 05:44.940 that it absorbs to itself. 05:44.940 --> 05:50.860 Its gravitational attraction essentially sweeps up and cleans up the debris in the inner 05:50.860 --> 05:52.400 solar system. 05:52.400 --> 05:58.400 For example, I was much younger, maybe 20 years ago, there was a comet that was viewable 05:58.400 --> 06:00.800 in the sky, the Shoemaker-Levy comet. 06:00.800 --> 06:01.920 And everybody was excited. 06:01.920 --> 06:03.300 It was in the news. 06:03.300 --> 06:06.560 And people would get out their telescopes and watch this comet. 06:06.560 --> 06:09.120 Well, eventually what happened to this comet? 06:09.120 --> 06:10.780 It crashed into Jupiter. 06:10.780 --> 06:12.420 And that's what Jupiter does. 06:12.420 --> 06:16.900 We are thankful to Jupiter because things crash into it. 06:16.900 --> 06:20.940 Asteroids and near-Earth objects that could potentially and sometimes do, you know, collide 06:20.940 --> 06:21.940 with the Earth. 06:21.940 --> 06:27.380 You know, the fact that they don't do that much more often is because of a massive gas 06:27.380 --> 06:34.900 giant, which Jupiter is, at a five astronomical unit orbit with very small eccentricity. 06:34.900 --> 06:40.700 What I mean by eccentricity is that the orbit of Jupiter is almost a perfect circle. 06:40.700 --> 06:45.180 If Jupiter had high eccentricity orbit, it would be an elliptical orbit. 06:45.180 --> 06:46.760 What does that mean? 06:46.760 --> 06:49.660 That means that here is the Earth orbit of the Earth. 06:49.660 --> 06:55.460 Now, orbit of Jupiter, if it comes in and out over a very long period of time, over millions 06:55.460 --> 06:59.660 of years, it can collide with the Earth and send us out of the solar system. 06:59.660 --> 07:05.140 This never happens because Jupiter's orbit is so well-behaved. 07:05.140 --> 07:13.620 So, high mass gas giant at a large, low eccentricity orbit is what we have with Jupiter, which is 07:13.620 --> 07:15.620 perfectly made for our convenience. 07:15.620 --> 07:21.220 And so, it is, you know, there's this principle that is supposed to be there that, what's called 07:21.220 --> 07:25.340 the principle of mediocrity, that says that we are nothing special. 07:25.340 --> 07:28.580 We shouldn't have this high view of ourselves. 07:28.580 --> 07:36.100 You know, but what we find is, in reality, that things are extremely well-matched to our 07:36.100 --> 07:37.100 health. 07:37.100 --> 07:39.980 You know, our planet is well-protected. 07:39.980 --> 07:42.440 We have the Moon doing what it's doing. 07:42.440 --> 07:43.680 We have the Earth. 07:43.680 --> 07:45.200 The Earth has a magnetosphere. 07:45.200 --> 07:49.480 The magnetosphere is protecting us from the solar activity. 07:49.480 --> 07:52.060 So the list is a very long list. 07:52.060 --> 07:57.780 And so there is, one could go a very long time talking about all the things that are true, 07:57.780 --> 08:00.100 in this case, you know, about the Earth's survivability. 08:00.100 --> 08:21.480 Absolutely.