Episode Transcript
[00:00:04] Speaker A: ID the Future, a podcast about evolution and intelligent design.
Is our solar system unique and do we live on a privileged planet? I'm Casey Luskin with ID the Future and today we have on the show with us Guillermo Gonzalez, a research scientist at Telus One Scientific in Huntsville, Alabama. Guillermo is a fellow with Discovery Institute. He is well known as he is a co author of the book the Privileged How Our Place in the Cosmos is Designed for Discovery. He's made many important scientific contributions. He's authored nearly 90 scientific peer reviewed papers as well as a major college level astronomy textbook with Cambridge University Press. His work has led to the discovery of two new planets outside of our solar system and his research has been featured in Science, Nature and on the COVID of of Scientific American. We're here with Guillermo today talking about his most recent chapter that he's written a chapter in the volume Science and Faith and Dialogue published by the South African academic publisher Eosis. And Guillermo, your book chapter is titled Local Fine Tuning in Habitable Zones. In our recent podcast we discussed some elements of the circumstellar habitable zone which you defined and we wanted to come back and continue the conversation. So thank you for joining us once again here.
[00:01:24] Speaker B: Happy to be here.
[00:01:25] Speaker A: So on the previous podcast we talked a little bit about what is required to get an Earth like planet, a habitable planet in a solar system. But what about the star at the center of a solar system? How does this affect this idea of a circumstellar habitable zone? And would you say that there's anything special about our sun that allows Earth to be life friendly?
[00:01:45] Speaker B: Well, the discussion of the circumstellar habitable zone that people have had over the years has always assumed that, you know, you have something identical to our solar system, including an identical sun, and you just move the Earth around and what happens to it? Is it able to maintain liquid water on its surface? But you know, there are many other factors that you have to consider and one of these is the host star. And we have a host star we call the sun, which is actually not that common. Some people say that, oh, the Sun's just a typical star. It isn't. It's quite exceptional a number of ways. So first of all, it's among the 8% most massive stars that we see around us in the Milky Way. So it's a relatively rare star in its mass. Its composition, which has now been compared to other sun like stars, is also unusual. So the particular pattern of the chemical elements that we can measure with spectroscopy ranks around the 10% level in terms of its unusual pattern of abundances. So only about 1 in 10 stars, sun like stars, meaning a G dwarf, will have a composition as unusual as the Sun. In addition, it appears that its light output is unusually stable compared to other sun like stars at its age. So the sun was a rambunctious youngster in its youth. It was much more active and it had more flares and its light output was more variable. Over the history of the sun, it's quieted down. And this is true. We see this in other stars, different ages, sun like stars that are very young versus middle age or the same age as the Sun. We see that its activity quiets down over time. But even comparing the sun to other stars of its age, it appears to be more photometrically quiet than those, which is a good thing for us because the stability of its output is what leads to long term stability of our climate. And also these larger light variations are accompanied by violent outbursts like flares, coronal mass ejections and things like that, which can produce short lived increases in high energy radiation, which is dangerous for life. So our sun appears to be more quiet and well behaved than most sun like stars.
[00:04:03] Speaker A: So when, when Carl Sagan said I believe it was in cosmos, he said we live on a insignificant planet of a humdrum star lost in a galaxy tucked away in some forgotten corner universe. Our star really is not a humdrum star. It's not necessarily the, the only star that's like it out there, but it is certainly a minority, small percentage of stars would be like our star in, in the sense of it being quiet and its radiation output and all of its other properties that make it friendly for life.
[00:04:32] Speaker B: Absolutely right.
[00:04:33] Speaker A: So let's talk about our galaxy. What is the galactic habitable zone and what are some of the parameters that affect it?
[00:04:39] Speaker B: So the galactic habitable zone is this idea that not all places in the Milky Way galaxy that we inhabit are equally habitable, that some places are better for life or more likely to host a planet with life than others. Now, the galaxy varies in its properties quite a bit from place to place. It's got a really dense center, very high star density. We have a supermassive black hole at the center of the galaxy. And it's got what's called the bulge of stars, which is stars with mostly randomly oriented orbits. Now, as you move out, the disk, the flattened disk of the Milky Way dominates, which contains gas, dust and stars moving around in mostly circular orbits. Not, not, not. And mostly flattened or low inclination orbits. So It's. It resembles a solar system in a. Because the solar system is very flat.
The orbits of the planets have very little inclination relative to each other. They're orbiting the same direction. And they're mostly circular. So analogous to this, the disk of the galaxy is where we live. About halfway out from the center to the visible edge. And as you go out towards the edge, the star density declines. The star formation rate is lower. The supernova rate is lower. The interstellar material is lower. Interstellar clouds are lower in density as well, so. So varies quite dramatically from place to place. Now, because the star formation has been going on at a faster rate. In the inner part of the galaxy. Compared to the outer part. The heavy elements have been building up over time more rapidly. So the elements are produced by massive stars. Synthesizing these elements in their interiors. And then blowing up and then scattering. These freshly synthesized elements. Throughout the interstellar medium. Which becomes the building blocks for the next generation of stars and planets around them. And so there's this known gradient of composition. In the disk of the Milky Way. As you go out from the center. The abundance of heavy elements becomes less and less. As you go out from the center. You need a certain minimum abundance of heavy elements. To form planets. Because planets are made of more than just hydrogen and helium. In particular, rocky planets are made of more. More than just hydrogen helium. You need oxygen and silicon and calcium and magnesium and so on. So there's this gradient, what was called a metallicity gradient. So you can't be too far out on the edge of the galaxy. Because then you don't have enough building blocks. To form something like the solar system. And not just the rocky planets. But the giant planets also need these rocky components. Because you first have to build a solid core for something like Jupiter. Once it gets to be big enough, then it can accrete. And hold onto the abundant hydrogen and helium. And so it's not just the rocky planets, but the giant planets, too. That need the heavy elements. The other thing that you need is not enough or not too many threats to life on a planet. So things that are threatening on the galactic scale Include supernovae, gamma ray outbursts. Outbursts of the supermassive black hole at the center. For example, the star gets too close to it gets ripped apart. Forms an accretion disk. It emits a lot of radiation. Passages through giant molecular clouds can cause problems. And that's also where massive stars tend to form. And go off as supernovae. So all these things are more dangerous towards the center of the galaxy. So you don't want to be too close to the center, but yet you can't be too far away from the center, because then you don't have enough of the elements you need to build planets. And so there's this kind of intermediate range of distances from the center in the disk which are optimized for making habitable planets. So that's the galactic habitable zone, the zone which minimizes threats, maximizes, or you have sufficient building blocks for life.
[00:08:36] Speaker A: So there's certainly a Goldilocks dynamic going on. You don't want to be too close to the center. You don't want to be too far from the center. You've got to be sort of just right to have the right amount of radiation and the right amount of heavy elements and all of that for life to exist. There's also another Goldilocks zone, so to speak, with regards to the age in which life can form in the universe. Can you explain for us the concept of the cosmic habitable age? And why are there some time periods where planetary life could not exist in the universe?
[00:09:07] Speaker B: Right. So this is very analogous to the galactic habitable zone. So what's going on in the Milky Way galaxy over the course of its history is mirrored to some degree in what's going on in the broader universe, over the history of the universe. So over time, stars will be forming, supernovae will be enriching the local interstellar medium with freshly synthesized heavy elements. So all this has been going on within the Milky Way, but also in other galaxies throughout the universe. And the one thing I didn't mention about the Milky Way galactic habitable zone is that there is a limit eventually on the age.
Because the Earth, as you mentioned before in the previous broadcast, has plate tectonics. And plate tectonics is a really important part of habitability, and that's driven in part mostly by the decay of radioactive elements in a planet's interior. And so, long live reactive elements like thorium and potassium 40 and uranium. And these are produced in massive stars as the star formation rate continues to decline. And in the future history of the universe, including the Milky Way, the production of these reductive elements is going to decline. So on timescales of roughly 10 billion years or so, the planets formed in the future will have lower abundance of these geologically important reductive isotopes than the Earth did when it was formed. Thorium being the longest half life is something like 15 billion years. And uranium two isotopes, one is about four and a half billion years. Happens to be the age of the Earth and the other one is shorter lived isotope of uranium 235, which is about 700 million years. All those are important for geology. The star formation rate peaked earlier in the history of the universe, similarly to the way it peaked early in the history of the Milky Way. And that was a very dangerous time because all these supernovae were going off at a much higher rate. And you had also these giant black holes forming in the nuclei of galaxies, spewing a huge amount of radiation. We see these most distant ones as quasars. And the more nearby ones are called Seifert galaxies. So from time to time, some object will fall into the black hole and a lot of radiation will be emitted. So in the early history of the universe it was much more dangerous. The heavy elements were still building up, and so you didn't have that many planets that were forming yet. But in the distant future history of the universe, star formation will continue to ramp down. You're going to form G type stars like the sun less and less often. Most of the stars will be red dwarfs, which for a number of reasons are probably not very habitable environments. And the long live radioactive isotopes will continue to decay. And so there's this optimum range of time in the history of the universe than what we call the cosmic habitable layer.
[00:12:04] Speaker A: So Guillermo, you have a figure in your chapter towards the end showing the many interacting parameters that determine whether a habitable planet can exist. And I was really struck by just how many parameters there are. You have, of course, the fine tuning at the beginning of the universe to allow for galaxies and planets and stars to form. But then even assuming you can get those, you have all kinds of other parameters that have to be just right for a planet to be habitable. Its mass, its internal heat. It's the obliquity of its orbit, its moon, the shape of its orbit, its rotation, whether there's an atmosphere, whether there's plate tectonics, and then the properties of its host star and its location within the galaxy. And these might lead you to have simple life, and they may not even lead you to have complex life. There's a whole host of parameters that you have to get just right. And I would encourage folks to who are interested in this to download Guillermo's chapter from this book and spend some time meditating on this diagram. It's really quite striking. So in your view, is it likely that there is another Earth like habitable planet out there in the universe? When you consider all these different parameters, some of which many of which we've talked about over this podcast and the previous one. I'm sure that there are quite a few more. But how likely is it that we're going to find another Earth? You know, we're finding extrasolar planets all the time right now. You can read the news and there's stories about extrasolar planets quite frequently. But is it likely that any of them are going to be habitable?
[00:13:37] Speaker B: Yeah, that's a good question. And basically, that diagram is a kind of a blueprint for astrobiology research that's going on now and that will continue in the coming decades. Answering this kind of question, what exactly do you need to have a planet that's as habitable as the Earth? How common are they in the galaxy or in the rest of the universe? What we're discovering and what this diagram shows in a very simple way is that the habitability factors are very numerous. They're interdependent on each other. So you have arrows of dependence pointing in both directions. And so things.
If you don't have the right property, for example, for a particular planet to be habitable, let's say it's not the right size, then you could say, okay, well, you can fix it by doing something else, maybe changing its composition. But then that affects habitability in other ways because each of those factors affects habitability in multiple different ways. The size of a planet will affect how quickly it loses its atmosphere, how much surface relief it has, how quickly it loses a magnetic field from the interior cooling, how it interacts with other bodies in its planetary system, whether a large moon can stabilize a tilt of its orbit, for example, what rotation it initially starts off with. So there are these. All these very complex interrelationships, which is why you can't really treat any one of these in isolation. But you kind of have to do everything at once, at least, you know, that's why it's been so hard to answer this question up to now, is because people, you know, they've been only kind of focusing on one aspect in isolation at a time, and they gradually are bringing in other factors that are interdependent and making this complex web of interdependencies. You know, we're learning that, hey, you can't just ignore the other planets in the solar system. Jupiter has influence on the properties of terrestrial planets that you form in a planetary system. How much water is delivered to those planets, how often it gets impacted by asteroids, for example. And so you're finding out that, wow, all these things that we thought we could Just ignore before are important. They're highly specific and interdependent. The habitability factors are. I'm not at the point yet where I can pin down or put a probability on these things or just too many things that are work in progress still and doing all these complex simulations and observations. So I don't know if we exhaust the probabilistic resources of the universe to have another Earth like planet. I'm willing to say that we're alone in the galaxy as far as a planet that can support complex life. Galaxy is a pretty big place. It's about 200 billion stars or so. So I'm willing to go out there and stick my neck out and say, yeah, we're probably alone in the galaxy, but not quite ready to say with confidence we're alone in the universe as far as the only Earth like planet. Complex life.
[00:16:49] Speaker A: Very wise to not go out on a limb and say that something is impossible in the universe. The universe is a very big place. But I guess, you know, we always use Carl Sagan as sort of our foil in these conversations because he was such an expositor of the idea that oh there's we're so insignificant, but yet the universe is so big, anything can happen. He talked about billions and billions of stars. Well, there's billions and billions of stars in our galaxy and even that might not be enough to form another habitable planet along the lines of Earth, perhaps elsewhere. But I mean certainly we don't live in the Star Trek world. I'm sort of a sci fi junkie. And in the Star Trek world, you know, most of the time they're just exploring within our galaxy and it's our galaxy where they're finding all these other planets with life. It doesn't seem like that's probably going to happen to find Earth like planet in our galaxy that can sustain life.
[00:17:38] Speaker B: Right? Yeah, that's right.
[00:17:40] Speaker A: Okay, well, I want to ask you one last question here, Guillermo, and this was not a question that was on the list. This is maybe going a little bit out on a limb here, going sort of beyond the science of intelligent design and getting in sort of to the larger implications. Because I gave a talk recently that was sort of a reprisal of Steve Myers return of the God hypothesis argument, which I'm guessing you're familiar with where he talks about we have the fine tuning. We have the big Bang and the fine tuning of the universe which points to a cosmic designer. We have the fine tuning of life on Earth and the information and complexity of life, which points to a biological designer. And he goes through some of the different potential models, even from a philosophical standpoint, not necessarily scientific, but that can explain this evidence. He talks about deism and theism and pantheism and alienism, panspermia and materialism and all these different sort of almost worldviews that exist and what can explain this best. And I think it's pretty clear that you need some kind of a transcendent designer to explain the global fine tuning we talked about. In the first podcast, you explained to us what global fine tuning is, where you have the fine tuning of parameters that affect the entire universe and had to be set at the initial stages of the universe from the very beginning. And that requires some intelligent cause that can create the universe, that can set the fine tuning parameters from the very beginning. And so that might rule out some of these within the universe designers, like an alien or pantheism, the idea that the universe itself is creating itself. Well, okay, no, you need some force outside the universe. Okay, fine. I want to ask you the question, though. Deism versus theism. Okay. A lot of what we've talked about looks at local fine tuning parameters, fine tuning that is specific to our solar system or our galaxy or our planet even. Do these local fine tuning parameters help us talk about the question of was there design in the universe not just at the very beginning at the initial conditions, but has there been design later in the history of the universe to allow for a. A very special habitable planet like Earth to come into existence? Do you see these local fine tuning parameters talking about whether there's been sort of active design during the history of the universe?
[00:20:04] Speaker B: Yeah, I don't make the assumption of active design during the history of the universe. It certainly doesn't. I don't exclude it. But what convinces me really that the Earth is fine tuned with us specifically in mind, with a designer and a creator who wanted us to discover the. The universe around us and that it points beyond itself, is what Jay Richards and I discuss in the privileged planet. Not only is our local conditions fine tuned for life and for us to be here, but they're fine tuned also for us to be able to do science and discover the world around us, to see the stars, to have a transparent atmosphere so we can see the stars, we can see the galaxies, we can discover that the universe had a beginning and that we can develop science, that there are clues out there, like the rainbow up in the sky and solar eclipses, to inspire us to discover other things like general relativity, all these things. So I know It's a little beyond the scope of today's questions. We didn't discuss how the were fine tuned for scientific discovery, but that aspect of it in particular convinces me that the designer had very much a purpose in mind in creating a universe, not just with complex life that could exist, but that it could discover things and get to know something about its designer. In the same way that a cabinet maker, you can learn about a cabinet maker, someone who's making a beautiful desk or something by the design of that. That object and learn something about the purposes of that. That carpenter, for example.
[00:21:45] Speaker A: Well, that's a very interesting answer, Guillermo, and I really like it. It's not the direction I was thinking, but I, you know, I wish we had time to talk about some of these parameters that talk about the fact that the universe seems to be designed for us to discover. Even our planet Earth seems to be specially situated for us to be able to do science and study the universe. And I would really encourage listener read Guillermo and Jay Richards book the Privileged Planet, which goes into these arguments in great detail how not only do we live on a planet that's designed for life, but it's also designed for scientific discovery. And so this argument you're making essentially is that the designer didn't just sort of make the universe and then peace out, not caring about us, but actually had us specifically in mind, hoping that we would be able to be able to then discover science and caring about our discovery of the grandness of the universe, maybe even discovering that there is a designer out there because we see how special the universe is for life. We couldn't understand any of this if our planet was not specially designed for discovery and to do science. So I think it's a very innovative argument you've made, Guillermo, for not just a creator, but a creator that actually had us in mind, that cares about us, that wants us to discover all this fine tuning and the amazing properties of the universe. So, Guillermo, thank you very much for your time. It's been a really fascinating conversation. It's a Saturday morning here. You've got to go mow the lawn. I've got friends coming over for brunch, so we probably better wrap it up. But thank you so much for explaining to us about the fine tuning of our. Of our special planet Earth.
[00:23:17] Speaker B: Thanks, I really enjoyed it.
[00:23:19] Speaker A: Yeah, it was a fun conversation. I really would encourage folks to check out the description of this podcast and download Guillermo's chapter in the book Science and Faith and Dialogue. The chapter is again titled Local Fine Tuning in Habitable zones. It's available for free online, so go and download it and also read Guillermo's book the Privileged Planet. It's a wonderful, more expansive treatment of these topics. I'm Casey Luskin with ID the Future. Thank you for listening.
Visit us at idthefuture.com and intelligentdesign.org this program is copyright Discovery Institute and recorded by its center for Science and Culture.
