WEBVTT

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Good afternoon. It's an honor to be here with you today. We live in an era where the dominant

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scientific worldview is based on materialism and metaphysics that holds aspects of this

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physical world such as matter and energy as self-existent. From the physical universe and

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its laws, this view claims, we can explain everything we see and everything we experience.

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The material universe is sufficient to explain the nature of all that exists and if that

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is true, then in the words of the late Stephen Hawking, science can explain the universe

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without the need for a creator. This or some version of this view is very common in our

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day, particularly in academic circles. Yet this view leaves many questions unanswered.

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For example, what is the nature of consciousness? What is the origin of morality? Does it even

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exist? What about love or mercy? Are these illusions? Are they simply electrochemical impulses? Did

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they simply arise as encoded reactionary patterns in our brains through evolution? If so, are

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moral principles simply reducible to mathematics and statistics? And finally, given these questions,

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a proponent of materialism lived their life consistently with their worldview? While these profound

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questions remain unanswered, materialists use ancillary arguments in support of their view. One such

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argument that I want to examine here is the appeal to mediocrity, sometimes called the Copernican

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Principle. To explain what I mean, consider the story of the Pale Blue Dot. In his book, The Pale

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Blue Dot, the late astronomer Carl Sagan recounts an event that occurred in the course of NASA's

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Voyager 1 mission. In 1990, 12 years after the launch of Voyager 1, the spacecraft had left the outer planets of the

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solar system. And on February 14th, it was commanded to turn around and take a family portrait of the

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planets in the solar system it was leaving forever behind. When the images were transmitted back, NASA

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scientists and engineers were having difficulty finding the Earth. Eventually, they found it as a pale blue dot

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near a shaft of light that was entering the camera, reflecting from some point on the spacecraft.

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And about this picture, Carl Sagan had this to say. Because of the reflection of sunlight,

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the Earth seems to be sitting in a beam of light as if there was some special significance to this small

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world. But it's just an accident of geometry and optics. Our posturings, our imagined self-importance,

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the illusion that we hold some privileged position in the universe are challenged by this point of pale

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light. Our planet is a lonely speck in the great enveloping cosmic dark. As you can sense here,

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this is actually not a scientific statement, but a philosophical, actually a theological one.

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But the claim is not supported by all the science that we've learned over the last few hundred years,

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in fact. In this talk, I would like to examine the assertions of this so-called Copernican principle

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in the light of modern science, and in particularly my field, which is extrasolar planets or exoplanets.

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Before we discuss exoplanets, let's take a brief historical look.

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It was Aristotle who, 2400 years ago, argued for a geocentric model of the universe.

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He envisaged the concentric set of crystalline spheres in which the heavenly bodies resided.

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Most nearby was the moon, then Venus, actually Mercury, then Venus and Mars, and then Jupiter and

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Saturn. Further out were the firmament, which are the stars, and these were all sent into motion by a

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prime mover. Aristotle said reason and common experience confirmed this view and no one doubted it.

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But there was problems with this simple view. One was the retrograde motion of the planets.

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For example, if you look in the night sky, look at Mars, which comes near us every two years. It

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comes to a point called opposition, which is the point on the sky opposite to the direction of the

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sun at that time. And if you watch its location relative to the background stars, you would notice

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a retrograde motion. Over the course of a few months, you see the planet moving one direction,

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then backwards, and then forward again in the same direction relative to the stars.

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This was difficult to explain in the basic geocentric view of Aristotle.

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500 years after Aristotle, in his great work called the Almagest,

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Ptolemy provided an explanation. He agreed with Aristotle that the perfect heavenly bodies have

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to have perfect motion, which meant they were going in circles. But the planets are actually

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traveling in smaller circles called epicycles, and the epicycles are centered on something he called

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deferreds, which in turn are centered on the earth. In this way, the planets can have retrograde motion.

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By setting the diameters and rotation rates just right, Ptolemy was able to make very accurate

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predictions of the locations of the planets. So good, in fact, that for the next 14 centuries, there was no rival to this picture.

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It wasn't until the 16th century

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that a serious alternative was proposed. And here it was Nicholas Copernicus, who in his own magnificent work,

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called On the Revolutions of the Heavenly Bodies,

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detailed a much more elegant system, the sun-centered or heliocentric system. The earth, he suggested,

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was not the center of the universe, and the heavenly bodies do not all revolve around the central point.

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With these and a few other axioms, he was able to explain the same observations more elegantly and simply.

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But it goes on further. In the 20th century, it was the astronomer Harlow Shapley of Harvard University

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who discovered that the sun is not at the center of our galaxy, which is called the Milky Way.

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He did this by measuring the locations of globular clusters

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on the sky, including their distances. Globular clusters are many galaxies with hundreds of thousands of stars.

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Shapley noticed that they're orbiting an area of our galaxy that is many thousands of light years from us.

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So he famously concluded, the solar system is off-center, that means we are off-center, and consequently man is too.

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So you see this pattern. Copernicus showed us that the earth is not at the center of the solar system.

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Then Shapley showed us that the sun is not at the center of the galaxy.

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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.

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Pointing to these observations, this so-called Copernican principle

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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.

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The claim seems to be well supported when I express it as I just did, but the claim gets some of the history wrong.

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For example, neither Copernicus nor Galileo would consider Earth's removal from the center a demotion.

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But also, the claim actually completely misses much of what we've learned in the last century about habitable planets.

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These are planets where life could at least survive if placed there.

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So now, we consider the question, what is a habitable planet?

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What do we need for a habitable planet?

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There are many requirements, but at a minimum, a habitable planet must be a terrestrial planet that support complex carbon and water-based life.

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It needs to be a planet in what is called the circumstellar habitable zone.

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And finally, it needs to be a planetary system in the galactic habitable zone.

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The first requirement, mainly that it should be a terrestrial planet, meaning a rocky planet, is already limiting.

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This is because much of the matter in the universe consists of hydrogen and helium.

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It takes complex processes in the stars to generate the heavy elements that make up a planet that is rocky, like the Earth.

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Beyond being rocky, however, it must also have water.

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And these are just minimum conditions.

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There is also the location of the planet.

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Their circumstellar habitable zone is defined as that region around the star

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where water could be liquid at some part of a rocky planet that is situated there.

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Since the surface heat of a planet is from the sunlight it absorbs,

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around a cold star, the habitable zone is close in.

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While around a hot star, it has to be further out.

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If a planet is located closer to its host star than the inner edge of the habitable zone,

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a runaway greenhouse effect will raise its temperatures,

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causing the water to evaporate into the atmosphere and be carried away by the solar wind,

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making the planet dehydrated.

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At the other extreme of the habitable zone,

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there will be precipitation in terms of ice and snow,

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and that will make the planet absorb less of the starlight and become colder still.

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And this leads to an uninhabitable snowball planet.

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In our solar system, only the Earth is inside the habitable zone.

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So the planet has to be the right distance from the star.

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As for the star,

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are all stars equally suitable?

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It turns out the answer is no.

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Many astronomy textbooks refer to our sun as an average star.

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This is true only in a limited sense.

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There are certainly stars that are more hot than our star,

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and there are stars that are cooler than our star, than our sun.

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But the sun is actually within the 10% most massive stars in the Milky Way.

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And in fact, stars that are much more massive than the sun

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are actually too unstable to be producing habitable zones.

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And then stars that are less massive than our star

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have habitable zones that are cooler,

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so they have habitable zones that are closer in,

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requiring that close, tight-in habitable zone.

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But then when a planet gets that close to a star,

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it suffers from an effect called tidal locking.

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So for the cool stars, the tidal locking problem occurs.

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The spin of the planet becomes equal in duration

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with its orbital period,

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and as a result,

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one side of the planet becomes permanently day,

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while the other side becomes permanently night.

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The day side becomes hot,

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and the moisture is transported to the other side,

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where it snows down and stays permanently frozen.

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Tidally locked planets are poor choices for life.

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Cool stars also have more frequent, life-threatening events,

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these bursts called coronal mass ejections.

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In the end, only 4% of the stars

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are main-sequence G stars, like our sun.

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And then what about the location of the star within the galaxy?

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To get heavy elements from which a rocky planet can form,

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you have to be closer to the center of the galaxy.

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On the other hand, if you get too close,

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life-threatening events like supernovae become more frequent,

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as supernovae can sterilize life

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within many light years around it.

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These are more frequent not only near the center,

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but also within the spiral arms.

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So the planetary system, to stay safe,

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needs to be at the right radius

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from the center of the galaxy.

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Not too far, not too close,

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and not within a spiral arm.

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And what about the galaxy itself?

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Here, too, we find ourselves in a privileged place.

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Our galaxy, the Milky Way,

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is among the 3% most massive galaxies

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in the nearby universe.

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Because it was so massive,

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it was able to accumulate heavy elements more quickly,

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and planet formation started here earlier,

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in the Milky Way.

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Almost two-thirds of the age of the universe

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had gone by by the time there was enough material

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that a planet like the Earth could be formed.

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So there was a brief window.

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There are, in fact, many parameters

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that we could discuss.

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The list is very long.

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Very briefly, at least we need a planet

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with a magnetosphere.

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Our magnetosphere on the Earth

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protects us from the cosmic rays

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and occasional solar bursts

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that would otherwise dehydrate our atmosphere.

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We need a large moon.

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The Earth's moon is unusually large

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relative to the Earth's size.

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This is important because our massive moon

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stabilizes the axial tilt of the Earth's rotation.

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And that helps to stabilize our climate.

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To support large living beings like animals

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and like us humans,

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a planet needs to have high enough oxygen content.

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But then if it has too much oxygen,

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there will be rapid fire growth.

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So there needs to be a neutral gas as well

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to avoid devastating fires.

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Our oxygen-nitrogen-dominated atmosphere

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is perfect balance of these requirements.

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Finally, the Earth's planetary neighbors

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play important roles.

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Jupiter, the largest planet in our solar system,

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has 300 times the mass of the Earth.

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It has a near circular orbit

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and orbits five times farther from the Sun

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than the Earth.

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This combination of being massive

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and having a large circular orbit

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makes Jupiter a benevolent agent

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in the solar system,

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absorbing to itself,

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like a massive vacuum cleaner,

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comets and asteroids

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that could potentially threaten life on the Earth.

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Many of these eventually crash

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into Jupiter and Saturn.

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We now move from theory to experiment.

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Over the last two decades,

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there has been many discoveries

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of exoplanets,

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planets around other stars.

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What have we learned from them?

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First, very briefly,

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I'd like to point out

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some of the techniques.

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In the first very important technique

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called radial velocity,

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the planet is not detected directly,

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but the wobble of the star

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in reaction to the pull of the planet

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is detected from the red and blue shifts

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of the star's spectrum.

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Another highly successful technique

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called transit

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looks for the very small drop in the light

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from a star when a planet transits,

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when the planet comes in front of the star.

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A third one that is special to me

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because this is the area in which I work

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is one of direct imaging

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where a technique is used

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to actually image the planetary system directly.

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Here you see a montage of many years

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of images of an exosystem

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and the planets growing around that.

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Now, what have we learned from these?

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From the radial velocity measurements,

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we've discovered one important lesson

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that Jupiters, like our Jupiter,

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are very uncommon.

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Most gas giant planets,

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and Jupiter and Saturn

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are examples of gas giant planets,

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have elliptical rather than circular orbits,

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it turns out.

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Over time, the elliptical orbit

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means they migrate towards the star,

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eventually settling from an elliptical orbit

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to a circular orbit

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very tightly around the star.

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Along the way,

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they can knock off other planets

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in the solar system.

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They are very dangerous when they do that.

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These kinds of planets are called hot Jupiters,

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and they're very dangerous.

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The other technique

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was the transit technique,

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and it has also provided us

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a picture of thousands

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of other planetary systems.

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But here, too, the results show

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that in the great majority

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of the planets discovered,

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they are closer to their host star

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than even our innermost planet, Mercury.

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So our solar system,

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by that comparison,

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is exceedingly unusual.

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So we see a large number of conditions

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are necessary for a life-hospitable planet.

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And when we look at the universe,

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we see that the usual condition,

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the usual situation,

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is that these conditions

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are not all present at the same time.

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In fact, one can make

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a statistical estimate

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of the expected rate

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following the approach

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of Frank Drake from the 60s,

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where he used a very simple calculation,

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and he estimated

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the number of planets in the Milky Way

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that could host advanced life,

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such as they could give us a radio signal.

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Considering a few conditions,

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he estimated that there should be

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on the order of a few million

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planetary systems in our galaxy

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that could send us a signal.

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But half a century later,

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the list of conditions

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are actually quite a bit more.

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And when you actually do

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the same type of calculation now,

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you expect much less than

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one in 10,000 Milky Ways

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where you could expect

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to see a planet like the Earth.

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So this isn't up to now.

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It's been an argument to say

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that the Earth is a very rare planet.

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But there is a yet more profound aspect

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to our existence here,

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and this is a notion

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of what is called

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the privileged planet.

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And this was first pointed out

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by astronomer Guillermo Gonzalez

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and philosopher Jay Richards.

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And their point was

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that the requirements

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for habitability

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appear to overall be coinciding

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with the requirements

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for discovery.

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That is,

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the same conditions

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that a planet should be habitable

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are all together

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what we would need

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for that habitable planet

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to be a place

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where intelligent beings

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could study

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and learn about the universe.

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An example of this

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that is beautiful

20:19.620 --> 20:21.000
is the example

20:21.000 --> 20:22.420
of the perfect eclipse.

20:23.100 --> 20:23.800
Did you know

20:23.800 --> 20:24.760
that the Earth,

20:25.420 --> 20:27.000
from the Earth's point of view,

20:27.140 --> 20:28.200
the moon on the sky

20:28.200 --> 20:29.740
and the sun on the sky

20:29.740 --> 20:31.500
are exactly the same diameter?

20:32.040 --> 20:32.920
And as a result,

20:33.060 --> 20:34.540
the Earth is the only place

20:34.540 --> 20:35.300
where we can have

20:35.300 --> 20:35.920
what is called

20:35.920 --> 20:37.520
perfect eclipses.

20:37.520 --> 20:39.220
If the moon was

20:39.220 --> 20:40.240
a little bit closer,

20:40.740 --> 20:41.500
it would not cover

20:41.500 --> 20:42.440
enough of the sun.

20:42.880 --> 20:44.240
If it was a little bit farther,

20:45.040 --> 20:45.940
if it was a little closer,

20:46.040 --> 20:47.000
it would cover too much

20:47.000 --> 20:48.040
and if it was a little farther,

20:48.160 --> 20:48.740
it would not cover

20:48.740 --> 20:49.500
enough of the sun.

20:50.000 --> 20:50.780
As it is,

20:50.860 --> 20:52.340
we have perfect eclipses

20:52.340 --> 20:53.640
and we can study

20:53.640 --> 20:54.800
aspects of the sun

20:54.800 --> 20:55.600
that were otherwise

20:55.600 --> 20:56.740
unavailable to us.

20:57.240 --> 20:57.820
For example,

20:58.000 --> 20:58.600
historically,

20:59.080 --> 21:00.240
it was from observing

21:00.240 --> 21:03.060
the spectra of the atmosphere

21:03.060 --> 21:03.860
of the sun

21:03.860 --> 21:05.640
during a perfect eclipse

21:05.640 --> 21:07.780
that astronomers first discovered

21:07.780 --> 21:08.920
that the sun

21:08.920 --> 21:10.280
is a hot ball of gas.

21:10.820 --> 21:11.980
It also enabled them

21:11.980 --> 21:13.220
to know

21:13.220 --> 21:14.880
what elements are present

21:14.880 --> 21:15.640
in the sun.

21:16.060 --> 21:16.680
This, in turn,

21:16.800 --> 21:17.560
opened the door

21:17.560 --> 21:19.200
for studying other stars.

21:19.980 --> 21:21.500
It was also during an eclipse

21:21.500 --> 21:23.580
that Einstein's theory

21:23.580 --> 21:24.260
of gravity,

21:24.580 --> 21:26.160
which eventually told us

21:26.160 --> 21:26.940
about the beginning

21:26.940 --> 21:27.780
of the universe,

21:28.920 --> 21:31.140
was put to its most famous test.

21:31.140 --> 21:32.680
The sun's mass

21:32.680 --> 21:33.760
bends the light

21:33.760 --> 21:34.760
from distant stars

21:34.760 --> 21:35.700
but the bending

21:35.700 --> 21:36.540
is so small

21:36.540 --> 21:37.480
that only stars

21:37.480 --> 21:39.340
seen very near the sun

21:39.340 --> 21:40.120
show an effect.

21:40.400 --> 21:41.440
But you can only see

21:41.440 --> 21:41.960
this effect

21:41.960 --> 21:43.240
during a perfect eclipse.

21:46.300 --> 21:48.400
Many of the other factors

21:48.400 --> 21:50.240
also facilitate discovery.

21:51.240 --> 21:51.860
But we're not,

21:52.020 --> 21:52.820
because we're not

21:52.820 --> 21:54.020
at the center of the galaxy,

21:55.360 --> 21:57.380
our night sky is dark.

21:57.480 --> 21:58.140
It's not bright.

21:58.220 --> 21:59.480
We can actually do astronomy.

21:59.480 --> 22:01.120
We also, remember,

22:01.260 --> 22:01.960
we said we need

22:01.960 --> 22:03.540
an oxygen-nitrogen atmosphere.

22:03.940 --> 22:05.340
Well, that's a clear atmosphere.

22:05.940 --> 22:06.800
By comparison,

22:07.340 --> 22:09.360
Venus has a carbon dioxide atmosphere

22:09.360 --> 22:10.120
which is opaque.

22:10.300 --> 22:11.280
You couldn't do astronomy

22:11.280 --> 22:12.320
from Venus.

22:13.600 --> 22:15.560
It's also 400 degrees Celsius

22:15.560 --> 22:16.680
on the surface of Venus.

22:17.020 --> 22:18.300
So it's not a good platform.

22:19.180 --> 22:20.520
The list of interconnected

22:20.520 --> 22:22.820
requirements for habitability

22:22.820 --> 22:24.540
and discovery is long.

22:25.100 --> 22:26.120
But the picture by now

22:26.120 --> 22:26.860
should be clear.

22:27.620 --> 22:28.500
There is abundant

22:28.500 --> 22:29.460
solid evidence

22:29.460 --> 22:31.240
that the world is designed

22:31.240 --> 22:33.080
and that we can infer

22:33.080 --> 22:34.520
as well

22:34.520 --> 22:35.780
that God wants us

22:35.780 --> 22:37.360
to study this world

22:37.360 --> 22:39.380
and to see its design

22:39.380 --> 22:40.680
and to realize

22:40.680 --> 22:42.340
the glory of its creator.

22:43.180 --> 22:44.440
So far from being

22:44.440 --> 22:46.460
a mere pale blue dot,

22:46.920 --> 22:48.160
our planet is not only

22:48.160 --> 22:49.540
made for supporting life,

22:49.880 --> 22:51.440
but it was also made

22:51.440 --> 22:52.660
to support the world.

22:52.660 --> 22:53.220
Thank you.

22:53.220 --> 22:53.280
Thank you.

22:53.280 --> 22:53.440
Thank you.