Today I'm going to address Thomas McAvoy's article, Why Our Unique Solar System Points to God
point by point. I will admit now that I have no impressive scientific credentials to compare with Mr. McAvoy's PhD in chemical engineering. I am simply an ordinary person, with perhaps slightly above average intelligence, and the ability to research well. In the interest of ease, all quotes listed here, unless specifically attributed, are of McAvoy from the article. So, going paragraph by paragraph...
The first paragraph is simply a link to, and brief description of, a related article by Robert Spitzer.
The second paragraph is where McAvoy announces the purpose of his article is to add to Spitzer's by pointing out "additional, unique features of our solar system which are also very highly improbable." He also says that he is basing his discussion on a book by Lee Strobel, which he claims has "two chapters justifying Intelligent Design and these chapters are extremely weak." Then he goes on to state his argument:
We can start from the general observation that in the universe there are billions of stars, and no doubt many of them have planets traveling around them. Surely there must be life on many of these planets. We can that demonstrate, using concrete facts, why Earth is indeed a very privileged and relatively unique planet.
His first statement is true, though he is off by several orders of magnitude. There are aproximately 300 billion stars in our galaxy alone, and by looking at a piece less than one tenth of one millionth the size of the total sky, the hubble telescope has photographed over 10,000 galaxies. If each of the stars in each of the galaxies that we have seen in that tiny piece of the sky, and each of the stars in our own galaxy all played the lottery, over 11 million of them would win. If we extrapolate how many galaxies exist in the observable universe, and how many stars those galaxies have on average, 35,842,294,000,000 of them would win. That is over 35 trillion stars winning the Mega Millions Jackpot. As for many of those stars having planets in orbit, according to NASA's Exoplanet Archive (http://exoplanetarchive.ipac.caltech.edu/) as the time of this writing (4/11/2014), astronomers have discovered 1,696 confirmed planets orbiting 1,027 stars. That number is updated weekly. McAvoy's assertion that he can demonstrate the Earth to be a very privileged and unique planet in a universe this large seems, at this point, laughable, but let's take a look at his arguments and evidence.
In his third paragraph, McAvoy says that the supermassive black holes that exist at the center of probably all galaxies emits radiation when accreting matter. He argues that the amount of radiation emitted makes solar systems that are too close to the center their galaxies, or too closely approach the center during their galactic orbit, unsuitable for life. Being neither an astrophysicist, nor an astronomer, I can not address his main claim, except to ask how close is too close? At no point does McAvoy attempt to say how close to the center of our galaxy (or any galaxy) a system would have to get to be irradiated enough to make it unsuitable for life. Even if we discount this question, there are still billions of stars that never approach their galactic centers any closer than we do, so this argument fails to make the Earth special both in its generalities, and in its (lack of) specifics.
McAvoy's next argument centers around red dwarf stars. Red dwarfs are, probably, the most common stars in our galaxy, though there is some dispute as to whether or not they comprise the 76% of stars in our galaxy that McAvoy claims. He describes red dwarf characteristics fairly well, but the inferences he draws from them regarding their ability to host habitable planets are questionable.
1) "Red dwarfs are less massive than our Sun" This is true. I only include it here because I will be refering back to it.
2) "Red dwarfs don’t emit as much energy as our Sun, and as a result vegetation would be more difficult to grow on a planet orbiting them." While this seems true, all it actually means is that in order to be habitable, a planet would have to be closer to the red dwarf than Earth is to Sol. This is why each solar system astronomers look at has a unique "Goldilocks Zone." This zone is the area around a star where a planet is close enough to its star to recieve enough heat, but far enough away to avoid being over heated. Saying that a star doesn't emit as much energy as our sun is simply another way of saying that a habitable planet has to be closer to that star than we are to ours.
3) "[Red dwarfs] emit radiation in the red spectrum, which makes photosynthesis, the process by which plants grow, less efficient." This completely ignores the fact that photosynthesis is the method plants on Earth evolved to make use ot the radiation emited by our Sun. If life were to evolve on a planet that recieved more red-spectrum light, and less blue-spectrum light than ours, it is not impossible to expect that it would evolve characteristics that would make it perfectly suitable to living in those conditions. It is not difficult to conceive of a photosynthesis-like method that utilizes high red-specturm light, and even, possibly, infrared more effeciently than plants currently growing on Earth. In fact, I would hypothosize that if one were to take common Earth plants and grow them under lights that mimic the radiation produced by a red dwarf for multiple generations that we would see those characteristics evolve.
4) "To prevent its liquid water from freezing, a planet would have to orbit closer to a red dwarf than we do to our Sun. However, as one moves closer, tidal forces would increase and a planet would end up in a tidal-locked state " I mentioned the first half of this point earlier when addressing point #2. McAvoy is attempting to address my earlier complaint. He is quite right that if two bodies orbit each other too closely then gravity will cause them to tidaly lock. What he leave out is that the point at which this occurs depends upon the gavitational pull (which is to say the mass) of the two bodies in question. Since point #1 was that red dwarf stars are less massive than our sun, it is also accurate to say that the point at which a planet would become tidally locked to that red dwarf is correspondingly closer. Since not even the planet Mercury (which orbits between 46 million and 70 million km away from the sun) is close enough to be tidaly locked to our sun, it is fairly safe to say that any planet close enough to a red dwarf to be tidaly locked would be a chared cinder, far too close to be inside the Goldilocks Zone.
5) "Finally, red dwarfs don’t produce much ultraviolet light. Early on in a planet’s existence, ultraviolet light is hypothesized to break up water into hydrogen and oxygen. The hydrogen is a light gas and it escapes the planet’s gravitational pull and flows into space, while the oxygen, being a heavier gas, remains and supports life." All I will say to this claim is what McAvoy himself says, this is a hypothesis and has yet to be confirmed by testing or evidence. There is currently no data showing that UV light is necissary for the formation of a planetary atmosphere.
The clearest refutation of McAvoy's claims here is in the fact that we have found earth-like planets in the Goldilock's Zone of red dwarf stars. Acording to this article in Space.com, approximately 6% of red dwarfs in the Milky Way are home to habitable earth-like planets (Note: This article lists the number of stars in our galaxy at 100 billion, while all other sources I have found say that the figure is actually 300-400 billion. All of these individual arguments in no way address the fact that even if we accept all of McAvoy's figures and postulates, this argument would still leave aproximately 75 billion stars in our galaxy alone that are not dealt with by this argument.
McAvoy's next paragraph contains several unfounded claims. There is scientific disagreement on whether or not the Moon stabilizes the axial tilt of the Earth, however, even using the models that show this to be the case, McAvoy's statements regarding the effect of changing obliquity (how far towards the sun the earth is tilted) are overstated. Under these models (and remember that there are models that show the lack of a moon would have little to no effect) it would take millions of years for the obliquity to go from its current 230 to 900. This slow rate of change would allow plenty of time for life to migrate from areas that are becoming uninhabitable to areas that are becoming habitable. McAvoy's next statement that the axial tilt of Mars varies widely because its moons are not large enough to stabalize it is likewise in dispute. At the end of this paragraph McAvoy attempts to insinuate that the events which caused the formation of our moon are improbably rare. To that I will say that since there is still no scientific concensus about how our moon was formed, we are in no position to make any definitive statements regarding how probable an event it was. It could be said, however, that of the eight planets in our solar system, three are considered "earth-like," Mars, Earth, and Venus. Of those three, one has a moon like ours. It could be argued that Luna-like moons occur in one out of every three earth-like planets. I'm not arguing in favor of that statistic, I'm simply saying this to point out that assigning probability to an event is completely dependent on the availible data and your point of reference.
Now we have moved even closer in and are taking a look at the Earth itself. First the assertion that if the Earth's gravity were lower then it would be incapable of holding an atmosphere sounds plausible, and it is...sort of. In actuallity, the ability of a planet to retain an atmosphere is a product of both its gravity and its rate of rotation. Meaning that a planet could have an earth like atmosphere and only have the gravity of earth if it simply rotated slower. The converse is also true, a planet could have twice the gravity of earth and still maintain an earth-like atmosphere if it rotated faster than the Earth does (http://quest.nasa.gov/aero/planetary/atmospheric/gravity.html).
McAvory next claims that if the gravity of the Earth were too high, then mountains could not exist. We will examine this by noting that the total difference in elevation between the lowest point on Earth (Challenger Deep) and the highest point (Peak of Mt. Everest) is 19.76km, or about 12 miles. To put it into perspective, that is the distance between the campuses of USC and UCLA (both of which are located in Los Angeles). By comparison the difference between the lowest and highest points on Mars (which has about 1/3 of the gavity of Earth is 29.43km, or 18.29mi. So reducing gravity by 66% gives us an increase in mountain height of 967 meters, or .6 miles, or about 10 blocks. I think, using this math, that it is readily apparent that gravity would have to be extremely high to reduce the height of mountains enough to make the difference that McAvoy claims.
We will ignore McAvoy's spurious claim that mountains are a requirement for life because without them the entire planet would be underwater, except to point to both the abundance of aquatic life that exists on this planet, and the generally accepted view that life on this planet began in the oceans. This argument also applies to his next claim that plate tectonics and continental drift are important to sustaining life on Earth.
In fact plate tectonics and continental drift are merely byproducts of the next point McAvory raises, that a planet must have a core (actually a mantle) of molten iron to produce a magnetic field which will protect the planet from cosmic radiation. This is, so far as we can determine at this time, true, however, McAvoy's next statement that planets "with a molten iron core" are not very comon is completely unsupportable. We do not yet know enough about the planets in other solar systems to say whether molton iron cores are rare, or extremely common, however, out of the eight planets in our solar system we have good evidence that not only do four of them have molten iron cores, but so do at least two moons. Since we are still awaiting data regarding planets outside of our solar system, this data is all we have, but it is fairly compelling and seems to resist McAvoy's attempts to claim that molten iron cores are rare.
The next paragraph is a brief rehash of a familiar claim, that if the Earth's orbit around the sun "were changed by ± 5% animal life would not be possible." This argument always depends on the reader being unaware of the fact that the Earth's distance from the sun regularly varies by about 3%. It also ignores the fact that the "Goldilocks Zone" for our sun is between .99AU and 1.7AU. For those who don't know, 1AU is the median distance from the Earth to the sun. This means that the Earth could be 108 million km farther away from the sun than it is, or 26 million km past Mars and still be habitable. (http://www.space.com/19522-alien-planet-habitable-zone-definition.html)
Thses are all the arguments that McAvoy is attempting to use in his article to conclude that:
...only a very, very tiny fraction of stars would have just the right conditions for intelligent life as we know it to exist on a planet orbiting them. In our universe, primitive life is likely, but intelligent life is far more rare. When faced with the extremely low probability of these facts being a random occurrence...I believe that the facts definitely point in the same direction that Fr. Spitzer discusses in his post, namely a super intellectual Creator.
Now, aside from whether or not I've managed to convince you that the reasoning Mr. McAvoy used to arrive at this conclusion is flawed, there are a could of things worth noting in his conclusion itself. First, when he says "only a very, very tiny fraction of stars," he is again misleading his reader by disguising the orders of magnitude. As I said before, even if we only count the stars in our own galaxy and the 10,000 galaxies we have seen by observing one tenth of one millionth (1/10,000,000) of the observable universe, and the odds of any star having a planet capable of supporting life are 1/259,000,000 (the odds of winning the lottery), there are still 11,000,000 stars capable of supporting life, if we extrapolate from what we have observed to the rest of the universe, then we can estimate that there are at least 70,000,000,000,000,000,000,000 stars in the universe, and if we apply those same odds, that gives us about 270,270,270,270,270 winners. Even if the odds of a star having a habitable planet were 3,990,000,000:1, or 3.99 billion to 1, there would still be more stars with habitable planets in our universe than there are dollars in the current US debt (>17.5 Trillion Dollars).
Also, the astute reader will notice that McAvoy starts hedging here by refering to "intelligent life as we know it." Since the only life we know of exists on this planet, this means that he is stating that intelligent life that evolved on this planet could only evolve on a planet like this one. This kind of circular reasoning should always be considered suspect.
Finally, McAvoy ends by saying that because the odds of this planet existing are so low that they couldn't happen randomly, that is evidence for the existence of a "super intellectual Creator." Once again, even if the odds of this planet existing were 70,000,000,000,000,000,000,000 to 1, random chance would still have created this planet at least once, and I think we can agree that McAvoy has come nowhere near proving that the odds are even close to being that long.
