There have been some interesting recent reports that two moons of the outer planets may have some form of life. Titan, which orbits Saturn, is often cited as a potential life-site because it meets one of the necessary conditions for life (high nitrogen content). The recent claims are that acetylene is rare on Titan's surface, and that hydrogen may be flowing down to the surface and disappearing. Both hydrogen and acetylene could theoretically be "consumed" by some primitive form of life on the surface, so their absence may be indicative of such processes actually taking place. More interesting (to me at least) is the unusual suggestion that Io may have some form of life, despite its proximity to Jupiter and its magnetosphere. The suggestion is that it might live deep under the surface, although it seems purely speculative to me.
Some say (and many more think) that the discovery of extraterrestrial life would essentially refute Christianity, since it would show that we don't need to appeal to God to explain our origins, or because it would contradict certain Christian doctrines about humanity's importance to God. Unfortunately it can be difficult to refute because it's difficult to find out what the actual argument is. Any attempt to address it, therefore, runs the distinct possibility of attacking a strawman. Nevertheless, I shall soldier on.
As far as I can tell, the argument is something along these lines:
a) If life or the remains of life are found beyond the earth,
b) then life would be a common phenomenon.
c) Therefore, it would be the product of natural processes.
d) Therefore, life would not be the product of supernatural process(es) or agent(s).
Two other conclusions are often drawn, although it's not clear whether they are drawn from b), c), or d). They are:
e) Therefore, the Christian claim that human beings are especially important to God is highly implausible.
f) Therefore, the Christian claim that God was incarnated as a human being (as opposed to one of the other myriad forms of life) is likewise highly implausible.
Now the philosophically minded will notice that this is a spectacularly poor argument. f) does not follow from a), b), c), d), e), or their conjunction; e), likewise, does not follow from a) through d); d) does not follow from c); c) does not follow from b); and b) does not follow from a). I'll go over each of these alleged inferences in turn, with the first below. For now I'll just point to how this charge fits into the metanarrative that science and Christianity are at odds with each other, and this because science is slowly but surely refuting Christianity. This is the conflict thesis -- James calls it the conflict myth -- and it is almost entirely rejected by historians of science.
So, first, does a) lead to b)? If we find life elsewhere in the universe, will it imply that life is a common phenomenon? Well, if we're talking about our solar system, the answer is no. Take Mars for example. Finding life or the remains of life on Mars would not indicate that life is common, for the simple reason that over the last few billion years, at least a hundred million tons of Earth has been dumped on Mars, most (not all) due to meteor collisions sending Earth material out into the solar system. The odds that none of it contained any biological material is remote in the extreme, although much of it would probably have been broken down by radiation. Hugh Ross has been predicting since at least the late 1980s that the remains of life will inevitably be discovered on Mars simply due to this cross-contamination. And this is true for virtually all possible life-sites in the solar system, including the moons around the outer planets: any biological material we find would be better explained as having its origin on Earth.
Moreover, the Anthropic Principle places severe limitations on what conditions must be met in order for life to exist on a planetary body. It must have a particular axial tilt, magnetic field, a moon of a particular size and distance, must orbit a particular type of star of a particular age at a particular distance, etc. There are several dozen such conditions. The only body that meets these conditions in the solar system is the Earth. There are sometimes sensationalistic claims that Mars might have had liquid water on its surface at some point in the past and so might have harbored life (since the presence of liquid water is one of the necessary preconditions). But this ignores the multiple other conditions that are not met by Mars or any other potential life sites in the solar system.
But what about beyond the solar system? What if we find life on planets orbiting other stars? Wouldn't that prove that life is ubiquitous in the universe? Again, the Anthropic Principle puts severe limitations on how many places in the universe could naturally support life. So, for example, the planet has to be in a spiral galaxy (not a common type of galaxy), and be between spiral arms. In any other place within any other type of galaxy there would be too much stellar radiation to allow life. Additionally, it has to exist in a very particular stellar neighborhood: nearby white dwarf binary stars which have lost some of their stellar material to interstellar space (this is the only natural source of fluorine, which is necessary for life); near enough to past supernovae to obtain the necessary heavy elements produced, but not so near as to receive too much radiation from them; etc. The point being that, even if we do find life elsewhere in the universe, it wouldn't contradict the Anthropic Principle's claim (which is recognized by all the relevant scientists) that most places are hostile to life, and so there are relatively few potential life sites in the universe. Indeed, when factoring all of the necessary preconditions into the equation, the odds of another planet anywhere in the universe being naturally capable of supporting advanced life is zero. Part of the problem here is whether we're talking about simple life forms or complex, perhaps complex enough to be intelligent and have a civilization. The more complex the life form, the more anthropic coincidences must be met in order for it to exist. Conversely, simple forms of life do not have to meet as many requirements, but it's still no walk in the park. The most popular book addressing this issue is Rare Earth: Why Complex Life Is Uncommon in the Universe, by geologist Peter Ward and astronomer Donald Brownlee. They argue that while simple forms of life may be common in the universe, advanced life almost certainly is not.
Of course, some may continue to ask, what if we find that other forms of life are everywhere in the universe? Wouldn't that refute the claims being made here? Well, the discovery that life is ubiquitous in the universe would certainly refute the claim that life is not ubiquitous. In the same way, the discovery that E does not equal mc2 would refute the claim that it does, and the discovery that earth is at the center of the universe would refute the claims that it's not. So it's not a very interesting line of argument. But, ignoring that, if we find other forms of life out there, the anthropic coincidences should certainly be looked at again to see if they merely represented a failure of imagination. Perhaps our conception of "life" was too narrow. But if, after looking at them, they still hold, then the occurrence of advanced life would have to be fit into the claim that the odds of there being a planet capable of supporting advanced life anywhere in the universe is too remote to be considered a realistic possibility. But that will be the subject of the next post.
(cross-posted at Quodlibeta)