We humans naturally philosophize. But we don't naturally philosophize well. So when science journalists and scientists try their hands at it they often make a mess of it. (See my Scientism category for plenty of examples.) This is why there is need of the institutionalized discipline of philosophy one of whose chief offices is the exposure and debunking of bad philosophy and pseudo-philosophy of the sort exhibited in so many 'scientific' articles. Although it would be a grave mistake to think that the value of philosophy resides in its social utility, philosophy does earn its social keep in its critical and debunking function. But now on to the topic.
Is there extraterrestrial life?
To answer this question, one would have to have at least a rough idea of what counts as living and what counts as nonliving. For example, "A working definition lately used by NASA is that 'life is a self-sustaining system capable of Darwinian evolution.'"
In a recent Scientific American article, Why Life Does not Really Exist, problems with the NASA definition are pointed out. I won't try to evaluate the putative counterexamples the author adduces, but simply assume that the NASA definition is not adequate. Indeed, I will assume something even stronger, namely, that no adequate definition is available, no razor-sharp definition, no set of properties that all and only living things possess, no set of properties that cleanly demarcates the animate from the inanimate, and is impervious to counterexample.
Supposing that is so, what could explain it? According to the Scientific American article (emphasis added) what explains the difficulty of defining life is that life does not really exist! It can't be defined because it is not there to be defined. You heard right, boys and girls:
Why is defining life so frustratingly difficult? Why have scientists and philosophers failed for centuries to find a specific physical property or set of properties that clearly separates the living from the inanimate? Because such a property does not exist. Life is a concept that we invented. On the most fundamental level, all matter that exists is an arrangement of atoms and their constituent particles. These arrangements fall onto an immense spectrum of complexity, from a single hydrogen atom to something as intricate as a brain. In trying to define life, we have drawn a line at an arbitrary level of complexity and declared that everything above that border is alive and everything below it is not. In truth, this division does not exist outside the mind. There is no threshold at which a collection of atoms suddenly becomes alive, no categorical distinction between the living and inanimate, no Frankensteinian spark. We have failed to define life because there was never anything to define in the first place.
This startling passage provokes a couple of questions.
The first is whether the author's conclusion, which we may take to be the conjunction of the bolded sentences, follows from the difficulty or even the impossibility of finding an adequate definition of life. The answer is: obviously not! One cannot conclude that nothing is living from the fact, if it is a fact, that it is difficult or even impossible to say what exactly all and only living things have in common that makes them living as opposed to nonliving. That would be like arguing that nothing is a game (to invoke Wittgenstein's overworked example) because there is nothing that all and only games have in common that distinguishes them from non-games. There are games and there are non-games and this is so whether or not one can say exactly what distinguishes them.
Not all concepts are such that necessary and sufficient conditions for their correct application can be specified. There are vague concepts, family-resemblance concepts, open-textured concepts. The concept bald, the concept game, the concept art. Their being vague, etc., does not prevent them from having clear instances and clear non-instances. A man with no hair on his head is bald. Your humble and hirsute correspondent is most definitely not bald. The fact that we don't know what to say about Donald 'Comb-Over' Trump does not change the fact that some of us assuredly are and some of assuredly not.
The second question is whether the author's conclusion, namely, that life is a concept that we have invented is even coherent. It isn't. I'll give two arguments. I beg the indulgence of those readers who will feel that I am wasting my time and yours with the dialectical equivalent of rolling a drunk or beating up a cripple. I agree that in general there is something faintly absurd about responding to a position whose preposterousness renders it beneath refutation.
A. If life does not exist, but is a mere concept we have invented, then a fortiori consciousness does not exist and is a mere concept we have invented. For if the difficulties in defining life are a reason for thinking there is no life, then the difficulties in defining consciousness are a reason to deny that there is consciousness. For example, there appears to be something very much like intentionality below the level of conscious mentality in the phenomena of potentiality and dispositionality. (See Intentionality, Potentiality, and Dispositionality: Some Points of Analogy.) This causes trouble for Brentano's claim that intentionality is the mark of the consciously mental. But it would surely be absurd to deny the existence of consciousness on the ground that defining it is not easy. There is a second point. Those of a naturalist bent are highly likely to maintain, with John Searle, that either conscousness is a biological phenomenon or at least cannot exist except in living organisms. So if there is no life, then there is no consciousness either.
But only conscious beings wield concepts. Only conscious beings classify and subsume and judge. So if there is no life, there are no concepts either, and thus no concept of life. Therefore, life cannot be a concept. It is incoherent to suppose that a lifeless material object could classify some other objects in its environment as living and others as nonliving.
Moreover, if consciousness does not exist, but is a mere concept we conscious beings have invented, then obviously consciousness is not a mere concept we have invented but rather the presupposition of there being any concepts at all. The notion that consciousness is a mere concept is self-refuting.
B. The author tell us that "What differentiates molecules of water, rocks, and silverware from cats, people and other living things is not 'life,' but complexity.
Note how the author takes back with his left hand what he has proferred with his right. He appeals to the difference between the nonliving and the living only to imply that there is no difference, the only difference being one of material complexity. But a difference between what and what? Now if he were maintaining that life emerges at a certain level of material complexity he would be maintaining something that, though not unproblematic, would at least not be incoherent. For then he would not be denying that life exists but affirming that it is an emergent phenomenon. But he is plainly not an emergentist, but an eliminativist. He is saying that life simply does not exist.
If the difference between the nonliving and the living is the difference between the less complex and the more complex, then actually infinite sets in mathematics are alive. For they are 'infinitely' complex. If you say that only material systems can be alive,, but no abstracta, what grounds your assertion? If life is a concept we impose, why can't we impose it on anything we like, including actually infinite sets of abstracta? Presumably we cannot do this because of the nature of sets and the nature of life where these natures are logically antecedent to us and our conceptual impositions. Sets by their very nature are nonliving. But then appeal is being made to what lies beyond the reach of conceptual decision, which is to say: life exists and is what it is independently of us, our language, and our conceptualizations. One cannot argue from our poor understanding of what life is to its nonexistence.
The fallacy underlying this very bad Scientific American piece could be called the eliminativist fallacy. An eliminativist is one who, faced with a problem he cannot solve -- in this case the problem of crafting an adequate definition of life -- simply denies one or more of the data that give rise to the problem. Thus, in this case, the author simply denies that life exists. But then he denies the very datum that got him thinking about this topic in the first place.