Nemesis. No, I don’t mean the tenth Star Trek film, a film that many of us Trekkers would like to simply imagine never happened (and thanks to J. J. Abrams’ rebooting of the franchise, we now can). Instead, I mean the long-theorized stellar companion to our Sun — perhaps a brown dwarf star — the existence of which could perhaps help to explain cycles of mass extinction on Earth. NASA’s WISE satellite, presently conducting a survey of the entire sky in the infrared spectrum, might be able to provide photographic evidence of Nemesis’ existence, although we wouldn’t be able to confirm that until about 2013 because of the time needed to process all of the data.

While it’s interesting in itself to think that we might be living in a binary-star system rather than in the single-star system that we’ve all been taught about for generations, what’s even more intriguing to me here are the curious methodological issues that the whole question of Nemesis’ existence or non-existence raises. Since we can’t see this hypothetical brown dwarf with any of our human-normal senses, any discussion of Nemesis necessarily takes place in the shadowy realm of the unobservable — which is a realm that anyone who has been following debates about scientific realism in IR or in the social sciences more generally has heard a lot about in recent years. In particular, we are often told that social structure, being unobservable, implies a scientific realist ontology in order to really make sense as a scientific concept.

I’m not sure that this is true either of social structure or of Nemesis, but not for the same reasons. There’s a key ambiguity in the notion of an “unobservable” that is sometimes exploited in scientific realist arguments in IR, in that the arguments often equivocate between things that theorists positing them say that we simply haven’t observed yet (like Nemesis) and things that theorists positing them say that we can’t possibly observe (like social structure, especially in the hands of scientific realists). Research implications follow, but first we have to be clear on the conceptual complexity involved.

First, a little basic ordinary-language philosophy. The most usual sense of the notion of “existence” involves something that we have direct sensory evidence of: I know that the book on my desk exists because I can see it, and can pick it up, and so forth. There are a whole series of conceptual calisthenics associated with teasing this notion out in a consistent way, many of which involve optical illusions or dreams or other hard cases, but I think that the basic point holds as far as ordinary speech is concerned and as long as we’re dealing with physical objects (and not definitionally transcendental objects like God or the soul; to say that such things do or do not exist gets us into a very tricky metaphysical realm that I want to avoid for the present discussion). If I don’t have direct sensory evidence of some physical object — if I haven’t actually seen a unicorn — it’s difficult for me to claim that it exists and to have those words mean what they conventionally mean in everyday speech.

In other words, our usual everyday notion of existence is pretty empiricist, to the extent that it relies on empirical evidence as the final court of appeal. Now, two caveats apply more or less immediately. First, relying on someone else’s direct sensory evidence does not seem to be a particularly complicated warrant, philosophically speaking; there are all kinds of practical or technical questions regarding the identification of reliable witnesses, but we do this all the time in everyday life so I see no reason that this ought to present any special conceptual challenge. Second, and a little more problematically, the boundary defining the things that are taken to be “direct sensory evidence” seems to be historically mutable. Most famously, the invention of the telescope did not immediately result in people regarding what one could see through a telescope as having the same epistemic status as what one could see with the naked eye; instead, it took time for the telescope to become popularly and philosophically regarded as a way of augmenting human senses such that telescope-mediated visual evidence was basically on par with direct sight. But once this was done, the telescope in effect ceased to present a perceptual problem, and looking through a telescope thereafter becomes a form of “direct sensory evidence.” Repeat the basic outlines of this story for the photographic camera, the scanning electron microscope, radar and sonar, etc., and we have a kind of “robust empiricism” which can deal with augmented human senses pretty easily.

The robust empiricist answer to the question of whether Nemesis exists, then, is pretty straightforward: look for it, and if you can see it, it exists. [I am not going to go into the various historical reasons why sight almost invariably gets privileged as the source of evidence in these discussions, but just realize that a) it does and b) that it does so is somewhat philosophically problematic, even though it doesn’t challenge robust empiricism to shift from sight to smell or touch.] One of the commentators on io9’s coverage of this story — which emphasizes the point that Nemesis is conjectured to cause periodic extinctions by disturbing the orbits of comets in the Oort Cloud and sending them speeding into the inner solar system — spells out the empiricist position on the issue quite well:

. . . we’re not even sure if the Oort Cloud is even there. Proof comes from observation, and not once have we EVER seen a comet at the distance required to prove the Oort Cloud is really there. We know the Kuiper Belt is there, because we can directly observe Kuiper Belt bodies. Not so with the Oort Cloud.

“Proof comes from observation” is the money-quote here, along with the implication that you could only really know that the Oort Cloud existed if you could get sufficient distance to actually see it and the comets that supposedly populate it. Otherwise, the Oort Cloud (the existence of which is accepted by basically all contemporary astronomers), and the brown dwarf Nemesis that might be affecting it, remain “theoretical” entities.

But note that this kind of robust empiricism has a directionality to it: even if we can’t presently have direct sensory evidence of the existence of the Oort Cloud or of Nemesis, there is nothing to prevent us from a) speculating about how its existence might help to solve certain puzzles and b) engaging in a more or less direct search for direct sensory evidence, which in this case means building a better piece of sensory augmentation equipment (the WISE satellite, which is basically designed to provide us with a better picture of the whole sky than we could get just by looking with our human-normal eyes — such survey-mapping is, so to speak, robust empiricism par excellence). Of course, we can’t say that something that we haven’t yet observed actually exists — or, better, we can’t say with any certainty whether it does or does not exist. But the point is that determining whether it does exist or not is a relatively straightforward matter of getting ourselves into the right position from which to observe it. Indeed, we might easily conclude that the point of scientific research is precisely to get ourselves in positions from which to observe as much as possible, and thus to steadily eliminate “theoretical” entities from our conceptual inventory by replacing them with observed ones.

In other words, Nemesis is what we might call an unobserved observable: an object that we could in principle observe under the proper circumstances, including the use of the proper sensory augmentation equipment. The appropriate research project for such an object, as I have suggested, is to find or build some way of observing it. Though there might be technical challenges or political obstacles to surmount in doing so, there is no reason in principle to suggest that the object couldn’t be observed, and hence no theoretical barrier to trying to do so. Matters are quite different with objects that the very theory and theorists that posit them declare to be in-principle unobservable: quarks, very high-energy fundamental particles like the Higgs boson, black holes, or social structures (at least as conceptualized by certain kinds of social theorists, in particular Marxists and feminists). The fact that the former three are thought to be in-principle unobservable because of physical laws, while the latter is thought to be unobservable because structures are dispositional conditions of possibility rather than entities reducible to their observed effects, is in this case immaterial; what matters is that all four of these objects are very different kinds of “unobservable” than Nemesis is.

As such, the terminus of research into any of these four objects cannot be a direct observation of them. According to the confinement principle of quantum chromodynamics, quarks cannot appear singly. The Higgs boson only exists at such high energy-levels that if one were to be created it would immediately decay into other particles (much like other fundamental particles, actually), so the best we can do is to indirectly detect such particles (which is why the massive machines built for the purpose are called particle detectors, and not particle observers). Black holes capture all of the energy within their event horizon, so all we can do is to infer their existence indirectly. And while we can observe what social structures make possible, we can’t build a structure-o-scope that would allow us to simply view capitalism or patriarchy — though we could and do measure the effects of those structures.

There’s more to say here, of course, particularly about how one might ever know that an in-principle unobservable object exists, and why it matters a lot if the unobservable in question is detectable or not — but I’ll save that for my next installment. For now, it suffices to conclude that whether or not Nemesis exists is a relatively straightforward question, easily answerable within the bounds of a slightly elaborated kind of common-sensical everyday empiricism, and the kind of fantastically impressive sensory augmentations that it easily accommodates.