Summary: The extraterrestrial hypothesis, or ETH, is formulated consistent with the accepted scientific framework for hypothesis induction. The null hypothesis to explain UFOs is that they are random, disparate misidentifications of atmospheric or artifical terrestrial phenomena. This is called the misidentification hypothesis. If rejected on sufficient grounds -- and due to the subjectivity we are probably facing a more Bayesian type of inference than an objective test approach -- then we accept the alternative hypothesis, which is that disk-shaped vehicles are in fact flying in our atmosphere.
The extraterrestrial hypothesis, or ETH, is formulated consistent with the accepted scientific framework for hypothesis induction. The null hypothesis to explain UFOs is that they are random, disparate misidentifications of atmospheric or artifical terrestrial phenomena. This is called the misidentification hypothesis. If rejected on sufficient grounds -- and due to the subjectivity we are probably facing a more Bayesian type of inference than an objective test approach -- then we accept the alternative hypothesis, which is that disk-shaped vehicles are in fact flying in our atmosphere.
Note that at this point, we are not concerned with the origin, since the alternative hypothesis is simply that the objects exist without regard to the origin of the objects. Put simply, we don't need to know the origin of the objects in order to determine their existence. In fact, nowhere in science is it necessary to establish the origin of a phenomenon prior to determining the very existence of the phenomenon. Yet skeptics contend that the objects cannot exist due to interstellar travel considerations, which is fallacious on two counts: first, for blending the two hypotheses into one by using the possible origin to debunk the very existence, and second, for establishing a rigid a priori probability of nearly zero for interstellar travel despite a lack of sufficient information to make such a determination.
After rejecting the null in favor of the alternative, which is that the objects exist, a rank-order series of hypotheses are formulated to hypothesize the origin of the objects. When guessing the origin, we see three elements that are observed in the majority of radar-visual cases:
Propulsion technology beyond human grasp
This is why radar-visual cases are so unique in their evidential value. Those three conditions are necessary and sufficient conditions to defend inducing the ETH; the question is the degree of corroboration for each of the conditions. When ranking possible origin hypotheses, Occam's Razor is the guiding principle here:
American or foreign government craft
Once one replaces the null with the alternative and looks for a hypothesis of origin, it is feasible to reject the first origin hypothtesis. It is absurd to think these are government craft, since the so-called "conspiracy" widens by a huge magnitude: the behavior of the flights are at variance with accepted flight-test procedures (e.g. chasing civilians), and the requisite physics for the observed propulsion would require enormous leaps in 1947 in all sorts of technology that the civilian community still has not grasped 50 years later.
The second hypothesis, that they are extraterrestrial craft, is the "Extra-Terrestrial Hypothesis", or ETH. Note that this is a specialized sub-hypothesis within the broader, original "alternative hypothesis", which is simply that the "saucers" do in fact exist. Some researchers, like Vallee, reject this and move to the third hypothesis, though that is beyond the scope of this article.
Falsifiability is a difficult area because the very approach to the subject is more subjective and inferential (hence the Bayesian approach -- see Sturrock, "Applied Scientific Inference", Journal of Scientific Exploration, vol. 8, no. 4). The very nature of the problem -- the vagueness, the lack of replicability on demand, and the elusiveness -- does not lend itself with ease to direct and irrefutable falsifiability.
However, there are certain "proxies" for falsifiability. It seems reasonable to suggest that if there are extraterrestrial vehicles buzzing through our atmosphere, the organization with the means and motive to determine this, above all other organizations, would have determined this by now. This organization is, of course, the US military. If there are flying saucers, our military should show a high level of interest and conviction that this is the case. Indeed, they do, at both the individual level and at the organizational level, from 1947 through the present day, as revealed through Freedom of Information Act documents and summarized in our government pages.
Then there are certain other testable predictions based on the corollary that the military and intelligence would conceal this knowledge. And they have found sufficient cause to conceal it, as their early documents alluded with references to "public panic" and "policies of public information to minimize mass panic". So, do we see signs of official secrecy? What would those signs be? One is leaks. We do, in fact, see quite a few highly compelling leaks from such scientists as Dr. Robert Sarbacher, Dr. Eric Walker, and other military and intelligence personnel on the military quotes page.
Another means of indirect falsification would be the discovery of one or more new terrestrial phenomena that are merely atmospheric in nature, but can adequately explain the body of UFO evidence, from radar-visual to ground-trace cases to machine-like disk-shaped vehicle mirages.
The very nature and structure of this phenomenon renders our typical approach somewhat impotent, and we are mostly left with a Bayesian approach that questions whether the body of evidence we do have is more consistent with the objects existing or with the objects not existing. Looking at the aggregate body of anomalous radar-visual cases, ground trace cases, scientifically tested photos and films from the military and civilian communities, credentialed leaks, and evidence of military and intelligence duplicity, it is more likely that something is indeed going on rather than not -- no matter how falsifiable this hypothesis may be, it doesn't change the aggregate body of evidence. The evidence is far more consistent with the objects existing than not existing.
Our approach must accommodate the phenomenon -- not vice versa. If the phenomenon cannot accommodate our approach, there is no sense in convincing ourselves that the phenomenon must not exist. We must accommodate this elusive, sporadic, and unreplicable but nonetheless existent phenomenon by blending our approach between objective hypothesis falsification and Bayesian inference.
As for the inductive reasoning, the approach is identical in process and in validity to the Big
Bang hypothesis which also has no physical proof. Both induce a hypothesis to explain a set
of observations without violating known laws of physics according to our existing body of knowledge. Both also make predictions that have been corroborated, and both explain the observations superior to any alternatives. The misidentification hypothesis is an utter failure in both logical process and in explanatory appeal, as detailed in the page on skeptical logical trickery and as judged by the inability to explain the most challenging cases, but the ETH is scientifically valid and superior to the alternative. The problem with the misidentification hypothesis is that the cases it fails to explain, according to USAF's Project Bluebook Special Report #14, happen to be the types of cases that the best observers were most likely to report and that do not suffer from insufficient information, but rather appear to be from a wholly different distribution than the the eventually identified UFO reports, based on a chi square analysis.
The misidentification hypothesis has a gaping flaw in its ability to explain the observations, and the ETH is a scientifically valid hypothesis that is the simplest available to explain globally repeating, highly reliable observations by eminently qualified observers of solid objects under intelligent control with propulsion technology irreproducible by human knowledge. All possible predictions of the ETH have been corroborated, and the inductive process is every bit as valid as the process that led to the Big Bang hypothesis.
Illogical skeptics will complain that any hypothesis can be induced in this framework, such as a giant purple unicorns or flying cats. But the problem is that our current physics predicts that aliens exist, and we know that interstellar travel is possible; it may be difficult, but it certainly is possible, and many scientists like Tipler feel that it is almost inevitable. This is why the ETH is the simplest hypothesis after the misidentification hypothesis is discarded. Hypotheses in between, such as an "unknown atmospheric phenomenon", are too vague and specious to be of any value, since they are the logical equivalent of postulating an "undetected flaw" in the analysis of a radar-visual case; but most of all, such a hypothesis fails to explain daylight sightings, and only relies on nocturnal luminosity reports, which is a selective filtration of the observations. Therefore, only the ETH can be of value after rejection of the misidentification hypothesis.