There Is No Fermi Paradox

The "Fermi Paradox," an argument that extraterrestrial intelligence cannot exist because it has not yet been observed, is a logical fallacy. This "paradox" is a formally invalid inference. both because it requires modal operators lying outside the first-order propositional calculus and because it is unsupported by the observational record. © 1985 Academic Press. Inc.

Note: This web version is derived from an earlier draft of the paper and may possibly differ in some substantial aspects from the final published paper.

Renewed activity in the field of Search for Extraterrestrial Intelligence (SETI) has stimulated interest in an old argument purporting to show that ETI cannot exist. Known as the "Where Are They?" question or the "Fermi Paradox," this sophism posits that in time an intelligent extraterrestrial species must achieve high technology, exploring and colonizing first its planetary system, and later the Galaxy, as humanity has explored and colonized the Earth. These beings should have been able to travel to Earth, but we see no evidence of such visitations, hence ETI cannot exist. Proponents of the "paradox" (e.g., Hart, 1975; Tipler, 1980; Hart and Zuckerman, 1982) admit that it is incomplete in the loose form outlined above. but argue that alternatives purporting to explain the paradox (e.g., Ball, 1973; Sagan and Newman, 1983) are invalid or lead to contradiction or impossibility. This position has been weakly challenged (Cox, 1976; Schwartzman, 1977; Papagiannis, 1980; Stephenson, 1982), but the debate continues.

the inference is semantically valid if and only if it is possible to assert that not-(probably C) is true. But the truth value of not(probably C) is indeterminate, so S2 is, classically, semantically invalid. The embedded uncertainty cannot be removed from the primary and secondary subjunctives because neither A ® B nor B®C is certainly true; not-C cannot imply not-A because C is a subset of B and B is a subset of A (Fig. 1). Hence the Fermi Paradox line of reasoning has no formal probative value whatsoever.

Probably can also be treated using modal first-order predicate calculi (Snyder, 1971; Bowen, 1979). Modal epistemic logics dealing in a limited way with what is known and with what is believed, credible, plausible (Rescher, 1964, 1974), or probable have been studied but show only weak transitivity because something being possible or probable is not incompatible with its not being so. To insist otherwise is to claim that whatever is probably so necessarily is so and that what is not so can have no probability of being so, demonstrably erroneous positions (White, 1975).

For example, an appropriate observational search limit for extraterrestrial messenger probe size is 1-10 m (Freitas, 1983b). A trans-Plutonian spherical solar system boundary encloses 260,000 AU³ and 10¹¹ km² of planetary and asteroidal surface area. The continuous visible sky search limit is perhaps +14 mag by amateurs, plus intermittent coverage to +21 mag with the Palomar Schmidt and +24 mag for the best ground-based telescopes. Thus current surveys could not have detected even a 1- to 10-m probe more than 0.01-1 AU from Earth, so heliocentric orbital space is at least 99.999% unexplored for 1- to 10-m artifacts. The space telescope cannot materially improve this situation because of narrow field and a tight schedule. IRAS data establish new IR search limits about as good as in the visible; microwave limits remain far poorer.

Less than 10% of the Earth's surface, 1% of the Moon, 0.1% of Mars, and 10^-7% of Venus (total 5 x 10⁷ km²) has been surveyed to 1- to 10-m visible resolution. This leaves 99.96% of Solar System surface area (1.3 x 10¹¹ km²) unexamined for likely artifacts. Interplanetary spacecraft and ground-based telescopes have photographed portions of some planets and asteroids down to 20-km resolution, plus a few tracts on some outer planet moons to 1-10 km. Objects buried or submerged are undetectable with current instrumentation. Large artificial habitats in the asteroid belt (Papagiannis, 1978) would appear visually indistinguishable from natural objects, especially since the belt population itself is poorly cataloged. The assertion that a resident artifact would alert us to its presence is an unwarranted, unsupportable, and untenable assumption.

There have been few serious searches (Freitas and Valdes, 1980; Valdes and Freitas, 1983) even for the most likely classes of oberservable artifacts, and none for less-likely classes. An active Search for Extraterrestrial Artifacts (SETA) program (Freitas, 1983a,b) would help fill this enormous and critical gap in the observational record.

See Also:

• R. A. Freitas, "Fermi's Paradox: A Real Howler," Issac Asimov's Science Fiction Magazine 8(September 1984):30-44.
• R. A. Freitas, "Extraterrestrial Intelligence in the Solar System: Resolving the Fermi Paradox," JBIS 36(November, 1983):496-500.