Zoo hypothesis

The zoo hypothesis states that superintelligent extraterrestrial life exists and does not contact life on Earth to allow for its natural evolution and development. This explains the apparent absence of extraterrestrial life despite the mounting evidence for its existence (Fermi Paradox).

Aliens might, for example, choose to allow contact once the human race has passed certain technological, political, or ethical standards. They might withhold contact until humans force contact upon them, possibly by sending a spacecraft to planets they inhabit. Zoo Hypothesis rests on the assumption that aliens have great reverence for independent, natural evolution and development.

These ideas are perhaps most plausible if there is a relatively universal cultural or legal policy among a plurality of extraterrestrial civilizations necessitating isolation with respect to civilizations at Earth-like stages of development. In a Universe without a hegemonic power, random single civilizations with independent principals would make contact. This makes a crowded Universe with clearly defined rules seem more plausible.

If there is a plurality of alien cultures, however, this theory may break down under the uniformity of motive concept because it would take just a single extraterrestrial civilization to decide to act contrary to the imperative within our range of detection for it to be abrogated, and the probability of such a violation increases with the number of civilizations. This idea, however, becomes more plausible if all civilizations tend to evolve similar cultural standards and values with regard to contact much like convergent evolution on Earth has independently evolved eyes on numerous occasions, or all civilizations follow the lead of some particularly distinguished civilization . . . the first civilization.

With this in mind, a modified Zoo Hypothesis becomes a more appealing answer to the Fermi Paradox. The time between the emergence of the first civilization within the Milky Way and all subsequent civilizations could be enormous. Monte Carlo simulation shows the first few inter-arrival times between emergent civilizations would be similar in length to geologic epochs on Earth. Just what could a civilization do with a ten million, one hundred million, or half billion year head start?

Even if this first grand civilization is long gone, their initial legacy could live on in the form of a passed down tradition. Beyond this, it does not even have to be the first civilization, but simply the first to spread its doctrine and control over a large volume of the galaxy. If just one civilization gained this hegemony in the distant past, it could form an unbroken chain of taboo against rapacious colonization in favour of non-interference in those civilizations that follow. The uniformity of motive concept previously mentioned would become moot in such a situation.

If the oldest civilization still present in the Milky Way has, for example, a 100 million year time advantage over the next oldest civilization, then it is conceivable that they could be in the singular position of being able to control, monitor, influence or isolate the emergence of every civilization that follows within their sphere of influence. This is analogous to what happens on Earth within our own civilization on a daily basis, in that everyone born on this planet is born into a pre-existing system of familial associations, customs, traditions and laws that were already long established before our birth and which we have little or no control over.

Much further development and refinement of this theory is possible. Mathematical models could be constructed to determine how long it would take for a civilization to spread its influence at different velocities. Spreading exponentially, it seems conceivable that vast quantities of spacetime could be covered.

It will eventually be possible to send spacecrafts to various planets in habitable zones. While this would take thousands of years, we potentially have billions of years to work with. However, contact may not be in Earth's best interest. Aliens would tell humans to go back to Earth and stay. Or they may have perfected a method of introducing intelligent life into the Galactic or Universal community.

Zoo hypothesis infers that aliens are benevolent, as it seems likely that hostile aliens would have exploited Earth long ago. Perhaps the Earth may has been set aside as an explicit experiment that contact would ruin.

While zoo hypothesis suggests that there is a rule prohibiting contact, it is possible that passive observations are allowed. If this is the case, Earth is probably under close study, because humans seem to be going through a critical phase in the evolution of life and intelligence.

Zoo hypothesis would be the latest case of anthropocentrism, the tendency for human beings to regard themselves as the central and most significant entities in the universe, leading to incorrect assumptions about reality which are ultimately shattered. Humans, though unique, would be a common result of a universal process, and once contact is established, we would seem to be the least intelligent "intelligent" civilization in the Universe.

Appearance in fiction

• In Olaf Stapledon's 1937 novel Star Maker, great care is taken by the Symbiont race to keep its existence hidden from "pre-utopian" primitives, "lest they should lose their independence of mind". It is only when such worlds become utopian-level space travellers that the Symbionts make contact and bring the young utopia to an equal footing.

• Arthur C. Clarke's The Sentinel (first published in 1951) and its later novel adaptation 2001: A Space Odyssey (1968) a beacon which is activated when the human race discovers it on the moon. An alien race has apparently visited us in the distant past.

• In Childhood's End, a novel by Arthur C. Clarke published in 1953, the alien cultures had been observing and registering the Earth's evolution and human history for thousands (perhaps millions) of years. At the beginning of the book, when mankind is about to achieve spaceflight, the aliens reveal their existence and quickly end the arms race, colonialism, racial segregation and the Cold War.

• In Star Trek (1966), the Federation (including humans) has a strict Prime Directive policy of nonintervention with less technologically advanced cultures which the Federation encounters. Also, the Vulcan race limited their encounters to observation until humans made their first warp flight, after which they initiated first contact.

• In Robert J. Sawyer's SF novel Calculating God (2000), Hollus, a scientist from an advanced alien civilization, denies that her government is operating under the prime directive.