Even with all of the advancements in modern technology, we still haven’t made contact with intelligent life on other planets. But what if our attempts to communicate have been ignored?

In 1973, a radio astronomer named John Ball came up with a possible theory as to why aliens – if they do exist – haven’t gotten back to us. Ball’s “Zoo Hypothesis” as it came to be known, posits that alien civilizations exist, and the most highly developed of them have been communicating. This elite alien “club” has come upon a mutual agreement to leave those deemed primitive or “lesser” life forms alone, only to be watched from a distance. Earthlings, therefore, did not make the cut with the galactic cool kids.

So assuming these aliens exist, under what circumstances could they all agree to keep us in the dark? A Scottish astronomer named Duncan Forgan has the answer.

“I was interested in this theory because it is so difficult to test in a scientific fashion,” Forgan told FoxNews.com. “The Zoo Hypothesis relies on us being unable to observe other aliens, so a failure to observe aliens can be used both as evidence for and against the hypothesis at the same time!”


Forgan decided to test the assumptions that make up the hypothesis, instead of the hypothesis itself. One of these assumptions is that intelligent extraterrestrials can agree on a “no contact with primitive worlds” policy.

“Agreement requires communication, which is limited by the speed of light,” Forgan explained.

This would assume that civilizations must have existed long enough for messages to go back and forth between them, a process limited by the speed of light. Another assumption is that life would be able to thrive in a galaxy–wide habitable zone. Forgan entered these assumptions into a computer program, which then went about simulating civilizations and randomly placing them around the habitable zone, measuring the distance between them and calculating the likelihood of any two of them making contact and communicating within their lifetimes.

The computer found that for a "leave the Earthlings alone" agreement to be likely, at least 500 civilizations must exist, each of them having lasted over one million years. Any less than 500 civilizations and there are too many groups of civilizations to form a pact; if any one civilization lasted less than a million years, then there are also too many civilization groups to form the galactic club. (A “civilization group,” Forgan explained, is “a collection of civilizations that are ‘culturally connected’, which basically means that a civilization is aware of the others in the group as soon as it is technologically ready.  Weirdly, the civilization groups are actually pretty well-mixed in space, which you wouldn't expect naively - the issue is their separation in space-time, not their separation in space.”)

In other words, Earth may not be in the universal doghouse after all.

“I was able to show that in general, a population of alien civilizations are sufficiently separate that instead of there being a single ‘Galactic Club’ of aliens agreeing to shield Earth, there are most likely many smaller ‘Galactic Cliques’, who are likely to disagree on whether planets like Earth should be kept in the dark,” Forgan said. “It's not really true that the computer ‘proved’ this result– it suggests that large numbers of long-lived civilizations (who all appear in the Universe in a short time interval) gives the best conditions to form a Galactic Club.”

So instead of one alien club there may be various smaller cliques scattered about the universe that haven’t managed to agree on what to do about Earth. Forgan’s paper, published at arXiv.org, notes that our planet may happen to be in a neighborhood overseen by a clique that doesn’t want to talk, which might change as our technology advances.

But is that necessarily a good thing? Some experts think it would be disastrous, with famed physicist Stephen Hawking believing advanced aliens would likely conquer and colonize Earth, as Europeans did the Americas.

Forgan said running such a scenario through the computer is unlikely at this point. “Hawking makes one of several assumptions about alien behavior to come to this conclusion: one– Aliens that explore the Galaxy in person do so because of their aggressive nature, or two– Intelligent beings only evolve from predators or naturally aggressive creatures, or three– Peaceful aliens do not explore the Galaxy,” he said. “These assumptions are tricky to test with computer simulations, as it requires us to simulate alien behavior, which we don't have any data for.”