This hypothesis claims that aliens can see us, but we cannot see them.

Ask your friends why scientists have failed to find aliens, and you can be sure that at least one of them will give the following answer: Humans don’t deserve it.

We are flawed beings. We routinely threaten each other, not to mention other species and the environment.

This doesn’t sound very civilized and provides a plausible explanation for the lack of alien contact. Maybe the aliens know we’re here, but they don’t want anything to do with us — either communicating or visiting.

This idea is endlessly appealing. It is also old. In 1973, MIT radio astronomer John Ball published a paper suggesting that the lack of success in the discovery of cosmic civilization was not due to a lack of aliens. It was because these sentient people from another world agreed to a policy of exclusion.

They kept their distance not because we are imperfect, but because of our right to pursue our destiny. Diversity is something that everyone in the cosmos is supposed to value, so life-bearing worlds should be left to their evolutionary development.

You might think of Ball’s idea as similar to Star Trek’s famous “prime directive,” which forbade Federation members in spaceships from doing anything that might interfere with other cultures or civilizations, even if that interference was well-intentioned. The MIT astronomer proposed that we’ve failed to make contact with aliens not because we’re unworthy, but because we’re worthy — like endangered eels.

The ball went further, proposing that we may live in a metaphorical zoo — a kind of cosmic Eden.

The aliens of the galaxy have somehow arranged things so that our planet is protected from them by one-way bars: they can notify us, but we cannot notice them.

One good thing about this conjecture is that it provides a solution to a long-standing puzzle known as Fermi’s Paradox. Discovered almost 70 years ago by the physicist Enrico Fermi, it is based on the fact that the universe is very old.

Consequently, if intelligent life is common, then some of it is surely advanced enough to have colonized the entire galaxy. We should see evidence of aliens everywhere. The fact that we cannot explain Ball’s hypothesis is that we are deliberately isolated.

The zoo hypothesis has been in the news recently because it also justifies an activity known as METI, short for Messaging Extraterrestrial Intelligence. Simply put, METI practitioners send radio signals into space with the hope of eliciting a response from any aliens who might pick them up. In 2017, a Norwegian antenna was used to transmit a message to a star system 12 light years away.

Earlier this March 2017, the entire operation was discussed by researchers at a meeting in Paris. Douglas Vakoch, president of METI International, a San Francisco-based organization that organized the Norwegian broadcast, cited the zoo hypothesis as a possible justification for the broadcast. After all, if the hypothesis is correct, then it is understandable why our efforts to find signals from space have not been successful. We’ve been mindlessly walking around in our earthly cage while the aliens keep their distance and watch.

But as Vakoch argues, this one-way scenario could be changed. If a zoo animal suddenly starts communicating through the bars, saying “I’m here and I think you’re there,” those on the other side might respond.
Simply put, deliberate transmissions by METI could lead to a discovery of the cosmic company because the transmissions would tell the aliens that we no longer need their education. We are old enough for them to contact us.

However, the zoo hypothesis depends on the fact that life on earth is really important — our existence is significant enough to dictate the behavior of societies that may be millions or billions of years more advanced. And Ball’s idea requires a galaxy-wide barrier to prevent all evidence of intelligent inhabitants — radio signals, laser flashes, even the construction of easily detectable megastructures — from being seen by Earthlings. How would you do that, even if you were a highly advanced alien?

Additionally, the idea that all aliens are out to keep our planet free and natural sounds weird, self-centered, and a little too altruistic. Let’s face it: the prime directive has never been fashionable with us. Indeed, we seem to prefer the opposite: on Earth, we interfere with each other’s cultural development all the time.

So the zoo hypothesis seems more than a little far-fetched.
On the other hand, we have to admit that she is wise.