“Where is everybody?” The Fermi Paradox

A paradox has been puzzling astronomers for decades.

In 1961 Frank Drake proposed his now famous Drake Equation, which is a thought experiment to simulate calculating the expected number of intelligent civilizations in the galaxy. It uses estimated values for things like the average number of planets around a star and how often life will form on a habitable planet. Though most of these values were complete guesses (some still are), we’re getting better at estimating the likelihood of extraterrestrial intelligence in our cosmic neighborhood.

As it turns out, we expect there to be thousands of civilizations on various planets throughout the Milky Way. Many of whom should have the ability to communicate and possibly even travel through the immense distances between solar systems. And yet, despite the Search for Extraterrestrial Intelligence (SETI) searching for signs of this life for many decades, we have no evidence of life anywhere else in the Galaxy. This is known as the Fermi Paradox after Enrico Fermi, the physicist who first proposed it.

Dozens of explanations for this paradox have been proposed over the years, but the true answer still eludes scientists. Let’s take a look at some of the common thoughts, as well as a few of the more curious solutions.

We are essentially alone

The most obvious explanation of this paradox is that the assumption of extraterrestrial intelligence currently existing in the galaxy is incorrect. This could be the case with a few different explanations:

  • Life is extremely rare to begin in the first place. Earth was a rare case where the necessary ingredients for life was a fluke, and is not a common occurrence on other planets.
  • Simple life is common on habitable planets, but rarely does it evolve into complex organisms, much less sentient, intelligent life that attempts communication.
  • Intelligent life does arise fairly often, however it destroys itself shortly after becoming spacefaring, thus the likelihood of another intelligent species currently able to communicate with us is low.

In any of these scenarios, the likelihood of finding evidence for complex life on other planets is extremely low. We may very well be the only sentient creatures in the galaxy.

We can’t find them

The Aricebo observatory in Peurto Rico

Alternative to the fact that we may be alone, is the idea that although intelligent life is relatively common in the universe, it difficult (or impossible) to find evidence of this. This assumes life, given the chance, will almost always evolve into more intelligent beings, eventually reaching a point where communication or space travel becomes possible. A number of explanations to this scenario have been proposed:

  • The distance between Earth and the nearest intelligent life is so far that communication is essentially impossible.
  • Even if a species possesses the technology to spread throughout the galaxy, it may not find it economical. Thus they remain in their local celestial neighborhood.
  • We have not been searching long enough, or looking for the right clues. Humans have been listening to only certain radio waves, and only for about 60 years. It is possible extraterrestrials are using something other than radio frequencies to communicate, such as gamma rays , or we do not understand how the information is formatted in their signals.
  • Earth is not as ideal for life as “superhabitable” planets, thus the effort of another species trying to communicate with us isn’t worthwhile.
  • Extra Terrestrials may not have any incentive to reach out to other species. This could be because they are solely interested in themselves, or perhaps because they don’t want to be found. In this scenario, a species may actually avoid detection for fear of a hostile engagement with another species.
  • Everybody is listening, and nobody is talking. SETI primarily focuses on listening to the airwaves for indications of intelligence, but does not actively transmit its own intelligent transmissions. The same could be happening for a majority of other beings.
  • Earth could be some sort of experiment, either by an extremely intelligent alien species, or entirely a computer simulation. This is known as the Planetarium Hypothesis.
  • Perhaps we have already been visited by aliens, and are either A) unknown to us, or B) occurred in the distant past, so we have no evidence.

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