I don’t know about you, but thinking of aliens brings up images of UFOs and bright green skin, bulbous heads and an echo of “Take me to your leader.” However, this representation of extraterrestrial life is simply something made up by Hollywood and pop culture. As far as we know, Earth has never been visited by a species from another planet, solar system or galaxy (regardless of what History Channel says). However, several scientists have argued that there is a high probability for the existence of extraterrestrial life, in spite of the lack of evidence. Let’s talk through why we think aliens could be there, and possibly why we haven’t met them yet.
Most people regard the issues of aliens as something antithetical to science, but scientists have been studying, thinking, and calculating the probability of extraterrestrial life for years. One of the most important arguments for the existence of aliens was presented by Italian physicist Enrico Fermi in 1950. He postulated that any civilization with some rocket technology and an imperial desire could easily colonize the galaxy, yet the paradox is that we have no evidence that this has happened even though it seems fairly simple. The Search for Extraterrestrial Intelligence Institute said of the Fermi paradox:
Within ten million years, every star system could be brought under the wing of empire. Ten million years may sound long, but in fact it’s quite short compared with the age of the Galaxy, which is roughly ten thousand million years. Colonization of the Milky Way should be a quick exercise.
Another astronomer who approached the thought of aliens was Dr. Frank Drake, an American radio astronomer. He created an equation, known simply as the Drake Equation, to calculate the probability of technological civilizations.
This equation is famous, but there are difficulties in using it. Some of the parameters, such as planets that develop intelligent life with interstellar communication, won’t be measurable until we actually discover these civilizations. Which, unfortunately, isn’t reality yet.
The fairly recent development of astronomers’ ability to detect exoplanets has also fueled the fire to find alien civilizations. There are thousands of confirmed planets in other solar systems, and definitely thousands more. Our current techniques for finding exoplanets places emphasize finding Jupiter-like planets at Mercury-like distances, so scientists have not been able to easily find Earth-like planets yet. However, as exoplanet discovery improves there is much possibility for finding other Earths, and with that possibly other life forms.
With the ideas of Fermi and Drake and the discovery of exoplanets, it seems like a strong case for the existence of aliens. However, Michael Hart, an American astrophysicist, responded to Fermi’s idea in 1975 with the hypothesis that maybe intelligent life just isn’t out there. While he did say more research was needed into astrobiology and planet formation to confirm anything, he discussed four arguments that could answer Fermi’s paradox.
- Aliens never came because space travel is not possible for them
- Aliens chose not to come to Earth
- Advanced civilizations developed too recently and aliens have not had time to reach us yet
- Aliens visited Earth in the past without observation
Other more recent responses to Fermi’s paradox hypothesize that Earth formed fairly early in terms of the universe for a habitable planet. Most of the elements needed to create planets that support life are still out in the universe and have been increasing in the 4.6 billion years since Earth’s birth. Supporting Hart’s argument that advanced civilizations developed too recently, Earth would be one of the first advanced civilizations rather than being in the middle of pack.
Another response was the argument that terrestrial planets can support life, but often not for very long (in space terms at least). Think Venus and Mars, for example. Before the run-away greenhouse effect and the loss of the atmosphere respectively, these planets could have supported life. This was a short gap of a couple hundred million years where life could have existed, but we would never know because it is all wiped out by now.
Arguments about the possibility of extraterrestrial life are plentiful, but the reality is that we will never know the truth until we either find another civilization or expand enough to confirm we are truly alone. The one prediction I’m betting on though? Bright green skin is and will always be just a Hollywood fabrication.