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Are we alone in the universe? Is alien life possible? Is there life on Mars? The existence and nature of extraterrestrial life have been debated as far back as we have records of people looking up into the sky. Prominent thinkers as far back as Ancient Greece and Rome have argued that the existence of many millions of stars in the night sky make it likely that other habitable planets existed which could play host to life. In our latest video, we give a brief overview of some of the key concepts in the modern search for alien life. Keep reading below for more fascinating facts about humanity’s history with the search for aliens.
Did the Ancient Greeks believe in aliens?
The idea that our universe might be host to multiple life-bearing planets has a surprisingly long heritage. The most popular understanding of the universe in antiquity came from Aristotle, whose work On the Heavens set the standard cosmological model for over a millennium: the Earth at the centre of the universe, surrounded by rotating spheres of perfect crystal in which all heavenly bodies were embedded. Yet other Greek scholars posited alternative theories, (correctly) imagining that our planet was just one among many, some of which might be home to other forms of life.
As our understanding of astrophysics and the relationship between our planet and the other objects visible in the night sky has developed over the last few millennia, many astronomers have suggested the possibility of alien life. However, religious oppression by the Catholic church throughout much of European history has meant that these suppositions were rarely sketched out or researched, due to fears that the existence of other life-bearing planets might be deemed heretical.
What is SETI?
SETI is a term which covers all manner of attempts to find evidence for or direct proof of the existence of intelligent life beyond our home planet. Since before the advent of radio communication, scientists and engineers have considered ways that we could theoretically converse with aliens. Today, the search for intelligent alien life is carried out by a number of nonprofit organisations, networks of amateur enthusiasts and state-funded scientific missions. Prominent physicists have supported efforts to seek out alien intelligence; in the 1970s, Carl Sagan was an influential public figure who successfully campaigned for US Congress to fund various search efforts by NASA, as well as putting the famous Golden Records on the Voyager probes.
Who is Frank Drake?
Frank Drake is an astrophysicist and astronomer who was involved in many of the most famous efforts to find and communicate with alien intelligence, including the Voyager Golden Records. He wrote the Arecibo message, which was a radio message broadcast in 1974 to the Great Globular Star Cluster, a group of stars in the constellation of Hercules over 22,000 light-years away from Earth. The Arecibo message was a binary-encoded series of pictograms meant to communicate certain facts about humanity, such as our ability to count, the chemical and physical structure of DNA, the shape and size of our bodies, a rough depiction of our solar system and our planet, and the telescope used to send the message.
How do you explain the Fermi Paradox?
The Fermi Paradox is the name given to the contradiction between two ideas: that the universe may be teeming with other life, and that we have yet to see any meaningful evidence for its existence. While Italian scientist Enrico Fermi wasn’t the first person to express this idea, the conversations he had with fellow scientists about the prospect of alien life were widely discussed in scientific circles and Fermi’s outburst of “Where is everybody?” became the stuff of legend.
There are many theories put forward to explain the Fermi Paradox, as discussed in the video. Many of these theories seem drawn out of science fiction: for example, one theory is called the Zoo Hypothesis, which states that extra-terrestrial life does exist, has a much higher level of technological capability than we do, and is intentionally concealing its existence for some reason.
While this may sound unlikely, many of our own scientists argue that, in a future where humanity has interstellar travel capabilities, we should maintain the same policy to prevent human interference from disrupting the natural development of less developed species. The idea is perhaps most famously explored in science fiction like Star Trek, where the United Federation of Planets follow a Prime Directive that forbids any interference in the internal and natural development of alien civilizations below a certain threshold of technological, scientific and cultural development.
How will we find aliens?
If you’re looking for life on other planets, where do you focus your search? For that matter, what do you look for? Scientists refer to the question of whether a planet (or natural satellite such as a large moon) could support life as “planetary habitability”. Because the only planet we currently know of which supports life is Earth, our search has focused on finding Earthlike planets. While there are many other factors, the four main criteria are:
1. A nearby star
Living things need energy to survive. All life on Earth ultimately feeds off energy absorbed from the Sun’s rays. A nearby star is the obvious energy source, which should be roughly the same size and age as our Sun, and consistent in the amount of energy it puts out without sharp spikes that could dramatically change the environment of the habitable planet.
2. Earth-like gravity
Our atmosphere not only circulates elements used by living things for respiration, but traps heat, meaning the planet isn’t subject to extreme swings in temperature between day and night. A sufficient mass pulling toward the centre of the Earth is also required for tectonic activity, which is now believed to be important in circulating resources through the Earth’s crust and creating diverse climates on the planet, maximising the chance of life developing, spreading and diversifying.
3. Liquid water
Water is an essential component of almost all organic chemical reactions that make up living beings. It’s almost certain that all life on Earth originated in increasingly complex water-borne microorganisms which could not have existed without free-moving chemicals interacting in a solvent like water. The four elements most vital to life on Earth are carbon, hydrogen, oxygen and nitrogen, so liquid water is a big sign of habitability.
4. A short day-night cycle
Frequent rotations of a planet mean that no one area is in light or darkness for too long, meaning temperature remains relatively stable, which supports the evolution of complex life forms. What’s more, rotation of a planet with a metal core creates a magnetic field which deflects harmful radiation, like our ionosphere.
For more fascinating scientific facts about our universe, check out our educational YouTube playlist.