An excerpt of The Fermi Paradox in the last chapter, ‘Chapter 9: Is Anybody Out There?’:
Italian physicist Enrico Fermi asked in an informal chat over lunch in 1950 with other physicists, “Where is everybody?”
The question has been asked as long as humans have known that space is filled with so much more than seemingly nearby twinkling lights, and the question boggles the brains of astronomers to this day.
When Fermi asked the famous question, scientists thought that there should be countless civilizations in nearby space, and at least some should be easily detectable.
The question by Fermi became known as the Fermi Paradox. Fermi and his colleagues considered it a conundrum that if intelligent life in the universe should be, based on their observations, plentiful, then why had we been unable to make contact with anyone? We know that there are billions of stars in the Milky Way, and at least 10% of those stars are sun-like and thus conducive to hosting a habitable planet. More recently we have learned that there are at least as many planets as there are stars. With this in mind, we may suppose that there could be millions of intelligent civilizations in the Milky Way galaxy alone! This again begs the question, “Where are they?”
While the majority of civilizations may never make it out of their star system, or even off their planet, pure statistical reasoning suggests that some of them should have. Humans on Earth have shown that it is possible to achieve space travel. We also know enough about physics and space to suggest that interstellar travel is not impossible. Amongst the intelligent lifeforms in the galaxy, humans, it ought to be presumed, are of average intelligence; if this is so, then it follows that aliens of greater intelligence should be able to travel through the galaxy. Space is vast, but Fermi and others thought that with technological prowess that far outweighs our own, some alien civilizations should have been able to tour the galaxy many times already.
Is life and eventually the evolution of intelligent creatures a freak occurrence in the cosmos? We know that there are about 40 billion sun-like stars in the galaxy and, according to data from the Keck Observatory and the Kepler spacecraft, 20% of sun-like stars in the Milky Way have an earth-sized planet in the habitable zone. Statistical probabilities alone tell us then that planets with life and, by extension, intelligent civilizations, should be scattered throughout the galaxy. Life then should not be a freak occurrence.
The mediocrity principle states that any single item selected at random from a set of items, such as any given star selected at random from a set of stars, will likely be a more common item in the set than a rarer item. For example, 70% of all stars in the galaxy are Red Dwarfs. The mediocrity principle suggests that if we randomly selected a star from the galaxy, it would likely be a Red Dwarf. The same goes for planets like Earth and, by extension, life and civilization. Since we know that Earth exists, then it is reasonable to assume that Earth is not of the rarest category of planet, and neither are we as intelligent creatures. Moreover, it becomes quite unreasonable to propose that we are entirely alone in the universe.
If this principle of mediocrity applies, then, indeed, where are they?
There are many theories about why we have not yet detected an alien civilization, but we can divide the theories into two groups: detection and existence. That alien civilizations are out there and we have simply failed to detect them is one possibility – it is quite another to realize that there may be none out there at all, at least at the present time. There may be an insurmountable progress barrier that stops them (and eventually us) from advancing far enough to be detected.
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