Fermi paradox

The Fermi paradox is the apparent contradiction between the high statistical likelihood that intelligent civilizations exist elsewhere in the universe and the lack of scientific evidence of their existence. The paradox was first proposed in 1950 by physicist Enrico Fermi who casually asked, "Where is everybody?" in response to why humans had not had contact with alien life. The question was further explored decades later by the work of several astrophysicists.

The argument of the Fermi paradox assumes that since the Milky Way galaxy has hundreds of billions of stars, it is almost certain that many of those stars would have planets able to support intelligent life. Because many of those stars are also far older than the Sun, it is highly likely advanced civilizations would have had time to develop. Yet, human astronomers have not detected any signs of such civilizations, and there is no evidence Earth has been visited by aliens in the past.

Background

Enrico Fermi was an Italian-born physicist who won the 1938 Nobel Prize for his work in nuclear fission. Near the start of World War II (1939–1945), Fermi fled Italy for the United States. In 1942, he created the world's first controlled nuclear chain reaction, an instrumental discovery in the advancement of nuclear technology. After that success, Fermi was recruited to work on the Manhattan Project, the secret effort by the United States government to develop an atomic weapon.

In 1944, Fermi rose to become the assistant director of the Los Alamos Laboratory in New Mexico, the site where the first atomic bombs were built. After the end of the war, he became a professor at the Institute for Nuclear Studies at the University of Chicago. He continued to work on nuclear-related projects until his death in 1954.

While on a return visit to Los Alamos in 1950, Fermi was having lunch with some colleagues when the conversation turned toward a recent increase in UFO sightings. According to eyewitnesses, the scientists were discussing a humorous magazine cartoon showing a flying saucer stealing trash cans from New York City when Fermi asked, "Where is everybody?" Fermi was known for asking theoretical questions about seemingly difficult-to-answer subjects. His comment began a scientific speculation about the existence of extraterrestrial intelligence, the possibility of interstellar travel, and whether humans were alone in the universe. Fermi did some basic mathematical calculations on the issue and concluded that Earth should have already been visited by alien life. He never published his work and never followed it up with significant research.

Overview

At the heart of the Fermi paradox is the knowledge that the universe must contain an incredibly large number of stars. Just using Earth's home galaxy as an example, astronomers estimate the Milky Way contains between 100 billion and 400 billion stars. Because the Sun is an average star, there must also be billions more stars like it in the galaxy. Laws of probability state that many of these stars would have planets similar to Earth, and on many of these worlds, intelligent life must have developed.

The paradox also takes into consideration that since the Sun is about 4.6 billion years old and the Milky Way about 13.6 billion years old, some of these civilizations must have had far more time to develop than humanity. They would be more technologically advanced and more than likely would have discovered some type of space travel. Even with the vast interstellar distances, given enough time, some alien civilizations must have found a way to colonize nearby planets and star systems.

Given all these seemingly inevitable occurrences, the paradox questions why there has never been any evidence of these extraterrestrial civilizations. No alien spacecraft have ever been proven to have visited Earth; no signs of past visitations have ever been discovered; and no interstellar transmissions have ever been detected.

Fermi's original speculation never claimed humans were alone in the universe; he only wondered why contact with extraterrestrials had not occurred. In the 1970s and 1980s, American astronomer Michael Hart and American physicist Frank Tipler built upon the paradox to suggest that humans may be the only intelligent civilization in the galaxy. Their arguments were based on the assumption that if aliens existed, they would have colonized the galaxy and humans should have encountered them; however, since that has not happened, aliens must not exist. Hart went so far as to say that searching for extraterrestrials was a "waste of time and money."

Most astronomers and physicists leave open the possibility of alien life and have suggested numerous reasons for the absence of evidence. Some of the theories border on the outlandish, such as the idea that aliens are already on Earth, but disguised as humans. Others claim that humans are themselves descended from aliens or that extraterrestrial civilizations may be choosing not to make contact until humanity becomes more technologically advanced.

More likely explanations focus on the immense size of the universe and the technological difficulties involved in interstellar travel. Space is so large that distances are measured in light-years (the distance it takes light to travel in a year). Since it is impossible to travel faster than the speed of light, it would take an alien civilization years, decades, or centuries just to reach other stars. For example, the closest star to the Sun, Proxima Centauri, is about four light-years away, meaning it would take four years to reach it traveling at light speed. However, the fastest spacecraft ever launched by humans come nowhere close to that speed; they would take tens of thousands of years to reach Proxima Centauri.

Earth also does not occupy a particularly important spot in the Milky Way. It is located in the outer part of one of the galaxy's minor spiral arms. Finding evidence of extraterrestrial life may be more difficult from that vantage point. In galactic terms, humans have only recently become technologically advanced enough to leave a cosmic footprint. The first radio signals left Earth in the early twentieth century, meaning they have only reached an area within one hundred light-years—a relatively small region of space. Alien civilizations may not be aware humans exist; conversely, alien signals may not have yet reached Earth or humans may not even know what to listen for.

Bibliography

Gray, Robert H. "The Fermi Paradox Is Not Fermi's, and It Is Not a Paradox." Scientific American, 29 Jan. 2016, blogs.scientificamerican.com/guest-blog/the-fermi-paradox-is-not-fermi-s-and-it-is-not-a-paradox/. Accessed 14 Nov. 2017.

Howell, Elizabeth. "Fermi Paradox: Where Are the Aliens?" Space.com, 24 Aug. 2023, www.space.com/25325-fermi-paradox.html. Accessed 20 Nov. 2024.

Lant, Karla. "Neil deGrasse Tyson Reveals When He Thinks We'll Find Aliens." Futurism, 3 Apr. 2017, futurism.com/neil-degrasse-tyson-reveals-when-he-thinks-well-find-aliens/. Accessed 14 Nov. 2017.

Lovett, Richard A. "Fermi's Paradox Finished? Perhaps ET Is Abundant and We Just Can't See It." Cosmos, 23 Oct. 2017, cosmosmagazine.com/space/fermi-s-paradox-finished-perhaps-et-is-abundant-and-we-just-can-t-see-it. Accessed 14 Nov. 2017.

Lucy, Michael. "What Is the Fermi Paradox?" Cosmos, 23 Oct. 2017, cosmosmagazine.com/space/what-is-the-fermi-paradox. Accessed 14 Nov. 2017.

"Manhattan Project Spotlight: Enrico Fermi." Atomic Heritage Foundation, 28 Oct. 2015, www.atomicheritage.org/article/manhattan-project-spotlight-enrico-fermi. Accessed 14 Nov. 2017.

Masetti, Maggie. "How Many Stars in the Milky Way?" National Aeronautics and Space Administration, 22 July 2015, asd.gsfc.nasa.gov/blueshift/index.php/2015/07/22/how-many-stars-in-the-milky-way/. Accessed 14 Nov. 2017.

Webb, Stephen. If the Universe Is Teeming with Aliens ... Where Is Everybody?: Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life. 2nd ed., Springer, 2015.