Earthlings have been working hard to find extraterrestrial civilizations

Recently, many media outlets have reported that the FAST radio telescope, known as the "China Sky Eye," has discovered suspicious signals from extraterrestrial civilizations. Although experts later clarified that FAST only discovered unidentified signals, the existence of aliens has once again become a topic of discussion. So, what efforts have humans made to detect extraterrestrial civilizations?

FAST radio telescope, known as the "China Sky Eye"

Motivation: Loneliness and curiosity

Karl Marx once said a famous saying: The essence of man is the sum of all social relations. This sentence shows that human beings are social animals. Similarly, when we look up at the stars and face the vast universe, we also hope to find aliens so that humans will no longer feel lonely in the universe.

Carl Sagan, an American scientist, said: The universe is bigger than anyone can imagine. If there are only humans in the universe, it would be a waste of space. Although we have not yet discovered aliens, Carl Sagan has long believed that there are alien civilizations in the universe based on his intuition.

When discussing extraterrestrial life, the famous physicist Fermi proposed the "Fermi Paradox": If aliens exist, where are they? Although Fermi did not give a clear negative conclusion, his paradox illustrates that humans have overestimated the possibility of the existence of extraterrestrial civilizations, suggesting that aliens do not exist.

The "Fermi Paradox" has attracted attention from scientists and science fiction writers, triggering numerous discussions and studies. Many theories, such as the Drake Equation and the Great Filter, have been proposed in succession, attempting to prove that humans are not the only intelligent life in the universe.

When we face numerous unknown phenomena in the vast universe, we always subconsciously try to get to the bottom of things and want to know why. Aliens are the most beautiful imagination of mankind for these unknown phenomena in modern times, making countless ordinary people enthusiastically support the detection and search for the existence of aliens.

In the 19th century, Italian astronomer Schiaparelli discovered some dark lines on the surface of Mars when observing it, and later named them "waterways", but when translated into English, they were mistakenly translated as "canals". Since then, the craze for finding Martians has become unstoppable.

The novel "The War of the Martians" written by British writer Wells further increased the popularity of the concept of Martians. Americans were also fascinated by it. In order to find Martians, American businessman Lowell spent a huge amount of money to build an observatory and spent his whole life searching for traces of Martians.

War of the Martians novel

For many years, the search for extraterrestrial civilizations has become one of the biggest motivations for humans to satisfy their curiosity.

Method: Radar optical full-band array

So far, humans have made many efforts to find extraterrestrial civilizations. In 1896, American scientist Nikola Tesla proposed a plan to use radio waves to communicate with extraterrestrial civilizations.

The real scientific research was proposed by Giuseppe Cocconi and Philip Morrison of Cornell University in 1959. They pointed out that interstellar communication can be established through high-power radio waves. Subsequently, they published a paper titled "Searching for Interstellar Communications" in the famous journal Nature, pointing out that large-caliber antennas can be used to capture alien radio signals.

In 1960, American astronomer Frank Drake launched the Search for Extraterrestrial Intelligence (SETI) Project Ozma, which aimed to use radio telescopes to search for signs of extraterrestrial life.

Project Ozma initially used the 26-meter antenna of the National Radio Astronomy Observatory in West Virginia, but later more and more radio astronomy observatory resources became available, and the famous Arecibo radio telescope also served part-time as a SETI listening mission.

In 1974, Arecibo sent a telegram containing basic information about humanity to the M13 star cluster. American businessman Paul Allen also donated to build the Allen Radio Telescope Array, which is dedicated to SETI searches. It consists of 42 antennas with a diameter of 6 meters, which greatly improves SETI's search capabilities.

Arecibo radio telescope (now facing demolition) Now, our "China Sky Eye", the 500-meter-diameter FAST radio telescope, is also listening to signals from space from time to time, hoping to find traces of extraterrestrial civilizations.

Radio telescopes are not the only way to search for aliens. Humans have also developed and deployed a large number of optical telescopes to observe space.

Optical telescopes can be used to search for habitable planets outside the solar system and to screen out planets that may host life.

At present, both the 10-meter-class large telescopes on the ground and the space telescopes represented by the American Kepler have made significant contributions to the search for habitable planets. In particular, the Kepler Space Telescope has discovered a large number of habitable planets during its service.

Kepler Space Telescope

So far, humans have discovered more than 5,000 exoplanets, some of which are habitable planets that may have liquid water on their surfaces, becoming the cradle of life.

Prospects: New detection tools are more powerful

Today, humans mainly rely on radio telescopes and optical telescopes to search for extraterrestrial civilizations, but the invention of radio is only about 100 years old, and the launch of large-aperture optical space telescopes has only been a matter of decades. With the existing observation methods and tools of humans, it is too early to assert whether aliens exist. Therefore, humans are also building various new detection tools to enhance their ability to search for extraterrestrial civilizations.

Let's look at the old assistant radio telescope first. Arecibo and FAST were built according to local conditions, basically reaching the limit of terrain design. The University of Cambridge in the UK proposed the concept of a radio telescope array with a comprehensive aperture as early as the 1950s, and built the first antenna array in 1964.

Radio telescope arrays can obtain more sensitive receiving capabilities through the interferometry of multiple radio antennas, so as to receive weaker radio wave signals. With the development of science and technology, countries such as the United Kingdom, China, Australia and South Africa are currently jointly building a larger square kilometer array radio telescope, which is expected to be completed in 2030.

Radio telescope array

The telescope's sensitivity will be 50 times higher than the most sensitive radio telescope currently available, and it will be able to hear more signals from suspected alien civilizations and find clues to the existence of aliens.

In addition, countries around the world are jointly building a number of super-large astronomical observation equipment such as the Large Magellan Telescope, the Thirty-meter Telescope and the European Extremely Large Telescope. They will not only help astronomers study various information such as the early days of the Big Bang, but will also be an important aid in the search for exoplanets and habitable planets.

At present, the space telescopes developed by the world's major space powers have also made great progress. The US Webb Space Telescope will release its first observation photo in July this year. This large space telescope with a diameter of 6.5 meters is also an important device for searching for exoplanets. It can analyze the spectrum to confirm whether there are organic substances in the atmosphere of the planet.

The Xuntian optical module, which my country will launch in 2023, uses a large off-axis three-reflector telescope with a diameter of 2.4 meters. It can part-time explore exoplanets and search for possible extraterrestrial civilizations.

Schematic diagram of the optical cabin of China's Sky Survey

In addition, humans are also trying to get close to detect traces of extraterrestrial civilizations. In 2016, Hawking launched the grand "Breakthrough Starshot" plan, which aims to launch thousands of small laser light sail spacecraft to explore the Alpha Centauri system, which is closest to the Earth. Because there are multiple exoplanets in the Alpha Centauri system, if we can get close to detect them, we believe there will be more discoveries.

Of course, the Breakthrough Starshot technology faces huge challenges and is difficult to achieve at this stage, but some of the world's major space powers are actively developing interstellar probes to fly out of the solar system. Like the Pioneer 10/11 and Voyager 1/2 interstellar probes launched in the last century, they will become signals of existence actively sent out by humans, and may be captured by aliens in the distant future and attract their communication signals.

In short, the universe is vast and boundless. With the development of aerospace technology, more and more secrets of the universe will be revealed by humans on Earth. There is no doubt that the pace of humans on Earth in exploring space and searching for extraterrestrial civilizations will be more powerful and courageous.