How close are we to finding aliens?

  China News Weekly reporter / Huo Siyi

  Published in the 1050th issue of "China News Weekly" magazine in 2022.7.4

  Recently, Zhang Tongjie, a professor of the Department of Astronomy at Beijing Normal University and chief scientist of the search for extraterrestrial civilizations in China, revealed to the media that his team used the "Chinese Sky Eye" to discover several cases of "possible technical traces and candidate signals of extraterrestrial civilizations from outside the earth".

Zhang Tongjie pointed out that these are several narrow-band electromagnetic signals different from the past, and the team is currently stepping up efforts to further screen and investigate.

  The 500-meter Aperture Spherical Radio Telescope (FAST), known as "China's Sky Eye", officially launched the search for extraterrestrial civilizations in September 2020, which is one of FAST's five scientific goals.

In 2020, when processing the observation data of FAST in 2019, Zhang Tongjie's team discovered two groups of suspicious signals of extraterrestrial civilization.

In 2022, the team found another suspicious signal from target observations of exoplanets.

  "These suspicious signals recently discovered by FAST are likely to come from Earth, not aliens." Dan Werheimer, chief scientist of the Center for Extraterrestrial Civilization Research at the University of California, Berkeley, told China News Weekly.

Werheimer has been engaged in "Search for Extraterrestrial Intelligence" (SETI) since 1979. He is one of the most authoritative SETI researchers in the world and an American collaborator of Zhang Tongjie's team.

Zhang Tongjie's team also said that the possibility that the suspicious signal is some kind of radio interference is very high.

  Werheimer pointed out that all the "suspected signals" humans have detected so far have come from "our own civilization", not "another civilization."

So, how far are humans from discovering aliens?

Why confuse human and alien signals?

  Where do suspicious signals come from?

  Werheimer explained that these signals may come from mobile phones, televisions, radars, satellites, as well as electronic equipment and computers near the observatory, and are received by FAST in the form of radio waves, because it is difficult for humans to distinguish the difference between them and alien signals, Therefore, it interferes with the observation.

"Although the experiments on FAST have just started, I am still learning how to deal with interference signals and analyze data, but before that, I have more than 20 years of experience, such as using the Arecibo radio telescope in Puerto Rico to observe, I have received There have been many signals very close to this one, and they always turned out to be a form of radio interference."

  Why do we always confuse human and alien signals?

In various extraterrestrial civilization search programs, capturing radio signals of specific frequencies through radio telescopes has always been the first choice of SETI researchers.

This is because of the various forms of electromagnetic radiation in the universe, radio waves have the strongest ability to “pass through” and can pass through the vast universe almost unhindered, reducing information loss as much as possible. This is an ideal “signal” received by humans.

  In 1960, Frank Drake, the pioneer of SETI, conducted the first human radio signal search for extraterrestrial civilizations at the Green Bank National Radio Astronomy Observatory in the United States, which Drake called "Project Ozma".

From April to July 1960, for six hours a day, Drake would tune the observatory's wireless receiver to 1420 MHz (megahertz), which he thought might be the alien "hello" frequency.

  The 1420 MHz frequency is the search object that all SETI personnel will focus on, because this is the emission frequency of hydrogen atoms, and when a hydrogen atom combines with a hydroxyl group, water is born, which is the original composition of life as we know it most important element.

1720 MHz is the emission frequency of hydroxyl, so between hydrogen and hydroxyl, the frequency range from 1420 to 1720 MHz is called a cosmic "water hole", which is considered by NASA as a possible accumulation of life The place.

  Currently, the main search range for extraterrestrial signals by radio telescopes is the "microwave window" from 1000-10000 MHz.

The signal of this "window" is the most easily identified and penetrating.

SETI researchers focused further, mainly looking for "narrowband signals" with frequency bandwidths below a few hundred hertz.

Werheimer explained that the signals sent by extraterrestrial civilizations are not necessarily narrowband. Humans look for narrowband signals just because it is easier to identify "unnatural" signals.

Stars, pulsars, quasars, and the turbulent and thin interstellar gas in the Milky Way all emit broadband signals. If we choose broadband signals to search, it is difficult for us to confirm whether it comes from extraterrestrial civilization or some kind of universe. natural phenomenon.

  The smallest frequency known to be emitted by a natural source is about 500 Hz, and the researchers believe that any signal with a bandwidth less than 300 Hz should be produced "unnaturally".

"Unfortunately, humans themselves produce a lot of narrowband signals, which makes SETI searches more difficult. That's the problem of radio frequency interference that has plagued us for years," Werheimer said.

  For FAST, solving this problem is more difficult.

Verheimer points out that FAST has the advantage of being more sensitive than any existing radio telescope, making it easier to pick up very weak signals in the distance, but the flip side of the coin is that it also creates more interference.

  Before FAST was put into use, the most sensitive extraterrestrial civilization observation equipment in the world was the Arecibo telescope in the United States that collapsed in December 2020 due to a structure out of control.

According to the research of Li Di, the chief scientist of FAST and a researcher at the National Astronomical Observatory of the Chinese Academy of Sciences, the comprehensive sensitivity of FAST is 10 times higher than Arecibo. FAST also has higher measurement accuracy and larger sky area coverage.

  In their paper "Synchronous Observation of Extraterrestrial Civilizations Based on the FAST Telescope" published in April 2020 by Zhang Tongjie et al., they pointed out that for suspicious candidate signals from aliens, the criteria for FAST screening are "signal bandwidths less than 500 Hz and durations less than 100 second".

Before screening, FAST will use the "Nebula" algorithm program to remove "narrowband" interference signals. The main method is to investigate whether the signals continue to appear in multiple sky areas. The narrowband signals that really come from extraterrestrial civilizations should only appear in fixed areas of the sky. .

Signals that appear in many sky areas at the same time are likely to be interference signals from the earth, which will be removed by the program.

However, the results show that after the algorithm has screened, a small part of the interference signal will still remain.

"So far, no algorithm can completely remove noise interference".

  A more fundamental solution, Verheimer believes, is to move the radio telescope from Earth to the far side of the moon, which would be free from radio pollution on Earth.

Another way is to use two radio telescopes to test at the same time, for example, one is in Guizhou and the other is in Shanghai, and the two telescopes are more than a thousand miles apart, so that we can more accurately know how far the signal source is from us, is it near the earth , or further away, "like triangulation".

  In the search for extraterrestrial civilizations, there are mainly two strategies. One is a more extensive sky survey, that is, sky survey observation, which scans a large area of ​​the sky with a telescope to look for strong extraterrestrial signals that may come from any direction, and the other is more targeted. , pointing the telescope at a designated stellar region where life may exist, and staying there for a long time to capture weaker signals.

Zhang Tongjie pointed out in the paper that one of the future goals of FAST is to obtain some good candidate target signals through 1-2 years of sky survey observations, and to conduct follow-up observations on the candidate targets to further test the credibility and repeatability of the candidate targets.

  According to Werheimer, FAST is very sensitive and can cover a wider area of ​​the sky.

In the next 5-10 years, human beings will use this beautiful telescope to conduct large-scale sky surveys, which requires huge computing power. Currently, about 20 billion signals can be analyzed per second, but it is far from enough.

"There are trillions of stars to look up to, and we're just getting started," says Werheimer.

"Are we alone in the universe?"

  On September 19, 1959, two years after the launch of the first artificial satellite, physicists Philip Morrison and Giuseppe Cocconi published their paper "Searching for Interstellar Communication" in Nature, analyzing the universe for the first time. rays of various frequencies, suggesting that radio waves could be used for interstellar communication.

In 1961, Drake proposed the famous "Drake Equation" at the first serious SETI conference held in Greenbank, hoping to calculate through the formula: How many can be detected by humans in the Milky Way? Alien Civilization (N).

Drake's own estimate of N is 10,000, but many scientists are skeptical.

  There have been many cases of suspected "N=1" in history, most of which have been proved to be oolongs, and others have not yet been answered.

The most famous of these was the "Wow!" signal received on August 15, 1977.

On this day, Ohio State University's "Big Ear" telescope detected a set of signals "very similar to extraterrestrial civilization", from the northwest direction of the Sagittarius M55 globular cluster, with a narrow band, high intensity, and most importantly, the signal frequency is exactly hydrogen The emission frequency of atoms is 1420 MHz.

The day's observer, Jerry Ehman, marked the signal's strength on data-logging paper and couldn't help but write "Wow!"

Unfortunately, astronomers have tried multiple times on different telescopes, but have never found repeated signals in the same direction.

Until now, "Wow!" is the strongest candidate of all "suspicious signals" that have been found.

  In November 1984, the SETI Institute, a non-profit scientific institution, was established. From 1995 to 2004, the Institute carried out the most comprehensive extraterrestrial civilization search project in the world at that time - "Phoenix Project", using the Australian Parkes Radio Telescope, Green Bank's National Observatory Telescope and the Arecibo Telescope in the United States together observe 800 star systems within 200 light-years of Earth.

Starting in 2007, the SETI Institute has a stronger "listening" device, the Allen Telescope Array.

The first radio telescope specifically designed for the search for extraterrestrial civilizations, it sits quietly deep in the Cascade Mountains north of San Francisco, with 42 radio antennas lined up on the ground.

The array design allows multiple stars to be searched simultaneously, increasing the search speed by at least a factor of 100.

The SETI Institute predicts that the Allen Telescope will allow humans to expand the search range to 1 million stars in the next two decades.

  At present, the Institute cooperates with NASA, and thousands of candidate "habitable" planets discovered by the Kepler telescope have become the key observation objects of the Allen Telescope Array.

In July 2015, NASA discovered a terrestrial planet "Kepler-4525b" that is "closest to Earth" so far outside the solar system.

But SETI Institute's observations of the Earth's "cousin" with the Allen Telescope yielded no results.

Currently, the system of the Allen Telescope receiver has been updated to cover signals from 1000 MHz to 15000 MHz.

  What puzzles mankind is why, for so many years, no extraterrestrial civilization has been discovered?

In 1950, Italian-American physicist Enrico Fermi asked the question that human civilization has wanted to answer for thousands of years: "Are we alone in the universe?" In 1973, MIT astronomer John Ball offers an explanation: Just as humans observe animals in zoos, aliens may be silently observing humans.

They deliberately avoid contact with humans and isolate human civilization, like a "natural reserve" in the universe, or just to "monitor" humans, which is the famous "zoo hypothesis".

  In 2016, Duncan Fogan, an astrophysicist at the University of St Andrews in the United Kingdom, questioned this hypothesis. He believed that the premise for the realization of the hypothesis is that a variety of alien civilizations must sign an agreement to establish a unified "galactic club", otherwise. All it takes is one "dissident" and the no-contact principle is broken.

It sounds like a completely human way of thinking.

In fact, all speculation as to what signals alien civilizations might send is based on human perceptions of their own societies.

  In Werheimer's view, the optimal SETI strategy is a multiple search, detecting as many wavelengths and signal types as possible, such as lasers and infrared, not just radio.

Human SETI studies to date have only examined "a small fraction" of the radio spectrum, he said, with a small number of studies looking at infrared wavelengths.

Therefore, people on earth are still groping in the "shallowest place", and even in the detected signals, there may be information of extraterrestrial civilizations hidden.

  In 2017, the SETI Institute launched a new program, "Laser SETI," focused on capturing "fast flickering laser signals" that might have previously been overlooked.

Compared with radio, the advantages of laser communication can "pack" more energy, in principle, laser can transmit 50 times more information per second than radio.

The first two telescopes have been built, in Sonoma County, California, and Maui, Hawaii.

When observing, the two telescopes were aimed at the same area of ​​the sky at the same time at different angles, scanning the 150-degree arc of the night sky more than a thousand times per second.

When all the telescopes are up and running, the program will be able to monitor about half of the night sky in the Western Hemisphere and enable truly continuous observations.

"All-day-round" has always been the goal pursued by SETI researchers.

  Seth Shostak, a senior astronomer at the SETI Institute, pointed out to "China News Weekly" that there may be two reasons why humans have not yet discovered the signals of extraterrestrial civilizations: one is that the monitoring has not covered a wide enough sky; Not enough to detect alien 'broadcasts'.

Should we take the initiative to "say hello" to aliens?

  In May 2022, the U.S. Congress held its first UFO hearing in more than half a century, where Pentagon officials showed several inexplicable images: a spherical object captured from the window of an FA-18 fighter jet; a glowing green triangle is moving in the air.

NASA then announced the formation of a dedicated UFO research team, its first involvement in a UFO investigation that had previously been dismissed as "not real science" by most scientists.

  For the "zoo hypothesis", many astronomers shudder at the "surveillance" behind it.

Since humans began to "listen" to the universe, whether to actively send signals to aliens has always been the center of intense debate among scientists. At present, the mainstream view holds a negative attitude.

American astrobiologist Douglas Wakoch is different. He believes that in order for the "galactic zoo" to show up, humans can introduce themselves to aliens by sending powerful and informative radio signals to nearby stars. "They may respond to us."

"They're out there and already know we're here, and in order to get into the Galaxy Club we have to submit an application, maybe even pay a little dues."

  Wakoch founded a group called METI International in 2015 to study how to send more "appropriate" messages to aliens.

Before that, Wakoch spent 16 years at the SETI Institute as Director of Interstellar Information Writing.

  In contrast to the "active search group", most scientists believe that active "hello" puts the earth at "risk of exposure".

In September 2015, at the launch of a "Breakthrough Listen" project to search for aliens, one of the initiators, Stephen Hawking, a cosmologist at the University of Cambridge, explicitly warned against "shouting" at the universe, because the Earth's Civilizations that read human information may be "billions of years older than us", and they will be more powerful.

He believes that these advanced alien civilizations may have the same characteristics of violence, aggression and genocide as humans.

This is the story described in The Three-Body Problem.

  As early as 1974, the Arecibo telescope sent the first radio message of mankind to space, the destination was the globular cluster M13 25,000 light-years away, and the sending time did not exceed three minutes. The information was transmitted through a binary code. go out.

Since then, "active search" scientists have been studying how to deliver the most about human society and species with the least information.

  In 2017, METI sent repeated signals for three consecutive days to Rutan's star 12 light-years away, the closest star system to Earth that contains a potentially "habitable planet."

Compared to the "Arecibo image", this message is more complex and contains a lot of basic math, physics concepts and some scientific knowledge, including telling aliens why 1+1=2, explaining how radio messages are read, and What is the human concept of time.

Vakoch is optimistic that if all goes well, humans could receive a reply from aliens by 2042.

The second METI message will be sent on October 4, 2022.

This time the target is TRAPPIST-1, a star 39 light-years from Earth, and TRAPPIST-1 will receive a richer "package": details of the periodic table, the composition of atoms, and a song by British jazz rock band The Comet Is Coming Song and "Ode to the Messenger of God: The Beauty of the Earth" by Russian musician Eduard Artemyev.

  In an "external communication" in 1977, the "golden records" carried by the two spaceships brought together the essence of human civilization: including 115 images, including the solar spectrum, Mercury, Mars, human anatomy, fetus, The relationship between men and women, the internal structure of the earth, continental drift, etc. The collected sounds include the sound of waves, wind, and thunder, the singing of humpback whales, and the continuous saying of "hello" in 55 ancient and modern human languages. Chinese Wu dialect , a selection of music by Bach, Beethoven, Mozart, etc.

  Contrary to what scientists imagined, more and more studies have shown that the general public is actually not that hostile to aliens, and the number of people who believe that "alien civilizations do exist" is increasing year by year.

Gallup polls show that between 1966 and 1987, the percentage of people who believe in the existence of alien civilizations rose from 34 percent to 50 percent.

In 1997, a survey by the Marist Institute for Public Opinion found that 86 percent of respondents considered galactic neighbors to be friendly, not enemies.

By July 2021, a new survey released by the Pew polling agency showed that 51% of Americans believe that "unidentified flying objects (UFOs)" may come from extraterrestrial intelligent life, and about 87% of respondents said that UFOs are not at all. does not pose a security threat to the United States.

  U.S. research on UFOs will begin this fall, last nine months and cost an estimated $100,000.

The group leader, American astrophysicist David Spergel, noted that such questions must be approached with "humility", saying, "I've spent most of my career as a cosmologist. , we don't know what 95% of the universe is made of," he said.

  Werheimer pointed out that UFO research and SETI research are different. There is no evidence that UFOs come from alien civilizations, and few scientists believe that the earth has been visited by aliens. Some people think that UFOs may be some kind of new military airplanes or atmospheric phenomena, "but it's always good to keep studying, and we might find something interesting."

  In his article "Fear, Chaos, Calm, and Joy: Human Responses to Alien Civilizations," Albert Harrison, a professor of psychology at the University of California, Davis, pointed out that, so far, human responses to aliens have been a combination of science, imagination and A mix of media hype.

Around the millennium, humans believed that alien civilizations were wise, kind and friendly, and that alien civilizations were "utopian societies" where there was no war, death and disease, and could help mankind stop nuclear tests.

In the era of artificial intelligence, some people believe that alien life exists in computer circuits and can "live" anywhere where 0 and 1 exist.

  If one day, human beings really find the signal of alien civilization, should we answer it?

  In 1989, the International Academy of Astronautics approved a "SETI Post-Detection Agreement". According to the agreement, after the discovery of extraterrestrial signals, any country, institution or individual is prohibited from "replying" to alien civilizations without reaching a global consensus on the content of the message. .

But the agreement has no legal effect.

Werheimer pointed out that this agreement is only the first step, and the United Nations would better let all countries adopt such a protocol before the signal is detected, because it is more difficult to reach an agreement after the signal is detected.

"The decision of whether to answer should be made by all countries and everyone on the planet. This is a question for all of humanity," Werheimer said.

  "China News Weekly" Issue 24, 2022

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