In Liu Cixin's famous science fiction novel "The Three-Body Problem", there is a scene in which female scientist Ye Wenjie uses the giant antenna at the Hong'an Base to launch the first message of human civilization into the universe through the mirror gain reflection effect of solar energy. Thus began a long story spanning tens of billions of years... And this scene of broadcasting information about human civilization to the universe is something that really happened in human history. The story starts with a radio telescope.

The Arecibo Observatory located in Arecibo on the island of Puerto Rico was once the world's largest single-diameter radio telescope. It was built in 1963. It is a spherical reflecting radio telescope with a fixed base. The diameter of the reflecting sphere At 305 meters, it was the world's largest single-aperture radio telescope at the time and held this record for nearly half a century. It was not until the completion of the Sky Eye FAST in Guizhou, my country that it was relegated to second place.

The Arecibo radio telescope consists of a 305-meter-diameter spherical reflector and a receiver with three towers suspended 150 meters above the spherical reflector through 18 steel cables. The receiver platform is heavy. Up to 900 tons, the platform can move the receiver within a certain range through a rotatable sliding track below, which is used to adjust the focus of the receiver to the radio signal reflection in different directions and achieve high-precision observation of the sky area at a certain angle. According to According to the data, the observable angle is about 40°.

Different from my country’s Sky Eye radio telescope, in addition to achieving high-sensitivity radio signal reception through the receiver, the Arecibo telescope is also equipped with four radar transmitters with different wavebands and different transmission powers. The frequency and transmit power are 2380MHz (20TW), 430MHz (2.5TW), 47MHz (300MW), and 8MHz (6MW) respectively. This means that in addition to receiving signals from the universe, it can also transmit signals to the universe!

As you already know at the beginning of the article, it did use its radar transmitter to emit a radio signal carrying information about human civilization into the universe...

In the 6th and 6th centuries of the last century, In the 1970s, scientists from various countries started a craze to search for extraterrestrial civilizations. The Hong'an Base where Ye Wenjie was located in the story of "The Three-Body Problem" was established against this background. In the real world, this is a real history. At the beginning, scientists only tried to find information about intelligent civilizations in electromagnetic wave signals coming from the depths of the universe. The first pulsar discovered by humans was mistaken for a signal from an alien civilization. It was later confirmed that this was just a periodic electromagnetic signal caused by the non-overlapping axis of rotation and magnetic axis.

It is against this background that an attempt that seems a bit crazy now was proposed - to send messages from earth civilization to the universe. For those of us who have watched "The Three-Body Problem" and know the laws of the dark forest, this move seems crazy and extremely dangerous, but for the scientists at that time, it was an interesting attempt. As the most powerful single-aperture radio telescope on Earth at the time, the Arecibo Telescope naturally assumed this great task. Based on the sky area that the Arecibo telescope can cover, scientists selected the Hercules globular star cluster and sent a segment of 1,679 binary signals to the Hercules globular star cluster M13, which is 22,200 light-years away from the Earth, on November 16, 1974. Digital radio messages, historically known as Arecibo messages.

The Arecibo message consists of the easiest to decipher binary code, including binary numbers 1-10, the atomic numbers of the five basic elements that make up life, the basic structure of human DNA, and the structure of human DNA. Double helix shape, man's height, shape, total world population, solar system sun and nine planets, Arecibo telescope related information.

The picture below shows the correct decoding result of the original information and the information comparison.

If an alien civilization intercepts this message, I don’t know if they can interpret it. I guess it’s a bit suspense... In fact, this message contains some wrong information, at least for now. It is said to be wrong information, such as the number of nucleotides, the total population, the number of planets, and another one is that the distance of the Hercules globular cluster M13 was measured at that time to be 25,000 light-years, and the current distance is 22,200 light-years...

In other words, the Arecibo message sent that year has now spread to 46 light-years away, and it will take 22,200 years to reach the destination M13 globular star cluster...

But in fact, With the radiation power that the Arecibo telescope’s radar transmitter can produce, don’t expect to be able to detect it 20,000 light-years away. That’s just a myth… As for whether it will be intercepted by a closer civilization midway, well, let’s say No...I'm not worried anyway...

Exposing human civilization is certainly not the only major thing that the Arecibo telescope has done. In fact, in its nearly half-century life cycle, it has achieved remarkable results. One that must be mentioned is an astronomical discovery that later won the Nobel Prize in Physics.

In the year when humans sent the Arecibo message to M13, Joseph Taylor and Russell Huls discovered a pulsar binary system based on the observation records of the Arecibo telescope. According to calculations , their orbital period is about 7.75 hours, which means they are very close to each other.

According to the general theory of relativity, this pair of binary pulsars will radiate strong gravitational waves during their orbit, resulting in a loss of kinetic energy, which will move the orbit of the binary stars inwards and shorten their orbit period. After nearly two decades of continuous observation of the pulsar binary through the Arecibo telescope, Taylor finally proved that the pulsar binary system does indeed have periodic changes, and the change results are consistent with theoretical calculations.

This result is considered to indirectly prove the existence of gravitational waves predicted by the general theory of relativity! Both men won the 1993 Nobel Prize in Physics for this discovery.

Although it has achieved brilliant observational achievements, time has left indelible traces on the Arecibo Telescope. After half a century of wind and sun, the Arecibo Telescope is aging. Yes, there have been many cases of steel cable breakage and damage to the reflection disk this year. The most recent breakage of the steel cable occurred on November 9. Subsequently, the US National Science Foundation (NSF), which manages the Arecibo Observatory, inspected the telescope. After a detailed assessment of the damage, it officially announced on Twitter on November 20, 2020 that it would give up repairs and demolish some high-risk structures.

Unfortunately, the Arecibo telescope did not wait until the day it could be safely dismantled. In the end, the steel cable broke and the entire 900-ton receiver platform fell from an altitude of more than 100 meters. Arecibo The Bo telescope was completely destroyed, marking the official end of a generation of the world's most powerful radio telescope. We look forward to the continued glory of my country's Sky Eye FAST!