The “Space Exploration Club” has added a new large scientific device. How can “Tianlai” hear the “echoes” of the universe?

On the edge of a mountain, far from the crowd, there are several "big pots" set up. They are like sunflowers facing the sun, facing the sky all day long. Their main function is to listen to the "sounds of nature": coordinate the earth, open their "ears" to capture the "sounds" of the origin of the universe -

Tianlai Array. Image source: National Astronomical Observatory

Recently, the "Tianlai" experiment, a scientific project located in Hami, Xinjiang, my country, passed the certification of the Square Kilometer Array Observatory and was selected as the "Pathfinder" of the Square Kilometer Array radio telescope (SKA).

"I know every word, but I can't understand it at all?" In the hot search of related terms, netizens said "I don't know what it means." Another major scientific device, a step closer to human exploration of the universe? To this end, the reporter contacted Cao Lin, an expert in popular science in the field of astronomy and a national leader in popular science work, to interpret the scientific principles behind "Tianlai".

A radio telescope is a large "radio"

According to relevant media reports, the word "Tianlai" comes from Zhuangzi's "Qiwu Lun", which means the natural sound of all things in the universe. The "Tianlai" experiment detects the sound waves of cosmic baryons, hence the name.

Tianlai cylindrical radio array Source: CCTV News

The Tianlai project is hosted by the National Astronomical Observatory of the Chinese Academy of Sciences. Currently, two types of telescope arrays have been built: a cylindrical radio array consisting of three cylindrical reflector antennas and a dish radio array consisting of 16 parabolic antennas.

They are of the type of "radio telescope" and are arranged to form a larger array.

"Radio astronomy is a very young and highly professional discipline." Cao Lin tried to use plain language to introduce the working principles of radio telescopes, but he could not avoid astronomical terms such as "electromagnetic waves", "Big Bang", "neutral hydrogen", etc., each of which can be extended into an independent course.

Stills from "Space Exploration Editorial Department"

Let’s start with radio waves. In the movie “Cosmic Exploration Editorial Department”, Tang Zhijun (character name) uses the “snowflakes” on a TV to receive signals from outer space. He solemnly said to the people outside the screen: “This is not an ordinary snowflake, this is the afterglow of the birth of the universe.”

"This statement is actually not accurate. The antennas of old-fashioned televisions cannot simply receive cosmic microwave radiation. However, humans have indeed gradually discovered through radio activities that there is a 'background sound' in the universe. This is the radio radiation in the form of microwaves from the energy of the Big Bang, which is distributed throughout the universe," Cao Lin explained.

"The cosmic microwave background radiation is a 'relic' of the Big Bang and a typical scene in radio astronomy, and the radio telescope is a device for observing and studying radio waves from celestial bodies." Cao Lin introduced that the radio and microwave light we usually see are all electromagnetic waves. The earth's atmosphere absorbs most of the electromagnetic waves from the universe, and only visible light and some radio waves can penetrate. Therefore, in astronomy, these electromagnetic waves with frequencies between 30MHz and 300GHz are called radio waves.

In addition to the cosmic microwave background radiation, radio objects such as neutron stars, pulsars, nebulae, and radio bursts can also emit radio signals. Cao Lin said: "In a more popular way, a radio telescope is more like a 'radio'. By receiving different signals, we can discover different celestial phenomena and even the process of its future evolution."

Earth-based telescopes team up to scan the universe

Chang Jin, an academician of the Chinese Academy of Sciences, once said in an interview that my country's astronomy has developed rapidly in recent years, and radio astronomy is now the only one that stands out. Cao Lin believes that the selection of Tianlai as a "pathfinder" for the Square Kilometer Array (SKA) radio telescope is a testament to my country's advanced radio astronomy technology.

SKA is a new generation of radio telescope jointly built and operated by multiple countries around the world. It is currently being built in South Africa and Australia. Its equivalent receiving area is at the square kilometer level. With its unprecedented ultra-high sensitivity and scientific discovery capabilities, it will become one of the largest and most advanced scientific facilities on Earth after completion.

"The resolution of a radio telescope with the same aperture is much lower than that of an optical telescope, so humans will build telescopes with huge apertures to improve the sensitivity of observations," Cao Lin introduced. "For example, China's Sky Eye FAST has an aperture of more than 500 meters. In many science fiction novels, celestial bodies themselves are also used to function as radio telescopes to achieve observation goals."

China's Sky Eye FAST Source: Xinhua News Agency

When the actual geographical space is not enough, smart people on Earth think that if they put various telescopes together, collect the data, and arrange them into a radio telescope array, they can obtain more radio astronomy data with scientific value.

"From the perspective of the universe, the earth is just a tiny dot. For us, countries may have radio telescopes far away, but once they are 'grouped', they will break through geographical limitations and become a larger earth 'radio'," said Cao Lin.

It is conceivable that when this "giant eye" of the Earth scans the universe, the once blurry celestial bodies will become clearer, and will further help humans understand the universe and basic physical laws. As a "pathfinder", the relevant technologies and latest discoveries of the Tianlai experiment will provide SKA with new scientific exploration opportunities and be applied to the construction of future radio telescopes.

Look up at the starry sky and communicate more with the universe

One of the goals of the Tianlai experiment is to discover the mysterious dark matter, which cannot be seen but makes up 26.8% of the universe. Scientists have found that the gravity provided by the mass of dark matter ensures the existence of galaxies and galaxy clusters and does not fly away. It is also the unknown energy that drives the accelerated expansion of the universe.

"The research on dark matter is still in its infancy, and scientists have not yet found dark matter itself." Cao Lin believes that "Tianlai" uses neutral hydrogen detection research as the "key" to search for dark matter, which is an important step towards the mystery of the origin of the universe.

In our daily lives, we cannot perceive the existence of radio waves or distant galaxies. However, the universe is something that is both out of reach and closely related to us.

For example, the activity of sunspots will affect our satellite activities, further affecting mobile phone signals, network communications, etc.; or the birth of human life is because we are in the habitable zone of the solar system. Within this range, water can exist in liquid form, making human metabolism possible; further, astronomer Carl Sagan once said that the nitrogen in our bodies, the calcium in our teeth, and the iron in our blood are all scattered from the thousands of stars during the Big Bang...

"So everyone is a child of the stars. Searching the universe, understanding the universe, and discovering the origin of the universe are of great significance from both scientific and humanistic perspectives," said Cao Lin.

The Perseid meteor shower photographed in Huangpi District, Wuhan City, Hubei Province on the night of August 12, 2024. Image source: Xinhua News Agency

As China Astronomy Day approaches on October 30, Cao Lin also hopes that more ordinary people will join the ranks of astronomy enthusiasts. "Looking up at the stars is a human instinct. Understanding it is a process of expanding the worldview and also an improvement of scientific knowledge and scientific literacy."

"I think that every ordinary person can pay attention to the celestial phenomena around them, such as meteors, solar eclipses, lunar eclipses, and comets, and have some basic observation capabilities. This is how we maintain communication with the world," said Cao Lin.