Shulou(Shulou.com)11/24 Report--

Photo Source: Pixabay although the sun will go out, traces of human use of solar energy will remain. Of course, this requires a further step in man's ability to use energy-to build a Dyson ball around the sun.

Some researchers estimate that humans are not far away from type I civilization and may only take 300 years. Then mankind will be able to use all the energy on the whole earth. And if mankind is lucky to get through this period and continue, the next step may be to consider the development of interstellar navigation technology, and the first threshold of this task is the issue of energy.

The energy of starships is likely to be controlled nuclear fusion technology, but even if future humans have achieved controlled nuclear fusion, the scale of nuclear fusion materials on Earth may not be large enough to support frequent interstellar voyages. Fortunately, there is a ready-made nuclear fusion energy pool around us-the sun. In order to achieve interstellar navigation, human beings will make more full use of the energy of the sun, thus evolving into an II civilization, when human beings will be able to make use of the energy generated by the whole sun.

In this process, humans will leave indelible traces in the solar system. Even if the sun dies many years later and becomes a white dwarf, humans have already emigrated to other galaxies, and other civilizations in the universe can see signs of human existence from the remnants of the solar system. According to a study published in the Royal Astronomical Society, the Dyson Ball, a star resource acquisition device built by the II civilization, can produce observable signals in interstellar space, even if the star burns out and becomes a white dwarf. the infrared radiation spectrum of white dwarfs will also expose the existence of these devices.

The solar energy that captures sunlight reaching the earth is only a very small fraction of the total energy released by the sun, but it is enough to drive the evolution of the earth's ecosystems and climate systems. Although human technology at this stage is unable to make use of the energy generated by the whole sun, some scientists have come up with feasible plans for this purpose. In 1960, physicist Freeman Dyson came up with the concept of a "Dyson sphere", a group of giant solar collectors that revolve around glowing stars and collect light from stars in other directions for use by civilizations on planets. If human beings can build a Dyson ball around the sun, it can not only completely solve the energy problem, but also explore interstellar navigation technology on this basis.

Although it is called a Dyson "ball", the device does not really wrap a star in a sphere, which is too large to maintain stable operation and is likely to collide with planets. A more feasible idea is to use a set of solar collectors to move around the sun like a swarm of bees. These devices may first form a ring around the sun, and then form a hollow sphere of multiple rings, wrapping the sun in the center. Such groups of devices may change the light emitted by stars, however, the interference is probably so small that if extraterrestrial civilizations built a Dyson ball around their star, it would be difficult for astronomers on Earth to observe it.

In a possible form of a Dyson ball, solar collectors form a ring around the sun, with multiple rings wrapping the sun in the center. (photo source: Wikipedia) nevertheless, astronomers have discovered some bizarre astronomical phenomena that look like Dyson balls. One of the representatives is a star called KIC 8462852, also known as Tabby's Star, which was observed in 2014. The star is about 1470 light-years from Earth, and its brightness has fallen by more than 15 per cent in the past century. This phenomenon shocked astronomers because apart from the near-death period, stars could not have undergone such a huge change in brightness in a short time. The general transiting phenomenon-that is, orbiting the planet to block the star-can only reduce the star's brightness by 1% at most, which does not explain such a big change.

Astronomers have to cite the interference of interstellar dust, comets and even black holes to explain this phenomenon, but none of the hypotheses can give a satisfactory explanation. In a study published in the Astrophysical Journal in 2016, astronomy analyzed the brightness variation of Tabi and concluded that it was a valuable target for extraterrestrial civilization detection. Its brightness changes may be caused by clusters of devices like Dyson balls, which can cause stars to change in brightness on various time scales, from hours to centuries. These astronomers even give the next step of observation statistics to distinguish whether the brightness change of Tabi is natural or "man-made".

Clues to stellar corpses although it is not clear whether Tabby exposed the structure of the Dyson ball, some scientists have gone further. In a recent study published in the Royal Astronomical Society, astronomers suggested that we should look not only at stars for Dyson balls, but also for the remains of Dyson balls around white dwarfs. And his reason is simple: a white dwarf is the body of a burned star, and if there is a Dyson ball around it, it must have been left by the original civilization of the star system, not by an interstellar civilization. Because no one is willing to go to great lengths to build such a large-scale project around the body of a star. Therefore, the Dyson sphere around the white dwarf can better reveal the information of the original civilization of the star system, and scientists can even verify whether the estimation of the birth rate of extraterrestrial civilization is reliable according to the number of such Dyson balls.

How to find the Dyson ball around the white dwarf star? The brightness of white dwarfs is not high, so it is difficult to observe the changes in brightness. Paper author Ben Zuckerman (Ben Zuckerman) suggested that we should look at the infrared radiation of white dwarfs. The Dyson ball absorbs thermal radiation from stars and converts it into other forms of energy. Since the energy conversion efficiency will not reach 100%, this process will leave some waste heat, which will escape in the form of infrared light. In the case of a white dwarf, the Dyson ball may increase the infrared radiation of the white dwarf at a certain characteristic temperature.

After burning hydrogen, many stars will become a white dwarf, which may not be as big as a giant planet like Jupiter. The picture shows a diagram of white dwarfs orbiting giant planets. (photo source: NASA's Goddard Space Flight Center) in existing astronomical observations, about a few percent of white dwarfs show excessive infrared radiation. However, these are not all traces of the Dyson ball, on the contrary, most of them can be explained by dust particles near the white dwarf, or the influence of its companion stars. Zuckerman said that in the future, more accurate astronomical observations, such as the James Webb Space Telescope, may be able to detect phenomena in the infrared radiation of white dwarfs that cannot be explained by natural processes. Of course, even if all the observations find nothing, this conclusion is still valuable because it sets an upper limit on the number of native alien civilizations, and scientists can revise their estimates of the birth rate of cosmic civilizations.

On the other hand, if humans develop interstellar navigation technology in the future and leave the solar system before the sun becomes a white dwarf, the Dyson ball left by humans-the energy source of interstellar navigation-is still increasing the infrared radiation of the sun's corpses. Perhaps civilizations in other corners of the universe can learn from this sign that this dead star system once gave birth to civilization.

Links to papers:

Https://iopscience.iop.org/article/10.3847/0004-637X/816/1/17#apj521657s4

Https://arxiv.org/abs/2204.09627

This article comes from the official account of Wechat: global Science (ID:huanqiukexue), written by Bai Defan, revised by Wang Yu

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