Human beings are afraid of the “dark forest” for the first time. Female graduate students find a mysterious signal. Do you want to reply?

I have seen “Three-Body”, and everyone feels deeply shocked by one of the laws of the universe, and even their backs feel cold. This is the law of the dark forest. In the dark forest of the universe where various “hunters” are lurking, each civilization will be careful and try to hide itself, otherwise it may attract a devastating blow from other more advanced civilizations. Every civilization wants to protect itself, and can only completely kill external threats in its cradle.

In fact, the law of the dark forest is an explanation of Fermi’s paradox. Human beings have not existed on the earth for more than 3 million years, but we have developed aerospace technology that has the ability to fly away from the earth and go to other planets.

On the other hand, the formation time of the Milky Way is estimated to be 13.5 billion years. In the long past, as long as alien intelligent species appeared hundreds of millions of years earlier than human beings, even millions of years, they will now have the ability to develop into a galaxy civilization and live in the entire galaxy.

However, the universe seems to be quiet, no alien civilization has ever visited or contacted the earth, and there has never been a response to the signals we send to the universe. Therefore, the physicist Fermi asked this question: Where are all the alien civilizations?

As early as 1967, mankind had feared the “dark forest” of the universe for the first time.

In addition to visible light, there are many radio waves invisible to the naked eye in the universe, which require radio telescopes to receive (my country’s Sky Eye is also a radio telescope). In the 1960s, radio astronomy has made many major discoveries. For example, the residual temperature left by the Big Bang-the cosmic microwave background radiation, and the active supermassive black hole in the center of a distant galaxy-quasars.

At that time, when Jocelyn Bell Burnell, a female graduate student at the University of Cambridge, was studying quasars through a radio telescope, she accidentally discovered a very regular pulse signal with a very stable period, beating every 1.337 seconds. once.

This weird signal will appear 3 minutes and 56 seconds earlier every day, which coincides with the time when the earth rotates once on its axis. In life, the time of a day is exactly 24 hours, which is the time it takes for the sun to pass the same meridian one day apart. But because the earth is still orbiting the sun, so after one solar day, the rotation angle of the earth has actually exceeded 360 degrees. In other words, the time for the earth to rotate 360 ​​degrees around its axis is less than 24 hours, which is a difference of 3 minutes and 56 seconds.

So Josephine determined that this special signal must come from somewhere in the universe. Whenever the earth turns in that direction, it can just receive the radio waves from that signal source, so this time difference appears.

Josephine could not explain the impulse signal she had discovered. She suddenly flashed a thought that this might be an alien signal. The communication of human civilization is based on radio waves. This is the inevitable result of the development of a scientific and technological civilization. If there are aliens in the universe, it is entirely possible for them to communicate using radio waves.

Josephine didn’t dare to say anything, she told her mentor, Professor Anthony Huish, of the newly discovered “alien signal”. After many studies and discussions, Professor Huish also believes that this signal is extraordinary, and its narrow-band frequency implies that it did not originate from nature.

They dare not rashly make this discovery public, for fear of causing trouble or even danger to the earth. Because if this is really an alien signal, and someone on Earth sends a signal to reply, it will be possible to attract an alien civilization with a technological level far beyond that of human beings, which will obviously put humanity in danger, just like “Three-Body” As depicted in.

After a few months, they discovered multiple regular pulse signals one after another, but the cycle was different. Later, after repeated studies, these signals were believed to be not sent by aliens, but from a very special celestial body-pulsars, which are neutron stars predicted by physicist Landau more than 30 years ago.

When a massive star with a mass 8 to 20 times the sun runs out of fuel, the core area will collapse violently, and the strong gravity will compress the electrons into the nucleus and neutralize the protons into neutrons, which will form neutrons. Composed of dense celestial bodies-neutron stars. In theory, the mass of a neutron star is about twice that of the sun, but its radius is less than 20 kilometers.

Since the magnetic axis and rotation axis of neutron stars do not overlap, when they rotate rapidly, radio waves emitted from the direction of the magnetic axis will sweep through the universe. If the earth is in the direction of the magnetic axis, we can receive a stable pulse signal, and the signal period is the rotation period of the neutron star.

Since then, the truth has come to light. Although what Josephine discovered was not an extraterrestrial signal, the discovery of pulsars is still extremely important. This strongly confirms the correctness of the theory of stellar evolution. It can also be used to test Einstein’s general theory of relativity. Future interstellar voyages provide coordinate positioning. Therefore, the discovery is also known as one of the greatest astronomical discoveries of the 20th century. Huish won the Nobel Prize in Physics for this, but unfortunately, the original discoverer, Josephine, missed the prize.

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