2020-10-17

Gravitational waves let us”hear” the secrets of the dark part of the universe

By yqqlm yqqlm

On September 14, 2015, mankind directly detected gravitational wave signals for the first time. This discovery opened a new window for mankind to observe the universe. This time the gravitational wave signal came from a distant universe 1.3 billion light-years away and was triggered by the collision and merger of two black holes.

In this double black hole merger, a black hole with 36 solar masses and a black hole with 29 solar masses The black hole merges into a black hole of 62 solar masses, radiating the energy of 3 solar masses, which is equivalent to the energy released by the simultaneous explosion of countless atomic bombs. They propagate outward in the form of gravitational waves, after 1.3 billion light years We have found the earth after a long journey.

In 2017, three scientists won the Nobel Prize in Physics. What are gravitational waves? Why does it make the scientific community so crazy?

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What are gravitational waves? It is a ripple of time and space

In the 17th century, when a legendary apple helped Newton discover the universal gravitation, more problems followed. What is gravity? How is gravity created? How does it affect everything in the world? These problems plagued the top scientists at the time. It was not until two hundred years later that someone came up with the most reliable inference that now seems to be the most reliable.

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Einstein believed that all objects exist in one space-time, and the different masses of the objects lead to space-time The degree of deformation is different. The greater the mass of an object, the greater the curvature of time and space.

This statement is difficult to understand even now, time and space are invisible and intangible, and what does this have to do with gravity? According to this inference, gravity is caused by the bending of space-time, and gravitational waves are the ripples caused by the bending of space-time.

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Take the analogy between the earth and the moon. The earth will affect time and space, making time and space bend a little bit, and the moon will also affect time and space, making time and space bend a little bit. When they revolve, it will drag each other. In this case, it is as if two things are fluctuating in time and space, and the fluctuations in time and space will also travel far away, which is the so-called gravitational wave.

How to detect gravitational waves? A big ruler with a length of 4 kilometers

Gravitational waves are equivalent to the fluctuations of time and space. If there are fluctuations in time and space between the left and right points, the distance between the two points will change. If we can measure this change, we can know whether there is a gravitational wave passing through the position between the two points.

However, it is very difficult to directly measure the change of distance.

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The gravitational wave detected on September 14, 2015, varied from 10 to minus 18 meters. This change is smaller than the atomic nucleus, one thousandth of the atomic nucleus. To measure such small changes, we must find a super accurate ruler. What is the best ruler in the world? It is a laser interferometer.

LIGO, the largest laser interference gravitational wave observatory today, relies on laser interferometers to detect gravitational waves. It consists of two vertical interference arms with a length of about 4 kilometers. A beam of laser light passes through a beam splitter and is divided into two vertical beams, and runs back and forth in a vacuum tube of the same length. Their speed is 300,000 kilometers per second.

Once a gravitational wave strikes, time and space will fluctuate, one arm will stretch, and the other will contract. The two beams of light are no longer synchronized, and interference will occur. At that time, this small change can be captured by a laser interferometer. In theory, LIGO can detect gravitational wave events at a distance of 300 million light-years.

Why do you want to detect gravitational waves?

In order to listen to the secrets of the dark world in the universe

Most areas of the universe are hidden in darkness.

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Optical telescopes, infrared telescopes, radio telescopes and high-energy telescopes such as X-ray gamma ray, these telescopes It is like eyes, which can help us see the depths of the universe. But if what happens in the depths of the universe does not emit light or emit any rays, these telescopes will be powerless.

A typical example is the merger of two black holes. They do not emit light during the merger, but they emit powerful gravitational waves. If you can detect gravitational waves, you can”hear” the most exciting and grand events in these dark universes.

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Source:CCTV Science and Education