# Movie "Gravitational Waves Explained" that understands "What is gravitational waves?" In about 3 minutes

The local time on February 11, 2016, the International Research Team gave the American laser interferometer Gravitational Wave Observatory "LIGO(Lygo) "Finally the observation of the gravitational wave succeededWhat is done has become a big topic. It is successful observation of the gravity wave expected to bring great progress to space research, but I understand what "gravity waves" are invisible and what this success implies There should not be too many people. It is perfect for such a person, a movie explaining the outline of gravity wave in just 3 minutes, its name is also "Gravitational Waves Explained(Explanation of gravity waves) ".

What is gravity wave? First of all, I will explain "gravity" before. A commonly used example is to compare the universe to one huge rubber sheet and drop the sphere with weight (mass) there. Although the rubber sheet is dented according to the weight of the sphere, this is the distortion of the spacetime and it is the source of gravity. In fact it is difficult to understand because the space is not a flat surface like a rubber sheet, but "Spatio-temporal distortion" is generally OK if you think that these things happen in three dimensions.

This rubber sheet sinks deeper as the mass increases. In other words, the higher the density and the larger the mass, the more distorted the surrounding space-time.

You can understand this by thinking of the sun as an example. Because the sun is very massive, it distorts so much space. The more distorted space, the greater the gravitational force that is generated, so the sun will have a very large gravity. It is the sun that is shown in yellow in the following figure, but in the space distorted by the sun in this way, the planets such as the earth are turning around while being grasped by gravity (= That is why. Here, furthermore, the moon revolves around the earth, where the balance of complex triple gravity is established is the place where I feel the fun of the universe and the size of the scale.

And the "gravity wave" is generated by the movement of the mass object like this, the change of the distortion of the space, and propagates to the surroundings at the same speed as the light. This is the reason why the gravitational waves are expressed like 'Sazanami of the space-time face'.

This gravitational wave generates anything as long as it has mass and energy. For example, spatio-temporal distortion occurs even if two people rotate round and round with their arms folded, and theoretically generates gravitational waves. However, since the change that occurs at this time is extremely small, it is said that it is equal to not being present and there is no problem level.

The force of gravity is very weak compared to the forces that exist in other universe. Therefore, in order to generate a gravitational wave large enough to be detected by humans, neutron stars and black holes, or combinations thereof are required to rotate at high speed,A situation in which a huge mass exercises at extremely high speedIt becomes necessary. The gravitational wave which succeeded in observation this time is also thought to be "Sazanami" which was created by rotation of two black holes.

Then, how is the gravitational wave observed? For example, you count the number of stones equally spaced on a plane and measure the distance. Although it seems to be able to measure the distance correctly at first glance, in practice the criterion itself is distorted according to the distortion of the space, so it is basically impossible to capture the change. In other words, it is like measuring the distance between two points with a tape measure. As the tape measure itself changes according to the distortion of the space, "1 meter" will be "1 meter" in any condition.

However, there is one thing that is unaffected by distortion in the universe. That is "light speed". If the distance between two points increases, the time it takes for the light to reflect and return is long.

Conversely, when the distance between two points becomes smaller, the time it takes is shorter. It is the principle of the detection device including LIGO to detect distortion of space by using the nature of this light.

This is a photograph of the research facility of LIGO. A long tunnel extends from the building in the center to a V shape of 90 degrees.

The length of the two tunnels is 4 km each. Laser light is emitted from the center facility towards the mirror at each end of the tunnel.

When gravitational waves reach here and distortion occurs in the space ... ...

The length of the tunnel changes slightly, the time the laser light reflects back to the mirror changes. In this way it is designed to detect spatiotemporal distortion due to gravity waves.

In order to detect this distortion, extremely high accuracy is required. The change that we must measure to detect the influence of the gravitational wave is unimaginable accuracy of 5 millimeters per 10 10 21 m. On the contrary, when converting it per meter, it is not clear how to say what it is saying to decompose one nanometer (one billionth of a meter) into 1 nanometer and further divide it by a factor of 1000 .

Although it is necessary to measure such precision, there is a big problem called "noise" there. All kinds of events on the earth, such as tracks running on the ground and lightning, affect the measurement results. For that reason, the research team has developed a variety of noise elimination methods and has devised a technique to extract only necessary information. Actually, the one that LIGO is installed in two places, Livingstone, Louisiana and Hanford, Washington, is one of them. The idea is that the same result must be observed on the two measuring devices in order to detect gravitational waves coming from outer space.

The news that this gravitational wave detection succeeded will give great progress to space research. This means that the sound that I could not hear so far seems to be heard suddenly one day, which means that observation in a completely different dimension has become possible. Although space observation so far was based on the observation of light and radio waves, by the addition of gravity wave here, it is expected to be able to see "things that could not be seen".

In this way, opening of the window of gravity wave can be said to be a big thing in space research. As for this incident, it seems that you can understand well when you read the following site etc. together.

Gravity wave, magnificent story that brought the discovery of the century | National Geographic Japan version site
http://natgeo.nikkeibp.co.jp/atcl/news/16/021200053/

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