- Introduction “Can you make a time machine?”
- What is the theory of relativity that even children can understand?
Introduction “Can you make a time machine?”
Before thinking about whether we can build a time machine, we need to think about whether time travel is possible according to the laws of physics. Let’s learn about time from the theory of relativity.
What is the theory of relativity that even children can understand?
The theory of relativity is a theory of the physics of time and space. Physicist Albert Einstein (Germany) announced the “Special Theory of Relativity” in 1905 and the “General Theory of Relativity” announced in 1915 with improvements are collectively called “Relativity“. It is called. Can you imagine time and space stretching and contracting? It’s like gum! It’s a theory you often hear, but I think few people understand it. As even a child can understand, I will explain the theory of relativity simply.
What is time?
Time often refers to a point in the flow of time. The length between the times. A variable for displaying before and after an event. The value taken by this variable is called the time, and the time interval between the times is called the time interval. 
What is space?
In physics, space is considered to be a continuum with an expansiveness, a reality that gives the whole of matter a place to exist. It is also believed that time, space, and matter are not independent and are closely related.
What is relative in the theory of relativity?
Einstein considered “relative time” or “relative space” in which time and space change depending on the observer, and said that the absolute “speed of light“ is the “speed of light.” The opposite word is absolute.
Putting the theory of relativity in a nutshell
It is a theory that the speed of light is constant, and that time and space are distorted in order to maintain it. Put your hand on a hot stove for a minute, and it seems like an hour. Sit with a pretty girl for an hour, and it seems like a minute. That’s relativity. If you put your hand on a hot stove for a minute, it will feel like an hour. If you sit with a cute girl for an hour, it feels like a minute, right? That is the theory of relativity. Einstein expressed the concept of relativity in this way. That’s the conclusion. Time and space change depending on the observer. It’s crazy to be able to say something genius and unique! Perhaps, because you love to study, the image of increasing the time is on the stove.
What is the principle of the speed of light invariance?
The principle of the speed of light invariant is that “whether a person who is stationary or a person who is traveling at a speed close to the speed of light is seen, the speed of light is equally traveling at 300,000 km per second.” Are. As an example, even if you chase light in a spaceship that flies at 200,000 km per second, the speed of light seen from inside the spaceship is “300,000 km – 200,000 km = 100,000 km per second” … Will not. Light travels at a speed of 300,000 km/s without changing, just as if it were seen by a stationary person. Some people may not understand it, but please feel that it is like that. 
“What is the relativity of time” in the theory of relativity
It is said that Einstein preferred to use optical clocks when explaining the theory of relativity to ordinary people. For example, an optical clock is a mirror on the ceiling and a mirror on the floor facing each other in a spacecraft. The time for light to travel between mirrors is 1 second. When the spacecraft is stationary, the light travels perpendicular (straight) to the mirror. 
However, when the spacecraft is moving, the internal optical clock also moves with it, so the light travels at an angle rather than perpendicular to the mirror. Since it is going diagonally, the distance of one round trip is longer. Now think of the universal principle of the speed of light. If a person in a spacecraft moving at close to the speed of light and a person stationary on the ground measure one second with an optical clock, the same physical phenomenon occurs in both according to the principle of relativity. One second of round trip from ceiling to floor passes equally. However, if you look at the optical clock inside the spacecraft moving at close to the speed of light from a person stationary on the ground, the light from the floor will appear to travel diagonally because the spacecraft has traveled a long distance by the time the light from the floor reaches the mirror on the ceiling. In other words, the light that travels diagonally is longer than the height of the optical clock. However, according to the “Principle of the Speed of Light Invariant“, the speed of light is 300,000 km per second, the speed of light is 300,000 km per second, so even if the optical clock on the ground has passed one second, the light has not reached the ceiling in the optical clock in the spacecraft, and not one second has passed. From the point of view of the person observing from the ground, the time in the spacecraft is delayed. 
In other words, what is the relative of time?
The faster the spaceship moves, the slower time flows relative to its surroundings. And when it gets close to the speed of light, it almost stops to the observer. One second of a spacecraft can be decades, hundreds, or thousands of years for a person on the ground.
What is the principle of relativity?
The laws of physics hold even if the viewpoint is different (that they do not change).
What is the Urashima effect?
“People on a spaceship traveling at the speed of light do not grow old when they return to Earth” is called the “Urashima effect.” The speed of light is about seven and a half revolutions around the Earth in one second. Even if it is 1 second for a spacecraft, it is 7.5 days ahead of humans on Earth. The spacecraft’s time is delayed. It’s a mystery to think that Urashima Taro was taken by aliens to travel through space. 
So, can you build a time machine?
* YouTube video “[Why what?] Can humans dodge bullets from guns?Please refer to. Since ancient times, it has been believed that time is “an absolute thing that flows in the same way for everyone.” However, based on the premise of the “principle of the constant speed of light,” it turns out that time flows differently from person to person, that is, it is relative.
Time travel to the future!
I yearn for time travel to an elegant future. Using the relativity of time, it is theoretically possible to go to the future. But it needs to move close to the speed of light. Is it possible to move at the speed of light? The relativity of time creates mysterious phenomena. For example, there is a phenomenon called “Lorentz contraction,” which means that the faster an object moves, the more it shrinks in a certain direction. Also, the faster the object moves, the greater the mass. The speed of light is unimaginably heavy, so it requires an enormous amount of energy just to move it. At present, it must be said that it is difficult to bring substances at the level of the human body or spacecraft closer to the speed of light, partly due to energy problems. 
Black holes have a gravity more than millions of times (depending on their size) than the Earth’s surface, and time flows slowly. If you stay nearby for a few hours in a spaceship, you will be swallowed by a black hole even though you 、、、 and cannot escape even with light! It turns out that graceful time travel to the future is realistically difficult. Various theoretical theories such as undetermined exotic substances and wormholes have been considered, but they are theoretical theories. If you could time travel to the future, would you go even if it was a one-way ticket? The earth may no longer exist, or life covered in magma and ice may not be able to survive.
Can you take the bullet train or airplane to the future?
The Shinkansen can go to the future only one billionth of a second into the future! That’s right! We were already in a time machine! * The error level does not interfere with daily life. 
Time travel to the past!
I think it is possible to go to the past (create a time difference) by thinking relatively, but it is realistically difficult to go to the past that you intentionally wanted. The act of going to the past violates the law of cause and effect. Actions that violate the laws of physics are difficult to realize and require new interpretations and theories. Unless a miracle happens, even with modern science, we will not be able to recover the pudding that was eaten.
What is the law of causality?
【Discussion】Images of the present, past, and future
Personally, time has the image that the present, the past and the future exist at the same time. Imagine a movie, a video. It has already existed from beginning to end, and we live in the present in it. That’s why murder scenes and battlefields can be disgusting or ghostly (see the past?). I think it will. Of course, it’s a fantasy, but I feel happy to have been born in this era. 
In that image, I think about whether I can go to the past without violating the law of cause and effect, but I feel that it is still difficult to go physically. Since it is possible to rewind and move in videos, etc., I think it is possible to move to any time, but there is a high possibility that the memory will also be lost. Through dimensional rifts, wormholes… However, it is full of uncertainties. If it’s a mental move, maybe…
Conclusion What is a time machine?
A time machine is a vehicle that allows you to move freely through time from the future to the past and from the past to the future. Time travel must have been fantasized about by many people even before the theory of relativity was advocated. It can be said that it is a popular subject in science fiction novels, manga, and anime. Famous works include novels such as The Time Machine (1895) and Movie, Back to the Future (1985) and Doraemon (1969-1996). Everyone dreams of “changing the past” or “making a lot of money by looking at the future” in a time machine, but the sad conclusion is that it is difficult in reality. Time travel to the future is theoretically possible, so if you are interested, please realize a vehicle that can “fly or run” at the speed of light. It all starts with a fantasy. We are traveling to the future with our friends on Spaceship Earth. We may have been unknowingly in a time machine (Earth) from birth. If you can’t change the past, cherish the present. I think the future will change just by thinking that we have been time traveling from a hopeless future to the past right now. There may be people who are struggling with life right now or losing hope. Right now, let’s be a little brave and do our best. Only you can change the future. In reality, Doraemon will not come.
Bibliography
Khrapatyi (ふらぱてぃ)
Don't forget to enjoy "children's hearts"!
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This is a blog that focuses on child-rearing articles, YouTube video introductions, and miscellaneous articles from a professional and father's perspective by a social worker.
♥ Furari-chan (6 years old) The most beautiful girl in Japan. Gluttonous but small meal. I love cute things.
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