Looking at the Earth from 2000 light years away

In the city, on the streets, there are crowds of people, people are busy passing by, and vehicles are running back and forth. Buses, high-speed trains, and airplanes are accustomed means of transportation, speeding by on their respective tracks. We are accustomed to it, but we do not know that these seemingly ordinary objects move, but they have changed our space-time structure. The small changes in , are not enough to make our senses feel. These changes are usually at the level of Planck's constant, which is 6.626*10^-34, followed by 34 0s after the decimal point. It can be said that the small ones are ignored. .

To make a simple analogy, two friends are saying goodbye at the airport, one is about to take a flight to a place 2,000 kilometers away, and both of them have the most accurate atomic clocks on their bodies. Atomic clocks use the principle of the energy transition of atoms to release electromagnetic waves, and use the resonance frequency of electromagnetic waves as a metronome to keep the clock accurate. Ordinary clocks have an error of one minute per year, while atomic clocks only have an error of one second in 20 million years. Three hours after the two were separated, the traveler got off the plane, took out the atomic clock in his hand, and compared it with the clock in the other person's hand, and found that the atomic clock after the air travel was several nanoseconds slower than the atomic clock that stayed in place ( 1 second = 10^9 nanoseconds). But don't underestimate these few nanoseconds. For an atomic clock that has an error of only one second in 20 million years, a nanosecond-level change in just a few hours is already astronomical. This shows that the time of the atomic clock in flight has slowed down.

According to the theory of relativity, the atomic clock on the plane is moving relative to the atomic clock on the land, and the moving speed is equal to the speed of the plane. It is because of this speed that the space-time structure in flight is compressed relative to the land, so that the time of the moving object becomes slower. . Aircraft is a high-speed vehicle that most of us have been able to access so far. When moving several times faster than the speed of sound, the time and space changes brought about are so small, but if the scale of relative motion is placed in cosmic space, the changes brought about will be amazing.

Imagine that we are now standing on a planet in the Kepler galaxy 2000 light-years away. At this time, we only need a bicycle to freely observe the past and future of the earth. We first aim at the direction of the connection between the Kepler galaxy and the earth, prepare the bicycle, turn the head back to the direction of the earth, and start to move away from the earth. Before motion, the space-time of the Kepler galaxy is the same as that of the Earth, which can be understood as being in the same space-time section. When we ride leisurely, we have a relative motion with the earth. This speed slightly compresses the space-time structure, so that the space-time section of the Kepler galaxy and the earth's space-time section produce a small angle. .

This angle is placed on the moon, on Mars and even on the distant Pluto, and the changes produced are insignificant to us. But in the cosmic space 2000 light-years away, the space-time section of our standing planet and the current earth's space-time section have an inverse angle, and the inner direction of the angle is toward the opposite direction of the earth's timeline, so you can see the past time of the earth. How far we can look back depends on our speed of movement. If we ride faster, we can increase the included angle of the space-time section, allowing us to see further in the past. Maybe if we put in a little more effort and speed up, we will be able to see the magnificent picture of Qin Shihuang swept across the eight wastelands and unified the country 2000 years ago.

In the same way, if we want to see the future of the earth, we turn the bicycle around, move in the direction of the earth, and reduce the distance from the earth. The space-time section will form a positive angle, and we will be able to see the future of the earth. . Maybe we're going fast enough to see Earth 2,000 years from now, when people are getting ready to board spaceships and embark on a great interstellar journey.