About time travel, is it really possible?

Everyone will think of time travel at least once in his life. Maybe you have thought that if you can go back and try to make some changes, there have been many sci-fi movies about time travel or time travel. But is it really possible to go back to the past or cross into the future? If this is really possible, what can we do to make time travel a reality? The idea of time travel and how to realize it are exciting. Scientists, especially astrophysicists, have been thinking about these issues for a long time. Is this the most wonderful thing?

The high probability of time travel becomes possible. Maybe we should learn the bad news about time travel first: we may not be able to go back in time and witness the Egyptians building pyramids. However, many theoretical hypotheses show that we can travel through time. Although going back to the past is more complicated, it doesn't mean that we can't go back to the past.

Albert Einstein was a great scientist in the 20th century. He put forward a theory called special relativity. Although most people think that time is relatively constant, Einstein proved that time is an illusion. Time is relative because people who travel through space at different speeds feel different time (length). The concept of special relativity is difficult to understand and imagine because it has nothing to do with our daily life experience, but other scientists have confirmed this theory. Special relativity holds that space-time is actually all aspects of the same thing, that is, "space-time". The speed limit of any object traveling through time and space is 300,000 kilometers per second (or 65,438+086,000 miles per second), even if light passes through a vacuum, it will not exceed this speed.

There are more surprises about the illusion of time. Special relativity reveals that when you travel through time and space, especially when you travel through time and space at the speed of light relative to other objects, the time you feel is much slower than that of those who are not as fast as you.

Unless you are in a relatively static space, you won't realize the influence of light speed flight. So as an experiment, let's assume that you left the earth in a spaceship near the speed of light at the age of 15, and celebrate your fifth birthday in space travel. When you come home at the age of 20, you will find that your classmates are all 65 years old. They have retired and left with their grandchildren! The reason for this difference is that your time is much slower. When your classmates have lived for fifty years, you have only lived for five years.

A spaceship is a tool or a machine, which is used to go to outer space. As an artificial satellite, spacecraft has many uses, including space communication, earth observation, meteorological monitoring, satellite navigation, space migration, planetary exploration, and transportation of people and goods. However, all spacecraft except single-stage orbiter need to rely on launcher (launch vehicle) to reach outer space.

In suborbital space flight, the spacecraft returned to the ground after entering outer space because it did not get enough energy or speed to realize the complete orbital flight of the earth. For orbital space flight, the spacecraft enters a closed orbit around the earth or other celestial bodies. Spacecraft used for human space flight only carry crew and passengers at the beginning or in orbit (space station), while spacecraft used for robotic space missions are automatic or programmed. Robot planes used to support scientific research belong to space probes, while satellites are constantly orbiting planets. So far, only a few interstellar probes, such as Pioneer 10 and 1 1, Voyager 1 and 2, and New Horizons, are in orbit outside the solar system.

Not all spacecraft in orbit are recyclable, and most of them are not. The recoverable spacecraft can be decomposed into wingless capsule and winged space plane by re-entering the earth. A recoverable spacecraft may be reusable (for two or more launches, such as the Dragon Spacecraft and the Space Shuttle Orbiter) or exhausted (such as Soyuz).