How to understand that a year spent in a spaceship traveling at the speed of light is equivalent to a million years on earth? For example, there should be no reference to time, it is absolute. For example, my watch in the spaceship will walk slower, the same watch, the pointer speed is the same, how can it be placed on the spaceship to walk one circle time, the earth will walk ten circles

How to understand that a year spent in a spaceship traveling at the speed of light is equivalent to a million years on earth? For example, there should be no reference to time, it is absolute. For example, my watch in the spaceship will walk slower, the same watch, the pointer speed is the same, how can it be placed on the spaceship to walk one circle time, the earth will walk ten circles

You don't feel time slowing down when you are on the spaceship. It's just that the earth's people observe your watch slower. At the same time, your observation of the earth's watch is slower than your watch, because if you take you as a reference, the earth is flying away. So time is relative. When you go back, there is a process of accelerating motion

Is it possible for a spaceship to fly at the speed of light?

No way
Chemical fuel
1. The acceleration of a chemical fuel rocket such as the space shuttle is 1.7g, which is only 1.7 times of the earth's gravity. It takes 10 years to reach gamma Centaurus, which is 4.3 light years away. It is impossible to accelerate continuously for more than two months. In order to accelerate continuously for two months, the space shuttle has to load more fuel, This makes it so heavy that it can't be separated from the launching platform
2. As we approach the speed of light, we have to face a problem ahead, which is the law of "Einstein's special relativity" that the faster the speed, the greater the mass. When the speed reaches about 0.75 times the speed of light, the mass will become 1.5 times. As the mass increases, even if the propulsion force increases, it can't accelerate, so the space shuttle must be made as light as possible
3. In the case of interplanetary space flight, the energy required is almost the same as that of today's ordinary flight. If a manned spacecraft is to fly at one third of the speed of light, it needs the energy equivalent to several years of power plants all over the world. If the atomic reaction reactor is used, the propulsion per unit mass of fuel will increase by 10 million times, It can be expected that the fusion reaction will occur in the combustion chamber by irradiating the nuclear fuel with a laser beam. However, it is very difficult to build a very complicated reactor
Antimatter flight
1. Theoretically, the energy produced by the disappearance of particles and antiparticles is 100 times that of nuclear fission and fusion. To accelerate a spacecraft with a mass of 1000 kg to 0.1 times the speed of light, only 9 kg of antimatter fuel is needed. However, antimatter is charged particles, which will produce repulsive force against each other. The higher the density of antimatter, the stronger the magnetic field used to restrain antimatter, This requires superconducting materials that can make the magnetic field strength beyond imagination
2. The second problem is quantity. Even if an efficient and large-scale antimatter production plant is built, it will take an extraordinary long time to produce 1 gram of antimatter. The international research group has produced only nine antihydrogen atoms in the three week experiment at CERN. Note that there are nine
Solar sail
1. After leaving the solar system, the flow of charged particles will become thin, and the spacecraft will stop in a "windless" state. It is obviously impossible to use the solar sail to go to other stars
How to get back?

On the speed of light
The time will be shorter and will stop. I saw the report that the time measured by our watch will slow down at high speed? I wonder, the watch is a mechanical movement. If there is no external force acting on the pointer to drive the gear, how can the watch slow down mechanically? Is there any external torque acting on the watch at the speed of light?

Maybe you don't understand it. The watch is just mechanical. It's a form of expression, so it will slow down. For example, when you speak on a superluminal spaceship, you are counting on the spaceship's time and space. If you just say one word, you feel that it's only two seconds later, and your watch, like you, has also walked for two seconds, but you return to the earth, I found that people on earth spent two seconds on your spaceship, they all talked for a whole day, they felt that they spent dozens of hours, their surface also spent dozens of hours. So the two watches are not the same. It is impossible for you to see that the watch doesn't go when you are on the speed of light spaceship, because the watch is a mechanical representation of your current time and space!
For example, when a particle is reflected by some object, the time is fixed, but you are not the same on the spaceship near the speed of light as on the earth, including the atomic clock
If you call the earth in a spaceship near the speed of light, the people on the spaceship speak for 2 seconds, while the people on the earth will take 1 day to hear it