How long does it take for a man to be on a spaceship at the speed of light?

How long does it take for a man to be on a spaceship at the speed of light?

Theoretically, infinity. This is the conclusion of special relativity, which is called time delay effect (clock slow effect), that is, the time loss speed of high-speed inertial frame is slower than that of low-speed frame. If you move at a very high speed, the time passing speed of your space-time will be slower, The speed of time passing is infinitely close to 0. Of course, the special theory of relativity also thinks that macro objects can't reach the speed of light, so I just say that infinitely close to the speed of light. So you can't be on the spaceship for a second, and the earth has passed forever, but it's very likely that when you come back from a one-year subluminal travel, you will find that your classmate's grandson is already an old grandfather