The faster the speed, the slower the time. What would happen if we flew close to the speed of light?

According to the time dilation effect of relativity, the faster an object moves, the slower its own time passes.

So there is a thought experiment called "twin paradox". "Twin paradox" refers to a pair of identical twins. The elder brother stays on Earth, while the younger brother leaves the Earth on a spaceship that is close to the speed of light. When the younger brother returns after driving the spaceship around, he finds that his elder brother has become an old man with a gray beard, while he still looks the same as when he set out. Why is this so? Because the spaceship is very fast, the passage of time on the spaceship slows down. Although decades have passed on Earth, only a few hours have passed on the spaceship. This sounds incredible. Why does speed affect time?

According to the mass-energy equation E=mc∧2, energy is equal to mass multiplied by the square of the speed of light. The speed of light is constant, so there is a close connection between the energy and mass of an object.

When the mass of an object increases, its energy will inevitably increase, and vice versa. The energy mentioned here refers to the total energy of the object. When an object starts to move, it has kinetic energy. The faster the speed of movement, the greater the kinetic energy. When the total energy of an object increases, its mass will inevitably increase. The increased mass here is called "inertial mass". Inertial mass is generated by movement, but it is equivalent to the gravitational mass of the object itself. According to the general theory of relativity, the gravitational mass of an object will cause the surrounding space-time to bend, and the inertial mass is equivalent to the gravitational mass, which will naturally cause the surrounding space-time to bend.

As an object moves faster and faster, its inertial mass becomes larger and larger, and the curvature of the surrounding space-time also increases.

Spacetime refers to time and space, which are an inseparable whole. Therefore, the curvature of spacetime caused by the increase of inertial mass will lengthen the time in the spacecraft, that is, the passage of time will slow down. This is the inherent principle of how speed affects time. Having said so much, it seems to be a theory and thought experiment. Does speed really affect time in reality? This is beyond doubt. Every day when we drive, we rely on navigation. The reason why navigation can accurately indicate the route depends on the navigation satellites operating in the earth's orbit. In order for the navigation satellite to accurately indicate the route, there is a process that is indispensable, that is, two-way time calibration.

Navigation satellites orbiting the Earth are moving at very high speeds. Because of their high speeds, the passage of time is slower than on the Earth's surface, so a time calibration is necessary.

In addition, since the satellite is far away from the earth, it is less subject to gravity than the earth's surface, so its time passes faster than the earth's surface, so a second time calibration must be performed, which is a two-way time calibration. What will happen if a two-way time calibration is performed? Taking GPS navigation satellites as an example, the positioning deviation will reach about 14 meters every 24 hours, which means that if the navigation satellite is not two-way time calibrated, the car would have driven into the ditch long ago. Speed ​​will affect the speed of time passing, and there should be no objection now.

Speed ​​affects time, so how much influence does speed have on the speed at which time passes?

What would happen if we flew for one minute at a speed close to the speed of light and then returned to Earth? "Close to the speed of light" is a bit vague. How fast is considered close to the speed of light? 50% of the speed of light? 99% of the speed of light? Or 99.99% of the speed of light? You will truly experience what a small difference can lead to a big mistake. The speed of light is 299,792,458 meters per second. Even at 50% of the speed of light, it is already very fast, but at this speed, the time dilation effect is still not very obvious, so we still start from 99% of the speed of light. To calculate the time dilation effect at 99% of the speed of light, we must apply the clock slow effect formula, that is, Δt=Δt/√(1-v∧2/c∧2).

Calculations show that if the speed can reach 99% of the speed of light, then time will expand 7 times, which means that the passage of time will slow down 7 times.

So if you fly at 99% of the speed of light for one minute and then return to Earth, then 7 minutes should have passed on Earth. Obviously, the change is not obvious enough. At this speed, it is not enough to turn your twin brother into an old man. What if it is 99.99% of the speed of light? This time the change is much more obvious. Time will expand 70 times, which means that 70 days have passed on Earth for one day of flying in a spaceship. This is really one day in heaven and two months on earth. If you still don’t feel satisfied, you can make the speed even faster. When the speed reaches 99.999999% of the speed of light, time will expand 7000 times, which means that 20 years have passed on Earth for one day of flying in the universe. Of course, no matter how you speed up, objects with mass cannot reach the speed of light. If they run at the speed of light, time will stop.

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