Scientific answers: What is the time dilation effect of relativity, and can it make people immortal?

Yesterday, I published an article introducing the gravitational lens effect. The core content of the article is that through the gravitational lens effect, people can intuitively see the distortion of space-time by mass, proving that Einstein's theory of space-time distortion is real and correct.

After reading the article, some friends finally agreed that space can be curved, but they raised questions: If space is curved, why must it be associated with the word "spacetime"? What does this have to do with time? In fact, in many of my previous articles, I have already explained the effects of time dilation. If you have read these articles, you will not ask this question.

What is time dilation?

The theory of space-time curvature and the theory of time dilation are both contents of Einstein's theory of relativity. In the special theory of relativity, Einstein mainly explained the relationship between speed and time, which is generally called the problem of speed time dilation; while in the general theory of relativity, the emphasis is on explaining the relationship between time and space curvature, that is, the problem of gravitational time dilation.

The core content of Einstein's theory of relativity is to explain the relationship between time, space and matter. Through a series of detailed mathematical and logical arguments, he believes that time, space and matter are a trinity, and proves that in different coordinate systems, time and space are relative, which fundamentally subverts the absolute view of time and space in classical physics.

The argumentation process is very complicated, so I won’t go into details here. The conclusion is very simple, that is, time will expand at different speeds and in different gravitational fields. To put it simply, the faster the speed, the shorter the distance will be, and the slower the time will pass; and in the coordinate system with greater gravity, time will pass slower.

But there are two ceilings: the speed of light and the Schwarzschild radius of a black hole, which is the end of time and space. When an object reaches the speed of light, or enters the event horizon of a black hole where the curvature of space-time is infinite (gravity is infinite), space becomes zero and time stops.

But the speed of light is the ceiling of our world. Any object with rest mass cannot reach it, let alone break through it. This is because of the mass increase effect. When an object approaches the speed of light, its kinetic energy and mass will become infinite. This means that even if it is a fundamental particle, if it wants to reach the speed of light, the energy it needs and the momentum it reaches will also be infinite.

Our universe is also finite, that is, it is impossible to have infinite energy to push an object with rest mass to the speed of light, and the momentum of the particle reaching the speed of light will exceed the mass of the universe, which is a paradox. I have explained this problem many times in the past, so I will not elaborate on it today.

Now we will only talk about the relationship between time, speed and space through two time dilation formulas.

The significance of the two time dilation formulas

The velocity time dilation formula given by special relativity is: t'=t/√[1-(v/c)²]

In the formula, t' is the value of the velocity time dilation effect; t is the time recorded by the first clock of the low-speed observer; v is the speed of the second clock relative to the first clock; and c is the speed of light.

The formula for calculating gravitational time dilation given by general relativity is: t'=tx√(1-2GM/rc²)

In the formula, t' is the value of the gravitational time dilation effect; t is the time passage value of the observer in the low-gravity inertial system; G is the gravitational constant, which is 6.67x10^-11N·m²/kg²; M is the mass of the celestial body; r is the radius of the celestial body; and c is the speed of light.

The derivation process is very complicated, so let's leave it to those "experts" who question the theory of relativity to nitpick. There is no need for us to understand such profound things for the sake of popular science.

According to the formula for speed-time dilation effect, when an object moves at half the speed of light, which is about 150,000 kilometers per second, time dilation will reach 1.15 times, or 15% slower. In this way, when one year passes for the people in the spacecraft, 1.15 years will pass for the people on Earth.

When the speed of light reaches 99%, the time dilation effect will reach 7 times, that is, after 1 year for the people on the spacecraft, 7 years have passed for the people on Earth. When the speed of light reaches 99.999999999999%, time will dilate 7.07 million times, that is, after 1 year for the people on the spacecraft, 7.07 million years have passed for the people on Earth.

Similarly, in a coordinate system with greater gravity, time dilation is greater, that is, time passes more slowly. In the science fiction film "Interstellar", the spacecraft arrives at a Miller planet near a black hole, which is 100 million times the mass of the sun. The movie does not give the distance to the black hole's event horizon, but gives that if the astronauts stay there for one hour, seven years will pass on Earth, that is, time has dilated more than 60,000 times.

So when astronaut Cooper returned to Earth, he was still the same, but his daughter was already in her 90s.

The largest known black hole in the universe, SDSS J073739.96+384413.2, has a mass 104 billion times that of the sun. How much time dilation will there be near it? Given the distance to the black hole's event horizon, we can calculate it using the formula.

Many people simply disdain to learn about the theory of relativity and deny the theory of time dilation based on the logic of eating, drinking, defecating and urinating. However, whether these people believe it or not, the theory of time dilation has long been applied in scientific research and various technical applications. The most typical and commonly used example is the navigation and positioning system. If the satellite and ground time are not adjusted according to the theory of relativity, the navigation will lead you to Java.

So can the time dilation effect make people live longer?

My answer is NO.

Many netizens have a misunderstanding: since the passage of time slows down near high-speed spacecraft or large gravitational fields, wouldn't people living in this coordinate system live longer?

In fact, this is not the case at all. Because people in this coordinate system feel that time is still passing normally, not slowing down at all. The feeling of 1 minute, 1 second, 1 hour, 1 day is the same as on Earth. If we ignore the various factors affecting space travel, such as radiation, weightlessness, etc., their lifespan will not change at all.

That is to say, if they can live to 100 years old on Earth, they can only live to 100 years old on the spacecraft.

In fact, the conditions of space travel are far less safe than those on Earth, so under the same medical security conditions, it will greatly affect life expectancy. But if they return to Earth and compare the passage of time with that of Earthlings, they will find that time passes faster for Earthlings than for them. How much faster depends on how fast their spacecraft is, or how strong the gravitational field they stay in is, and how long they stay.

According to the speed-time dilation formula, if one takes a spaceship at 99.99% the speed of light and flies for one year and comes back, 70 years will have passed for the people on Earth. If one takes a spaceship at 99.999999999999% the speed of light to the Andromeda Galaxy 2.54 million light-years away and comes back, it will only take the travelers 0.7 years, or a little over eight months, while 5.08 million years will have passed on Earth.

If the spacecraft is very slow, below 50% of the speed of light, or even slower, the time dilation effect is very small and has little impact. However, the current spacecraft speed is only a dozen kilometers per second, so the time dilation effect of travelers is completely negligible compared to people living on Earth.

The passage of time slows down, and it slows down in all aspects

The time dilation effect is not that time feels slower, but that you don't feel it at all. The so-called length contraction and time dilation effect can be understood as the faster the speed, the shorter the distance, and the less time is needed. How much shorter is it? This corresponds to the multiple of time dilation.

For example, if you take a spacecraft traveling at 99.9999999999999% of the speed of light to the Andromeda Galaxy, which is 2.54 million light-years away, time will dilate 7.07 million times, which means the distance will be shortened 7.07 million times. Therefore, a distance of 2.54 million light-years is only about 0.35 light-years, and the round-trip distance is only 0.7 light-years. The speed of the spacecraft is close to the speed of light, so of course the travel time will only be about 0.7 years.

This calculation is only to illustrate the theoretical value of this problem, ignoring the time of acceleration, deceleration and dwelling. Please do not get stuck on it.

Therefore, the people on the spacecraft did not feel that only such a long time had passed, but it was actually only such a long time that had passed. This speed of time passing was not superficial, but inherent. From their conscious feelings and every cell in their body, and even the various atomic elements that make up the cells, the metabolic cycle has only experienced this change in time.

The same time dilation effect occurs in gravitational systems.

Therefore, for high-speed travelers, compared to people who are relatively stationary on Earth, time itself "passes" more slowly. For them, the real feeling is that one day is just one day, and they do not feel that they have gained any extra time.

This is a bit like what we often call frozen age, that is, age is frozen, or people are frozen in the snow and then woken up after many years. To the awakened people, many years have passed in the world, but can this be said to be the longevity of the frozen people?

Future deep space voyages will minimize the time dilation effect

The time dilation effect is an objective existence and a law of the universe. It does not bring any benefits to people traveling in space, but will add a lot of trouble. For example, if there is a spacecraft that is close to the speed of light, when people leave the earth and go to a planet, their loved ones will be gone and the earth will have changed a lot. What is the meaning of such exploration or travel?

Therefore, for future deep space travel, increasing speed is only one aspect. When the speed is below 50% of the speed of light, the time dilation effect is not too troublesome and people can still accept it. But faster journeys may not rely on increasing speed, but on finding another way.

At present, the scientific community believes that there are two ways to break through the bottleneck of deep space travel speed, namely wormhole travel and warp drive. In layman's terms, these two methods are to reach the destination by drilling tunnels and taking shortcuts. From the perspective of the overall travel distance and time, it seems to exceed the speed of light by many times, but in fact, the speed is not increased, so it is not limited by the speed of light, and there will be no speed expansion effect.

These methods are still in the science fiction stage, and it is hard to say whether they can be realized in the future. I have introduced these in the past. Friends who are interested can refer to the relevant articles I have published in the past. I hope it will be helpful to everyone. Thank you for reading and welcome to discuss.

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