How long will it take to reach Proxima Centauri? When will humans be able to visit that Three-Body World?

The Three-Body World described in the novel "The Three-Body Problem" is set on Proxima Centauri, where there are three suns. Proxima Centauri is the smallest of them and the closest star to us. I have already described the general environmental conditions there in my previous article "Where is the Three-Body World in Reality? Is it the Same as Described in Science Fiction?", so I will not elaborate on it here.

A friend in need is always a friend indeed. From the perspective of the Milky Way, Proxima Centauri is the closest neighbor of our solar system and will be the first stop for mankind to enter the interstellar space. As a result, people are very interested in it. Astronomers have been continuously observing it. As of February 2022, it has been found that Proxima Centauri has at least three planets, and liquid water and life may exist on two of them.

In fact, even with the largest and most powerful astronomical telescopes, we can only see the dim bright spots of this red dwarf star, not to mention the planets that are tens of thousands of times smaller than the stars. Our current understanding of Proxima Centauri and its planets is obtained through observing its spectral changes, scientific analysis and modeling. It is still just a hypothesis and conjecture. To truly confirm what this three-body world looks like, we have to send a probe or a manned spacecraft to take a look there.

Unfortunately, although this star is the closest to the solar system, it is still 4.22 light years away, or about 40 trillion kilometers away. With human aerospace technology, this interstellar scale is still out of reach. So when will humans be able to visit Proxima Centauri? Let's analyze and understand.

First, let’s take a look at the current level of human spaceflight.

The farthest unmanned probe built and launched by humans is called Voyager 1. This probe was launched by NASA in the 1970s and has been drifting alone in space for 45 years. It has now reached the outer edge of the solar system, 23.8 billion kilometers away from us. A few years ago, it flew over the top of the solar wind and came into contact with the interstellar plasma in space. It can be said that it has entered interstellar space.

However, the solar system is generally considered to be a sphere with a radius of about 1 light year, and the edge of this sphere is wrapped in a shell of comets, called the Oort Cloud. Of course, this is still a hypothesis, and this shell is far less dense than people imagine. It is generally very sparse, so sparse that there is no obstruction to observing the space outside the solar system. The probability of a probe hitting an asteroid or comet is much smaller than winning the lottery jackpot.

Voyager 1's current speed is about 17 kilometers per second. At this speed, it will take 17,600 years to fly out of the Oort Cloud belt of the solar system and more than 74,000 years to fly to Proxima Centauri.

The fastest man-made probe currently in flight is the Parker Solar Probe, which relies on the gravity of planets and the sun to accelerate. Its current flight speed has reached over 100 kilometers per second. By the end of December 2024, the Parker Solar Probe will pass through the high-temperature corona only 6 million kilometers away from the sun, and its speed will reach 200 kilometers per second.

If we build a probe at this speed and fly to Proxima Centauri, it will take 1,500 years.

Moreover, these probes are unmanned probes. If they are to be converted into manned spacecraft, there are still many insurmountable difficulties, such as power, fuel, life support systems, etc. Even if these can be overcome, it will take 3,000 years to go back and forth. How many boys and girls will have to be selected to pass on their family lineage for many generations before they can return.

Even if we can return, the earth has changed a lot and who knows who will be there.

Conclusion: With the current speed of human space travel, it is completely impossible to explore Proxima Centauri.

So, when will we be able to travel to Proxima Centauri in the future?

Humans have only traveled as far as the moon, which is about 384,000 kilometers away from us. Unmanned probes have visited all the planets in the solar system and some dwarf planets and asteroids. The farthest unmanned probe has traveled is only 23.7 billion kilometers, which is only 0.0025 light years if converted into light years. Therefore, this distance is completely different from the 4.22 light years of Proxima Centauri.

How long will it take for humans to explore Proxima Centauri? According to some current space programs in the world, it will take about 100 years.

This plan, which allows humans to fly out of the solar system and into deep space, is called the "Centennial Starship" plan. It is a space exploration plan jointly developed by NASA (National Aeronautics and Space Administration) and DARPA (Defense Advanced Research Projects Agency) of the United States. The goal is to allow humans to fly beyond the solar system and reach other star systems within a hundred years.

The key to this plan is to design and manufacture a spaceship suitable for interstellar travel. Information disclosed online includes: the starship is designed to weigh 50,000 tons, is powered by nuclear fusion energy, and can fly in space at a speed of 12% of the speed of light; more radical research plans believe that the starship's ultimate speed will reach a quarter of the speed of light.

If the speed reaches 12% of the speed of light, it will take at least 35 years to reach Proxima Centauri. If the explorer is 20 years old when he sets out, he will be at least 90 years old when he returns. If the speed reaches one-quarter of the speed of light, it will only take a little over 16 years to reach Proxima Centauri. 40 years for a round trip will be enough. In this way, a 20-year-old explorer will be only 60 years old when he returns from Proxima Centauri, which is still in his prime.

Therefore, only by increasing the speed of the spacecraft to more than one-fifth of the speed of light and increasing the life expectancy of humans can a round trip to Proxima Centauri be completed within one generation. Some people worry about the time dilation effect in such a high-speed spacecraft, and whether things will be different when they return.

This worry is unnecessary because the time dilation effect is only very obvious when the speed is very close to the speed of light. The time dilation effect of 25% of the speed of light is only about 1.03 times, that is to say, the time for people on the spacecraft will be 3% slower than that of the earthlings. So it took the explorers 33.76 years to travel 4.22 light years back and forth, while it took the earthlings 34.77 years.

That is to say, people at home on Earth will only be one year older than explorers riding on a spacecraft traveling at 25% the speed of light. This age change is basically not noticeable to people in their sixties and seventies, but because of the different environments they have experienced, it will have a greater impact on people's appearance.

The Centennial Starship Project was supported by then-US President Clinton and officially launched on September 13, 2012. Later, the project was still a hot topic for a while, and the spacecraft concept map and the first captain were released, but in recent years, there has been little news. It is unknown whether it is being carried out in a low-key and secret manner or has been shelved.

In addition, there is the Daedalus Project proposed by the United Kingdom in the 1970s and the Orion Project proposed by the United States, both of which are plans to build high-speed spacecraft or unmanned probes to nearby star systems such as Proxima Centauri. The former is believed to be a successor to the Centennial Starship Project that was launched later, while the latter uses a series of nuclear bomb explosions to accelerate the probe, but was abandoned due to a shortage of funds and controversy over the environmental pollution caused by nuclear bombs.

Then, only the Centennial Starship Project has not been officially announced to be stagnant or failed. This is the only long-term plan for manned deep space voyages that has been launched in the world so far. If it succeeds, humans will most likely fly out of the solar system and fly to Proxima Centauri by the end of this century.

Will an unmanned probe reach Proxima Centauri earlier?

When the famous physicist and popular science writer Hawking was alive, he launched a project called Breakthrough Starshot. The core of this project was to launch a series of mini probes to Proxima Centauri.

Hawking's team envisions building 1,000 mini probes, which are only the size of a fingernail and are gram-level chips equipped with mini cameras, photon propulsion devices, power systems, navigation and communication equipment. 1,000 of these probes can be launched at a time using a rocket.

When the rocket launches these probes into Earth orbit, the probes will unfold their huge light sails. At this time, the high-energy laser array installed on Earth will accurately illuminate the light sails to accelerate them. After intermittent continuous acceleration, the probes carried by the light sails will eventually be accelerated to 20% of the speed of light, that is, 60,000 kilometers per second.

In this way, it will only take 21 years to reach Proxima Centauri, photograph and detect the situation there and then send it back. The radio waves will take 4.22 years to reach the Earth, and humans will know the basic situation there.

But things are not as simple as imagined. Many Chinese and foreign scientists believe that this plan itself is unlikely to be realized. First, it is difficult to carry such a small probe with camera equipment, power system, propulsion device, navigation and communication equipment with current technology. Second, it is also a fantasy to propel the light sail to 20% of the speed of light with laser, because to accelerate 1 gram of object to 20% of the speed of light, at least more than 400 tons of TNT explosives are needed. The laser emitted by the earth will also be attenuated by the atmosphere, so it is impossible to generate such energy.

In addition, a distance of 4.22 light years requires extremely precise navigation and direction adjustment systems. A slight error will lead to a huge mistake, and these probes will disappear if there is any mistake. And for such a long distance, communication transmission must be powerful. Can the communication facilities on the small mini probe do it?

Even if the above problems are solved, it is impossible for these probes to brake when they reach Proxima Centauri. They will pass by at a speed of 60,000 kilometers per second. The cameras and detection devices must be turned on in time in that flash of lightning to obtain the situation of Proxima Centauri and the entire Alpha Centauri complex and transmit it back. Can this be done accurately?

Hawking, the main initiator of the project, passed away in 2018. Since then, there have been few reports on the Breakthrough Starshot project. I don’t know whether it is still ongoing or whether there has been any progress. I think this project may still be just a science fiction.

So, can humans really visit Proxima Centauri? The answer is yes, it's just a matter of time. Human society has entered an era of explosive development of scientific information, and many science fictions are becoming reality. Just on January 24, NASA Administrator Bill Nelson announced that the research and development results of thermonuclear engines for future trips to Mars will be demonstrated in 2027. This engine will enable astronauts to fly faster in deep space and reach their destination earlier.

Therefore, I believe that the human desire to visit Proxima Centauri will definitely come true, and it is likely to be realized before the end of this century. What do you think about this? Welcome to discuss.

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