Scientific data of interstellar travel

Besides the sun, the nearest star is Alpha Centauri, which is 4.3 light years away. ("light year" is a unit of length, not a unit of time. Refers to the distance that light moves in one year. The distance from the earth to Alpha Centauri is 25 trillion miles.

Transportation time:

In order to escape from the earth, the speed of a spaceship must exceed 25,000 miles per hour. At a speed of 25,000 miles per hour, the spacecraft will need 1 100 million hours to reach Alpha Centauri-the total transportation time is 1 14000 years. It is terrible to design a self-sufficient human migration team that can successfully sustain itself for more than 654.38 million+years. It needs faster speed.

Even at the speed of light, it will take four years to reach Alpha Centauri, but we have good physical reasons to think that it is impossible to approach this speed. Sebastian von Hellner thinks that 3% of the speed of light is the maximum speed we can expect, that is, 22 million miles per hour. At this rate, it will take 140 years from the earth to Alpha Centauri. Travel takes five generations. Some people may think that future technological progress can shorten transportation time; But on the other hand, what if Alpha Centauri doesn't have an imaginary planet suitable for human life? In this case, our may flower spacecraft will "set sail" again, and its passengers are expected to discover a new earth, perhaps five generations later.

Energy:

Don't think that the Mayflower spacecraft can be self-sufficient through ordinary agriculture like the earth. Sunlight can only make the green plants on the spacecraft grow in the first few months of the trip. Long before the spacecraft flew to Neptune, sunlight was not enough for photosynthesis, and everyone knew how dim distant stars were. In the dark, plants should inhale oxygen, just as animals have been doing. So plants will compete with humans for oxygen long before they get close to Neptune. Since Alpha Centauri is the nearest star, it means that most of the travel in 140 will be accompanied by starlight. There is no doubt that this is very romantic, but it is not very nutritious. It is necessary to use the energy on the spacecraft to regenerate oxygen. From what channels can members of the immigration team get the energy they need to live in the dark for five generations?

Freeman Dyson suggested that travelers could drop hydrogen bombs one by one at the tail of the spacecraft, and capture 65,438+00% energy by using the barrier between the spacecraft and the explosion. Obviously, there are still many engineering details to be solved before our spaceship leaves! The mobile migration team needs a safe way to store and use 140 years of energy.

Cost:

The savings and donations that our ancestors used to pay for the historic Mayflower trip to the United States can be expressed as the years of hard work needed to accumulate the necessary capital. Dyson believes that it takes 7.5 years of labor for a person to pay for a family's travel expenses during the journey that Mayflower brought the Puritans' predecessors to North America. For the historic trip of Mormons from Illinois to Utah in the19th century, he calculated that each family needed to spend 2.5 people a year. For a well-designed space migration team project, he estimated that the cost of each family was10.5 million person/year. If there are four people in each family, it means that everyone will pay for space travel with 375 years of labor income.

When we use the basic term of working years to express travel expenses, it is obvious that almost no passenger can afford his travel expenses. A person who works for 50 years in his life (from 15 to 65) only works for 50 years, and consumes most of this number in the course of his life. It's hard to say how much he can accumulate, but certainly not much. Therefore, every imaginary immigrant on the spaceship must be supported by a large group of people who stay on the earth. This scientific fact obviously requires some tolerance of the political system.

Although the dollar is not the basic measure compared with the number of years of work, we will also gain something by roughly expressing the travel expenses in dollars. Consider the situation of nuclear submarines. This is an ingenious mechanical device, but it is obviously not as complicated as a spaceship capable of interstellar travel in 140 years. The cost of a typical nuclear submarine is 10 billion USD, and it carries 140 sailors. The boarding fee for each sailor is $7 million (we also ignore a considerable part of the operating costs). If every sailor has to buy his position on the submarine (just as British gentlemen in the19th century have to buy their qualifications in official institutions), can an ordinary person earn enough money to pay the boarding fee before he is too old to board the ship? It is rare that an ordinary person can save $65,438+00,000 a year from an ordinary job. According to this optimistic savings rate, it will take him 700 years to accumulate the required boarding fees.