What are the views on time travel in science fiction?

Problem description:

In recent years, there are many articles about time travel and time machines in science fiction. What kinds are there? What are their theoretical bases? What are the representative works? What are the ideas in China's science fiction?

Analysis:

In fact,

Science World: It is said that time travel.

There are three questions left in the article "When does the Time Machine Depart" in the 9th issue of this journal. Readers showed great interest in these issues and actively participated in the discussion: going to the parallel universe and setting up a time travel agency; Use the energy of lightning or become an electromagnetic ghost. They think this can solve the paradox that may be caused by running back and forth between the past and the future. While waiting for the machine designed by scientist paul davis to take us to travel in the future, let's take a look at the whimsical ideas of readers!

About the first question: getting young by plane.

Using the formula mentioned above, it can be concluded that you can earn 15× 10- 14 seconds per second. Time is really short! When a person travels by air continuously for a whole year, the time will be about 5 microseconds slower.

Many readers have worked out this problem. It is conceivable that under normal circumstances, traveling at the fastest speed we can achieve every day is not much younger in life.

On the second question: Back to the future.

For travel in the past, paul davis provided an answer based on wormholes, and most readers thought this idea was very novel. However, it is impossible to travel in time using wormholes before they are made. If we build a wormhole today and the time span at both ends is 100 years, then a century later, someone can travel back to 2003.

technical matters

Many readers agree that future travel is possible, but we can't do it just because of some technical details. Some readers said: "It is impossible for a' future person' to break in, because the time machine cannot return to the era that has not yet come out." Others think: "People who travel in the past can't go back to the future, because people can't travel in time either in the past or now, so travelers can't go back to their time."

Some readers made it clear that "we don't have a time machine now, and future travelers won't have such a stay, so they can't visit us."

Others think that it is possible that we will be patronized by time travelers, "but we will only know it in future time travel."

Some people think that this problem is more profound: "With the time machine conceived by Davis, we can only reach a point where the information has not yet reached in the past, not the source of the information! Therefore, it is impossible for future generations to interact with information sources, and we will not encounter the past' he'. "

Some people think that it is only possible to travel in the future without looking back, so "we can meet two kinds of time travelers: time travelers on earth and time travelers outside the earth, but only those in the past." If we fail to meet the first group of travelers because of technical problems, another problem may arise for the second group: "Since they have built a time machine to go to the future, there may be a gap with our civilization, and their civilization level is much higher, then this effort is not worth it."

What should I do if I run out of gasoline?

One of Davis' questions about future travel is energy. Some readers think this is an insurmountable obstacle. "After a little calculation, I know that if hydrogen is used as the propellant of the spacecraft, the dosage is almost 1 cubic kilometer."

However, some people are optimistic about the possibility of reducing costs: "Why not use the energy of lightning or hurricanes?"

We don't know what paul davis thinks, but we should ask what kind of container contains energy!

Is this crazy or ... ...

"I don't know if anyone will be sent to a mental hospital because he says he is from the future, but my doubt is, even if there is a time traveler from the future, will he tell the truth?" Someone said in the letter: "If one day someone knocks on our door and says that he is our descendant, who among us will believe it?"

Others have the same view: "Maybe we have future travelers now, but we haven't found them yet. So, how do we distinguish the two? Even if he says he is from the future, who will believe him? "

Some people think further: "We think of ourselves as time travelers, and we come to 1930. If we talk to people like this, they will think we are crazy and put us in an insane asylum! "

Go crazy together.

Some readers are more imaginative: we might as well imagine that time travel has become a common thing in the distant future. By then, we need a world-class travel agency to arrange everything for us.

"Travel agencies must be divided into two specific groups. Some people are engaged in administrative management, responsible for public relations propaganda and planning, and the other group is responsible for accompanying scientists and other tour groups to prevent future residents from contacting their relatives or others in the past. "

Someone thought of the legal problem: "There must be a principle of non-interference to avoid time travelers being recognized."

People are reminded to be cautious: "Time travelers should take precautions and not be completely confused by the time they are going." For example, if a time traveler decides to go to the Middle Ages, he should prepare knight's armor, learn chivalry and be talkative. "

Some readers naively believe that there should be some rules to prevent reckless time travelers from interfering with the times they are visiting. "I think measures should be taken to prevent possible interference and avoid meeting others through short trips. Perhaps it is only necessary to convince the scientific community in the past to try to avoid direct contact between travelers and their ancestors. "

pessimist

What if time travel is impossible? Not because of technical problems, but because we used to live in a universe parallel to us. Some people are convinced that "if someone wants to travel in time, the huge magnetic field deformation will make his memory completely lost." Some readers think that time travel is impossible. If we admit the paradox, it means that there is no real universe and no scientific and reasonable order. Some people think it's not that complicated. "Everything in the universe exists in the absolute present tense at all times. No time to travel! "

parallel universes

Stephen Hawking's idea of parallel universes has attracted many readers. Some readers believe that "travelers from the future can only enter the past or present of a parallel universe and will not affect our present". Some readers' ideas are more interesting: "once we meet our descendants, natural forces will throw us into a parallel universe and leave our' copy' to travelers."

Some people think so: "Anyone who travels through the past will interfere with history and eventually enter a parallel universe, not our universe."

Someone put forward an answer, time travelers "will undergo a molecular transformation, making them an electromagnetic ghost, which can't affect the body or anything else."

Although some people don't believe in the possibility of time travel, they are deeply attracted by this theory: "Our universe may be one of countless possible variants in the endless universe, each with its own history and life."

Like a movie.

The past is described as indelible, so it cannot be changed. This is the view of some people: "Why should we change the status quo and correct past mistakes? We are just traveling. " If we use film to record a person's life one by one, then this film is the person's past and cannot be changed because it is recorded.

Some people use movies to explain that it is impossible to interact with the past when time goes back: "We can see the movie going backwards, but we can't walk into the movie (where we travel)."

On the third question: whose contribution?

The paradox between teachers and students put forward by David deutsch is the most troublesome. There are no internal contradictions, and I don't know where the news came from. Deutsch himself thinks that it cuts to the core of natural order and rationality and can be compared with the idea of perpetual motion machine.

Some people think it is the professor's credit.

Some readers think: "judging from a series of things experienced by professors, we tend to attribute them to professors." However, this may not be a question of the right of discovery, but a theory and a specific way of putting it forward are completely irrelevant. The important thing is to bring it up. "

Some readers said humorously, "Discovery has no source, it just exists and becomes a part of the universe."

Others think that the right of discovery belongs to the professor: "Without his discovery, students have nothing to publish. It can be said that it was his help to the students that led her to develop and publish this solution later. "

Some people also support students.

Some people think that this discovery belongs to female students in the first process of event development. "After teaching time travel, because the cognitive process has changed, we can no longer regard him as the same person." Someone said, "If this idea hadn't entered her mind, the professor would never have found the information describing these solutions."

In the eyes of some people, there is no doubt about this, because "the only purpose of going back to the past is to teach his students the solution, which will lead to another past for the professor", and there is no influence between them.

Multidimensional travel

However, readers' creative thinking is not limited to these.

Some people have also raised new questions. For example, some people expressed doubts about "whether there is actual time" and made a philosophical summary: "Sometimes truth will go far beyond illusion. The latest physical research shows that we live in a world with 1 1 or even more dimensions. Then why are we talking about time travel instead of dimensional travel? And it is all-round! "

What an interesting idea! Everything has to wait for the experts to build a time machine.

Three questions

1. According to the theory of relativity, any movement is time travel, and the faster the speed, the more obvious the effect of time travel. So, if we want, all of us can travel in time today. Flying on an ordinary flight is a short trip.

In fact, flying in the sky is slower than sitting at home alone. Although people can't perceive this difference, it is measurable and increases with the increase of speed.

How much younger can a person be if he travels by plane with an average speed of 600 km/h?

The following formula can be used to calculate the specific value of motion deceleration time:

Where v is the actual speed of a moving object and c is the speed of light.

Compared with traveling by air, when talking about time travel, people will think of taking a big step in the past or in the future. If we are really building a machine that allows people to travel in the past, why hasn't anyone seen their descendants travel in the future? This is a question put forward by Stephen Hawking. Do you know how to answer him?

Time flies for 50 years, and time travel has become a common thing. In 2050, a professor of mathematics went to 2060 driven by curiosity. In the library of his school, he found an amazing solution of Einstein's equation, which was published by a young female student in Science World.

Excited by this discovery, the professor went back to 2050 to look for the female student and found her among the first-year students. The professor described the solution of the equation to her.

Female students learned about this solution and published it in Science World.

Professor, what is the real source of this discovery?

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"Relativity provides us with two ways to travel in the future. One is high-speed motion, and the time distortion caused by this motion is explained by special relativity. If we have a spaceship with a speed of 99.99999%, we can enter 3000 years in six months. " This kind of travel is the result of relativity, related to the famous twin paradox, and also a direct result of Einstein's theory. The elder of the twin brothers started his space trip at a speed close to the speed of light, while the younger brother stayed at home. Brothers arrive at the destination 10 light years away and return at the same speed immediately.

For the younger brother who stayed on the earth, 20 years have passed, that is, the time when the younger brother traveled at nearly the speed of light. But for my traveling brother, time passes much more slowly. In fact, relativity tells us that time will slow down with the increase of speed. It's only been three years for my brother. When he returns to the earth, he will find that he has entered the future time after 17 years.

According to these theories, people can travel very close to the speed of light, but can they actually reach such a high speed?

There is no forbidden zone in this respect, it is only a matter of cost. In order to accelerate a load weighing 10 ton to 99.9% of the speed of light, it is necessary to use 1000 billion joules, which is equivalent to the total energy production of all mankind for several months. "

The cost of further approaching the speed of 300,000 kilometers per second will of course be higher.

Therefore, as long as we have the necessary capital, we can set out for the future?

"I don't rule out that we can do this. There are inexhaustible energy sources in space, as long as we develop them. In fact, this has become a political issue: making the decision to carry out the necessary technology research and development in space so that human beings can make use of the vast amount of energy in the universe. But there is still a problem: time travel in high-speed systems may only enter the future but there is no way to come back. In fact, if our super spaceship arrives in 3000 AD and then returns, it may be just another big step for the future time of the earth. "

This is because time travel does not depend on the direction of motion, but only on its speed.

But the possibility of time travel in the past has caused some real, fascinating and seemingly insoluble contradictions. The simplest thing is that a time traveler goes back to the past and kills the birth mother who was a girl at that time, but in this way, he can't be born and can't finish the murder. These contradictions make the concept of causality in trouble, and science based on causal logic is also difficult to stand on. Stephen Hawking ended the problem with his "sequence protection conjecture": nature will always find a way to stop people from crossing the past.

Paul davis believes that subsequent events can affect previous events, but only those events without causality can form some closed timelines. For example, a rich man's wealth comes from a benefactor who helped his great-grandmother 1 century ago. He went to look for this kind man in a time spaceship. After meeting his great-grandmother, he explained that he was a time traveler. In order to convince each other, he showed his great-grandmother a newspaper he brought from the future. After reading the stock price in the newspaper, his great-grandmother began to invest in the stock market, which brought great wealth to future generations. The rich businessman finally realized that he was the man. This example is not a problem for Davis, but the problem brought by the time traveler who killed his mother cannot be solved. No one can kill his ancestors.

David Deutsch, an expert in time travel, uses some laws of quantum physics to solve these contradictions. In the subatomic world, quantum uncertainty dominates: an electron hitting a proton may turn left or right, and there is no law to follow. In the eyes of some physicists, this uncertainty leads to the multiplicity of the universe. Every time an electron turns right, it forms a new universe with an electron that turns left. In deutsch's view, the contradiction mentioned above can be solved in the same way: if time travelers interfere with history, the universe will be divided into two or more branches, and the killed mother will go to another parallel universe instead of entering the universe where the mother-killer belongs.