About the universe, about the earth, about ourselves, there are too many puzzles waiting for us to dig. But what is the most important unsolved mystery, and how far are we from finding the answer? On July 1 day this year, in commemoration of the 25th anniversary of the founding of the American Science magazine1day, scientists summed up 125 questions that we have not been able to answer well so far, of which 25 are the most important.

1. What is the universe made of?

The blurted answer is: it is made up of those shining stars. But in recent decades, scientists have increasingly found that this answer is incorrect. Astronomers believe that the matter that makes up stars, planets, galaxies and, of course, us, or ordinary matter, accounts for less than 5% of the total mass of the universe. They estimate that another 25% may be dark matter composed of undiscovered particles. What about the remaining 70%? Astronomers think it may be dark energy-the force that accelerates the expansion of the universe. What is the nature of dark matter and dark energy? Scientists are using accelerators and telescopes to find the answers to these questions. If they find it, their meaning must be great.

2. Are we unique in the universe?

Forty-five years ago, astronomer Falk Drake first launched the Ozma program to explore extraterrestrial civilization-using a huge antenna (radio telescope) to receive signals from extraterrestrial civilization. Forty-five years later, the efforts of astronomers continue. However, even the largest "Phoenix" project so far has not found any radio signals from alien civilizations.

3. How does the interior of the earth work?

More than 40 years ago, there was a revolution in earth science. The theory of plate tectonics has updated the knowledge about the earth itself. However, questions about the internal structure of the earth still follow the knowledge before the revolution. What scientists have done in these 40 years is to further refine this egg model-divided into crust, mantle and core. With the help of more and more advanced seismic imaging technology, scientists are studying the operation process of this huge machine. However, it may take another half century to start another scientific revolution.

4. How hot will the global greenhouse become?

Although the concentration of carbon dioxide in the atmosphere will definitely continue to increase in this century, although this increase will definitely bring about global warming, the degree of warming is still uncertain. Scientists generally believe that doubling the concentration of carbon dioxide in this century will bring about an increase in the temperature of 1.5℃ ~ 4.5℃. But this is not accurate enough. Scientists are developing new mathematical models to try to make these figures more convincing.

5. Can the laws of physics be unified?

Apple falls to the ground, lightning flashes across the sky, uranium atoms in nuclear power plant reactors decay at the same time to release energy, and super accelerators smash protons: these phenomena represent the functions of four basic forces in nature, namely gravity, electromagnetic force, weak force and strong force. All physical phenomena in the universe can be explained by these four basic forces. But scientists are not satisfied. Is it possible to unify these four forces into one? In 1960s, physicists found that weak force and electromagnetic force can be unified, and they are different sides of the same thing, collectively referred to as electric weak force. But can the other two forces be unified with it?

6. Is there a deeper principle under quantum uncertainty and nonlocality?

The birth of quantum theory 100 years ago has produced convincing application results, but it also brings counter-intuition: the uncertainty principle of quantum mechanics points out that we cannot obtain the momentum and position of an object accurately at the same time. However, nonlocality makes the entangled states of two quantum entangled particles collapse at the same time, no matter how far apart they are. Einstein once said that although quantum mechanics left a deep impression on him, "an inner voice told me that it was not true."

7. How far can we push chemical self-assembly?

In a sense, chemists are a group of people who like to invent most because they are always making new molecules. Although chemists can make very complicated chemical structures now, can they make the work simple and complicated? In other words, let the "raw material" atoms "assemble" themselves into complex structures, just like the self-assembly characteristics of life. There have been some examples of chemical self-assembly, such as making double-layer membrane structures similar to cell membranes. But more advanced self-assembly, such as making integrated circuits from the bottom up, is still a dream.

8. What is the limit of traditional calculation?

Some things seem simple, but they are very complicated to solve. For example, a salesman has to travel around several interconnected cities, so how can he get the shortest total distance? The increase in the number of cities will frighten the most powerful electronic computers. In the 1940s, Shannon, the father of information theory, put forward the physical law that information (in the form of bits) should be stored and transmitted. No traditional computer can go beyond this rule. So, in engineering, how powerful a computer can we finally build? Non-traditional computers may not be subject to these restrictions, such as quantum computers that have appeared in recent years.

9. What is the biological basis of consciousness?

/kloc-French philosophers in the 0 th and 7 th centuries have a famous saying: "I think, therefore I am." It can be seen that consciousness has always been a topic of philosophical discussion. Modern science believes that consciousness comes from the cooperation of hundreds of millions of neurons in the brain. But this is still too general. Specifically, how do neurons produce consciousness? In recent years, scientists have found some methods and tools to study this most subjective and personal thing objectively, and with the help of patients with brain injury, scientists can get a glimpse of the mystery of consciousness. In addition to finding out how consciousness works, scientists also want to know the answer to a deeper question: why does it exist and how does it originate?

10, what controls organ regeneration?

Some creatures have extraordinary repair skills: cut earthworms can regenerate half their bodies, while salamanders can rebuild damaged limbs ... In contrast, human beings seem to have a little poor regeneration ability. No one can grow fingers again, and the use of bones is always the same. A little comforting is the liver. The partially resected liver can be restored to its original state. Scientists have found that animals that can regenerate organs will restart the genetic program when necessary during embryonic development, thus growing new organs. So, can human beings replace their own parts in a similar way under manual control?

1 1. How do skin cells become nerve cells?

In the middle of last century, biologists put the frog's somatic cell nucleus into the enucleated egg cell of frog, and as a result, tadpoles were cloned. In recent years, the research on human embryonic stem cells is in full swing-human somatic cell nucleus is implanted into egg cells, and scientists are looking forward to producing various human somatic cells, such as nerve cells, osteoblasts, myocardial cells and so on. Although scientists have achieved some success, they still know little about the reasons why this somatic cell nuclear transfer technology can succeed. Indeed, enucleated eggs play a vital role in this process-but what is the specific mechanism?

12. How did a somatic cell become a whole plant?

In a sense, plants seem to be more flexible than animals. Plant somatic cells can become plant embryonic cells again without complicated somatic cell nuclear transfer technology. Scientists have used this characteristic of plants for a long time. With a small piece of plant tissue, you can cultivate seedlings that can be used in a forest in the laboratory. But why do plant cells have such flexibility? Scientists have found some clues, such as the role of auxin in plants in this process.

13. How and where did life originate?

Scientists have discovered microbial fossils 3.4 billion years ago, and traces of biological photosynthesis can also be found on older rocks. So which came first on earth, protein or DNA, the two pillars of life? Still together? Scientists believe that it is more likely that RNA appeared earlier than the first two. Another question is, under what circumstances did life originate? One hypothesis is that life originated from hot water at the bottom of the sea. Nowadays, on the one hand, scientists explore the development process from simple organic matter to self-replicating organic matter in the laboratory, on the other hand, studying comets and Mars will also bring important enlightenment to this problem.

14. What determines species diversity?

This is a planet full of life, but not every corner of life is equally prosperous. There are more species living in some areas than others. Tropical zone has higher species diversity than cold zone. Why is this happening? Just because the tropics are hotter than the frigid ones? Scientists believe that the interaction between biology and environment plays a key role in diversity. Of course, there are other forces that change diversity, such as the relationship between predation and prey. However, the first problem that scientists face is how to get the basic data about the global species diversity-how many species are there.

15. How did cooperative behavior evolve?

You can easily see altruism in social animals. For example, bees send food information to other bees. Humans and other primate societies are also full of cooperative behaviors. Darwin, the founder of evolution theory, put forward some explanations for the phenomenon of cooperation, such as mutual help between relatives, which will actually promote the possibility of the whole family's reproduction. Nowadays, scientists are looking for the genetic basis of cooperative behavior. Game theory is a mathematical theory about competition, cooperation and rules of the game. It can also help scientists understand how cooperative behavior works. Darwin observed the phenomenon of cooperation and explained it. Today's scientists hope to make this explanation deeper and answer how it came into being.

16, how to get a panoramic view from a large number of biological data?

Life is so complicated that almost every biologist can only explore in a small field. Although a large number of descriptive data are generated in each field. But scientists can get an overall concept from these massive data, such as how organisms work? The emerging discipline of systems biology provides some hope for answering these questions. It tries to connect all branches of biology by means of mathematics, engineering and computer science, and make biology more quantitative. However, no one knows whether these methods can finally let scientists know the whole picture of biological operation.

17, why are there so few human genes?

In 2003, when the human genome project was nearly completed, biologists cheered this achievement and were surprised to find that the number of human genes was less than originally estimated. Yes, there are only about 25,000 people, while it was originally thought that there should be 65,438+10,000. In contrast, a very simple organism, the nematode, also has 20,000 genes. Arabidopsis plants have slightly more genes than humans, while rice has twice as many genes as humans. Scientists believe that the working mode of genome should be more flexible and complex than previously thought, and they are exploring these molecular mechanisms for doing more with fewer genes.

18. What is the relationship between genetic differences and individual health?

Scientists have long discovered that some people react differently to certain drugs than other patients. For example, some kind of muscle relaxant used for anesthesia will make some people unable to breathe. Finally, scientists found that the reason for this phenomenon is that they have certain genes. This also brings a question: can studying the genetic differences between different people promote the development of more advanced medical treatments, that is, the development of "dosage drugs" based on individual DNA? Scientists have discovered many genes that interact with drugs. But it is still too early to realize "quantitative genre medicine".

19, how long can people's life span be extended?

Although there are still few centenarians, the average life expectancy of human beings (especially in developed countries) has been extended in the past few decades. But how long can this trend last? Through the study of experimental animals, scientists have found that some methods, including limiting calorie intake, can significantly prolong their life. But can these methods be successfully applied to humans and how long can they prolong life? Some scientists believe that it can at least become a routine for human beings to live to 100 years old. However, even so, longevity will bring other troubles, such as social insurance.

20. What genetic differences make us unique human beings?

With the improvement of gene sequencing technology, the complete genome sequences of more and more species have entered the database of scientists, including ourselves and several primate relatives, such as chimpanzees. It is easy for us to distinguish between humans and chimpanzees, but it is not so easy at the molecular level. The DNA difference between us and chimpanzees is about 1.2%. This is a small number, but in absolute terms, this difference means more than 30 million base pairs. What are the more than 30 million differences that make us so unique after being separated from chimpanzees? Scientists are looking for genetic differences that distinguish us from other primate species, and of course, there are factors other than culture, language and technology.

How is the memory accessed?

Good memories, sad memories, memories of solving equations and memories of English words are undoubtedly stored in our brains. But where are they?

In the 1950s, scientists discovered that the "hippocampus" in the brain played a vital role in storing information-if the hippocampus was removed, the previous memories would disappear together. But how do neurons in the hippocampus fix information? Scientists have found that some molecules are related to the formation of memory. In addition, the formation of synapses in nerve cells is also related to memory. However, scientists don't know enough about the working mechanism of memory at present-and this mechanism is very important for understanding ourselves.

22. Can we selectively turn off some immune responses?

Nowadays, organ transplantation has become a less rare operation, but a big problem faced by doctors and patients still exists to some extent: immune rejection. The patient's immune system may attack that the transplanted organ is "non-China", thus making the operation fall short. In order to prevent this from happening, doctors should carefully choose donor organs, and some patients need to take immunosuppressive drugs for life-this is obviously not a good idea. Scientists have found several possible ways to make the immune system work normally without rejecting transplanted organs, but it will take a long time to realize clinical application.

23. Is there an effective AIDS vaccine?

Every year, the National Institutes of Health alone invests $500 million in research and development of AIDS vaccine. But so far, no vaccine has shown practicality. Sceptics believe that AIDS vaccine will never succeed, because human immunodeficiency virus is changeable. Supporters believe that the vaccine can have an effect on simian immunodeficiency virus, so the AIDS vaccine may also be successful.

24. What can replace cheap oil? What time?

No one denies that oil will eventually run out. In addition, oil production may soon begin to decline. Even if these factors are not taken into account, the danger of global warming urges mankind to find an energy source to replace oil as soon as possible-solar energy? Wind energy? Nuclear energy? Each one looks promising, but it's not mature enough.

25. Is Malthus still wrong?

1798, Malthus published his masterpiece "Population Theory", in which he pointed out that the growth of population can never keep up with the growth of food supply (sic), and only disaster can stop the growth. After 200 years, the total population of the earth increased to 6 billion (six times that of Malthus), but the catastrophe predicted by Malthus did not happen. Science and technology have largely prevented this disaster. But mankind still faces a problem, how to ensure that there will be no catastrophe in the future?