Richard feynman, a great physicist at California Institute of Technology, once said that if you have to condense the history of science into one important sentence, it is: "Everything is made of atoms." Atoms are everywhere. Atoms make up everything. Look around, there are atoms everywhere. Not only walls, tables, sofas and other solids are atoms, but also the air in the middle is atoms. There are so many atoms that it is almost unimaginable.
The basic working form of atoms is molecules (from Latin, meaning "small mass substances"). A molecule is two or more atoms working together in a relatively stable form: one oxygen atom plus two hydrogen atoms, and you get a water molecule. Chemists tend to think in terms of molecules rather than elements, just as writers tend to think in terms of words rather than letters, so they calculate molecules. There are at least a lot of molecules. At sea level and temperature of zero degrees Celsius, one cubic centimeter of air (about the space occupied by a cube of sugar) contains as many as 450 billion molecules. There are so many molecules in every cubic centimeter of space around you. Think about how many cubic centimeters there are in the world outside your window-how many cubes of sugar do you need to fill your vision. Then think about how much such space is needed to form the universe. In short, there are many atoms.
The lifetime of atoms is very long. Because atoms have a long life, they can really roam around. Every atom in you must have passed through several planets before becoming you, and was once a part of millions of creatures. Each of us has a large number of atoms; These atoms have strong vitality and can be reused after we die; A considerable number of atoms in our bodies-it is estimated that there are as many as 65.438 billion atoms in each of us-are probably Shakespeare's atoms, Sakyamuni, Genghis Khan, Beethoven and other historical figures you pointed out, each of whom contributed 65.438 billion atoms. (Obviously, it must be a historical figure, because it takes decades or so for atoms to completely redistribute; No matter how strong your desire is, you can't have the slightest Elvis Presley. )
So, we are all reincarnations of others-though short-lived. After we die, our atoms will be far apart, looking for new uses elsewhere-becoming a leaf or other part of the human body or a drop of dew. The atom itself will exist forever. Actually, no one knows the lifetime of an atom, but according to martin rees, its lifetime is about1035-this number is so large that even I am willing to use mathematical symbols to express it.
Besides, atoms are very small-in fact, very small. A row of 500 thousand atoms can't cover a hair. At this ratio, an atom is too small to imagine. But of course we can try.
Let's start with 1 mm, such a long line: one. Now, let's assume that this line is divided into 1000 segments of equal width. The width of each segment is 65438 0 micron. This is the size of microorganisms. For example, a standard paramecium-a single-celled freshwater organism-is about 2 microns wide, that is, 0.002 mm, which is really tiny. If you want to see paramecium swimming in a drop of water with naked eyes, you must enlarge the drop to 12 meters wide. However, if you want to see the atoms in the same water drop, you must enlarge the water drop to 24 kilometers wide.
In other words, atoms exist completely on another tiny scale. To know the size of an atom, you have to pick up this micron-sized thing and cut it into 10000 smaller things. That's one tenth of the size of an atom:1mm. Such a small thing is far beyond our imagination. However, just remember that an atom is equivalent to the thickness of a piece of paper for the above line 1 mm, and you have a general idea of its size for the height of the Empire State Building in New York.
Of course, atoms are so useful because they are numerous, have a very long life, and are too small to be detected and identified. People first discovered that atoms have three characteristics-small, abundant and almost indestructible-and everything is made of atoms. You might think that it was not discovered by Antoine Laurent lavoisier, or even by Henry cavendish or humphry davy, but by an amateur Quaker named john dalton.
Dalton's hometown is located on the edge of the English Lake District, not far from Kirkmouth. He was born in 1766 into a poor and devout Quaker weaver family. (Four years later, the poet william wordsworth also came to Kirkmoss. He is a clever student-he is really clever, and he became the principal of the local Quaker school at the age of 12. This may explain Dalton's precocity and the situation of that school, but it may not explain anything. We know from his diary that at about this time, he was reading Newton's principles-or the original Latin-and other works with similar challenges. 15 years old, on the one hand, he continued to be the principal, on the other hand, he found a job in the nearby Kendall town; 10 years later, he moved to Manchester. In the last 50 years of his life, he hardly moved. In Manchester, he became a whirlwind of knowledge, publishing books and writing papers, covering everything from meteorology to grammar. He suffers from color blindness. Because of this research, he has long been called Dalton's disease. However, what finally made him famous was a thick New System of Chemical Philosophy published by 1808.
In this book, the academic community first came into contact with the atom which is almost a modern concept. Dalton's point of view is simple: at the bottom of all substances, there are extremely tiny and irreversible particles. "Creating or destroying a hydrogen particle may be as impossible as introducing a new planet into the solar system or destroying an existing planet." He wrote.
Neither the concept of atom nor the word "atom" itself is new. Both were invented by the ancient Greeks. Dalton's contribution is that he considered the relative size and properties of these atoms and their combination methods. For example, he knows that hydrogen is the lightest element, so his atomic weight is 1. He also thinks that water is composed of seven parts of oxygen and one part of hydrogen, so he gives the atomic weight of oxygen as 7. In this way, he can get the relative weights of known elements. He is not always accurate-the atomic weight of oxygen is actually 16, not 7, but this principle is very reasonable and has become the basis of modern chemistry and many other sciences.
This achievement made Dalton famous-even with a Quaker low profile. 1826, French chemist p.j. pelletier came to Manchester to meet the atomic hero. Pelletier thought he belonged to a big organization, so he was surprised when he found Dalton teaching children basic arithmetic in an alley primary school. According to e.j. Holmyard, a historian of science, pelletier was at a loss at the sight of this great man and stammered:
"Excuse me, is this Mr. Dalton?" Unable to believe his eyes, the famous European chemist is teaching children to add, subtract, multiply and divide. "That's right," Quakers said drily. "Please sit down and let me teach the child this arithmetic problem first."
Although Dalton wanted to stay away from all honors, he was elected as a member of the Royal Society against his will and won a large number of medals and considerable government pensions. When 1844 died, 40,000 people came out to pay tribute to his coffin, and the funeral procession was more than 3 kilometers long. His entries in the British Celebrity Dictionary are one of the most numerous. Among the scientists in the19th century, only Darwin and Lyle can compare with him in terms of space.
A century after Dalton put forward his idea, it is still a complete hypothesis. Some outstanding scientists-especially the Austrian physicist ernst mach, who named the unit of sound speed after himself-still have no doubt about the existence of atoms. "Atoms can't be seen or touched ... they are imaginary things in the brain." He wrote. Especially in the German-speaking world, people view the existence of atoms with such suspicion. It is said that this is one of the reasons why ludwig boltzmann, a great theoretical physicist and enthusiastic supporter of atoms, committed suicide.
It was in 1905 that Einstein put forward irrefutable evidence to prove the existence of atoms for the first time with that paper on Brownian motion, but it did not attract much attention. In any case, Einstein was soon busy with the study of general relativity. Therefore, the first real hero of the atomic age was ernest rutherford, if he was not the first person who appeared at that time.
Rutherford 187 1 was born in the "inland area" of New Zealand. In Stephen Weinberg's words, his parents moved from Scotland to New Zealand to grow some flax and raise a lot of children. He grew up in a remote area of a remote country, and he was far from the mainstream of science. But in 1895, he won a scholarship and had the opportunity to come to Cavendish laboratory of Cambridge University. This place is about to become the hottest place in physics in the world.
Physicists especially look down on scientists in other fields. When the great Austrian physicist Wolfgang Pauli's wife left him and married a chemist, he was too surprised to believe it. "If she marries a matador, I can understand," he said to a friend in surprise. "But marrying a chemist ..."
Rutherford can understand this feeling. "Science is either physics or collecting stamps." He once said. This sentence was later quoted repeatedly. Ironically, however, he won the Nobel Prize in chemistry in 1908, not the physics prize.
Rutherford was a lucky man-lucky to be a genius; But fortunately, he lives in an era when physics and chemistry are so exciting and so antagonistic (not to mention his own feelings). These two subjects will never overlap as before.
Despite his great achievements, he is not a particularly clever man. In fact, his math is still very poor. In the process of teaching, he often confuses his own equations and has to stop halfway to let the students work out the results themselves. According to james chadwick, a long-time colleague and discoverer of neutron, he is not particularly good at experiments. He is strong and open-minded. He replaced cleverness with shrewdness and a little courage. In the words of a biographer, in his view, his brain "always doesn't matter, and goes much further than most people". If he encounters a difficult problem, he is willing to work harder and spend more time than most people, and he is more likely to accept unorthodox explanations. Because he is willing to sit in front of the screen and spend a lot of boring time counting the so-called alpha particle scintillation times-this kind of work is usually assigned to others-he has the biggest breakthrough. He was one of the first people-probably the first-to discover that once the inherent energy in atoms was used, bombs could be made, which were powerful enough to "wipe out the old world".
Physically, he is big and strong, and his voice can scare the timid. Once, a colleague learned that Rutherford was going to give a radio speech on the other side of the Atlantic and asked coldly, "Why use radio?" He is also confident and has a good attitude. When someone told him that he always seemed to live on waves, he replied, "Oh, I created this wave after all, didn't I?" C.P. Si Nuo recalled that he once overheard Rutherford say in a tailor's shop in Cambridge, "My waistline is getting thicker and thicker, and I am getting more and more knowledgeable."
However, when he 1895 came to Cavendish laboratory, it was still out of reach. His waistline will become thicker and his reputation will become louder, but that will be many years later. The year Rutherford arrived at Cambridge University, wilhelm rontgen discovered X-rays at the University of Wü rzburg. The following year, henry beck Rael discovered the radiation phenomenon. Cavendish laboratory itself will embark on a long and brilliant road. At 1897, J.J. Thompson and his colleagues will find electrons there; 19 1 1 year, where C.T.R Wilson will make the first particle detector (we will talk about it); At 1932, james chadwick will find neutrons there. In the future, 1953, james watson and francis crick will discover the DNA structure in Cavendish laboratory.
At first, Rutherford studied radio waves and made some achievements-he successfully sent a clear signal to 1 km away, which was quite possible at that time-but he gave up because a senior colleague advised him that radio had no future. On the whole, Rutherford's career in Cavendish laboratory was not smooth. After staying there for three years, he felt that he had not made much progress, so he accepted a position at McGill University in Montreal and steadily embarked on a long and brilliant road. By the time he won the Nobel Prize (according to the official praise, "because he studied the decay of elements and the chemical properties of radioactive substances"), he had transferred to Manchester University. In fact, it is there that he will get the most important results and determine the structure and properties of atoms.
By the beginning of the 20th century, people had known that an atom was made up of several parts-Thomson established this view when he discovered electrons-but what we still don't know is that an atom has several parts; How they fit together; What shapes are they? Some physicists think that atoms may be cubes, because cubes can be stacked neatly without wasting any space. However, the more common view is that atoms are more like a piece of raisin bread, or raisin pudding: a dense solid with positive charges and covered by negatively charged electrons, just like raisins on raisin bread.
19 10 Rutherford (with the help of his student hans geiger. Geiger later invented a radiation detector with his name on it) to emit ionized helium atoms or alpha particles to a piece of gold foil. To Rutherford's surprise, some particles bounced back. He said it was like firing a 38-centimeter shell at a piece of paper, and the shell bounced off his knee. This is something that should not happen. After thinking hard, he felt that there was only one explanation: the particles that bounced back hit the small and dense things in the atom, while other particles passed through without hindrance. Rutherford realized that the interior of atoms is mainly empty space, and only high-density nuclei are in it. This is a very satisfying discovery. But a problem immediately appeared. According to all the laws of traditional physics, atoms should not exist.
Let's pause and consider the atomic structure as we know it now. Each atom consists of three basic particles: positively charged protons, negatively charged electrons and uncharged neutrons. Protons and neutrons are contained in the nucleus, while electrons revolve around it outside. The number of protons determines the chemical properties of atoms. Atoms with protons are hydrogen atoms; Atoms with two protons are helium atoms; Atoms with three protons are lithium atoms; So it increases upward. Every time you add a proton, you get a new element. Because the number of protons in an atom is always in balance with the same number of electrons, you sometimes find that some books define an element by the number of electrons, and the result is exactly the same. Someone explained this to me: protons determine the identity of atoms and electrons determine the temperament of atoms. )
Neutrons will not affect the identity of atoms, but will increase their mass. Generally speaking, the number of neutrons and protons is roughly equal, but it can be a little more or less. Add or subtract one or two neutrons and you will get isotopes. Isotopes are used to determine age in archaeology-for example, carbon-14 is a carbon atom composed of six protons and eight neutrons (because their sum is 14).
Neutrons and protons occupy the nucleus. The nucleus is very small-only one trillion times the total capacity of the atom, but the density is extremely high. It actually constitutes all the substances of the atom. Cropper said that if the atom is enlarged to the size of a church, the nucleus is only about the size of a fly-but the fly is several thousand times heavier than the church. 19 10 Rutherford pondered over this spacious space-this amazing and unexpected spacious space.
It is still surprising that atoms are mainly vacuum space, and the entities around us are just illusions. If two objects touch each other in the real world-we often take billiards as an example-they don't actually hit each other. "On the contrary," timothy ferriss explained, "the negative charge fields of the two balls repel each other ... if there is no charge, they are likely to pass through each other like galaxies." When you sit in a chair, you are not actually sitting in the chair, but floating on the chair, with a height of 1 angstrom (one hundredth of a centimeter). Your electron and its electron are irreconcilable, and it is impossible to get closer.
Almost everyone has a picture of an atom in his mind, that is, one or two electrons rotate rapidly around the nucleus, just like a planet rotates around the sun. This image was created by a Japanese physicist named Kantaro Nagaoka in 1904, which is a clever imagination. It is completely wrong, but it is still full of vitality. As isaac asimov likes to point out, it has inspired generations of science fiction writers to create stories about the world in the world. The atom has become a small inhabited solar system, and our solar system has become a particle in a much larger system. Even CERN takes Nagaoka's image as the logo of its website. Physicists soon realized that in fact, electrons are not like planets in orbit at all, but like the rotating blades of an electric fan, trying to fill every space in orbit at the same time. But there is an important difference, that is, the blades of electric fans just look everywhere at the same time, while electrons are really everywhere at the same time. )
Needless to say, in 19 10 years, or many years later, few people knew this knowledge. Rutherford's discovery immediately caused several big problems. In particular, electrons orbiting the nucleus may collide. According to the traditional electrodynamics theory, rapidly rotating electrons will soon run out of energy-just for a moment-and then hover and fly into the nucleus, which will bring disastrous consequences to both. Another question is, how can positively charged protons stay in the nucleus together without blowing themselves and other parts of the atom to pieces? Obviously, no matter what happens in Xiaotian, it is not governed by the laws applicable to our macro world.
As physicists go deep into this subatomic world, they realize that it is not only different from anything we are familiar with, but also different from anything we can imagine. "Because the behavior of atoms is so different from ordinary experience," richard feynman once said, "it's hard for you to get used to it. In the eyes of everyone, whether it is a novice or an experienced physicist, it seems strange and mysterious. " When Feynman made this comment, physicists had half a century to adapt to the strange behavior of atoms. Therefore, you can imagine how Rutherford and his colleagues felt in the early 20th century. It was completely new at that time.
Among the people who worked with Rutherford, there was an amiable Danish young man named Niels Bohr. 19 13 while thinking about the atomic structure, he suddenly had an exciting idea. He postponed his honeymoon and wrote an epoch-making paper.
Physicists cannot see such a small thing as an atom. They have to try to determine its structure according to its performance under external conditions, such as emitting alpha particles to gold foil like Rutherford. Sometimes, such experimental results are puzzling, which is not surprising. There is a long-standing problem related to the spectral reading of hydrogen wavelength. The shapes they produce show that hydrogen atoms release energy at some wavelengths and do not release energy at other wavelengths. Just like a man being watched, he keeps appearing in a certain place, but he has never seen how he ran over. Nobody knows why.
It was while thinking about this question that Bohr suddenly thought of an answer and quickly wrote his famous paper. The title of the paper is "On the Structure of Atoms and Molecules", which holds that electrons can only stay in some clearly defined orbits and will not fall into the nucleus. According to this new theory, electrons traveling between two orbits will disappear in one orbit and immediately appear in the other orbit without passing through the middle space. This view-the famous "quantum leap"-is of course extremely strange, but it is too good to be true. It not only shows that electrons will not spiral into the nucleus catastrophically, but also explains the puzzling wavelength of hydrogen. Electrons only appear in certain orbits, because they only exist in certain orbits. This is a great insight, so Bohr won the Nobel Prize in Physics in 1922, the year after Einstein won the prize.
At the same time, the tireless Rutherford has returned to Cambridge University to replace J·J· Thomson as the director of Cavendish Laboratory. He designed a model to explain why the nucleus wouldn't explode. He thinks that the positive charge of protons must be offset by some kind of neutralizing particles, which he calls neutrons. The idea is simple and moving, but it is not easy to prove. Rutherford's colleague james chadwick spent 1 1 year searching for neutrons, and finally succeeded in 1932. 1935, and he also won the nobel prize in physics. As Boolean and his colleagues pointed out in their history of physics, it may be a good thing to discover neutrons later, because it is necessary to master neutrons in order to develop an atomic bomb. Because neutrons have no charge and will not be repelled by the electric field in the center of the atom, they can shoot into the nucleus like a small torpedo and start a destructive process called fission. They believe that if neutrons can be isolated in the 1920s, "the atomic bomb is likely to be first developed in Europe, and there is no doubt that it is German".
In fact, Europeans were busy at that time, trying to figure out the strange behavior of electrons. The main problem they face is that electrons sometimes behave like particles and sometimes like waves. This incredible duality almost drove physicists to the wall. In the next 10 years, physicists all over Europe were thinking, scribbling and putting forward contradictory assumptions. In France, Prince Louis-Victor de Broglie, who came from a duke's family, found that if electrons were regarded as waves, some abnormal phenomena of electronic behavior would disappear. This discovery attracted the attention of Austrian Irving Schrodinger. He skillfully made some refinements and designed an easy-to-understand theory called wave mechanics. Almost at the same time, the German physicist Werner Heisenberg put forward an opposing theory called matrix mechanics. That theory involves complicated mathematics. In fact, almost no one understands it, including Heisenberg himself ("I don't even know what a matrix is." Heisenberg once said to a friend in despair, but it did seem to solve some unexplained problems in Schrodinger's wave mechanics.
Therefore, there are two theories in physics, which are based on conflicting premises but reach the same result. This is an incredible situation.
1926, Heisenberg finally came up with an excellent compromise and put forward a new theory that was later called quantum mechanics. The core of this theory is Heisenberg's uncertainty principle. It thinks that electrons are particles, but they can be described by waves. As the basis of this theory, the "uncertainty principle" holds that we can know the path of electrons in space and the position of electrons at a certain moment, but we can't know both. Any attempt to determine one is bound to interfere with the other. This is not a simple problem that requires more sophisticated instruments; This is an unchangeable feature of the universe.
What it really means is that you can never predict the position of an electron at any given moment. You can only think that it may be there. In a sense, as Dennis Overby said, only by observing electrons can you say that they really exist. In other words, in a slightly different way, you have to think that electrons are "everywhere, but everywhere" before they are observed.
If you are confused by this statement, you should know that it also confuses physicists, which is gratifying. Overby said: "Once, Bohr said that if someone was not angry when he first heard about quantum theory, it meant that he didn't understand." When someone asked Heisenberg if he could imagine an atom, he replied, "Don't do that."
Therefore, it turns out that atoms are not entirely created by most people. Electrons don't revolve around the nucleus like planets revolve around the sun, but more like a cloud with no fixed shape. The "shell" of atoms is not some kind of hard and smooth skin, as many illustrations sometimes encourage us to imagine, but only the outermost layer of this fluffy electron cloud. In essence, the cloud itself is only a statistical probability region, which means that electrons will only cross this range in rare cases. Therefore, if you understand, the atom is more like a furry tennis ball than a metal ball with a hard outer edge. In fact, they are not very similar, in other words, they are not very similar to anything you have seen. After all, the world we are discussing here. It is very different from the world around us. )
Strange things seem to keep popping up. As James Trevor said, for the first time, scientists have encountered "an area in the universe that our brains can't understand". Or, as Feynman said, "The performance of small things is not like the performance of big things at all." With the deepening of research, physicists realize that they have discovered a world: in that world, electrons can jump from one orbit to another without passing through any space in the middle; Matter suddenly came from nothing-"But," in the words of Allen Letterman of MIT, "it suddenly came from nothing."
There are many incredible places in quantum theory, the most striking of which is Wolfgang Pauli's view in 1925' s "incompatibility principle": even if some pairs of subatomic particles are far apart, one side will immediately "know" the situation of the other side. Particles have a property called spin. According to quantum theory, once you determine the spin of a particle, the sister particle will immediately start to rotate in the opposite direction at the same speed, no matter how far away it is from you.
In the words of science writer Lawrence Joseph, it's like you have two identical billiards, one in Ohio and the other in Fiji. When you rotate one, the other immediately rotates in the opposite direction at exactly the same speed. Miraculously, this phenomenon was confirmed in 1997. Physicists at the University of Geneva in Switzerland send two photons in opposite directions to a distance of 1 1 km. The results show that as long as one of them is disturbed, the other one will respond immediately.
Things have reached the point where, at a meeting, Bohr said when talking about a new theory, the question is not whether it is absurd, but whether it is absurd enough. In order to illustrate the intuition of the quantum world, Schrodinger put forward a famous thought experiment: suppose a cat is put into a box, at the same time, an atomic radioactive substance is put in, and a small bottle of hydrocyanic acid is attached. If the particle decays within an hour, it will start a mechanism to break the bottle and poison the cat. Otherwise, the cat will live. However, we can't know what will happen, so we can't make a scientific choice. We can only think that the cat is 100% alive and 100% dead. As Stephen Hawking said with a little excitement (understandably), this means that you can't "accurately predict what will happen in the future, if you can't even accurately determine the present situation of the universe".
Because of so many strange features, many physicists don't like quantum theory, at least in some aspects, especially Einstein. This is ironic, because it is he who convincingly explained in the miracle year 1905 that photons can sometimes behave like particles and sometimes like waves-this is the core insight of new physics. "Quantum theory deserves attention." He thought politely, but he didn't like it in his heart. "God doesn't roll dice." He said.
Einstein can't stand the idea that God created a universe, and some things in the universe can never be known. Moreover, the idea of action at a distance-that is, one particle can immediately affect another particle trillions of kilometers away-completely violates special relativity. Nothing can travel faster than the speed of light, but physicists here insist that information can be carried out in some way at the subatomic level. By the way, so far no one can explain how particles do it. According to physicist Yakir Kharanov, the way scientists treat this problem is "no"