Chapter 2 Chapter 1 The Golden Age

one Our story begins in Germany in 1887.Karlsruhe, located on the banks of the Rhine, is a beautiful city with a famous eighteenth-century palace in its center.The lush forest and warm climate also make this small town a tourist attraction in Europe.However, these pleasant scenery does not seem to distract Heinrich.Rudolph.Heinrich Rudolf Hertz's attention: Right now he's fiddling with his instruments in a laboratory at the University of Karlsruhe.At that time, Hertz was just thirty years old. Perhaps he would not have thought that he would become as famous a figure as his teacher Hermann von Helmholtz in the history of science, nor would he have thought that he would be as famous as Karl.Benz (Carl Benz) has also become the pride of this small town.Now his mind is completely devoted to his device.

Hertz's device is very simple in today's view: its main part is an electric spark generator, with two small copper balls closely spaced as capacitors.Hertz stared intently at the two copper balls facing each other, and then closed the circuit switch.Suddenly, the magic of electricity began to unfold in this simple system: an invisible electric current passed through the induction coil in the device and began to charge the copper ball capacitor.Hertz stared at his device coldly, imagining in his heart the situation where the voltage at the two stages of the capacitor continued to rise.After studying in the field of electricity for so long, Hertz has full confidence in his knowledge. He knows that as the voltage rises, the air between the two small balls will soon be broken down, and then the entire system will be broken down. Form a high-frequency oscillation circuit (LC circuit), but what he wants to observe now is not this.

Sure enough, after a while, with a slight snap, a bunch of beautiful blue electric sparks exploded between the two copper balls, and the whole system formed a complete loop, and the tiny current beams flew continuously in the air. It kept twisting, and a faint fluorescent light bloomed. On the contrary, Hertz became even more nervous. He stared at the string of electric sparks and the air next to the electric sparks, imagining one scene after another in his heart.He didn't want to see how this device would produce a spark short circuit. The purpose of his experiment was to prove the existence of that ethereal electromagnetic wave.What kind of thing is that? It cannot be seen or touched. No one has seen or verified its existence until then.However, Hertz firmly believed in its existence because it was a prediction of Maxwell's theory.And Maxwell's theory, oh, it's mathematically perfect like a miracle!It was like a poem written by the hand of God.Such a theory is hard to imagine being wrong.Hertz took a breath and smiled again: No matter how impeccable the theory is, it still needs to be verified by experiments after all.He stood there looking at it for a while, and after thinking about it several times in his heart, he finally confirmed that his experiment was correct: if Maxwell was right, then an oscillating electric field should be generated between the two copper balls, and at the same time an outward electric field should be generated. Propagated electromagnetic waves.Hertz turned his head. On the other side of the laboratory, there was an open copper ring, and a small copper ball was embedded in each opening.That is the receiver of the electromagnetic wave. If Maxwell's electromagnetic wave really exists, it will pass through this room to the other end, and induce an oscillating electromotive force at the receiver, thereby also exciting an electric spark at the opening of the receiver. Come.

The laboratory was quiet, and Hertz stood there motionless, as if his eyes had seen the invisible electromagnetic waves traveling through space.The copper ring receiver suddenly seemed a little strange, and Hertz couldn't help but screamed. He put his nose in front of the copper ring, and clearly saw that there seemed to be a faint spark in the air between the two copper balls. flickering.Hertz quickly ran to the window and closed all the curtains, and now it is clearer: light blue electric flowers are constantly blooming in the gaps in the copper ring, but the entire copper ring is an isolated system, neither connected nor connected. Batteries also don't have any source of energy.Hertz stared at it for a full minute. In his eyes, those blue sparks looked so beautiful.Finally he rubbed his eyes and straightened his waist: Now there is no need to doubt, the electromagnetic wave really exists in the space, it is it that stimulates the electric spark on the receiver.He won and successfully solved the problem that was proposed by the Prussian Academy of Sciences in Berlin eight years ago; at the same time, Maxwell's theory also won, and a new peak in physics, electromagnetic theory, was finally established.The great Michael Faraday laid its foundations, the great Maxwell built its main body, and today his great Hertz caps the edifice.

Hertz carefully moved the receptors to different locations, and the electromagnetic waves behaved exactly as predicted by theory.According to the experimental data, Hertz obtained the wavelength of the electromagnetic wave, and multiplied it by the oscillation frequency of the circuit, the advancing speed of the electromagnetic wave can be calculated.This value is exactly equal to 300,000 km/s, or the speed of light.Maxwell's astonishing prediction has been confirmed: it turns out that electromagnetic waves are not mysterious at all. The light we usually see is a kind of electromagnetic wave, but its frequency is limited to a certain range, so we can see it.

In every sense, this is a remarkable discovery.The ancient optics can finally be fully contained in the emerging electromagnetism, and the assertion that light is a kind of electromagnetic wave has finally drawn a seemingly irrefutable conclusion on the long-debated issue of the nature of light (we will go to Just look at this protracted and brilliant battle).The reflection, diffraction and interference experiments of electromagnetic waves were quickly done, and these experiments further confirmed the consistency of electromagnetic waves and light waves, which is undoubtedly a great achievement of electromagnetic theory.

Hertz's name could finally be engraved brilliantly in the Hall of Fame of the History of Science. However, as a pure and serious scientist, Hertz did not think of the huge commercial significance contained in his discovery.In the laboratory at the University of Karlsruhe, all he thought about was how to get closer to the ultimate mystery of nature, and he never expected what kind of revolution his experiment would bring about.Hertz died young, and left the world he was infatuated with before he was thirty-seven.However, in that year, a 20-year-old Italian youth on vacation in Lombardy read his paper on electromagnetic waves; two years later, this youth had performed radio communication performances in public, and soon his The company was established and successfully obtained the patent certificate.By 1901, the seventh year after Hertz's death, wireless telegraphy could cross the Atlantic Ocean and realize instant communication between two places.This young man from Italy is Guglielmo.Marconi (Guglielmo Marconi), while Russia's Aleksandr Popov (Aleksandr Popov) also made the same contribution in the field of wireless communication.They set off a revolutionary storm and brought the entire human race into a brand new information age.I don't know how Hertz would feel if there was knowledge behind him?

Still, it feels like Hertz will just laugh it off.He is the kind of pure scientist who regards the pursuit of truth as the greatest value of life.I'm afraid even if he thought of the commercial prospects of electromagnetic waves, he would not bother to put it into practice, right?Perhaps, walking among the beautiful forests and lakes, pondering the ultimate mysteries of nature, and discussing academic issues with students on the campus with fallen leaves in autumn, this is his real life.Today, his name has become the unit of frequency, a physical quantity, and is constantly mentioned by everyone. However, maybe he still thinks that we disturb his peace?

two Last time we mentioned that in 1887, Hertz's experiment confirmed the existence of electromagnetic waves, and also confirmed that light is actually a type of electromagnetic waves, and both have the same wave characteristics.This brings to an end what seems to be an irrevocable debate over the nature of light. Having said that, our story must first go back and look back at the war about light through time and space.This may be the longest and most intense debate in the history of physics.It runs through almost the entire development process of modern physics, and has left an indelible imprint in history.

Light is the thing that everyone sees the most (it's not bad to see the most and use it here).Since ancient times, it has been taken for granted as one of the most primitive things in this universe.In ancient myths, it is often a bright light that splits chaos and darkness, and the world begins to revolve.In people's minds, light always represents life, vitality and hope.In the Bible, when God wants to create the world, the first thing he wants to create is light, which shows its unique position in this universe. But what exactly is light?Or is it a thing at all? People in ancient times didn't seem to regard light as a real thing. In their view, light and darkness are just a difference in environment.It was only in ancient Greece that scientists began to pay close attention to the problem of lighting.One thing is for sure: we can see things because of the effect of light on them.It was then supposed that light is something that emanates from our eyes, and when it reaches something we see it.For example, Empedocles (Empedocles) believed that the world is composed of the four elements of water, fire, air, and earth, and human eyes are lit by the goddess Aphrodite (Aphrodite), when the fire element ( That is, light. In ancient times, light and fire were often not distinguished) when it sprayed out from the human eye and reached the object, we were able to see things.

But it is clear that this explanation is not enough.It can explain why we can see with our eyes open but not with our eyes closed; but it cannot explain why we cannot see in dark places even with our eyes open.To resolve this difficulty, much more complex assumptions have been introduced.For example, it is believed that there are three different kinds of light, which come from the eyes, the object to be seen and the light source respectively, and vision is the result of the combined action of the three. This assumption is undoubtedly too complicated.In the Roman era, the great scholar Lucretius proposed in his immortal book "On the Nature of Things" that light reaches people's eyes directly from the light source, but his point of view has never been accepted by people.The correct understanding of light imaging was not realized until about 1000 AD by a Persian scientist Al.Al-Haytham proposed: It turns out that the reason why we can see objects is only the result of light reflected from objects into our eyes.He put forward many evidences to prove this point, the most powerful of which is the experiment of small hole imaging. When we see that the light passes through the small hole and becomes an inverted image, we have no doubts about the correctness of this statement. . People have also started to study some properties of light very early.Based on the assumption that light always travels in a straight line, Euclid studied the reflection of light in his book Catoptrica.Ptolemy, Hassan, and Johannes Kepler all studied the refraction of light, and the Dutch physicist W. Snell built on their work in 162 Summed up the law of refraction of light in one year.In the end, the various properties of light were finally attributed to a simple law by Pierre de Fermat, known as the king of amateur mathematics, that is, light always takes the shortest route.Optics has finally been formally established as a physical subject. However, when people are familiar with the various behaviors of light, there is still one most basic problem that has not been resolved, that is: what is light in essence?This question does not seem to be so difficult to answer, but people probably would not have imagined that the exploration of this question would take such a long time, and the process of this exploration would have such a profound and significant impact on physics. Its significance was beyond anyone's imagination at the time. People in ancient Greece always tended to regard light as a stream of very fine particles, in other words, light was composed of very small light atoms.On the one hand, this point of view is very consistent with the popular theory of elements at that time. On the other hand, people at that time did not know much about other forms of matter besides particles.We call this theory the particle theory of light.Intuitively, the theory of particles is very reasonable. First of all, it can explain why light always travels in a straight line, why it is strictly and classically reflected, and even refraction can be caused by particles flowing in different media. The speed change is explained.But the theory of particles also has some obvious difficulties: for example, it was difficult for people to explain why the two beams of light did not bounce off each other when they collided with each other, and it was also impossible for people to know where these tiny light particles were hiding before lighting the lights. Yes, can their number be infinitely many, and so on. After the dark ages passed, people had a better understanding of the natural world.The fluctuation phenomenon has been deeply understood and studied, and the recognition that sound is a kind of fluctuation has gradually been accepted by people.People began to wonder: since sound is a kind of wave, why can't light also be a wave?In the early seventeenth century, Des Cartes first proposed the possibility in Refractive Optics, one of the three appendices to his Discourse: Light is a pressure that travels in a medium.Not long after, Francesco Maria Grimaldi, a mathematics professor in Italy, conducted an experiment. He let a beam of light pass through two small holes and shine it on the screen in the dark room, and found that there are An image with light and dark stripes.Grimaldi immediately thought of the diffraction of water waves (you should have seen this in the illustrations of middle school physics), so he proposed that light may be a wave similar to water waves, which is the earliest light wave theory. The wave theory holds that light is not a material particle, but a wave produced by the vibration of the medium.If we imagine a water wave, it is not an actual transfer, but the result of the vibration of the water surface along the way.The fluctuation of light is easy to explain the light and dark stripes in the projection, and it is also easy to explain that the light beams can pass through each other without interfering with each other.Regarding the problem of straight-line propagation and reflection, people quickly realized that the wavelength of light is very short, and in most cases, the behavior of light is still the same as that of classical particles.Diffraction experiments further prove this point.However, there is a basic difficulty in the theory of fluctuations, that is, any fluctuation needs a medium to be transmitted, such as sound, which cannot be transmitted in a vacuum.Light, on the other hand, seems to move forward at will without any medium.To give a simple example, starlight can come to the earth through the almost empty space, which is obviously very unfavorable to fluctuations.But the wave theory cleverly gets rid of this problem: it assumes an invisible and intangible medium to realize the propagation of light. This medium has a very loud and impressive name called Aether. In such a wonderful atmosphere, the theory of light fluctuations stepped onto the stage of history.As we will soon see, this new force seems to be the former enemy of Moxie, and it is destined to start a centuries-long war with the latter.The destinies of the two of them have always been entangled with each other. Without each other, neither of them can say that they are still complete.In the end, they simply existed for the sake of their opponents.From the foreshadowing at the beginning, this wonderful drama went through two ups and downs and reached a dazzling climax.And the wonderful ending in the end makes us believe that their dialogue is almost a kind of fate that can be met but not sought after.In the middle of the seventeenth century, it was the last darkness before the dawn of science, and no one could have foreseen that these two small sparks would spark a raging fire. Gossip after dinner: talk about Aether. As we have seen above, aether was originally posited as a medium for light waves.But the origin of the word ether was as early as in ancient Greece: Aristotle expounded his understanding of celestial bodies in the book "On the Sky".He believed that the sun, the moon and the stars revolved around the earth, but their composition was different from the four elements of water, fire, air, and earth on the ground.Heavenly things are supposed to be perfect, they can only be composed of a purer element, which is what Aristotle called the fifth element ether (αηθηρ in Greek).Since this concept was borrowed into science, the status of ether in history can be said to be quite subtle. On the one hand, it has played such an important role that it has become the basis of the entire physics; on the other hand, When its glory was gone, it was also ridiculed.Although it struggled again and again unwillingly, changed its appearance, and gave itself a new meaning, it still could not escape the fate of being abandoned in the end, and even became a special term for pseudoscience for a while.But no matter what, the concept of ether still occupies its place in the history of science. Although the light medium and the absolute reference system it once represented have withdrawn from the stage, they can still evoke our nostalgia for that golden age until today. .It is like a yellowed photo, recording the glorious past of an aristocrat.Today, Aether is used as another concept to name a network communication protocol (Ethernet). When you see this word, do you often feel a little sigh? Hats off to ether. three As mentioned last time, regarding the question of what light is, there were two possible hypotheses in the middle of the seventeenth century: the particle theory and the wave theory. However, at the beginning, the armed forces of both sides were very weak.Mote theory has a long history, but its power is very limited.The problem of linear propagation of light and the problem of reflection and refraction were originally its traditional domains, but after the army developed its own theory in terms of fluctuations, it quickly equalized with particles on these two battlefields.As a new theory of wave theory, Grimaldi's light diffraction experiment is the greatest magic weapon for its fortune, but it drags a heavy burden, that is, the hypothesis of light ether, this imaginary medium, will be in the future. For a long time, it has become a burden to the fluctuating army. There was no armed conflict between the two forces at first.In Descartes' Discourse on Method, they still stand together calmly for everyone to review.The fuse that led to the outbreak of the first microwave war was a theory put forward by Robert Boyle in 1663.He believes that the various colors we see are not the properties of the object itself, but the effect of the light on it.The argument itself has nothing to do with particle fluctuations, but it has sparked a heated debate about the properties of color. In Grimaldi's eyes, the difference in color is caused by the difference in the frequency of light waves.His experiments aroused the interest of Robert Hooke.Hooke was originally Boyle's experimental assistant, a member of the Royal Society at the time, and also served as an experimental administrator.He repeated Grimaldi's work and carefully observed the colors of light reflected in soap bubbles and the brilliance of light passing through thin mica sheets.According to his judgment, light must be some kind of rapid pulse, so he explicitly supported the wave theory in Micrographia published in 1665. The book "Microscopy" quickly won Hooke a worldwide academic reputation, and the wave theory seemed to gain the upper hand for a while because of the addition of this general. However, I don't know if it was a coincidence, or a secret arrangement, a seemingly unrelated event changed the development of the entire battle situation. In 1672, a man named Isaac.Newton's young people submitted a paper to the Royal Society Review Committee called "A New Theory of Light and Color".Newton was thirty years old at the time and had just been elected a fellow of the Royal Society.This is the first formal scientific paper published by Newton, and its content is about his experiments on the dispersion of light, which is also one of Newton's most famous experiments.The scene of the experiment is rendered very impressive in some science books: Newton stayed in a hut wearing a thick wig in the unbearably hot summer.All the windows on all sides were sealed, and the inside of the room was stuffy and hot, and it was pitch black, with only a beam of bright light coming in from a small hole specially set out for it.Regardless of the sweat on his body, Newton walked up and down the room with full concentration, and inserted a prism in his hand into the small hole from time to time.Whenever the prism was inserted, the original white light disappeared, and on the wall of the room, a long colored broadband was reflected: the color ranged from red to purple.With this experiment, Newton came to the conclusion that white light is a mixture of colorful lights. In this paper, however, Newton compared the recombination and decomposition of light to the mixing and separation of particles of different colors.Hooke and Boyle, who were members of the Senate at the time, fiercely attacked this view.Hooke claimed that the correct part of Newton's thesis (namely the compounding of colors) was stolen from his 1665 ideas, while Newton's original particle theory was not worth mentioning.Newton was furious, immediately withdrew the paper, and angrily declared that he would no longer publish any research results. In fact, before that, Newton's point of view was still vacillating between particles and fluctuations, and he did not completely deny the theory of fluctuations.When Hooke published his views in 1665, Newton had just graduated from Trinity College, Cambridge, and was probably still thinking about his gravitational problem in front of the apple tree.But after this incident, Newton began to support the particle theory overwhelmingly.Whether this is due to the psychology of revenge or the spirit of science is impossible to know today, and there must be factors in both aspects.However, Newton's character is known for being stingy and calculating, which can also be seen in the dispute between him and Leibniz about the invention of calculus. However, because of Hooke's fame on the one hand, and because Newton's attention was more shifted to kinematics and mechanics on the other hand, Newton still has not formally and comprehensively demonstrated the theory of particles (only refuted Hu Ke in several papers). gram).At this time, the Volatile Front began their modernization process and equipped themselves with theory.Dutch physicist Christiaan Huygens (Christiaan Huygens) became the leader of the wave theory. Huygens has a very high genius in mathematical theory. He inherited Hooke's thought, believed that light is a longitudinal wave propagating in ether, and introduced the concept of wave front, successfully proving and deriving the light The laws of reflection and refraction.Although his wave theory was still very rough, the success he achieved was outstanding.At that time, with the continuous deepening of optical research, new battlefields were constantly being opened up: in 1665, Newton discovered in experiments that if light is irradiated on an optical flat glass plate through a large curvature convex lens, it will be seen between the lens and the glass plate. A group of colored concentric ring stripes appear at the contact point, which is the famous Newton's ring (friends who are interested in images and photography must know it).In 1669, E. Bartholinus of Denmark discovered that when light passes through a calcite crystal, birefringence occurs.Applying his theory to these new discoveries, Huygens found that his fluctuating armies could easily occupy these new positions with only minor modifications (such as the introduction of the concept of elliptical waves).In 1690, Huygens's book "Traite de la Lumiere" (Traite de la Lumiere) was published, marking the peak of the wave theory at this stage. Unfortunately, the temporary gains in volatility look destined to become short-lived bubbles.Because standing over their opponents is a radiant and great figure: Isaac.Mr. Newton (and soon to be Sir).Regardless of his reasons, this scientific giant has decided to deal a merciless fatal blow to the army of the wave theory.In order to avoid further disputes with Hooker and unnecessary misunderstandings, Newton also made careful tactical arrangements.It was not until the second year after Hooke's death, that is, in 1704, that Newton published his brilliant masterpiece "Optics" (Optics).In this epoch-making work, Newton expounded in detail the color superposition and dispersion of light, and explained the light transmission of thin films, Newton's rings and various phenomena found in diffraction experiments from the perspective of particles.He refuted the wave theory, questioning why light cannot move around obstacles if it is like sound waves.He also studied the phenomenon of birefringence and raised many problems that cannot be explained by wave theory.The basic difficulties of particles were solved by Newton with his genius.He absorbed many things from his wave opponents, such as introducing some useful concepts of waves such as vibration and period into particle theory, thus solving the problem of Newton's rings well.On the other hand, Newton combined the theory of particles with his mechanical system, so that this theory suddenly showed unparalleled power. This is completely a devastating blow.At that time, Newton was no longer the young man who could be questioned in the council.Newton at that time was already the Newton who published "Principles of Mathematics", and the Newton who invented calculus.At that time, he was already a member of Congress, President of the Royal Society, and had become a mythical figure in the history of science.All over the world, people pay homage to his mechanical system, as if they have seen the revelation of God.But the theory of volatility has no leader (Huygens also died earlier in 1695), and this army that lost its leader suffered a devastating blow before it had time to build a few stronger fortresses on its territory.They were terrified and routed, losing almost all their positions overnight.On the one hand, this is due to the deficiencies in the fortifications of Wave itself, and its theory is still not perfect; on the other hand, it is also because the strength of the opponent is too strong: Newton, as a master in the field of optics, his talent and authority cannot be questioned. of.The first microwave war ended in a fluctuating fiasco. As a result of the war, the particle theory firmly occupied the mainstream of the physics world.Volatility was forced underground, unable to lift its head for a century.However, it still has not been wiped out. The pioneering work done by Huygens and others makes it still have tenacious vitality, silently lurking for the day when it will make a comeback. After-dinner gossip: Hooke and Newton Hooker and Newton can also be regarded as a happy couple in history.Both have made great contributions in mechanics, optics, instruments, etc.The two inspire each other, but there are also many disputes between them.In addition to the debate about the nature of light, there is also a dispute between them, that is, who discovered the inverse square law of gravity.Hooke has spent a lot of effort in mechanics and planetary motion. He has studied Kepler's laws in depth, and in 1964 he proposed the idea that planetary orbits are bent into ellipses due to gravity.In 1674 he proposed the theory of planetary motion based on the revised principle of inertia.In 1679, in his letter to Newton, he proposed the concept that the gravitational force is inversely proportional to the square of the distance, but he made it vague and did not quantify it (the original text is: my supposition is that the Attraction always is in a duplicate proportion to the distance from the center reciprocal).After the publication of Newton's Principia, Hooke asked to be recognized for his prior discovery of this law, but Newton's final answer was to delete all references to Hooke from Principia. It should be said that Hooke is also a great scientist. He helped Boyle discover Boyle's law and discovered plant cells with his own microscope. His work in geology (especially the observation of fossils) has influenced This subject has been a full thirty years, and the instruments he invented and manufactured (such as microscopes, air pumps, spring balance wheels, wheel barometers, etc.) were unparalleled at that time.The law of elasticity he discovered is one of the most important laws of mechanics.At that time, he was a great scientist second only to Newton in terms of mechanics and optics, but it seemed that he would always live in Newton's shadow.Today's Newton is famous all over the world, but today's middle school students only know Hooke's name from Hooke's law (the law of elasticity) in textbooks. Hooke had become cynical before his death, and his words were full of sarcasm.There is not even a portrait of him left after his death, it is said that he is too ugly. Four As mentioned last time, in the first confrontation between particles and fluctuations, the theory of particles headed by Newton defeated the fluctuations and achieved a generally recognized position in physics. In the blink of an eye, nearly a century has passed.The status of the Newtonian system has been so lofty that one cannot help feeling dizzy.And the idea that light is a particle he advocated has become so popular that people almost forgot the existence of its opponent back then. However, on June 13, 1773, a boy named Thomas was born in a Christian family in Milverton, England.Young (Thomas Young).The growth history of this future rebel leader is a typical genius process. He was able to read all kinds of classics when he was two years old. He began to learn Latin at the age of six. He wrote an autobiography in Latin at the age of fourteen. At the age of 10, he was able to speak ten languages, and studied scientific works such as Newton's "Principles of Mathematics" and Lavoisier's "Chemistry Outline". When Yang was nineteen, influenced by his uncle who was a doctor, he decided to study medicine in London.In the days that followed, he went to the universities of Edinburgh and Göttingen to study, and finally returned to Emmanuel College in Cambridge to end his studies.When he was a student, Yang studied the structure of the human eye, began to touch some basic problems in optics, and finally formed his idea that light is a wave.Yang's understanding is derived from the so-called interference phenomenon in fluctuations. We all know that ordinary substances are additive, one drop of water plus one drop of water must be two drops of water, and they will not disappear together.But the wave is different. An ordinary wave has a peak and a valley. If two waves meet, when they are both at the peak, the superimposed wave will reach twice the peak. , if they are all in the trough, the result of the superposition will be twice as deep as the trough.But wait, what if exactly one wave is at its peak and the other wave is at its valley? The answer is that they cancel each other out.If two waves meet in this way (physically called out of phase), then where they overlap, the waves will be mirror flat, with no peaks or valleys.It's like one person pulls you to the left, and another person pulls you to the right with the same force, and the result is that you will stand still. Thomas.Young was struck by this idea of ​​fluctuations when he was studying the light and dark fringes of Newton's rings.Why do bright and dark stripes form?An idea gradually took shape in Yang's mind: Isn't it easy to explain it with waves?Where the light is bright, that's because the two lights are exactly in phase, and their peaks and troughs just reinforce each other, resulting in twice the light effect (as if two people are pulling you on the left or right at the same time); Those stripes must be two lights in opposite phase, their crests and troughs are opposite, just canceling each other out (as if two people are pulling you on both sides at the same time).This bold and imaginative insight made Yang very excited. He immediately started a series of experiments, and published paper reports in 1801 and 1803 respectively, explaining how to use the interference effect of light waves. To explain Newton's rings and diffraction phenomena.Even through his experimental data, he calculated that the wavelength of light should be between 1/36000 and 1/60000 inches. In 1807, Young published his Lectures on Natural Philosophy, which synthesized his work on optics and described for the first time his famous experiment: the double slit of light. put one's oar in.Later history proved that this experiment can be ranked among the top five most classic experiments in the history of physics, and today, it has appeared in every middle school physics textbook. Yang's experimental method is extremely simple: a candle is placed in front of a piece of paper with a small hole, thus forming a point light source (a light source emitted from a point).Now put another piece of paper behind the paper, the difference is that two parallel slits are made on the second piece of paper.從小孔中射出的光穿過兩道狹縫投到螢幕上，就會形成一系列明、暗交替的條紋，這就是現在眾人皆知的干涉條紋。 楊的著作點燃了革命的導火索，物理史上的第二次微波戰爭開始了。波動方面軍在經過了百年的沉寂之後，終於又回到了歷史舞臺上來。但是它當時的日子並不是好過的，在微粒大軍仍然一統天下的年代，波動的士兵們衣衫襤褸，缺少後援，只能靠游擊戰來引起人們對它的注意。楊的論文開始受盡了權威們的嘲笑和諷刺，被攻擊為荒唐和不合邏輯，在近二十年間竟然無人問津。楊為了反駁專門撰寫了論文，但是卻無處發表，只好印成小冊子，但是據說發行後只賣出了一本。 不過，雖然高傲的微粒仍然沉醉在牛頓時代的光榮之中，一開始並不把起義的波動叛亂分子放在眼睛裡。但他們很快就發現，這些反叛者雖然人數不怎麼多，服裝並不那麼整齊，但是他們的武器卻今非昔比。在受到了幾次沉重的打擊後，干涉條紋這門波動大炮的殺傷力終於驚動整個微粒軍團。這個簡單巧妙的實驗所揭示出來的現象證據確鑿，幾乎無法反駁。無論微粒怎麼樣努力，也無法躲開對手的無情轟炸：它就是難以說明兩道光疊加在一起怎麼會反而造成黑暗。而波動的理由卻是簡單而直接的：兩個小孔距離螢幕上某點的距離會有所不同。當這個距離是波長的整數值時，兩列光波正好互相加強，就形成亮點。反之，當距離差剛好造成半個波長的相位差時，兩列波就正好互相抵消，造成暗點。理論計算出的明亮條紋距離和實驗值分毫不差。 在節節敗退後，微粒終於發現自己無法抵擋對方的進攻。於是它採取了以攻代守的戰略。許多對波動說不利的實驗證據被提出來以證明波動說的矛盾。其中最為知名的就是馬呂斯（Etienne Louis Malus）在一八○九年發現的偏振現象，這一現象和已知的波動論有抵觸的地方。兩大對手開始相持不下，但是各自都沒有放棄自己獲勝的信心。楊在給馬呂斯的信裡說：您的實驗只是證明了我的理論有不足之處，但沒有證明它是虛假的。 決定性的時刻在一八一九年到來了。最後的決戰起源於一八一八年法國科學院的一個懸賞徵文競賽。競賽的題目是利用精密的實驗確定光的衍射效應以及推導光線通過物體附近時的運動情況。競賽評委會由許多知名科學家組成，這其中包括比奧（JB Biot）、拉普拉斯（Pierre Simon de Laplace）和泊松（SD Poission），都是積極的微粒說擁護者。組織這個競賽的本意是希望通過微粒說的理論來解釋光的衍射以及運動，以打擊波動理論。 但是戲劇性的情況出現了。一個不知名的法國年輕工程師菲涅耳（Augustin Fresnel，當時他才三十一歲）向組委會提交了一篇論文《關於偏振光線的相互作用》。在這篇論文裡，菲涅耳採用了光是一種波動的觀點，但是革命性地認為光是一種橫波（也就是類似水波那樣，振子作相對傳播方向垂直運動的波）而不像從胡克以來一直所認為的那樣是一種縱波（類似彈簧波，振子作相對傳播方向水準運動的波）。從這個觀念出發，他以嚴密的數學推理，圓滿地解釋了光的衍射，並解決了一直以來困擾波動說的偏振問題。他的體系完整而無缺，以至委員會成員為之深深驚歎。泊松並不相信這一結論，對它進行了仔細的審查，結果發現當把這個理論應用於圓盤衍射的時候，在陰影中間將會出現一個亮斑。這在泊松看來是十分荒謬的，影子中間怎麼會出現亮斑呢？這差點使得菲涅爾的論文中途夭折。但菲涅耳的同事阿拉果（Franois Arago）在關鍵時刻堅持要進行實驗檢測，結果發現真的有一個亮點如同奇蹟一般地出現在圓盤陰影的正中心，位置亮度和理論符合得相當完美。 菲涅爾理論的這個勝利成了第二次微波戰爭的決定性事件。他獲得了那一屆的科學獎（Grand Prix），同時一躍成為了可以和牛頓，惠更斯比肩的光學界的傳奇人物。圓盤陰影正中的亮點（後來被相當有誤導性地稱作泊松亮斑）成了波動軍手中威力不下於干涉條紋的重武器，給了微粒勢力以致命的一擊。起義者的烽火很快就燃遍了光學的所有領域，把微粒從統治的地位趕了下來，後者在嚴厲的打擊下捉襟見肘，節節潰退，到了十九世紀中期，微粒說挽回戰局的唯一希望就是光速在水中的測定結果了。因為根據粒子論，這個速度應該比真空中的光速要快，而根據波動論，這個速度則應該比真空中要慢才對。 然而不幸的微粒軍團終於在一八一九年的莫斯科嚴冬之後，又於一八五○年迎來了它的滑鐵盧。這一年的五月六日，傅科（Foucault，他後來以傅科擺實驗而聞名）向法國科學院提交了他關於光速測量實驗的報告。在準確地得出光在真空中的速度之後，他也進行了水中光速的測量，發現這個值小於真空中的速度。這一結果徹底宣判了微粒說的死刑，波動論終於在一百多年後革命成功，登上了物理學統治地位的寶座。在勝利者的一片歡呼聲中，第二次微波戰爭隨著微粒的戰敗而宣告結束。 但是波動內部還是有一個小小的困難，就是乙太的問題。光是一種橫波的事實已經十分清楚，它傳播的速度也得到了精確測量，這個數值達到了三十萬公里／秒，是一個驚人的高速。通過傳統的波動論，我們必然可以得出它的傳播媒介的性質：這種媒介必定是十分的堅硬，比最硬的物質金剛石還要硬上不知多少倍。然而事實是從來就沒有任何人能夠看到或者摸到這種乙太，也沒有實驗測定到它的存在。星光穿越幾億億公里的乙太來到地球，然而這些堅硬無比的乙太卻不能阻擋任何一顆行星或者彗星的運動，哪怕是最微小的也不行！ 波動對此的解釋是乙太是一種剛性的粒子，但是它卻是如此稀薄，以致物質在穿過它們時幾乎完全不受到任何阻力，就像風穿過一小片叢林（湯瑪斯．楊語）。乙太在真空中也是絕對靜止的，只有在透明物體中，可以部分地被拖曳（菲涅耳的部分拖曳假說）。這個觀點其實是十分牽強的，但是波動說並沒有為此困惑多久。因為更加激動人心的勝利很快就到來了。偉大的麥克斯韋於一八五六，一八六一和一八六五年發表了三篇關於電磁理論的論文，這是一個開天闢地的工作，它在牛頓力學的大廈上又完整地建立起了另一座巨構，而且其輝煌燦爛絕不亞於前者。麥克斯韋的理論預言，光其實只是電磁波的一種。這段文字是他在一八六一年的第二篇論文《論物理力線》裡面特地用斜體字寫下的。而我們在本章的一開始已經看到，這個預言是怎麼樣由赫茲在一八八七年用實驗證實了的。波動說突然發現，它已經不僅僅是光領域的統治者，而是業已成為了整個電磁王國的最高司令官。波動的光輝到達了頂點，只要站在大地上，它的力量就像古希臘神話中的巨人那樣，是無窮無盡而不可戰勝的。而它所依靠的大地，就是麥克斯韋不朽的電磁理論。 飯後閒話：阿拉果（Dominique Franois Jean Arago）的遺憾 阿拉果一向是光波動說的捍衛者，他和菲涅耳在光學上其實是長期合作的。菲涅耳關於光是橫波的思想，最初還是來源於湯瑪斯．楊寫給阿拉果的一封信。而對於相互垂直的兩束偏振光線的相干性的研究，是他和菲涅耳共同作出的，兩人的工作明確了來自同一光源但偏振面相互垂直的兩支光束，不能發生干涉。但在雙折射和偏振現象上，菲涅耳顯然更具有勇氣和革命精神，在兩人完成了《關於偏振光線的相互作用》這篇論文後，菲涅耳指出只有假設光是一種橫波，才能完滿地解釋這些現象，並給出了推導。然而阿拉果對此抱有懷疑態度，認為菲涅耳走得太遠了。他坦率地向菲涅耳表示，自己沒有勇氣發表這個觀點，並拒絕在這部分論文後面署上自己的名字。於是最終菲涅耳以自己一個人的名義提交了這部分內容，引起了科學院的震動，而最終的實驗卻表明他是對的。 這大概是阿拉果一生中最大的遺憾，他本有機會和菲涅耳一樣成為在科學史上大名鼎鼎的人物。當時的菲涅耳還是無名小輩，而他在學界卻已經聲名顯赫，被選入法蘭西研究院時，得票甚至超過了著名的泊松。其實在光波動說方面，阿拉果做出了許多傑出的貢獻，不在菲涅耳之下，許多還是兩人互相啟發而致的。在菲涅耳面臨泊松的質問時，阿拉果仍然站在了菲涅耳一邊，正是他的實驗證實了泊松光斑的存在，使得波動說取得了最後的勝利。但關鍵時候的遲疑，卻最終使得他失去了物理光學之父的稱號。這一桂冠如今戴在菲涅耳的頭上。 five 上次說到，隨著麥克斯韋的理論為赫茲的實驗所證實，光的波動說終於成為了一個板上釘釘的事實。 波動現在是如此的強大。憑藉著麥氏理論的力量，它已經徹底地將微粒打倒，並且很快就拓土開疆，建立起一個空前的大帝國來。不久後，它的領土就橫跨整個電磁波的頻段，從微波到X射線，從紫外線到紅外線，從γ射線到無線電波普通光線只是它統治下的一個小小的國家罷了。波動君臨天下，振長策而禦宇內，四海之間莫非王土。而可憐的微粒早已銷聲匿跡，似乎永遠也無法翻身了。 赫茲的實驗也同時標誌著經典物理的頂峰。物理學的大廈從來都沒有這樣地金碧輝煌，令人歎為觀止。牛頓的力學體系已經是如此雄偉壯觀，現在麥克斯韋在它之上又構建起了同等規模的另一幢建築，它的光輝燦爛讓人幾乎不敢仰視。電磁理論在數學上完美得難以置信，著名的麥氏方程組剛一問世，就被世人驚為天物。它所表現出的深刻、對稱、優美使得每一個科學家都陶醉在其中，玻爾茲曼（Ludwig Boltzmann）情不自禁地引用歌德的詩句說：難道是上帝寫的這些嗎？一直到今天，麥氏方程組仍然被公認為科學美的典範，即使在還沒有赫茲的實驗證實之前，已經廣泛地為人們所認同。許多偉大的科學家都為它的魅力折服，並受它深深的影響，有著對於科學美的堅定信仰，甚至認為：對於一個科學理論來說，簡潔優美要比實驗資料的準確來得更為重要。無論從哪個意義上來說，電磁論都是一種偉大的理論。Roger.彭羅斯（Roger Penrose）在他的名著《皇帝新腦》（The Emperor's New Mind）一書裡毫不猶豫地將它和牛頓力學，相對論和量子論並列，稱之為Superb的理論。 物理學征服了世界。在十九世紀末，它的力量控制著一切人們所知的現象。古老的牛頓力學城堡歷經歲月磨礪風雨吹打而始終屹立不倒，反而更加凸現出它的偉大和堅固來。從天上的行星到地上的石塊，萬物都必恭必敬地遵循著它制定的規則。一八四六年海王星的發現，更是它所取得的最偉大的勝利之一。在光學的方面，波動已經統一了天下，新的電磁理論更把它的光榮擴大到了整個電磁世界。在熱的方面，熱力學三大定律已經基本建立（第三定律已經有了雛形），而在克勞修斯（Rudolph Clausius）、範德瓦爾斯（JD Van der Waals）、麥克斯韋、玻爾茲曼和吉布斯（Josiah Willard Gibbs）等天才的努力下，分子運動論和統計熱力學也被成功地建立起來了。更令人驚奇的是，這一切都彼此相符而互相包容，形成了一個經典物理的大同盟。經典力學、經典電動力學和經典熱力學（加上統計力學）形成了物理世界的三大支柱。它們緊緊地結合在一塊兒，構築起了一座華麗而雄偉的殿堂。 這是一段偉大而光榮的日子，是經典物理的黃金時代。科學的力量似乎從來都沒有這樣的強大，這樣地令人神往。人們也許終於可以相信，上帝造物的奧秘被他們所完全掌握了，再沒有遺漏的地方。從當時來看，我們也許的確是有資格這樣驕傲的，因為所知道的一切物理現象，幾乎都可以從現成的理論裡得到解釋。力、熱、光、電、磁一切的一切，都在控制之中，而且用的是同一種手法。物理學家們開始相信，這個世界所有的基本原理都已經被發現了，物理學已經盡善盡美，它走到了自己的極限和盡頭，再也不可能有任何突破性的進展了。如果說還有什麼要做的事情，那就是做一些細節上的修正和補充，更加精確地測量一些常數值罷了。人們開始傾向於認為：物理學已經終結，所有的問題都可以用這個集大成的體系來解決，而不會再有任何真正激動人心的發現了。一位著名的科學家（據說就是偉大的開爾文勳爵）說：物理學的未來，將只有在小數點第六位後面去尋找。普朗克的導師甚至勸他不要再浪費時間去研究這個已經高度成熟的體系。 十九世紀末的物理學天空中閃爍著金色的光芒，象徵著經典物理帝國的全盛時代。這樣的偉大時期在科學史上是空前的，或許也將是絕後的。然而，這個統一的強大帝國卻註定了只能曇花一現。喧囂一時的繁盛，終究要像泡沫那樣破滅凋零。 今天回頭來看，赫茲一八八七年的電磁波實驗（準確地說，是他於一八八七︱一八八八年進行的一系列的實驗）的意義應該是複雜而深遠的。它一方面徹底建立了電磁場論，為經典物理的繁榮添加了濃重的一筆；在另一方面，它卻同時又埋藏下了促使經典物理自身毀滅的武器，孕育出了革命的種子。 我們還是回到我們故事的第一部分那裡去：在卡爾斯魯厄大學的那間實驗室裡，赫茲銅環接收器的缺口之間不停地爆發著電火花，明白無誤地昭示著電磁波的存在。 但偶然間，赫茲又發現了一個奇怪的現象：當有光照射到這個缺口上的時候，似乎火花就出現得更容易一些。 赫茲把這個發現也寫成了論文發表，但在當時並沒有引起很多的人的注意。當時，學者們在為電磁場理論的成功而歡欣鼓舞，馬可尼們在為了一個巨大的商機而激動不已，沒有人想到這篇論文的真正意義。連赫茲自己也不知道，量子存在的證據原來就在他的眼前，幾乎是觸手可得。不過，也許量子的概念太過爆炸性，太過革命性，命運在冥冥中安排了它必須在新的世紀中才可以出現，而把懷舊和經典留給了舊世紀吧。只是可惜赫茲走得太早，沒能親眼看到它的誕生，沒能目睹它究竟將要給這個世界帶來什麼樣的變化。 終於，在經典物理還沒有來得及多多體味一下自己的盛世前，一連串意想不到的事情在十九世紀的最後幾年連續發生了，仿佛是一個不祥的預兆。 一八九五年，倫琴（Wilhelm Konrad Rontgen）發現了X射線。一八九六年，貝克勒爾（Antoine Herni Becquerel）發現了鈾元素的放射現象。一八九七年，居里夫人（Marie Curie）和她的丈夫皮埃爾．居裡研究了放射性，並發現了更多的放射性元素：釷、釙、鐳。一八九七年，JJ湯姆遜（Joseph John Thomson）在研究了陰極射線後認為它是一種帶負電的粒子流。電子被發現了。一八九九年，盧瑟福（Ernest Rutherford）發現了元素的嬗變現象。 如此多的新發現接連湧現，令人一時間眼花繚亂。每一個人都開始感覺到了一種不安，似乎有什麼重大的事件即將發生。物理學這座大廈依然聳立，看上去依然那麼雄偉，那麼牢不可破，但氣氛卻突然變得異常凝重起來，一種山雨欲來的壓抑感覺在人們心中擴散。新的世紀很快就要來到，人們不知道即將發生什麼，歷史將要何去何從。眺望天邊，人們隱約可以看到兩朵小小的烏雲，小得那樣不起眼。沒人知道，它們即將帶來一場狂風暴雨，將舊世界的一切從大地上徹底抹去。 但是，在暴風雨到來之前，還是讓我們抬頭再看一眼黃金時代的天空，作為最後的懷念。金色的光芒照耀在我們的臉上，把一切都染上了神聖的色彩。經典物理學的大廈在它的輝映下，是那樣莊嚴雄偉，溢彩流光，令人不禁想起神話中宙斯和眾神在奧林匹斯山上那亙古不變的宮殿。誰又會想到，這震撼人心的壯麗，卻是斜陽投射在龐大帝國土地上最後的餘暉。