In physics, what is the reason for the opposition between waves and particles?

Mainly because the exact nature of visible light is a mystery that has puzzled mankind for centuries, whether it is waves or particles. Scientists of the Pythagorean school in ancient Greece assumed that every visible object would emit a steady stream of particles, while Aristotle concluded that the way of light propagation in the ocean was similar to that of Apollo. Although these views have undergone numerous revisions and great development in the past 20 centuries, the essence of the debate established by Greek philosophers still exists.

One view is that light is essentially wavy, and the way the energy generated passes through the space is similar to the ripples that spread on the surface of a still pond after being disturbed by falling rocks. The opposite view is that light is composed of a steady stream of particles, much like small water droplets sprayed from hose nozzles in the garden. In the past few centuries, the understanding of public opinion has been vacillating. One view dominated for a period of time, but it was finally overthrown by the evidence of another view. It was not until the first decades of the 20th century that sufficient convincing evidence was collected to provide a comprehensive answer. To everyone's surprise, both theories have been proved to be correct, at least to some extent.

In the early18th century, the debate about the nature of light has divided the scientific community into two camps, and they fought fiercely for the validity of their favorite theories. A group of scientists who agreed with the wave theory focused their argument on the discovery of the Dutchman christiaan huygens. The opposition camp cited Sir isaac newton's prism experiment as evidence to prove that light propagates in the form of particle streams, and each particle stream moves in a straight line until it is refracted, absorbed, reflected, diffracted or otherwise disturbed. Although Newton himself seems to have some doubts about his particle theory about the nature of light, his reputation in the scientific community is so important that his supporters ignored all other evidence in the heated debate.

Huygens' theory of refractive index of light is based on the concept of light fluctuation, which holds that the speed of light in any substance is inversely proportional to its refractive index. In other words, Huygens assumes that the more light is "bent" or refracted by a substance, the slower it travels through it. His followers concluded that if light is composed of particle streams, the opposite effect will occur, because when light enters a dense medium, it will be attracted by molecules in the medium, and its speed will increase rather than decrease. Although the best way to solve this problem is to measure the propagation speed of light in different substances, such as air and glass, the instruments at that time could not complete this task. No matter what substance light passes through, it seems to move at the same speed. 150 years have passed before people can measure the speed of light with high enough accuracy, thus proving that Huygens' theory is correct.

Although Sir isaac newton enjoyed a high reputation, in the early18th century, many outstanding scientists did not agree with his particle theory. Some people think that if light is composed of particles, when two beams of light cross, some particles will collide with each other, resulting in beam deviation. Obviously, this is not the case, so they come to the conclusion that light can't be composed of a single particle.

Huygens proposed in his monograph traitéde la lumière 1690 that light waves propagate in space with ether as the medium. Ether is a mysterious weightless substance, which exists in the whole air and space as an invisible entity. In the 19th century, the exploration of ether consumed a lot of resources until it finally ended. Ether theory lasted at least until the late 9th century/kloc-0. Charles Wheatstone's model proves that ether propagates light waves through vibrations perpendicular to the direction of light propagation, and james clerk maxwell's detailed model describes the structure of this invisible substance. Huygens believes that the ether vibrates in the same direction as light, and when it carries light waves, it will form waves. In his later work Huygens Principle, he skillfully described how each point on the wave produces its own wavelet, and then these wavelets are superimposed to form a wavefront. Huygens used this idea to put forward a detailed theory of refraction phenomenon, and also explained why light rays do not collide with each other when crossing paths.

When a beam of light propagates between two media with different refractive indexes, it will be refracted and change direction when it enters the second media from the first media. Determine whether the beam is composed of waves or particles, and each can design a model to explain this phenomenon. According to Huygens wave theory, a small part of the wavefront at each angle should affect the wavefront reaching the interface before the second medium. While the rest of the wave is still propagating in the first medium, this part will start to pass through the second medium, but it will move more slowly due to the high refractive index of the second medium. Because the wavefront now travels at two different speeds, it will bend into the second medium, thus changing the angle of propagation. In contrast, particle theory is difficult to explain why light particles change direction when they enter from one medium to another. Supporters of this theory believe that when particles enter the second medium, there is a special force perpendicular to the interface, and its function is to change the speed of particles. The exact nature of this force remains to be speculated, and no evidence has been collected to prove this theory.

Another excellent comparison between the two theories involves the difference that occurs when light is reflected from a smooth mirror (such as a mirror). Wave theory predicts that light waves emitted by light sources can propagate in all directions. When incident on the mirror, the waves will be reflected according to the incident angle, but each wave will be reflected backwards, resulting in the opposite image. The shape of the incident wave depends largely on the distance between the light source and the mirror. The light from the near light source still maintains a spherical and highly curved wavefront, while the light from the far light source will spread more and affect the mirror with an almost planar wavefront.

As far as reflection phenomenon is concerned, the particle nature of light is much stronger than refraction phenomenon. The light emitted by the light source, no matter how far or near, reaches the mirror in the form of particle streams, which are reflected from the smooth surface. Because the particles are very small, the number of particles involved in the propagating beam is very large, and they move very closely side by side in the beam. When particles hit the mirror, they will bounce back from different points, so their order in the light beam will be reversed when reflected, resulting in an inverse image. Both particle theory and wave theory can fully explain the reflection of smooth surfaces. However, particle theory also shows that if the surface is very rough, particles will bounce from different angles and scatter light. This theory is in good agreement with the experimental observation.

When particles and waves meet the edge of an object to form a shadow, their behavior will be different. Newton quickly pointed out in his book Optics in 1704 that "light will never travel along a curved channel and will never bend into a shadow". This concept is consistent with particle theory, which holds that light particles must always move in a straight line. If particles touch the edge of an obstacle, they will cast a shadow, because particles that are not blocked by obstacles will go straight ahead and cannot be unfolded behind the edge. On the macro scale, this observation is almost correct, but on the smaller scale, it is inconsistent with the experimental results of light diffraction.

When light passes through a narrow slit, the beam will expand and become wider than expected. This extremely important observation provides considerable credibility for the wave theory of light. Just like waves in water, when light waves meet the edge of an object, they seem to bend around the edge and enter the geometric shadow of the object, which is an area that is not directly illuminated by the light beam. This behavior is similar to water waves around the end of a raft, rather than reflection.

Nearly a hundred years after Newton and Huygens put forward their theory, an English physicist named Thomas Young conducted an experiment, which strongly supported the fluctuation of light. Because he believes that light is composed of waves, Yang infers that when two light waves meet, some kind of interaction will occur. To test this hypothesis, he used a screen with a single slit to generate coherent beams (including phase propagation waves) from ordinary sunlight. When sunlight meets a slit, they will diffuse or diffract, producing a single wavefront. If this can illuminate the second screen in front, there will be two slits next to each other, and the two additional coherent light sources are completely mutually generated. The light goes from each gap to a point, and the two gaps in the middle should reach a perfect step. The resulting waves will reinforce each other to form bigger waves. However, if one point on both sides of the center point is considered, the light emitted from one slit must travel further to reach another point opposite the center point. The light from the slit near the second point will arrive before the light from the distant slit, so the two waves will be out of sync and may cancel each other out, resulting in darkness.

As Yang guessed, he found that when the light waves in the second group of slits propagate (or diffract), they meet and overlap. In some cases, the overlap makes the two waves completely synchronized. However, in other cases, the combination of light waves is slightly or completely out of sync with each other. Yang found that when these waves meet synchronously, they are superimposed through a process called coherent interference. Waves that meet asynchronously will cancel each other out. This phenomenon is called destructive interference. Between these two extremes, constructive and destructive interference will occur to varying degrees, resulting in waves with wide spectrum amplitude. Yang Can observed the influence of interference on a screen with a fixed distance behind two slits. After diffraction, the light recombined by interference produces a series of bright and dark stripes on the screen.

Although it seemed important, Yang's conclusion was not widely accepted at that time, mainly because people had overwhelming belief in particle theory. Besides observing the interference phenomenon of light, Yang also thinks that different colors of light are composed of waves with different wavelengths, which is a widely accepted basic concept. In contrast, advocates of particle theory believe that different colors are produced by particles with different masses or moving speeds.

Interference effects are not limited to light. The waves generated on the surface of a pool or pond will propagate in all directions and have the same behavior. When two waves meet synchronously, they will be superimposed by constructive interference to form a larger wave. The unsynchronized collision waves will cancel each other through destructive interference, resulting in a horizontal plane on the water surface.

When the beam behavior between cross polarizers is carefully examined, more evidence of light fluctuation will be found. Polarization filter has a unique molecular structure, which only allows light in a single direction to pass through. In other words, the polarizer can be regarded as a special type of molecular louver with small rows of one-way plates in the polarizing material. If a beam of light is allowed to strike the polarizer, only light parallel to the polarizer can pass through the polarizer. If the second polarizer is located behind the first polarizer and faces in the same direction, the light passing through the first polarizer will also pass through the second polarizer.

However, if the second polarizer rotates at a small angle, the amount of light passing through will decrease. When the second polarizer is rotated so that its direction is perpendicular to that of the first polarizer, the light passing through the first polarizer will not pass through the second polarizer. This effect can be easily explained by wave theory, but particle theory can't explain how light is blocked by the second polarizer. In fact, particle theory is not enough to explain interference and diffraction, and these effects are later found to be the performance of the same phenomenon.

The effect observed with polarized light is very important for the development of the concept that light is composed of transverse waves, whose components are perpendicular to the propagation direction. Each transverse component must have a specific direction so that it can pass through or be blocked by the polarizer. Only those waves with transverse components parallel to the polarizing filter will pass, while other waves will be blocked.

By the middle of19th century, scientists were more and more convinced of the wave characteristics of light, but there was still a problem that could not be ignored. What is light? When james clerk maxwell, a British physicist, discovered that all forms of electromagnetic radiation represented a continuous spectrum and propagated in a vacuum at the same speed (654.38+0.86 million miles per second), he made a breakthrough. Maxwell's discovery firmly nailed the coffin of particle theory. By the beginning of the 20th century, it seems that the basic problems of light and optical theory have finally been solved.

19 in the late 1980s, the wave theory suffered a great blow. At that time, scientists first discovered that under certain conditions, light can separate electrons from atoms of several metals. Although it was a strange and unexplained phenomenon at first, it was soon discovered that ultraviolet rays can make electronic atoms in various metals release positive charges. German physicist Philipp Lenard became interested in these observations, which he called photoelectric effect. Learnard uses a prism to decompose white light into different colors, and then selectively focuses each color on a metal plate to expel electrons.

Leonard's discovery puzzled and surprised him. For light with a specific wavelength (such as blue light), electrons generate constant potential energy, or fixed energy. Reducing or increasing the amount of light will correspondingly increase or decrease the number of electrons released, but the energy of each electron remains unchanged. In other words, the energy of electrons escaping from atomic bonds depends on the wavelength of light, not the intensity of light. This is contrary to the expectation of wave theory. Learnard also found the connection between wavelength and energy: the shorter the wavelength, the greater the electron energy.

/kloc-At the beginning of the 9th century, William Hyde wollaston discovered that the light spectrum of the sun is not a continuous band, but contains hundreds of missing wavelengths, which laid the foundation for the connection between light and atoms. German physicist Joseph von Fraunhofer drew more than 500 thin lines corresponding to disappearing wavelengths, and he assigned letters to the largest interval. It was later found that these gaps were caused by the absorption of specific wavelengths by atoms in the outer layer of the sun. These observations were the first connection between atoms and light, although the basic effects were not known at that time.

In 1905, Albert Einstein assumed that light may actually have particle characteristics, although there is overwhelming evidence that it is fluctuating. When Einstein developed his quantum theory, he mathematically proposed that electrons attached to atoms in metals can absorb a certain amount of light (originally called quantum, and later turned into photons), thus making energy escape. He also speculated that if the energy of photons is inversely proportional to the wavelength, the shorter the wavelength, the higher the energy electrons will be produced. This hypothesis actually comes from Learnard's research results.

In the 1920s, the experiment of American physicist Arthur H. Compton consolidated Einstein's theory. Compton proved that photons have momentum, which is a necessary condition to support the theory that matter and energy can be exchanged. Almost at the same time, the French scientist Louis-Victor de Broglie suggested that all matter and radiation have characteristics similar to particles and waves. De Broglie, under the leadership of Max Planck, deduced Einstein's famous formulas about mass and energy, including Planck's constant:

E = mc2？ = hν

Where e is the energy of the particle, m is the mass, c is the speed of light, h is Planck constant, and ν is the frequency. De Broglie's work relates the frequency of waves to the energy and mass of particles, which is the basis for developing a new field and will eventually be used to explain the fluctuation of light and the properties similar to particles. Quantum mechanics was born from the research of Einstein, Planck, De Broglie, niels bohr and Irving Schroeder. They try to explain how electromagnetic radiation appears in the so-called duality, or shows the behavior of particles and waves at the same time. Sometimes it appears as a particle, and sometimes it appears as a wave. This complementary or dual action of light behavior can be used to describe all known characteristics that have been observed by experiments, from refraction, reflection, interference and diffraction to the results of polarized light and photoelectric effect. The combination of the characteristics of light enables us to observe the beauty of the universe.