What is wave-particle duality? This is a characteristic of photons and other subatomic particles that behave as waves under some conditions, and as particles under other conditions.
The wave-particle duality of substances and light is an important part of quantum mechanics, because with its help it is best demonstrated that such concepts as “waves” and “particles” that work perfectly in classical mechanics are not enough to explain the behavior of some quantum objects .
The dual nature of light gained recognition in physics after 1905, when Albert Einstein described the behavior of light using photons, which were described as particles. Einstein then published the less famous special theory of relativity, in which light was described by the behavior of waves.
Particles exhibiting dual behavior
Best of all, the principle of wave-particle duality is observed in the behavior of photons. These are the lightest and smallest objects that exhibit dual behavior. Among the larger objects, such as elementary particles, atoms, and even molecules, one can also observe elements of wave-particle duality, however, larger objects behave like waves of extremely short lengths, so it is very difficult to observe them. Usually, the concepts used in classical mechanics are quite sufficient to describe the behavior of larger or macroscopic particles.
Evidence of wave-particle duality
People for many centuries and even millennia have thought about the nature of light and matter. Until relatively recently, physicists believed that the characteristics of light and matter must be unambiguous: light can be either a stream of particles or a wave, as well as a substance, or consisting of individual particles that completely obey the laws of Newtonian mechanics, or that is a continuous, inseparable medium .
Initially, in modern times, the theory of the behavior of light as a stream of individual particles, that is, a corpuscular theory, was popular. Newton himself adhered to it. However, later physicists, such as Huygens, Fresnel and Maxwell, came to the conclusion that light is a wave. They explained the behavior of light by the oscillation of the electromagnetic field, and the interaction of light and matter in this case fell under the explanation of the classical field theory.
However, at the beginning of the twentieth century, physicists were faced with the fact that neither the first nor the second explanation could completely cover the area of the behavior of light under various conditions and interactions.
Since then, numerous experiments have proven the dualism of the behavior of certain particles. However, the properties of quantum objects had a special influence on the appearance and adoption of wave-particle duality in the first, earliest experiments, which put an end to the debate about the nature of the behavior of light.
Photo effect: light is made up of particles
The photoelectric effect, also called the photoelectric effect, is the process of the interaction of light (or any other electromagnetic radiation) with matter, as a result of which the energy of light particles is transferred to particles of matter. During the study of the photoelectric effect, the behavior of photoelectrons could not be explained by the classical electromagnetic theory.
As far back as 1887, Heinrich Hertz noted that directing ultraviolet light to electrodes increased their ability to create electrical sparks. Einstein in 1905 explained the photoelectric effect by the fact that light is absorbed and emitted by certain quantum portions, which he initially called quanta of light, and then christened them photons.
Robert Milliken’s experiment in 1921 confirmed Einstein’s judgment and led the latter to receive the Nobel Prize for discovering the photoelectric effect, while Milliken himself received the Nobel Prize in 1923 for working on elementary particles and studying the photoelectric effect.
Davisson-Germer Experience: Light is a Wave
The Davisson-Germer experiment confirmed de Broglie's hypothesis of wave-particle duality of light and served as the basis for the formulation of the laws of quantum mechanics.
Both physicists studied the reflection of electrons from a single crystal of nickel. The installation, which was in vacuum, consisted of nickel single crystal polished at a certain angle. A beam of monochromatic electrons was directed directly perpendicular to the plane of the cut.
Experiments have shown that, as a result of reflection, electrons are scattered very selectively, that is, in all reflected rays, regardless of speeds and angles, maximums and minimums of intensity are observed. Thus, Davisson and Jermer experimentally confirmed the presence of wave properties in particles.
In 1948, the Soviet physicist V.A. Fabrikant experimentally confirmed that wave functions are inherent not only to the flow of electrons, but also to each electron individually.
Young's experience with two slits
Thomas Jung’s hands-on experiment with two slots demonstrates that both light and matter can exhibit characteristics of both waves and particles.
Jung’s experiment practically demonstrates the nature of wave-particle duality, despite the fact that it was first carried out at the beginning of the 19th century, even before the theory of dualism appeared.
The essence of the experiment is as follows: the light source (for example, a laser beam) is directed to a plate where two parallel slits are made. The light passing through the slits is reflected on the screen behind the plate.
The wave nature of light causes the light waves passing through the slits to mix, producing light and dark stripes on the screen, which would not happen if the light behaved exclusively like particles. However, the screen absorbs and reflects light, and the photoelectric effect is proof of the corpuscular nature of light.
What is wave-particle duality of matter?
The question of whether matter can behave as dually as light does, de Broglie took up. He belongs to the bold hypothesis that, under certain conditions and depending on the experiment, not only photons, but also electrons, can demonstrate wave-particle duality. Broglie developed his idea of probability waves not only of photons of light, but also of particles in 1924.
When the hypothesis was proved with the help of the Davisson - Germer experiment and a repetition of Jung's experiment with two slits (with electrons instead of photons), de Broglie received the Nobel Prize (1929).
It turns out that matter can also behave like a classical wave under the right circumstances. Of course, large objects create waves so short that it makes no sense to observe them, but smaller objects, such as atoms or even molecules, show a noticeable wavelength, which is very important for quantum mechanics, which is practically based on wave functions.
The meaning of wave-particle duality
The main meaning of the concept of wave-particle duality is that the behavior of electromagnetic radiation and matter can be described using a differential equation that represents a wave function. This is usually the Schrödinger equation. The ability to describe reality using wave functions is the basis of quantum mechanics.
The most common answer to the question of what is wave-particle duality is that the wave function represents the probability of finding a particular particle in a certain place. In other words, the probability of a particle being in a predicted place makes it a wave, and its physical form and shape are not a wave.
What is wave-particle duality?
While mathematics, albeit in an extremely complicated way, makes accurate predictions based on differential equations, the meaning of these equations for quantum physics is much more difficult to understand and explain. An attempt to explain what wave-particle duality is, to this day lies at the center of the debate of quantum physics.
The practical significance of wave-particle duality also consists in the fact that any physicist must learn to perceive reality in a very interesting way, when thinking of almost any object in the usual way is no longer enough for an adequate perception of reality.