Quantum physics beginning. Quantum theory. Briefly about the history of quantum physics
I think it's safe to say that no one understands quantum mechanics.
Physicist Richard Feynman
It is no exaggeration to say that the invention of semiconductor devices was a revolution. Not only is this an impressive technological achievement, but it also paved the way for events that will change modern society forever. Semiconductor devices are used in all kinds of microelectronic devices, including computers, certain types of medical diagnostic and treatment equipment, and popular telecommunications devices.
But behind this technological revolution is even more, a revolution in general science: the field quantum theory. Without this leap in understanding the natural world, the development of semiconductor devices (and more advanced electronic devices under development) would never have succeeded. Quantum physics is an incredibly complex branch of science. This chapter only provides a brief overview. When scientists like Feynman say "no one understands [it]", you can be sure that this is a really difficult topic. Without a basic understanding of quantum physics, or at least an understanding of the scientific discoveries that led to their development, it is impossible to understand how and why semiconductor electronic devices work. Most electronics textbooks try to explain semiconductors in terms of "classical physics", making them even more confusing to understand as a result.
Many of us have seen atomic model diagrams that look like the picture below.
Rutherford atom: negative electrons revolve around a small positive nucleus
Tiny particles of matter called protons and neutrons, make up the center of the atom; electrons revolve like planets around a star. The nucleus carries a positive electrical charge due to the presence of protons (neutrons have no electrical charge), while the balancing negative charge of an atom resides in the orbiting electrons. Negative electrons are attracted to positive protons like planets are attracted to the Sun, but the orbits are stable due to the movement of electrons. We owe this popular model of the atom to the work of Ernest Rutherford, who experimentally determined around 1911 that the positive charges of atoms are concentrated in a tiny, dense nucleus, and not evenly distributed along the diameter, as explorer J. J. Thomson had previously assumed.
Rutherford's scattering experiment consists of bombarding a thin gold foil with positively charged alpha particles, as shown in the figure below. Young graduate students H. Geiger and E. Marsden got unexpected results. The trajectory of some alpha particles was deviated by a large angle. Some alpha particles were scattered backwards, at an angle of almost 180°. Most of the particles passed through the gold foil without changing their trajectory, as if there was no foil at all. The fact that several alpha particles experienced large deviations in their trajectory indicates the presence of nuclei with a small positive charge.
Rutherford scattering: a beam of alpha particles is scattered by thin gold foil Although Rutherford's model of the atom was supported by experimental data better than Thomson's, it was still imperfect. Further attempts were made to determine the structure of the atom, and these efforts helped pave the way for the strange discoveries of quantum physics. Today our understanding of the atom is a bit more complex. Yet despite the revolution of quantum physics and its contribution to our understanding of the structure of the atom, Rutherford's depiction of the solar system as the structure of an atom has taken root in popular consciousness to the extent that it persists in the fields of education, even if it is misplaced.
Consider this brief description of the electrons in an atom, taken from a popular electronics textbook:
The spinning negative electrons are attracted to the positive nucleus, which leads us to the question of why the electrons don't fly into the nucleus of the atom. The answer is that the rotating electrons remain in their stable orbit due to two equal but opposite forces. The centrifugal force acting on the electrons is directed outward, and the attractive force of the charges is trying to pull the electrons towards the nucleus.
In accordance with Rutherford's model, the author considers electrons to be solid pieces of matter occupying round orbits, their inward attraction to the oppositely charged nucleus is balanced by their movement. The use of the term "centrifugal force" is technically incorrect (even for orbiting planets), but this is easily forgiven due to the popular acceptance of the model: in fact, there is no such thing as force, repulsiveany rotating body from the center of its orbit. This seems to be so because the body's inertia tends to keep it moving in a straight line, and since the orbit is a constant deviation (acceleration) from rectilinear motion, there is a constant inertial reaction to any force that attracts the body to the center of the orbit (centripetal), whether either gravity, electrostatic attraction, or even the tension of a mechanical bond.
However, the real problem with this explanation in the first place is the idea of electrons moving in circular orbits. A proven fact that accelerated electric charges emit electromagnetic radiation, this fact was known even in Rutherford's time. Since rotational motion is a form of acceleration (a rotating object in constant acceleration, pulling the object away from its normal rectilinear motion), electrons in a rotating state must emit radiation like mud from a spinning wheel. Electrons accelerated along circular paths in particle accelerators called synchrotrons are known to do this, and the result is called synchrotron radiation. If electrons were to lose energy in this way, their orbits would eventually be disrupted, and as a result they would collide with a positively charged nucleus. However, inside atoms this usually does not happen. Indeed, electronic "orbits" are surprisingly stable over a wide range of conditions.
In addition, experiments with "excited" atoms have shown that electromagnetic energy is emitted by an atom only at certain frequencies. Atoms are "excited" by external influences such as light, known to absorb energy and return electromagnetic waves at certain frequencies, much like a tuning fork that does not ring at a certain frequency until it is struck. When the light emitted by an excited atom is divided by a prism into its component frequencies (colors), individual lines of colors in the spectrum are found, the spectral line pattern is unique to a chemical element. This phenomenon is commonly used to identify chemical elements, and even to measure the proportions of each element in a compound or chemical mixture. According to the solar system of Rutherford's atomic model (relative to electrons, as pieces of matter, freely rotating in an orbit with some radius) and the laws of classical physics, excited atoms must return energy in an almost infinite range of frequencies, and not at selected frequencies. In other words, if Rutherford's model was correct, then there would be no "tuning fork" effect, and the color spectrum emitted by any atom would appear as a continuous band of colors, rather than as several separate lines.
Bohr's model of the hydrogen atom (with the orbits drawn to scale) assumes that electrons are only in discrete orbits. Electrons moving from n=3,4,5 or 6 to n=2 are displayed on a series of Balmer spectral lines A researcher named Niels Bohr tried to improve Rutherford's model after studying it in Rutherford's laboratory for several months in 1912. Trying to reconcile the results of other physicists (in particular, Max Planck and Albert Einstein), Bohr suggested that each electron had a certain, specific amount of energy, and that their orbits were distributed in such a way that each of them could occupy certain places around the nucleus, like balls. , fixed on circular paths around the nucleus, and not as free-moving satellites, as previously assumed (figure above). In deference to the laws of electromagnetism and accelerating charges, Bohr referred to "orbits" as stationary states to avoid the interpretation that they were mobile.
Although Bohr's ambitious attempt to rethink the structure of the atom, which was more consistent with experimental data, was a milestone in physics, it was not completed. His mathematical analysis predicted the results of experiments better than those performed according to previous models, but there were still unanswered questions about whether why the electrons must behave in such a strange way. The statement that electrons existed in stationary quantum states around the nucleus correlated better with experimental data than Rutherford's model, but did not say what causes the electrons to take on these special states. The answer to this question was to come from another physicist, Louis de Broglie, some ten years later.
De Broglie suggested that electrons, like photons (particles of light), have both the properties of particles and the properties of waves. Based on this assumption, he suggested that the analysis of rotating electrons in terms of waves is better than in terms of particles, and can give more insight into their quantum nature. Indeed, another breakthrough was made in understanding.
A string vibrating at a resonant frequency between two fixed points forms a standing wave The atom, according to de Broglie, consisted of standing waves, a phenomenon well known to physicists in various forms. Like the plucked string of a musical instrument (pictured above), vibrating at a resonant frequency, with "knots" and "anti-knots" in stable places along its length. De Broglie imagined electrons around atoms as waves curved into a circle (figure below).
"Rotating" electrons like a standing wave around the nucleus, (a) two cycles in an orbit, (b) three cycles in an orbit Electrons can only exist in certain, specific "orbits" around the nucleus, because they are the only distances where the ends of the wave coincide. At any other radius, the wave will collide destructively with itself and thus cease to exist.
De Broglie's hypothesis provided both a mathematical framework and a convenient physical analogy to explain the quantum states of electrons within an atom, but his model of the atom was still incomplete. For several years, physicists Werner Heisenberg and Erwin Schrödinger, working independently, have been working on de Broglie's concept of wave-particle duality in order to create more rigorous mathematical models of subatomic particles.
This theoretical advance from de Broglie's primitive standing wave model to models of the Heisenberg matrix and the Schrödinger differential equation has been given the name of quantum mechanics, and it has introduced a rather shocking feature into the world of subatomic particles: the sign of probability, or uncertainty. According to the new quantum theory, it was impossible to determine the exact position and exact momentum of a particle at one moment. A popular explanation for this "uncertainty principle" was that there was a measurement error (that is, by trying to accurately measure the position of an electron, you interfere with its momentum, and therefore cannot know what it was before you started measuring the position, and vice versa). The sensational conclusion of quantum mechanics is that particles do not have exact positions and momenta, and because of the relationship of these two quantities, their combined uncertainty will never decrease below a certain minimum value.
This form of "uncertainty" connection also exists in fields other than quantum mechanics. As discussed in the "Mixed Frequency AC Signals" chapter in Volume 2 of this book series, there are mutually exclusive relationships between the confidence in the time domain data of a waveform and its frequency domain data. Simply put, the more we know its component frequencies, the less accurately we know its amplitude over time, and vice versa. Quoting myself:
A signal of infinite duration (an infinite number of cycles) can be analyzed with absolute accuracy, but the fewer cycles available to the computer for analysis, the less accurate the analysis ... The fewer periods of the signal, the less accurate its frequency. Taking this concept to its logical extreme, a short pulse (not even a full period of a signal) doesn't really have a defined frequency, it's an infinite range of frequencies. This principle is common to all wave phenomena, and not only to variable voltages and currents.
To accurately determine the amplitude of a changing signal, we must measure it in a very short amount of time. However, doing this limits our knowledge of the frequency of the wave (a wave in quantum mechanics does not need to be similar to a sine wave; such similarity is a special case). On the other hand, in order to determine the frequency of a wave with great accuracy, we must measure it over a large number of periods, which means that we will lose sight of its amplitude at any given moment. Thus, we cannot simultaneously know the instantaneous amplitude and all frequencies of any wave with unlimited accuracy. Another oddity, this uncertainty is much greater than the inaccuracy of the observer; it is in the very nature of the wave. This is not the case, although it would be possible, given the appropriate technology, to provide accurate measurements of both instantaneous amplitude and frequency simultaneously. In a literal sense, a wave cannot have the exact instantaneous amplitude and the exact frequency at the same time.
The minimum uncertainty of particle position and momentum expressed by Heisenberg and Schrödinger has nothing to do with a limitation in measurement; rather, it is an intrinsic property of the nature of the wave-particle duality of the particle. Therefore, electrons do not actually exist in their "orbits" as well-defined particles of matter, or even as well-defined waveforms, but rather as "clouds" - a technical term. wave function probability distributions, as if each electron were "scattered" or "smeared out" over a range of positions and momenta.
This radical view of electrons as indeterminate clouds initially contradicts the original principle of the quantum states of electrons: electrons exist in discrete, definite "orbits" around the nucleus of an atom. This new view, after all, was the discovery that led to the formation and explanation of quantum theory. How strange it seems that a theory created to explain the discrete behavior of electrons ends up declaring that electrons exist as "clouds" and not as separate pieces of matter. However, the quantum behavior of electrons does not depend on electrons having certain values of coordinates and momentum, but on other properties called quantum numbers. In essence, quantum mechanics dispenses with the common concepts of absolute position and absolute moment, and replaces them with absolute concepts of types that have no analogues in common practice.
Even if electrons are known to exist in disembodied, "cloudy" forms of distributed probability, rather than separate pieces of matter, these "clouds" have slightly different characteristics. Any electron in an atom can be described by four numerical measures (the quantum numbers mentioned earlier), called main (radial), orbital (azimuth), magnetic and spin numbers. Below is a brief overview of the meaning of each of these numbers:
Principal (radial) quantum number: denoted by a letter n, this number describes the shell on which the electron resides. The electron "shell" is a region of space around the nucleus of an atom in which electrons can exist, corresponding to de Broglie and Bohr's stable "standing wave" models. Electrons can "jump" from shell to shell, but cannot exist between them.
The principal quantum number must be a positive integer (greater than or equal to 1). In other words, the principal quantum number of an electron cannot be 1/2 or -3. These integers were not chosen arbitrarily, but through experimental evidence of the light spectrum: the different frequencies (colors) of light emitted by excited hydrogen atoms follow a mathematical relationship depending on specific integer values, as shown in the figure below.
Each shell has the ability to hold multiple electrons. An analogy for electron shells is the concentric rows of seats in an amphitheater. Just as a person sitting in an amphitheater must choose a row to sit down (he cannot sit between the rows), electrons must "choose" a particular shell in order to "sit down". Like rows in an amphitheatre, the outer shells hold more electrons than the shells closer to the center. Also, the electrons tend to find the smallest available shell, just as people in an amphitheater look for the place closest to the central stage. The higher the shell number, the more energy the electrons have on it.
The maximum number of electrons that any shell can hold is described by the equation 2n 2 , where n is the principal quantum number. Thus, the first shell (n = 1) can contain 2 electrons; the second shell (n = 2) - 8 electrons; and the third shell (n = 3) - 18 electrons (figure below).
The main quantum number n and the maximum number of electrons are related by the formula 2(n 2). Orbits are not to scale. The electron shells in the atom were denoted by letters rather than numbers. The first shell (n = 1) was designated K, the second shell (n = 2) L, the third shell (n = 3) M, the fourth shell (n = 4) N, the fifth shell (n = 5) O, the sixth shell ( n = 6) P, and the seventh shell (n = 7) B.
Orbital (azimuth) quantum number: a shell composed of subshells. Some may find it more convenient to think of subshells as simple sections of shells, like lanes dividing a road. Subshells are much weirder. Subshells are regions of space where electron "clouds" can exist, and in fact different subshells have different shapes. The first subshell is in the shape of a ball (Figure below (s)), which makes sense when visualized as an electron cloud surrounding the nucleus of an atom in three dimensions.
The second subshell resembles a dumbbell, consisting of two "petals" connected at one point near the center of the atom (figure below (p)).
The third subshell usually resembles a set of four "petals" clustered around the nucleus of an atom. These subshell shapes resemble graphical representations of antenna patterns with onion-like lobes extending from the antenna in various directions (Figure below (d)).
Orbitals: (s) triple symmetry;
(p) Shown: p x , one of three possible orientations (p x , p y , p z), along the respective axes;
(d) Shown: d x 2 -y 2 is similar to d xy , d yz , d xz . Shown: d z 2 . Number of possible d-orbitals: five.
Valid values for the orbital quantum number are positive integers, as for the principal quantum number, but also include zero. These quantum numbers for electrons are denoted by the letter l. The number of subshells is equal to the principal quantum number of the shell. Thus, the first shell (n = 1) has one subshell with number 0; the second shell (n = 2) has two subshells numbered 0 and 1; the third shell (n = 3) has three subshells numbered 0, 1 and 2.
The old subshell convention used letters rather than numbers. In this format, the first subshell (l = 0) was denoted s, the second subshell (l = 1) was denoted p, the third subshell (l = 2) was denoted d, and the fourth subshell (l = 3) was denoted f. The letters came from the words: sharp, principal, diffuse and Fundamental. You can still see these designations in many periodic tables used to denote the electron configuration of the outer ( valence) shells of atoms.
(a) the Bohr representation of the silver atom, (b) Orbital representation of Ag with division of shells into subshells (orbital quantum number l).
This diagram does not imply anything about the actual position of the electrons, but only represents the energy levels.
Magnetic quantum number: The magnetic quantum number for the electron classifies the orientation of the electron subshell figure. The "petals" of the subshells can be directed in several directions. These different orientations are called orbitals. For the first subshell (s; l = 0), which resembles a sphere, "direction" is not specified. For a second (p; l = 1) subshell in each shell that resembles a dumbbell pointing in three possible directions. Imagine three dumbbells intersecting at the origin, each pointing along its own axis in a triaxial coordinate system.
Valid values for a given quantum number consist of integers ranging from -l to l, and this number is denoted as m l in atomic physics and z in nuclear physics. To calculate the number of orbitals in any subshell, you need to double the number of the subshell and add 1, (2∙l + 1). For example, the first subshell (l = 0) in any shell contains one orbital numbered 0; the second subshell (l = 1) in any shell contains three orbitals with numbers -1, 0 and 1; the third subshell (l = 2) contains five orbitals numbered -2, -1, 0, 1 and 2; and so on.
Like the principal quantum number, the magnetic quantum number arose directly from experimental data: the Zeeman effect, the separation of spectral lines by exposing an ionized gas to a magnetic field, hence the name "magnetic" quantum number.
Spin quantum number: like the magnetic quantum number, this property of the electrons of an atom was discovered through experiments. Careful observation of the spectral lines showed that each line was in fact a pair of very closely spaced lines, it has been suggested that this so-called fine structure was the result of each electron "spinning" around its own axis, like a planet. Electrons with different "spins" would give off slightly different frequencies of light when excited. The spinning electron concept is now obsolete, being more appropriate for the (incorrect) view of electrons as individual particles of matter rather than as "clouds", but the name remains.
Spin quantum numbers are denoted as m s in atomic physics and sz in nuclear physics. Each orbital in each subshell can have two electrons in each shell, one with spin +1/2 and the other with spin -1/2.
Physicist Wolfgang Pauli developed a principle that explains the ordering of electrons in an atom according to these quantum numbers. His principle, called Pauli exclusion principle, states that two electrons in the same atom cannot occupy the same quantum states. That is, each electron in an atom has a unique set of quantum numbers. This limits the number of electrons that can occupy any given orbital, subshell, and shell.
This shows the arrangement of electrons in a hydrogen atom:
With one proton in the nucleus, the atom accepts one electron for its electrostatic balance (the proton's positive charge is exactly balanced by the electron's negative charge). This electron is in the lower shell (n = 1), the first subshell (l = 0), in the only orbital (spatial orientation) of this subshell (m l = 0), with a spin value of 1/2. The general method of describing this structure is by enumerating the electrons according to their shells and subshells, according to a convention called spectroscopic notation. In this notation, the shell number is shown as an integer, the subshell as a letter (s,p,d,f), and the total number of electrons in the subshell (all orbitals, all spins) as a superscript. Thus, hydrogen, with its single electron placed at the base level, is described as 1s 1 .
Moving on to the next atom (in order of atomic number), we get the element helium:
A helium atom has two protons in its nucleus, which requires two electrons to balance the double positive electrical charge. Since two electrons - one with spin 1/2 and the other with spin -1/2 - are in the same orbital, the electronic structure of helium does not require additional subshells or shells to hold the second electron.
However, an atom requiring three or more electrons will need additional subshells to hold all the electrons, since only two electrons can be on the bottom shell (n = 1). Consider the next atom in the sequence of increasing atomic numbers, lithium:
The lithium atom uses part of the capacitance L of the shell (n = 2). This shell actually has a total capacity of eight electrons (maximum shell capacity = 2n 2 electrons). If we consider the structure of an atom with a completely filled L shell, we see how all combinations of subshells, orbitals, and spins are occupied by electrons:
Often, when assigning a spectroscopic notation to an atom, any fully filled shells are skipped, and unfilled shells and top-level filled shells are denoted. For example, the element neon (shown in the figure above), which has two completely filled shells, can be described spectrally simply as 2p 6 rather than as 1s 22 s 22 p 6 . Lithium, with its fully filled K shell and a single electron in the L shell, can simply be described as 2s 1 rather than 1s 22 s 1 .
The omission of fully populated lower-level shells is not only for convenience of notation. It also illustrates a basic principle of chemistry: the chemical behavior of an element is primarily determined by its unfilled shells. Both hydrogen and lithium have one electron on their outer shells (as 1 and 2s 1, respectively), that is, both elements have similar properties. Both are highly reactive, and react in almost identical ways (binding to similar elements under similar conditions). It doesn't really matter that lithium has a fully filled K-shell under an almost free L-shell: the unfilled L-shell is the one that determines its chemical behavior.
Elements that have completely filled outer shells are classified as noble and are characterized by an almost complete lack of reaction with other elements. These elements were classified as inert when they were considered not to react at all, but they are known to form compounds with other elements under certain conditions.
Since elements with the same configuration of electrons in their outer shells have similar chemical properties, Dmitri Mendeleev organized the chemical elements in a table accordingly. This table is known as , and modern tables follow this general layout, shown in the figure below.
Periodic table of chemical elements Dmitri Mendeleev, a Russian chemist, was the first to develop the periodic table of elements. Even though Mendeleev organized his table according to atomic mass, not atomic number, and created a table that was not as useful as modern periodic tables, his development stands as an excellent example of scientific proof. Seeing patterns of periodicity (similar chemical properties according to atomic mass), Mendeleev hypothesized that all elements must fit into this ordered pattern. When he discovered "empty" places in the table, he followed the logic of the existing order and assumed the existence of yet unknown elements. The subsequent discovery of these elements confirmed the scientific correctness of Mendeleev's hypothesis, further discoveries led to the form of the periodic table that we use now.
Like this must work science: hypotheses lead to logical conclusions and are accepted, changed or rejected depending on the consistency of experimental data with their conclusions. Any fool can formulate a hypothesis after the fact to explain the available experimental data, and many do. What distinguishes a scientific hypothesis from post hoc speculation is the prediction of future experimental data that has not yet been collected, and possibly the refutation of that data as a result. Boldly lead the hypothesis to its logical conclusion(s) and the attempt to predict the results of future experiments is not a dogmatic leap of faith, but rather a public test of this hypothesis, an open challenge to the opponents of the hypothesis. In other words, scientific hypotheses are always "risky" because of trying to predict the results of experiments that have not yet been done, and therefore can be falsified if the experiments do not go as expected. Thus, if a hypothesis correctly predicts the results of repeated experiments, it is disproven.
Quantum mechanics, first as a hypothesis and then as a theory, has been extremely successful in predicting the results of experiments, and hence has received a high degree of scientific credibility. Many scientists have reason to believe that this is an incomplete theory, since its predictions are more true at microphysical scales than macroscopic ones, but nevertheless, it is an extremely useful theory for explaining and predicting the interaction of particles and atoms.
As you have seen in this chapter, quantum physics is essential in describing and predicting many different phenomena. In the next section, we will see its significance in the electrical conductivity of solids, including semiconductors. Simply put, nothing in chemistry or solid state physics makes sense in the popular theoretical structure of electrons existing as individual particles of matter circling around the nucleus of an atom like miniature satellites. When electrons are viewed as "wave functions" existing in certain, discrete states that are regular and periodic, then the behavior of matter can be explained.
Summing up
The electrons in atoms exist in "clouds" of distributed probability, and not as discrete particles of matter revolving around the nucleus, like miniature satellites, as common examples show.
Individual electrons around the nucleus of an atom tend to unique "states" described by four quantum numbers: principal (radial) quantum number, known as shell; orbital (azimuth) quantum number, known as subshell; magnetic quantum number describing orbital(subshell orientation); and spin quantum number, or simply spin. These states are quantum, that is, “between them” there are no conditions for the existence of an electron, except for states that fit into the quantum numbering scheme.
Glanoe (radial) quantum number (n) describes the base level or shell in which the electron resides. The greater this number, the greater the radius of the electron cloud from the nucleus of the atom, and the greater the energy of the electron. Principal quantum numbers are integers (positive integers)
Orbital (azimuthal) quantum number (l) describes the shape of an electron cloud in a particular shell or level and is often known as a "subshell". In any shell, there are as many subshells (forms of an electron cloud) as the main quantum number of the shell. Azimuthal quantum numbers are positive integers starting from zero and ending with a number less than the main quantum number by one (n - 1).
Magnetic quantum number (m l) describes what orientation the subshell (electron cloud shape) has. Subshells can have as many different orientations as twice the subshell number (l) plus 1, (2l+1) (that is, for l=1, m l = -1, 0, 1), and each unique orientation is called an orbital. These numbers are integers starting from a negative value of the subshell number (l) through 0 and ending with a positive value of the subshell number.
Spin Quantum Number (m s) describes another property of the electron and can take the values +1/2 and -1/2.
Pauli exclusion principle says that two electrons in an atom cannot share the same set of quantum numbers. Therefore, there can be at most two electrons in each orbital (spin=1/2 and spin=-1/2), 2l+1 orbitals in each subshell, and n subshells in each shell, and no more.
Spectroscopic notation is a convention for the electronic structure of an atom. Shells are shown as integers, followed by subshell letters (s, p, d, f) with superscript numbers indicating the total number of electrons found in each respective subshell.
The chemical behavior of an atom is determined solely by electrons in unfilled shells. Low-level shells that are completely filled have little or no effect on the chemical binding characteristics of the elements.
Elements with completely filled electron shells are almost completely inert, and are called noble elements (previously known as inert).
Physics is the most mysterious of all sciences. Physics gives us an understanding of the world around us. The laws of physics are absolute and apply to everyone without exception, regardless of person and social status.
This article is intended for persons over 18 years of age.
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Fundamental discoveries in quantum physics
Isaac Newton, Nikola Tesla, Albert Einstein and many others are the great guides of mankind in the wonderful world of physics, who, like prophets, revealed to mankind the greatest secrets of the universe and the ability to control physical phenomena. Their bright heads cut through the darkness of ignorance of the unreasonable majority and, like a guiding star, showed the way to humanity in the darkness of the night. One of these conductors in the world of physics was Max Planck, the father of quantum physics.
Max Planck is not only the founder of quantum physics, but also the author of the world famous quantum theory. Quantum theory is the most important component of quantum physics. In simple terms, this theory describes the movement, behavior and interaction of microparticles. The founder of quantum physics also brought us many other scientific works that have become the cornerstones of modern physics:
- theory of thermal radiation;
- special theory of relativity;
- research in the field of thermodynamics;
- research in the field of optics.
The theory of quantum physics about the behavior and interaction of microparticles became the basis for condensed matter physics, elementary particle physics and high energy physics. Quantum theory explains to us the essence of many phenomena of our world - from the functioning of electronic computers to the structure and behavior of celestial bodies. Max Planck, the creator of this theory, thanks to his discovery allowed us to comprehend the true essence of many things at the level of elementary particles. But the creation of this theory is far from the only merit of the scientist. He was the first to discover the fundamental law of the universe - the law of conservation of energy. The contribution to science of Max Planck is difficult to overestimate. In short, his discoveries are priceless for physics, chemistry, history, methodology and philosophy.
quantum field theory
In a nutshell, quantum field theory is a theory of the description of microparticles, as well as their behavior in space, interaction with each other and mutual transformations. This theory studies the behavior of quantum systems within the so-called degrees of freedom. This beautiful and romantic name says nothing to many of us. For dummies, degrees of freedom are the number of independent coordinates that are needed to indicate the motion of a mechanical system. In simple terms, degrees of freedom are characteristics of motion. Interesting discoveries in the field of interaction of elementary particles were made by Steven Weinberg. He discovered the so-called neutral current - the principle of interaction between quarks and leptons, for which he received the Nobel Prize in 1979.
The Quantum Theory of Max Planck
In the nineties of the eighteenth century, the German physicist Max Planck took up the study of thermal radiation and eventually received a formula for the distribution of energy. The quantum hypothesis, which was born in the course of these studies, marked the beginning of quantum physics, as well as quantum field theory, discovered in the 1900th year. Planck's quantum theory is that during thermal radiation, the energy produced is emitted and absorbed not constantly, but episodically, quantumly. The year 1900, thanks to this discovery made by Max Planck, became the year of the birth of quantum mechanics. It is also worth mentioning Planck's formula. In short, its essence is as follows - it is based on the ratio of body temperature and its radiation.
Quantum-mechanical theory of the structure of the atom
The quantum mechanical theory of the structure of the atom is one of the basic theories of concepts in quantum physics, and indeed in physics in general. This theory allows us to understand the structure of everything material and opens the veil of secrecy over what things actually consist of. And the conclusions based on this theory are very unexpected. Consider the structure of the atom briefly. So what is an atom really made of? An atom consists of a nucleus and a cloud of electrons. The basis of the atom, its nucleus, contains almost the entire mass of the atom itself - more than 99 percent. The nucleus always has a positive charge, and it determines the chemical element of which the atom is a part. The most interesting thing about the nucleus of an atom is that it contains almost the entire mass of the atom, but at the same time it occupies only one ten-thousandth of its volume. What follows from this? And the conclusion is very unexpected. This means that the dense matter in the atom is only one ten-thousandth. And what about everything else? Everything else in the atom is an electron cloud.
The electron cloud is not a permanent and even, in fact, not a material substance. An electron cloud is just the probability of electrons appearing in an atom. That is, the nucleus occupies only one ten thousandth in the atom, and everything else is emptiness. And if we take into account that all the objects around us, from dust particles to celestial bodies, planets and stars, are made of atoms, it turns out that everything material is actually more than 99 percent of emptiness. This theory seems completely unbelievable, and its author, at least, a delusional person, because the things that exist around have a solid consistency, have weight and can be felt. How can it consist of emptiness? Has a mistake crept into this theory of the structure of matter? But there is no error here.
All material things appear dense only due to the interaction between atoms. Things have a solid and dense consistency only due to attraction or repulsion between atoms. This ensures the density and hardness of the crystal lattice of chemicals, of which everything material consists. But, an interesting point, when, for example, the temperature conditions of the environment change, the bonds between atoms, that is, their attraction and repulsion, can weaken, which leads to a weakening of the crystal lattice and even to its destruction. This explains the change in the physical properties of substances when heated. For example, when iron is heated, it becomes liquid and can be shaped into any shape. And when ice melts, the destruction of the crystal lattice leads to a change in the state of matter, and it turns from solid to liquid. These are clear examples of the weakening of bonds between atoms and, as a result, the weakening or destruction of the crystal lattice, and allow the substance to become amorphous. And the reason for such mysterious metamorphoses is precisely that substances consist of dense matter only by one ten-thousandth, and everything else is emptiness.
And substances seem to be solid only because of the strong bonds between atoms, with the weakening of which, the substance changes. Thus, the quantum theory of the structure of the atom allows us to take a completely different look at the world around us.
The founder of the theory of the atom, Niels Bohr, put forward an interesting concept that the electrons in the atom do not radiate energy constantly, but only at the moment of transition between the trajectories of their movement. Bohr's theory helped explain many intra-atomic processes, and also made a breakthrough in the science of chemistry, explaining the boundary of the table created by Mendeleev. According to , the last element that can exist in time and space has the serial number one hundred thirty-seven, and elements starting from one hundred and thirty-eighth cannot exist, since their existence contradicts the theory of relativity. Also, Bohr's theory explained the nature of such a physical phenomenon as atomic spectra.
These are the interaction spectra of free atoms that arise when energy is emitted between them. Such phenomena are typical for gaseous, vaporous substances and substances in the plasma state. Thus, quantum theory made a revolution in the world of physics and allowed scientists to advance not only in the field of this science, but also in the field of many related sciences: chemistry, thermodynamics, optics and philosophy. And also allowed humanity to penetrate the secrets of the nature of things.
There is still a lot to be done by humanity in its consciousness in order to realize the nature of atoms, to understand the principles of their behavior and interaction. Having understood this, we will be able to understand the nature of the world around us, because everything that surrounds us, starting with dust particles and ending with the sun itself, and we ourselves - everything consists of atoms, the nature of which is mysterious and amazing and fraught with a lot of secrets.
In 1803, Thomas Young directed a beam of light at an opaque screen with two slits. Instead of the expected two streaks of light on the projection screen, he saw several streaks, as if there was an interference (superposition) of two waves of light from each slot. In fact, it was at this moment that quantum physics was born, or rather questions at its foundation. In the 20th and 21st centuries, it was shown that not only light, but any single elementary particle and even some molecules behave like a wave, like quanta, as if passing through both slits at the same time. However, if a sensor is placed near the slits, which determines what exactly happens to the particle in this place and through which particular slit it nevertheless passes, then only two bands appear on the projection screen, as if the fact of observation (indirect influence) destroys the wave function and the object behaves like matter. ( video)
The Heisenberg uncertainty principle is the foundation of quantum physics!
Thanks to the 1927 discovery, thousands of scientists and students are repeating the same simple experiment by passing a laser beam through a narrowing slit. Logically, the visible trace from the laser on the projection screen becomes narrower and narrower after the gap decreases. But at a certain point, when the slit gets narrow enough, the spot from the laser suddenly starts getting wider and wider, stretching across the screen and fading until the slit disappears. This is the most obvious proof of the quintessence of quantum physics - the uncertainty principle of Werner Heisenberg, an outstanding theoretical physicist. Its essence is that the more precisely we define one of the pair characteristics of a quantum system, the more uncertain the second characteristic becomes. In this case, the more precisely we determine the coordinates of the laser photons by the narrowing slit, the more uncertain the momentum of these photons becomes. In the macrocosm, we can just as well measure either the exact location of a flying sword, taking it in our hands, or its direction, but not at the same time, since this contradicts and interferes with each other. ( , video)
Quantum superconductivity and the Meissner effect
In 1933, Walter Meissner discovered an interesting phenomenon in quantum physics: in a superconductor cooled to minimum temperatures, the magnetic field is forced out of its limits. This phenomenon is called the Meissner effect. If an ordinary magnet is placed on aluminum (or another superconductor), and then it is cooled with liquid nitrogen, then the magnet will take off and hang in the air, as it will “see” its own magnetic field of the same polarity displaced from the cooled aluminum, and the same sides of the magnets repel . ( , video)
Quantum superfluidity
In 1938, Pyotr Kapitsa cooled liquid helium to a temperature close to zero and found that the substance had lost its viscosity. This phenomenon in quantum physics is called superfluidity. If cooled liquid helium is poured onto the bottom of a glass, it will still flow out of it along the walls. In fact, as long as the helium is chilled enough, there are no limits for it to spill, regardless of the shape and size of the container. At the end of the 20th and the beginning of the 21st centuries, superfluidity under certain conditions was also discovered in hydrogen and various gases. ( , video)
quantum tunneling
In 1960, Ivor Giever conducted electrical experiments with superconductors separated by a microscopic film of non-conductive aluminum oxide. It turned out that, contrary to physics and logic, some of the electrons still pass through the insulation. This confirmed the theory of the possibility of a quantum tunneling effect. It applies not only to electricity, but also to any elementary particles, they are also waves according to quantum physics. They can pass through obstacles if the width of these obstacles is less than the wavelength of the particle. The narrower the obstacle, the more often the particles pass through them. ( , video)
Quantum entanglement and teleportation
In 1982, physicist Alain Aspe, a future Nobel Prize winner, sent two simultaneously created photons to oppositely directed sensors to determine their spin (polarization). It turned out that the measurement of the spin of one photon instantly affects the position of the spin of the second photon, which becomes opposite. Thus, the possibility of quantum entanglement of elementary particles and quantum teleportation was proved. In 2008, scientists were able to measure the state of quantum-entangled photons at a distance of 144 kilometers, and the interaction between them still turned out to be instantaneous, as if they were in one place or there was no space. It is believed that if such quantum-entangled photons end up in opposite parts of the universe, then the interaction between them will still be instantaneous, although light overcomes the same distance in tens of billions of years. Curiously, according to Einstein, there is no time for photons flying at the speed of light either. Is it a coincidence? The physicists of the future do not think so! ( , video)
The Quantum Zeno Effect and Stopping Time
In 1989, a group of scientists led by David Wineland observed the rate of transition of beryllium ions between atomic levels. It turned out that the mere fact of measuring the state of ions slowed down their transition between states. At the beginning of the 21st century, in a similar experiment with rubidium atoms, a 30-fold slowdown was achieved. All this is a confirmation of the quantum Zeno effect. Its meaning is that the very fact of measuring the state of an unstable particle in quantum physics slows down the rate of its decay and, in theory, can completely stop it. ( , video english)
Delayed choice quantum eraser
In 1999, a group of scientists led by Marlan Scali sent photons through two slits, behind which stood a prism that converted each emerging photon into a pair of quantum entangled photons and separated them into two directions. The first sent photons to the main detector. The second direction sent photons to a system of 50% reflectors and detectors. It turned out that if a photon from the second direction reached the detectors that determined the slot from which it flew out, then the main detector recorded its paired photon as a particle. If a photon from the second direction reached the detectors that did not determine the slit from which it flew out, then the main detector recorded its paired photon as a wave. Not only was the measurement of a single photon reflected on its quantum-entangled pair, but this also happened outside of distance and time, because the secondary system of detectors recorded photons later than the main one, as if the future determined the past. It is believed that this is the most incredible experiment not only in the history of quantum physics, but quite in the history of all science, as it undermines many of the usual foundations of the worldview. ( , video English)
Quantum superposition and Schrödinger's cat
In 2010, Aaron O'Connell placed a small metal plate in an opaque vacuum chamber, which he cooled to near absolute zero. He then applied an impulse to the plate to make it vibrate. However, the position sensor showed that the plate vibrated and was at rest at the same time, which was exactly in line with theoretical quantum physics. This was the first time to prove the principle of superposition on macroobjects. In isolated conditions, when there is no interaction of quantum systems, an object can simultaneously be in an unlimited number of any possible positions, as if it were no longer material. ( , video)
Quantum Cheshire cat and physics
In 2014, Tobias Denkmayr and his colleagues split the neutron flux into two beams and made a series of complex measurements. It turned out that under certain circumstances, neutrons can be in one beam, and their magnetic moment in another beam. Thus, the quantum paradox of the Cheshire cat's smile was confirmed, when particles and their properties can be located, according to our perception, in different parts of space, like a smile apart from a cat in the fairy tale "Alice in Wonderland". Once again, quantum physics turned out to be more mysterious and surprising than any fairy tale! ( , video english.)
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Quantum physics (aka quantum theory or quantum mechanics) is a separate branch of physics that deals with the description of the behavior and interaction of matter and energy at the level of elementary particles, photons and some materials at very low temperatures. A quantum field is defined as the "action" (or in some cases angular momentum) of a particle that is within the size range of a tiny physical constant called Planck's constant.
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Planck's constant
- For example, the angular momentum of an electron bound to an atom or molecule is quantized and can only take values that are multiples of the reduced Planck constant. This quantization increases the orbital of the electron by a series of integer primary quantum number. In contrast, the angular momentum of nearby unbound electrons is not quantized. Planck's constant is also used in the quantum theory of light, where the quantum of light is a photon, and matter interacts with energy through the transfer of electrons between atoms, or the "quantum jump" of a bound electron.
- The units of Planck's constant can also be thought of as the time moment of energy. For example, in the subject area of particle physics, virtual particles are represented as a mass of particles that spontaneously emerge from vacuum over a very small area and play a role in their interaction. The life limit of these virtual particles is the energy (mass) of each particle. Quantum mechanics has a large subject area, but Planck's constant is present in every mathematical part of it.
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Learn about heavy particles. Heavy particles go from classical to quantum energy transition. Even if a free electron, which has some quantum properties (such as rotation), as an unbound electron, approaches an atom and slows down (perhaps due to its emission of photons), it goes from classical to quantum behavior as its energy drops below ionization energy. An electron binds to an atom and its angular momentum with respect to the atomic nucleus is limited by the quantum value of the orbital that it can occupy. This transition is sudden. It can be compared to a mechanical system that changes its state from unstable to stable, or its behavior changes from simple to chaotic, or it can even be compared to a rocket ship that slows down and goes below the liftoff speed, and orbits around some star or another celestial object. Unlike them, photons (which are weightless) do not make such a transition: they simply traverse space unchanged until they interact with other particles and disappear. If you look up into the night sky, photons from some stars travel light years unchanged, then interact with an electron in your retinal molecule, emit their energy, and then disappear.
Start by learning the physical concept of Planck's constant. In quantum mechanics, Planck's constant is the quantum of action, denoted as h. Similarly, for interacting elementary particles, quantum angular momentum is the reduced Planck's constant (Planck's constant divided by 2 π) denoted as ħ and is called "h with a dash". The value of Planck's constant is extremely small, it combines those moments of impulse and designations of actions that have a more general mathematical concept. Name quantum mechanics implies that some physical quantities, like angular momentum, can only change discretely, not continuous ( cm. analogue) way.
