Quantum mechanics is a very small science. This explains the behavior of matter and its interaction with energy at the atomic and subatomic levels.
In contrast, classical physics only describes matter and energy on a scale familiar to human experience, including the behavior of astronomical objects such as the Moon. Classical physics is still used in many modern science and technology. However, towards the end of the 19th century, scientists discovered phenomena in the big (macro) and small (micro) world that can not be explained by classical physics. The desire to resolve the inconsistencies between observed phenomena and classical theory led to two major revolutions in physics that created a shift in the original scientific paradigm: the theory of relativity and the development of my quantum mechanics. This article explains how physicists discover the limitations of classical physics and develop a major concept of quantum theory that replaced it in the early decades of the 20th century. It describes these concepts in approximately the order in which they were first discovered. For a more complete history of the subject, see History of quantum mechanics .
Light behaves in some ways like particles and in other things like waves. The material - the "stuff" of the universe consisting of particles such as electrons and atoms - shows wave-like behavior as well. Some light sources, such as fluorescent lights, emit only certain light frequencies. Quantum mechanics shows that light, along with all other forms of electromagnetic radiation, is present in discrete units, called photons, and predicts energy, color, and spectral intensity. One photon is quantum , or the smallest observable number, of the electromagnetic field because the partial photons are never observed. More broadly, quantum mechanics suggests that many quantities, such as angular momentum, appear continuously in the view of classical mechanics enlarged, apparently (on the scale of small quantum mechanics enlarged) quantized . Angular momentum is required to take one of a set of allowed values, and since the gap between these values ​​is very small, discontinuity is seen only at the atomic level.
Many aspects of quantum mechanics are counterproductive and seem paradoxical, because they describe behavior that is very different from that seen on a larger scale. In the words of quantum physicist Richard Feynman, quantum mechanics deals with "nature as He is - unreasonable". For example, the principle of the uncertainty of quantum mechanics means that the more tightly one pin goes down one measurement (such as the particle's position), the less accurate the other measurements associated with the same particle (such as its momentum) must be.
Video Introduction to quantum mechanics
The first quantum theory: Max Planck and black body radiation
Thermal radiation is the electromagnetic radiation emitted from the surface of an object because of the internal energy of the object. If an object is heated enough, it begins to emit light at the red end of the spectrum, as it becomes red hot.
Further heating causes the color to change from red to yellow, white, and blue, because it emits light at shorter wavelengths (higher frequencies). The perfect emitter is also a perfect absorber: when it cools down, such an object looks very black, as it absorbs all the light that falls onto it and emits nothing. As a result, the ideal thermal transmitter is known as the black body, and the radiation it emits is called the black body radiation.
By the end of the 19th century, thermal radiation had been well characterized experimentally. However, classical physics caused the law of Rayleigh-Jeans, which, as shown in the figure, agrees with experimental results at both low frequencies, but strongly disagrees at high frequencies. Physicists seek a theory that explains all experimental results.
The first model capable of explaining the full spectrum of radiant heat was proposed by Max Planck in 1900. He proposed a mathematical model in which thermal radiation was in equilibrium with a set of harmonic oscillators. To reproduce the experimental results, it must assume that each oscillator emits an integer number of energy units at a single characteristic frequency, rather than being capable of emitting an arbitrary amount of energy. In other words, the energy emitted by the oscillator is quantized . The quantum energy for each oscillator, according to Planck, is proportional to the oscillator frequency; the proportionality constant is now known as Planck's constant. Planck's constant, usually written as h , has a value of 6,63 ÃÆ' - 10 -34 Ã , J s . Thus, the energy of E of a frequency oscillator f is given by
To change color like a radiating body, it is necessary to change its temperature. Planck's law explains why: increasing body temperature allows it to radiate more energy as a whole, and means that a greater proportion of energy is toward the purple end spectrum.
Planck's law was the first quantum theory in physics, and Planck won the Nobel Prize in 1918 "in recognition of the service he gave for the advancement of Physics with the discovery of his energy quanta". However, at the time, Planck's view was that pure quantization is a heuristic mathematical construction, not (as is now believed) a fundamental change in our understanding of the world.
Maps Introduction to quantum mechanics
Photon: quantisation of light
In 1905, Albert Einstein took an extra step. He suggested that quantisation is not just a mathematical construct, but that energy in a beam of light actually takes place in individual packets, which are now called photons. The energy of a photon is given by its frequency multiplied by Planck's constant:
For centuries, scientists have been arguing between two possible light theories: is it a wave or is it made up of tiny particle streams? In the 19th century, debates were generally considered to have been solved for wave theory, being able to explain observed effects such as bias, diffraction, interference and polarization. James Clerk Maxwell has shown that electricity, magnetism, and light are manifestations of the same phenomenon: the electromagnetic field. The Maxwell equation, which is a complete series of classical electromagnetism laws, describes light as a wave: a combination of an oscillating electric and magnetic field. Because of the mounting evidence supporting the wave theory, Einstein's ideas were initially filled with great skepticism. Finally, however, the photon model is a favorite. One of the most important pieces of evidence that is advantageous is its ability to explain some of the confusing properties of the photoelectric effect, described in the following sections. Nevertheless, a fixed wave analogy is necessary to help understand other characteristics of light: diffraction, refraction and interference.
Photoelectric effect
In 1887, Heinrich Hertz observed that when light with sufficient frequency touched the metal surface, it emitted electrons. In 1902, Philipp Lenard discovered that the maximum possible energy of the excited electron corresponds to the frequency of light, not the intensity: if the frequency is too low, no electrons are released regardless of their intensity. A strong light ray toward the red end of the spectrum may not produce any electrical potential at all, while a weak light beam toward the purple end of the spectrum will produce higher and higher voltages. The lowest frequency of light that can cause electrons to be emitted, called threshold frequency, is different for different metals. This observation goes against the classical electromagnetic, which predicts that the electron energy must be proportional to the intensity of the radiation. So, when physicists first discovered a device that showed a photoelectric effect, they initially expected that a higher light intensity would produce a higher voltage than a photoelectric device.
Einstein explains the effect by postulating that the light beam is a particle stream ("photon") and that, if the emission of a frequency is f , each photon has an energy equal to hf . An electron is likely to be struck only by one photon, which imparts the most energy hf to the electron. Therefore, the intensity of the rays has no effect and only the frequency determines the maximum energy that can be given to the electron.
To explain the threshold effect, Einstein argues that it takes a certain amount of energy, called the function and is denoted by ? , to remove electrons from metal. The amount of this energy is different for each metal. If the photon energy is less than the work function, then it is not enough energy to remove electrons from the metal. The threshold frequency, f 0 , is the frequency of photons whose energy is the same as the work function:
Jika f lebih besar dari f 0 , energi hf cukup untuk menghapus elektron. Elektron yang dikeluarkan memiliki energi kinetik, E K , yang paling banyak, sama dengan energi foton dikurangi energi yang dibutuhkan untuk mengeluarkan elektron dari logam:
Einstein's description of light as composed of particles extends Planck's idea of ​​quantised energy, namely that a photon of a given frequency, f , gives an unchanging amount of energy, < span> hf . In other words, individual photons can produce more or less energy, but only depending on their frequency. In nature, single photons are rarely encountered. The sun and emission sources available in the 19th century emitted a large number of photons every second, so the importance of the energy carried by each photon is not clear. Einstein's idea that the energy contained in individual light units depending on their frequencies makes it possible to explain experimental results that until now appear to be quite counter-positive. However, although photons are particles, it is still described as having wave frequency properties. Effectively, light notes as particles are insufficient, and their wave-like nature is still needed.
Consequences light is quantised
The relationship between the frequency of electromagnetic radiation and the energy of each photon is why ultraviolet light can cause sunburn, but visible light or infrared can not. Ultraviolet light photons provide a high amount of energy - enough to contribute to cell damage such as occurs in sunburn. Photons of infrared light produce less energy - just enough to warm a person's skin. Thus, infrared lights can warm a large surface, may be large enough to keep people comfortable in a cold room, but can not burn people in the sun.
All photons of the same frequency have identical energy, and all different frequency photons have a proportional (order 1, E foton = hf ) different energy. However, although the energy given by the photons is invariant at a certain frequency, the initial energy state of the electrons in the photoelectric device before the absorption of light is not necessarily uniform. Anomalous results can occur in the case of individual electrons. For example, an electron already excited above the equilibrium level of a photoelectric device may be expelled when absorbing unusually low frequency light. Statistically, however, the characteristic behavior of a photoelectric device reflects the behavior of most of its electrons, which is at their equilibrium level. This point is helpful in understanding the differences between the study of individual particles in quantum dynamics and the study of mass particles in classical physics.
Quantisation of matter: Bohr model of atom
At the beginning of the 20th century, evidence required an atomic model with a negatively charged diffuse electron cloud that surrounds a small, dense, positively charged nucleus. These properties suggest a model in which electrons surround a nucleus like planets orbiting the sun. However, it is also known that the atoms in this model will be unstable: according to classical theory, orbiting electrons are experiencing centripetal acceleration, and therefore must emit electromagnetic radiation, the loss of energy also causes them to rotate toward the nucleus, colliding with it in a fraction of a second.
Secondly, the related puzzle is the atomic emission spectrum. When a gas is heated, it provides light only at discrete frequencies. For example, visible light released by hydrogen is composed of four different colors, as shown in the figure below. The intensity of light at different frequencies is also different. In contrast, white light consists of continuous emissions across the visible frequency range. At the end of the nineteenth century, a simple rule known as Balmer's formula shows how the frequencies of different lines are related to each other, even without explaining why , or making predictions about intensity. The formula also predicts some additional spectral lines in ultraviolet and infrared light that have never been observed at the time. These lines are then observed experimentally, increasing the confidence in the value of the formula.
In 1913 Niels Bohr proposed a new model of atoms that included the quantized orbit of electrons: electrons still orbit the nucleus like planets orbiting around the sun, but they are only allowed to inhabit a particular orbit, not to orbit at any distance. When the atoms emit (or absorb) energy, the electrons do not move in a continuous path from one orbit around the nucleus to another nucleus, as one might expect classically. Instead, the electrons will jump instantly from one orbit to another, releasing the emitted light in the form of photons. The possible energy of the photons released by each element is determined by the energy difference between the orbits, so that the emission spectrum for each element will contain a number of lines.
Starting from just one simple assumption about the rules that orbit must obey, the Bohr model is able to connect the observed spectral lines in the hydrogen emission spectrum to the previously known constants. In the Bohr model, electrons are not allowed to radiate energy continuously and hit an atomic nucleus: once in the nearest orbit permitted, it is stable for good. The Bohr model does not explain why the orbit should be quantized in that way, nor can it make accurate predictions for atoms with more than one electron, or to explain why some of the spectral lines are brighter than others..
Some of the fundamental assumptions of the Bohr model soon proved to be false - but the main result that the discrete line in the emission spectrum is because some of the properties of the electrons in the quantized atom are correct. The way electrons really behave is very different from Bohr atoms, and from what we see in the world of our everyday experience; Modern quantum mechanical models of these atoms are discussed below.
wave-particle duality
Just as light has wave-like and particle-like properties, matter also has properties like waves.
Materials that behave as waves are first shown experimentally for electrons: a beam of electrons can indicate diffraction, such as light beams or water waves. Similar wave-like phenomena are then shown for atoms and even molecules.
Panjang gelombang, ? , terkait dengan objek apa pun terkait dengan momentumnya, p , melalui constant Planck, h :
The relationship, called the de Broglie hypothesis, applies to all types of matter: all matter exhibits particle and wave properties.
The concept of wave-particle duality says that both the classical concept of "particle" and "wave" can fully describe the behavior of quantum-scale objects, both photons and matter. The wave-particle duality is an example of the principle of complementarity in quantum physics. An elegant example of wave-particle duality, a double slit experiment, is discussed in the section below.
Double slot experiment
In a double-slit experiment, as Thomas Young and Augustin Fresnel did in 1827, a beam of light was directed through two adjacent narrow slits, producing a pattern of light interference and dark lines on the screen. If one of the gaps is covered, one may naively hope that the fringe intensity due to the disturbance will be split in two everywhere. In fact, a simpler pattern is seen, a simple diffraction pattern. Closing a slit produces a much simpler pattern diametrically opposite to the open gap. The exact same behavior can be shown in water waves, so a double slit experiment is seen as a demonstration of the nature of light waves.
Variations of double-slit experiments have been performed using electrons, atoms, and even large molecules, and the same type of interference pattern is seen. It has thus been shown that all matter has particle and wave characteristics.
Even if the source intensity is rejected, so that only one particle (eg photons or electrons) passes through the apparatus at a time, the same interference pattern develops over time. Quantum particles act as waves as they pass through the double gap, but as particles when detected. This is a distinctive feature of quantum complementarity: quantum particles act as waves in experiments to measure the nature of their waves, and like particles in experiments to measure their particle-like properties. The point on the detector screen where each individual particle appears is the result of a random process. However, the distribution patterns of many individual particles mimic the diffraction patterns generated by the waves.
App to Bohr model
De Broglie expanded the Bohr model of the atom by showing that electrons in orbit around the nucleus can be considered to have properties like waves. In particular, an electron is only observed in situations that allow waves to stand around the nucleus. An example standing wave is a violin string, which is mounted at both ends and can be made to vibrate. The waves created by the stringed instrument seem to oscillate in place, moving from the top to the trough in an up-and-down motion. The wavelength of the standing wave is related to the length of the vibrating object and the boundary conditions. For example, since the violin string is fixed at both ends, it can carry wavelengths , where l is long and n is a positive integer. De Broglie suggests that the allowed electron orbitals are those whose orbital spheres will be integers of wavelengths. Therefore the electron wavelength determines that only the Bohr orbit from a certain distance from the nucleus is possible. In turn, at any distance from a nucleus smaller than a certain value, it is impossible to form an orbit. The minimum possible distance from the nucleus is called the Bohr radius.
De Broglie's treatment of quantum events served as a starting point for SchrÃÆ'¶dinger as he began to construct wave equations to describe quantum theoretical events.
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In 1922, Otto Stern and Walther Gerlach shot silver atoms through a magnetic field (not homogeneous). In classical mechanics, magnets thrown through a magnetic field may, depending on their orientation (if it points with the north pole up or down, or somewhere in between), deflecting a small or large distance up or down. The atoms that Stern and Gerlach shoot through the magnetic field act in the same way. However, while the magnet can be deflected variable distances, the atoms will always be deflected with a constant distance up or down. This implies that the atomic property corresponding to the magnetic orientation must be quantised, taking one of two values ​​(either up or down), as opposed to freely chosen from any angle.
Ralph Kronig derives the theory that particles such as atoms or electrons behave as if they are spinning, or "spinning", about an axis. Spin will take into account the lost magnetic moment, and allow two electrons in the same orbital to occupy different quantum states if they "spin" in opposite directions, thus fulfilling the exceptions principle. The quantum number represents the meaning (positive or negative) of the round.
The choice of magnetic field orientation used in the Stern-Gerlach experiment is arbitrary. In the animation shown here, the plane is vertical and the atoms are deflected up or down. If the magnet is rotated a quarter of a turn, the atoms are turned left or right. Using a vertical field indicates that the rotation along the vertical axis is quantized, and using the horizontal plane indicates that the rotation along the horizontal axis is quantised.
If, instead of hitting the detector screen, one of the atomic beams coming out of the Stern-Gerlach apparatus is passed to a similarly oriented inhomogeneous magnetic field, all atoms are deflected the same way in this second. field. However, if the second plane is oriented at 90 ° to the first, then half of the atoms are bent one way and the other half, so the atomic rotation of the horizontal and vertical axes is independent of each other. However, if one of these blocks (eg atoms being deflected upwards then gone) is passed to a third magnetic field, oriented in the same way as the first, half the atoms go to one and the other half, though everything goes in that direction the same initially. The action of measuring atomic rotation to the horizontal plane has changed its rotation by observing the vertical plane.
The Stern-Gerlach experiment shows a number of important features of quantum mechanics:
- a feature of the natural world has been shown to be quantised, and is only capable of retrieving certain discrete values ​​
- the particle has an intrinsic angular momentum which is very similar to the classical rotating angle of a object Measures
- change the system measured in quantum mechanics. Just rotate an object in one knowable direction, and observe another turn in the direction of destroying the original information about the rotation. The quantum mechanics
- is probabilistic: whether the spin of individual atoms sent to the equipment is positive or negative random.
Development of modern quantum mechanics
In 1925, Werner Heisenberg tried to solve one of the problems that the Bohr model missed, explaining the intensity of the different lines in the hydrogen emission spectrum. Through a series of mathematical analogies, he wrote analog quantum mechanics for classical intensity calculations. Shortly thereafter, Heisenberg's colleague Max Born realized that Heisenberg's method of calculating probabilities for transitions between different energy levels can be expressed using matrix matrix concepts.
In the same year, based on the de Broglie hypothesis, Erwin SchrÃÆ'¶dinger developed an equation describing the behavior of quantum mechanical waves. The mathematical model, called the SchrÃÆ'¶dinger equation after its author, is the center of quantum mechanics, defines the permissible stationary status of the quantum system, and illustrates how the quantum status of a physical system changes over time. The wave itself is explained by a mathematical function known as "wave function". SchrÃÆ'¶dinger says that the wave function provides "the means to predict the likelihood of measurement results".
SchrÃÆ'¶dinger was able to calculate the energy levels of hydrogen by treating hydrogen atomic electrons as classical waves, moving in a potential electricity well created by protons. This calculation accurately reproduces the energy level of the Bohr model.
In May 1926, SchrÃÆ'¶dinger proved that Heisenberg's matrix mechanics and wave mechanics themselves make the same predictions about the nature and behavior of electrons; Mathematically, both theories have an underlying general form. But the two men disagreed with the interpretation of their mutual theory. For example, Heisenberg accepts the theoretical predictions of the leap of electrons between orbitals in an atom, but Schrödinger hopes that a theory based on the properties of a continuous wave can avoid what he calls (as paraphrased by Wilhelm Wien) "this quantum nonsense jump. "
Copenhagen interpretation
Bohr, Heisenberg, and others try to explain what the experimental results and mathematical models really mean. Their description, known as the Copenhagen interpretation of quantum mechanics, aims to describe the nature of reality being examined by measurement and described by mathematical formulations of quantum mechanics.
Prinsip-prinsip utama penafsiran Kopenhagen adalah:
- Suatu sistem sepenuhnya dijelaskan oleh fungsi gelombang, biasanya diwakili oleh huruf Yunani ("psi"). (Heisenberg)
- Bagaimana perubahan dari waktu ke waktu diberikan oleh persamaan Schrödinger.
- Deskripsi alam pada dasarnya bersifat probabilistik. Probabilitas suatu peristiwa - misalnya, di mana pada layar partikel muncul dalam dua percobaan celah - terkait dengan kuadrat nilai absolut dari amplitudo fungsi gelombangnya. (Lahir aturan, karena Max Born, yang memberikan arti fisik untuk fungsi gelombang dalam interpretasi Kopenhagen: amplitudo probabilitas)
- Tidak mungkin mengetahui nilai dari semua properti sistem pada saat yang sama; sifat-sifat yang tidak dikenal dengan presisi harus dijelaskan oleh probabilitas. (Prinsip ketidakpastian Heisenberg)
- Materi, seperti energi, menunjukkan dualitas gelombang-partikel. Eksperimen dapat mendemonstrasikan sifat seperti partikel materi, atau sifat-sifatnya yang mirip gelombang; tetapi tidak keduanya pada saat bersamaan. (Prinsip Komplementaritas karena Bohr)
- Perangkat pengukur pada dasarnya adalah perangkat klasik, dan mengukur properti klasik seperti posisi dan momentum.
- Deskripsi mekanika kuantum sistem besar harus mendekati deskripsi klasik. (Prinsip Korespondensi Bohr dan Heisenberg)
The consequences of these principles are discussed in more detail in the following subsections.
Uncertainty principle
Suppose it is desired to measure the position and velocity of an object - eg a car through a radar speed trap. It can be assumed that the car has a fixed position and speed at any given time. How accurately these values ​​can be measured depends on the quality of the measuring equipment. If the precision of the measuring instrument is improved, it gives a result that is close to the true value. It may be assumed that the speed of the car and its position can be determined operationally and measured simultaneously, as precisely as desired.
In 1927, Heisenberg proved that this last assumption was not true. Quantum mechanics shows that certain pairs of physical properties, such as position and velocity, can not be measured simultaneously, nor are they defined in operational terms, with arbitrary precision: the more precisely one property is measured, or defined in operational terms, the more inappropriate the others can be. This statement is known as the uncertainty principle. The principle of uncertainty is not just a statement about the accuracy of our measuring instruments, but, more deeply, is about the conceptual nature of measurable quantities - the assumption that the car simultaneously defines the position and velocity of not working in quantum mechanics. On a car and people scale, this uncertainty can be ignored, but when dealing with atoms and electrons they become critical.
Heisenberg gave, for illustration, the measurement of the position and momentum of an electron using a light photon. In measuring the position of electrons, the higher the frequency of photons, the more accurately the measurement of the position of the impact of photons with electrons, but the greater the electron interference. This is because of the impact with photons, the electrons absorb a certain amount of random energy, rendering the measurements obtained from the momentum increasingly uncertain (momentum is the speed multiplied by mass), because one must measure the post-impact of disturbed momentum from the crash product and not its original momentum. With low frequency photons, interference (and hence uncertainty) in less momentum, but so does the impact position measurement accuracy.
The uncertainty principle shows mathematically that the product of uncertainty in the position and momentum of the particle (momentum is the speed multiplied by mass) can never be less than a certain value, and that this value is related to Planck's constant.
The wave function collapses
The collapse of the wave function is a forced expression for whatever has just happened when it becomes appropriate to replace the description of the uncertain state of the system by the system description in the exact state. The explanation for the nature of the process is definitely controversial. Anytime before the photon "appears" on the detection screen, it can only be explained by a set of probabilities for its appearance. When it appears, for example in an electronic camera CCD, the time and space in which it interacts with the device is known within very strict limits. However, the photon has disappeared, and the wave function has been lost with it. Instead, some physical changes on the detection screen have emerged, for example, an open spot on a photographic film, or a potential electrical change in some CCD cells.
Eigenstates and eigenvalues ​​
- For a more detailed introduction to this subject, see: Introduction to eigenstates
Because of the uncertainty principle, statements about the position and momentum of a particle can only give the probability that the position or momentum has some numerical value. Therefore, it is necessary to clearly define the difference between the state of something uncertain, such as electrons in the cloud of probability, and the state of something having a definite value. When an object can certainly be "pinned" in some ways, it is said to have eigenstate.
In the Stern-Gerlach experiment discussed above, the atomic rotation of the vertical axis has two eigenstates: up and down. Before measuring it, we can only say that each individual atom has the same chance of being found spinning or spinning down. The measurement process causes the wave function to collapse into one of two states.
The spin eigenstates about the vertical axis do not simultaneously spin eigenstates about the horizontal axis, so these atoms have the same probability found to have spin values ​​about the horizontal axis. As described in the above section, measuring the rotation of the horizontal axis can allow the rotating atom to rotate: measuring its rotation of the horizontal axis collapsing its wave function into one of the eigenstates of this measurement, meaning it is no longer in the spin eigenstate about the vertical axis , so it can take good value.
The Pauli exclusion principle
In 1924, Wolfgang Pauli proposed a new quantum degree of freedom (or quantum number), with two possible values, to resolve the inconsistencies between the observed molecular spectrum and the predictions of quantum mechanics. In particular, the spectrum of a hydrogen atom has a doublet, or a pair of distinct lines with a small amount, in which only one line is expected. Pauli formulates his exclusion principle, stating that "No atom can exist in a quantum state like two electrons in [it] have the same set of quantum numbers."
A year later, Uhlenbeck and Goudsmit identified a new level of Pauli freedom with a property called spin whose effect was observed in the Stern-Gerlach experiment. Application
to hydrogen atom
The Bohr atom model is essentially a planet, with electrons orbiting around the nuclear "sun". However, the uncertainty principle states that an electron can not simultaneously have the exact location and velocity in the way the planet does. Instead of a classical orbit, electrons are said to inhabit the atomic orbitals. Orbital is the "cloud" of possible locations where electrons can be found, the probability distribution rather than the exact location. Each orbital is a three-dimensional, not two-dimensional orbit, and is often described as a three-dimensional region where there is a 95 percent chance of finding electrons.
SchrÃÆ'¶dinger is able to calculate the energy levels of hydrogen by treating hydrogen atom electrons as waves, represented by "wave functions" ? , in potential electric potential, V , created by protons. The solution for the Schrödinger equation is the probability distribution for the position of the electron and the location. Orbitals have different shapes in three dimensions. Different orbital energies can be calculated, and they accurately correspond to the energy levels of the Bohr model.
In the SchrÃÆ'¶dinger image, each electron has four properties:
- An "orbital" designation, which indicates whether the particle waves are one that is closer to the nucleus with less energy or one farther away from the nucleus with more energy;
- "Shape" of orbital, spherical or otherwise;
- "Tilt" of the orbital, determining the orbital magnetic moment around z -axis.
- The "spin" of the electron.
The collective name for this property is the electron quantum state. The quantum state can be explained by assigning a number to each of these properties; this is known as the quantum number of electrons. The quantum state of the electron is represented by its wave function. The Pauli exclusion principle requires that no two electrons in the atom may have the same value of all four numbers.
Properti pertama yang mendeskripsikan orbital adalah bilangan kuantum utama, n , yang sama dengan model Bohr. n menunjukkan tingkat energi dari setiap orbital. Nilai yang mungkin untuk n adalah bilangan bulat:
The next quantum number, the azimuthal quantum number, denoted l , describes the orbital shape. The shape is a consequence of orbital angular momentum. The angular momentum symbolizes the resistance of rotating objects to accelerate or slow down under the influence of external forces. The azimuth quantum number represents the angular momentum of the electron orbital around its nucleus. Possible values ​​for l are integers from 0 to n - 1 (where n is the primary quantum number of electrons):
The shape of each orbital is usually called by letter, not by its azimuth quantum number. The first form ( l = 0) is denoted by the letter s (mnemonic creature " s phere "). The next form is denoted by the letter p and has a dumbbell shape. Other orbitals have more complex forms (see atomic orbitals), and are denoted by the letters d , f , < span> g , etc.
Bilangan kuantum ketiga, bilangan kuantum magnetik, menggambarkan momen magnetik elektron, dan dilambangkan dengan m l (atau hanya m ). Nilai yang mungkin untuk m l adalah bilangan bulat dari - l ke l (di mana l adalah jumlah kuantum azimut elektron):
Quantum quantum numbers measure the component of angular momentum in a particular direction. Selection of arbitrary direction, conventionally the z-direction is selected.
The fourth quantum number, the spin quantum number (related to the "orientation" of the electron spin) is represented by m s / 2 or - 1 / 2 .
Chemist Linus Pauling writes, for example:
In the case of a helium atom with two electrons in a 1 s orbitals, the Pauli Exclusion Principle requires that two electrons differ in the value of one quantum number. Their values ​​are n , l , and m l is the same. Thus they must differ in the value of m s , which can have 1 / 2 for one electron and - 1 / 2 for another. "
This is the basic structure and symmetry of the atomic orbitals, and the way the electrons fill it, leading to the organization of the periodic table. The way the atomic orbitals of different atoms combine to form molecular orbital determines the structure and strength of chemical bonds between atoms.
Dirac wave equation
In 1928, Paul Dirac extended the Pauli equation, which describes spinning electrons, to explain special relativity. The result is a theory that is handled correctly with events, such as the speed at which an electron orbits a nucleus, occurs at most of the speed of light. By using the simplest electromagnetic interaction, Dirac was able to predict the magnetic moment values ​​associated with the electron spin, and found the value observed experimentally, which is too large to be a spinning ball that is governed by classical physics. He was able to break the spectral lines of hydrogen atoms, and to reproduce from the first physical principles, Sommerfeld's successful formula for the fine structure of the hydrogen spectrum.
The dirac equation sometimes produces a negative value for energy, where it proposes a new solution: it expresses the existence of an antielectron and a dynamic vacuum. This led to the theory of many-particle quantum fields.
Quantum entanglement
Pauli exclusion principle says that two electrons in one system can not be in the same condition. Nature leaves the possibility open, however, that two electrons can have both states "superimposed" on top of each. Remember that the simultaneous wave function of the double slit arrives on the detection screen in a superposition state. Nothing is sure until the superimposed wave "collapses". At that moment an electron appears somewhere corresponding to the probability that is the square of the absolute value of the number of amplitude appreciated by the complex of two superimposed waveforms. The situation there is very abstract. Concrete ways of thinking about entangled photons, photons in which two opposing states are superimposed on each of them in the same event, are as follows:
Imagine that the superposition of a country labeled blue , and other states labeled red then appear (in imagination) as the purple state. Two photons are produced as a result of the same atomic event. Perhaps they are generated by crystal excitation that typically absorb certain photons of frequency and emit two half-original photons of the original frequency. So two photons came out purple. If the experiment now performs several experiments that determine whether one of the photons is blue or red , then the experiment that converts the involved photons from the superposition blue and red characteristics for photons that have only one of these characteristics. The problem Einstein had with the situation imaginable was that if one of these photons continues to bounce between the mirror in the laboratory on earth, and the other has traveled halfway to the nearest star, when his twin is made to reveal itself as either blue or red, it means that the distant photon must now lose its purple status as well. So whenever it may be investigated after its twin is measured, it will always appear in a state contrary to whatever the twin has revealed.
In attempting to show that quantum mechanics is not a complete theory, Einstein began with predictive theories that two or more particles interacting in the past can appear highly correlated when their various properties are then measured. He tried to explain this apparent interaction in the classic way, through their past, and preferably not by some "spooky action from a distance." This argument is worked out in famous papers, Einstein, Podolsky, and Rosen (1935: abbreviated EPR), establishing what is now called the EPR paradox. Assuming what is now commonly referred to as local realism, the EPR seeks to demonstrate from the quantum theory that a particle has a position and momentum simultaneously, whereas according to the Copenhagen interpretation, only one of two traits actually exists and only at that moment is measured. EPR concludes that quantum theory is incomplete because it refuses to consider physical properties that are objectively present in nature. (Einstein, Podolsky, & Rosen 1935 is currently Einstein's most widely quoted publication in physics journals.) That same year, Erwin SchrÃÆ'¶dinger used the word "winding" and declared: "I would not call it one but the nature of the quantum mechanical characteristics. "The question of whether entanglement is a real condition is debatable. Bell's inability is the most powerful challenge to Einstein's claim.
Quantum field theory
The idea of ​​quantum field theory began in the late 1920s with the British physicist Paul Dirac, when he tried to measure the electromagnetic field - a procedure for constructing a quantum theory beginning with classical theory.
The field of in physics is "a region or space in which certain effects (such as magnets) exist." Other effects that manifest themselves as terrain are gravity and static electricity. In 2008, physicist Richard Hammond wrote it
Sometimes we distinguish between quantum mechanics (QM) and quantum field theory (QFT). QM refers to a system in which the number of particles is fixed, and fields (such as electromechanical fields) are continuous classical entities. QFT... goes a step further and allows the creation and destruction of particles....
He adds, however, that quantum mechanics is often used to refer to "the whole idea of ​​quantum views."
In 1931, Dirac proposed the existence of particles which came to be known as antimatter. Dirac shared the Nobel Prize in Physics for 1933 with Schrüdinger, "for the discovery of new, productive forms of atomic theory."
On the surface, quantum field theory allows an infinite number of particles, and passes it to the theory itself to predict how much and by which the probability or number should be. When developed further, theories often conflict with observations, so that the creation and destruction of operators can be empirically tied up. Furthermore, empirical conservation legislation like mass-energy suggests certain restrictions on the mathematical form of theory, which is mathematically speaking fussy. The latter facts both serve to make quantum field theory difficult to handle, but also lead to further restrictions on acceptable form theory; complications are listed below under the rubric of renormalization.
Quantum electrodynamics
Quantum electrodynamics (QED) is the name of the quantum theory of electromagnetic forces. Understanding QED begins with understanding electromagnetism. Electromagnetism can be called "electrodynamics" because it is a dynamic interaction between electrical and magnetic forces. Electromagnetism begins with an electrical charge.
The electrical charge is the source, and creates, the electric field. The electric field is a field that gives force to every particle that carries an electrical charge, at any point in space. These include electrons, protons, and even quarks, among others. When force is given, electrical charge moves, current flows and a magnetic field is generated. The changing magnetic field, in turn, causes an electric current (often moving electrons). The physical features of charged particles interacting, electric currents, electric fields, and magnetic fields are called electromagnetism.
In 1928, Paul Dirac produced the quantum theory of relativistic electromagnetism. It is the ancestor of modern quantum electrodynamics, because it contains important elements of modern theory. However, the problem of insoluble infinity is developed in this relativistic quantum theory. Years later, renormalization largely solves this problem. Originally viewed as a suspect, a temporary procedure by some of its originators, renormalization was finally embraced as an important and independent tool in QED and other fields of physics. Also, in the late 1940s, Feynman diagrams illustrate all possible interactions associated with a given event. The diagram shows that the electromagnetic force is the interaction of photons between the particles interacting with each other.
The Sheep Shift is an example of an experimental verified quantum electrodynamic prediction. This is the effect in which the quantum properties of an electromagnetic field make the energy levels in atoms or ions to deviate slightly from what they should be. As a result, the spectral lines can be shifted or split.
Similarly, in a propagating free electromagnetic wave, the current may also be only an abstract displacement current, rather than involving a charge operator. In QED, the full description makes the use of important virtual particles important. There, QED again validates an earlier and somewhat mysterious concept.
Standard Model
In the 1960s physicists realized that QED was damaged at a very high energy. Of this inconsistency, the Standard Model of particle physics is found, which improves the higher energy interference in theory. This is an additional quantum field theory that unites electromagnetic interaction and weak interaction into a single theory. This is called electroweak theory.
In addition the Standard Model contains the high energy union of electro-leak theory with strong strength, which is described by quantum chromodynamics. It also postulates connections with gravity as another measuring theory, but the relationship is in 2015 still poorly understood. The prediction of Higgs's particle theory to explain the mass of inertia has been a recent empirical test in the Large Hadron Collider, and thus the Standard model is now regarded as a more complete and basic description of particle physics as we know it.
Interpretation
Physical measurements, equations, and predictions related to quantum mechanics are all consistent and have a very high level of confirmation. However, the question of what these abstract models say about the nature of the real world has received a competitive answer.
Apps
Applications of quantum mechanics include lasers, transistors, electron microscopes, and magnetic resonance imaging. Special classes of quantum mechanics applications are related to macroscopic quantum phenomena such as superfluid helium and superconductors. Semiconductor studies led to the discovery of diodes and transistors, which are indispensable for modern electronics.
Source of the article : Wikipedia
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