“quantum mechanics”的概念、定义、翻译、参考文献-科学参考

quantum mechanics

Physics

A system of mechanics based on quantum theory, which arose out of the failure of classical mechanics and electromagnetic theory to provide a consistent explanation of both electromagnetic waves and atomic structure. Many phenomena at the atomic level puzzled physicists at the beginning of the 20th century because there seemed to be no way of explaining them without making use of incompatible concepts. One such phenomenon was the emission of electrons from the surface of a metal illuminated by light. Einstein realized that the classical description of light as a wave on an electromagnetic field could not explain this photoelectric effect, as it is called. Experiments showed that electrons would be emitted only if the incident light was of a sufficiently short wavelength, while the intensity of the light appeared not to be relevant. It seemed not to make sense that small ripples of short wavelength could easily knock electrons out of the metal, but a huge tidal wave of long wavelength could not. In 1905 Einstein abandoned classical mechanics and sought an explanation of this photoelectric effect in Planck’s work on thermal radiation (see Planck’s radiation law). In this work light energy is regarded as being imparted to matter in discrete packets rather than continuously, as one might expect from a wave. Einstein assumed that in the photoelectric effect, light behaves as a shower of particles, each with energy E given by Planck’s expression:

$E = h f,$

where f is the light’s frequency and h is the Planck constant. Each particle of light, which Einstein called a photon, would impart its energy to a single electron in the metal. The electron would be liberated only if the photon could impart at least the required amount of energy. However many photons were falling on the surface of the metal, no electrons would be liberated unless individual photons had the required energy (hf) to break the attractive forces holding the electrons in the metal. This elegantly quantified reversion to Newton’s corpuscular theory of light by Einstein was one of the milestones in the development of quantum mechanics.

Further verification that light could indeed behave as a shower of particles came from the Compton effect. In Compton scattering, X-radiation is scattered off an electron in a manner that resembles a particle collision. The momentum imparted to the electron can be predicted by assuming that the X-ray possesses the momentum of a photon. An expression for photon momentum is suggested by the classical theory of radiation pressure. It is known that if energy is transported by an electromagnetic wave at a rate W joules per unit area per second, the wave exerts a radiation pressure W/c, where c is the speed of light. Planck’s expression for the energy of photons therefore led to an equivalent expression for the momentum p of these photons:

$p = h / λ,$

where λ‎ is the wavelength of the light. Experimental studies of the Compton effect produce results in good agreement with this expression.

Both the photoelectric effect and the Compton effect imply that light imparts energy and momentum to matter in the form of packets. It is as if energy and momentum are fundamental ‘currencies’ of physical interaction, and that these currencies exist in denominations that are all multiples of the Planck constant. These quantities are said to be ‘quantized’ and a packet of energy or momentum is called a quantum. Quantum mechanics is essentially concerned with the exchange of these quanta of energy and momentum. For more than a century before the birth of quantum mechanics, experiments had indicated that light behaves as a wave. The successful explanation of the photoelectric and Compton effects demonstrated that in some situations light interacts with matter as if it is a shower of particles. The principle that two models are required to explain the nature of light was called by Niels Bohr complementarity. This principle had been used by the French aristocrat Louis de Broglie, who suggested in 1923 that particles of matter might also behave as waves in certain circumstances.

Louis de Broglie received the Nobel Prize for this idea in 1929 after the successful measurement of the de Broglie wavelength of an electron in 1927 by Clinton Davisson and Lester Germer, who had observed the diffraction of electrons by single crystals of nickel. The behaviour of individual electrons seemed random and unpredictable, but when a large number had passed through the crystal a typical diffraction pattern emerged. This provided proof that the electron, which until then had been thought of simply as a particle of matter, could under the right circumstances exhibit wavelike properties. Classical mechanics and electromagnetism were based on two kinds of entity: matter and fields. In classical physics, matter consists of particles and waves are oscillations on a field. Quantum mechanics blurs the distinction between matter and field. Modern physicists are forced to concede that the universe is made up of entities that exhibit a wave–particle duality.

A new representation of matter and field is needed to fully appreciate this wave–particle duality. In quantum mechanics, an electron is represented by a complex number called a wave function that depends on time and space coordinates. The wave function behaves like a classical wave displacement on a medium (e.g. on a string), exhibiting wave behaviour, interference, diffraction, etc. However, unlike a classical wave displacement, the wave function is essentially a complex quantity. Since an electron’s observable properties do not involve complex numbers, it follows that an electron’s wave function cannot itself be identified with a single physical property of the electron. The diffraction of electrons observed by Davisson and Germer revealed that, although the behaviour of the individual electrons is random and unpredictable, when a large number have passed through the apparatus, a diffraction pattern is formed whose intensity distribution is proportional to the intensity of the associated wave function. The intensity of the wave function, Ψ‎, is the square of its absolute value |Ψ‎|². Therefore, although an electron’s wave function itself has no physical significance, the square of its absolute value at a point turns out to be proportional to the probability of finding an electron at that point. The electron wave function must satisfy a wave equation based on the conservation of energy and momentum for the electron. There are two main ways of treating this wave equation: a classical or a relativistic treatment. The resulting wave equations are called eigenvalue equations because they have the same form as equations in a branch of mathematics called eigenvalue problems, i.e.

$Ω Ψ = ω Ψ,$

where Ω‎ is some mathematical operation (multiplication by some number, differentiation, etc.) on the wave function ψ‎ and ω‎, called the eigenvalue in quantum mechanics, is always a real number. In such an equation the wave function is often called the eigenfunction. This form of treatment of quantum mechanics is known as wave mechanics (see also Schrödinger equation).

The energy E and momentum p of an electron are associated with the frequency f and wavelength λ‎ of the electron’s wave using the expressions E=hf and p=h/λ‎. While the wave equation expresses the behaviour of the wavelike properties of a particle, it does not define the physical attributes it has as a particle. As a particle, the electron has an easily defined spatial and temporal position, not possessed by an oscillation of some kind of field, whose influence extends over a region of space and time. The incompatibility of these two views of the electron leads to the Heisenberg uncertainty principle. Heisenberg recognized that if matter had wavelike properties, the physical attributes normally associated with matter (position, momentum, kinetic energy, etc.) would have to be expressed in a statistical, rather than a deterministic, manner. This is illustrated by the electron diffraction patterns of Davisson and Germer. Individual electrons somehow fell onto the apparatus to form a pattern statistically consistent with the intensity of a wave function. It is as if the final wave function were made up of a superposition of all the possible positions that the electrons could fall onto, the waves of electrons constructively and destructively interfering to form the final diffraction pattern.

It is known that a clever superposition of waves of different wavelengths can lead to a construction of a wave packet of finite extension (see Fourier analysis). However, to produce a packet that exists at a point of zero width requires an infinite number of waves to superimpose. Heisenberg realized that these packets of waves must account for the way in which matter particles, such as electrons, could retain some semblance of their particle-like qualities. However, this must also mean that there is an inherent uncertainty in position and momentum associated with electrons and indeed all particles of matter (see uncertainty principle). Since waves of different wavelength correspond to different possible momentum values of an electron, a superposition of such waves to form a particle at a point would correspond to an infinite uncertainty in the momentum of the electron. Therefore the more one knows about the position of an electron the less one will know about its momentum and vice versa. A similar uncertainty between the energy of the electron and its temporal position also exists. Quantities that are related by such an uncertainty principle are said to be incompatible.

An alternative to the wave-mechanical treatment of quantum mechanics is an equivalent formalism called matrix mechanics, which is based on matrices. See also Bell’s theorem; hidden-variables theory.

Chemistry

A system of mechanics that was developed from quantum theory and is used to explain the properties of atoms and molecules. Using the energy quantum as a starting point it incorporates Heisenberg’s uncertainty principle and the de Broglie wavelength to establish the wave-particle duality on which the Schrödinger equation is based. This form of quantum mechanics is called wave mechanics. An alternative but equivalent formalism, matrix mechanics, is based on matrices.

Chemical Engineering

A branch of mechanics that is based on the quantum theory used for interpreting and understanding the behaviour of elementary particles, atoms, and molecules, which do not obey Newtonian mechanics.

Electronics and Electrical Engineering

The theory of atomic and nuclear systems, providing a mathematical framework for quantum theory. In 1926 Erwin Schrödinger developed a wave equation to describe the behaviour of elementary particles in materials by treating them as matter waves or de Broglie waves, following the hypothesis by de Broglie that electrons, etc., could be described both in terms of particle-like and wave-like behaviour. This wave equation, now known as the Schrödinger equation, described the motion of de Broglie waves in a given potential energy, for instance in a potential well, or inside a crystalline solid. The Schrödinger equation for the electron, for example, is:
$(\frac{- ℏ^{2}}{2 m}) \nabla^{2} Ψ + V Ψ = j ℏ (\frac{\partial Ψ}{\partial t})$
where $ℏ$ is the rationalized Planck constant, m is the mass of the electron, V is the potential in which it moves, and ∇² is the Laplace operator. This is a differential equation in the quality Ψ, which is known as the wavefunction; this is a complex quality that can be thought of as a measure of the amplitude of the de Broglie wave describing the electron. Hence the square of the wavefunction is a measure of the intensity of the electron wave, or
$| Ψ (x, y, z, t) |^{2} d x d y d z$
gives the probability of finding an electron at time t in the incremental volume element dxdydz located at (x, y, z).
Solutions of the Schrödinger equation can be found analytically only for simple examples, usually by eliminating the time dependence by assuming the de Broglie waves have a typical exp(jωt) time dependence and solving the time-independent Schrödinger equation:
$(\frac{- ℏ^{2}}{2 m}) \nabla^{2} ψ + V ψ = E ψ$
Now ψ is the time-independent component of the wavefunction and E is the total energy of the electron, and the equation describes the physical variation of the electron wavefunction in space. Analytical solutions of the time-independent Schrödinger equation can be used to provide valuable insight into the behaviour of electrons in atoms and solids. For example, the solution of a particle in a potential well leads to the concept of quantum numbers describing the allowed energy states in the well. This structure is known as a quantum well. By using a periodic value for the potential energy V, solutions of the Schrödinger equation are found to describe the origins of energy-band structure in crystalline solids; this is the Kronig–Penney model of energy-band structure.
https://www.livescience.com/33816-quantum-mechanics-explanation.html A short introduction to quantum mechanics, with links for further reading

Philosophy

Quantum theory, introduced by Max Planck (1858–1947) in 1900, was the first serious scientific departure from Newtonian mechanics. It involved supposing that certain physical quantities can only assume discrete values. In the following two decades it was applied successfully to different physical problems by Einstein and the Danish physicist Niels Bohr (1885–1962). It was superseded by quantum mechanics in the years following 1924, when the French physicist Louis de Broglie (1892–1987) introduced the idea that a particle may also be regarded as a wave. The Schrödinger wave equation relates the energy of a system to a wave function: the square of the amplitude of the wave is proportional to the probability of a particle being found in a specified position. The wave function expresses the lack of possibility of defining both the position and momentum of a particle (see Heisenberg uncertainty principle). The allowed wave functions, or ‘eigenfunctions’, have ‘eigen-values’ that describe stationary states of the system.
Part of the difficulty with the notions involved is that a system may be in an indeterminate state at a time, characterized only by the probability of some result for an observation, but then ‘become’ determinate (‘the collapse of the wave packet’) when an observation is made (see also Einstein-Podolsky-Rosen thought experiment, Schrödinger’s cat). It is as if there is nothing but a potential for observation or a probability wave before observation is made, but when an observation is made the wave becomes a particle. The wave-particle duality seems to block any way of conceiving of physical reality in quantum terms. In the famous two-slit experiment, an electron is fired at a screen with two slits (like a tennis ball thrown at a wall with two doors in it). If one puts detectors at each slit, every electron passing the screen is observed to go through exactly one slit. But when the detectors are taken away, the electron acts like a wave process going through both slits, and interfering with itself. A particle such as an electron is usually thought of as always having an exact position, but its wave nature ensures that the amplitude of its waves is not absolutely zero anywhere (there is therefore a finite probability of it ‘tunnelling’ from one position to emerge at another).
The unquestionable success of quantum mechanics has generated a large philosophical debate about its ultimate intelligibility and its metaphysical implications. The wave-particle duality is already a departure from ordinary ways of conceiving of things in space, and its difficulty is compounded by the probabilistic nature of the fundamental states of a system as they are conceived in quantum mechanics. Philosophical options for interpreting quantum mechanics have included variations of the belief that it is at best an incomplete description of a better-behaved classical underlying reality (Einstein), the Copenhagen interpretation according to which there are no objective unobserved events in the micro-world (Niels Bohr and W. K. Heisenberg, 1901–76), an ‘acausal’ view of the collapse of the wave packet (J. von Neumann, 1903–57), and a ‘many worlds’ interpretation in which time forks perpetually towards innumerable futures, so that different states of the same system exist in different parallel universes (H. Everett).
In recent years the proliferation of subatomic particles (there are 36 kinds of quark alone, in six flavours and three colours) has prompted physicists to look in various directions for unification. One avenue of approach is superstring theory, in which the four-dimensional world is thought of as the upshot of the collapse of a ten-dimensional world, with the four primary physical forces (gravity, electromagnetism, and the strong and weak nuclear forces) becoming seen as the result of the fracture of one primary force. While the scientific acceptability of such theories is a matter for physics, their ultimate intelligibility plainly requires some philosophical reflection. See also Bell’s theorem.

单词	quantum mechanics
释义	quantum mechanics Physics A system of mechanics based on quantum theory, which arose out of the failure of classical mechanics and electromagnetic theory to provide a consistent explanation of both electromagnetic waves and atomic structure. Many phenomena at the atomic level puzzled physicists at the beginning of the 20th century because there seemed to be no way of explaining them without making use of incompatible concepts. One such phenomenon was the emission of electrons from the surface of a metal illuminated by light. Einstein realized that the classical description of light as a wave on an electromagnetic field could not explain this photoelectric effect, as it is called. Experiments showed that electrons would be emitted only if the incident light was of a sufficiently short wavelength, while the intensity of the light appeared not to be relevant. It seemed not to make sense that small ripples of short wavelength could easily knock electrons out of the metal, but a huge tidal wave of long wavelength could not. In 1905 Einstein abandoned classical mechanics and sought an explanation of this photoelectric effect in Planck’s work on thermal radiation (see Planck’s radiation law). In this work light energy is regarded as being imparted to matter in discrete packets rather than continuously, as one might expect from a wave. Einstein assumed that in the photoelectric effect, light behaves as a shower of particles, each with energy E given by Planck’s expression: $E = h f,$ where f is the light’s frequency and h is the Planck constant. Each particle of light, which Einstein called a photon, would impart its energy to a single electron in the metal. The electron would be liberated only if the photon could impart at least the required amount of energy. However many photons were falling on the surface of the metal, no electrons would be liberated unless individual photons had the required energy (hf) to break the attractive forces holding the electrons in the metal. This elegantly quantified reversion to Newton’s corpuscular theory of light by Einstein was one of the milestones in the development of quantum mechanics. Further verification that light could indeed behave as a shower of particles came from the Compton effect. In Compton scattering, X-radiation is scattered off an electron in a manner that resembles a particle collision. The momentum imparted to the electron can be predicted by assuming that the X-ray possesses the momentum of a photon. An expression for photon momentum is suggested by the classical theory of radiation pressure. It is known that if energy is transported by an electromagnetic wave at a rate W joules per unit area per second, the wave exerts a radiation pressure W/c, where c is the speed of light. Planck’s expression for the energy of photons therefore led to an equivalent expression for the momentum p of these photons: $p = h / λ,$ where λ‎ is the wavelength of the light. Experimental studies of the Compton effect produce results in good agreement with this expression. Both the photoelectric effect and the Compton effect imply that light imparts energy and momentum to matter in the form of packets. It is as if energy and momentum are fundamental ‘currencies’ of physical interaction, and that these currencies exist in denominations that are all multiples of the Planck constant. These quantities are said to be ‘quantized’ and a packet of energy or momentum is called a quantum. Quantum mechanics is essentially concerned with the exchange of these quanta of energy and momentum. For more than a century before the birth of quantum mechanics, experiments had indicated that light behaves as a wave. The successful explanation of the photoelectric and Compton effects demonstrated that in some situations light interacts with matter as if it is a shower of particles. The principle that two models are required to explain the nature of light was called by Niels Bohr complementarity. This principle had been used by the French aristocrat Louis de Broglie, who suggested in 1923 that particles of matter might also behave as waves in certain circumstances. Louis de Broglie received the Nobel Prize for this idea in 1929 after the successful measurement of the de Broglie wavelength of an electron in 1927 by Clinton Davisson and Lester Germer, who had observed the diffraction of electrons by single crystals of nickel. The behaviour of individual electrons seemed random and unpredictable, but when a large number had passed through the crystal a typical diffraction pattern emerged. This provided proof that the electron, which until then had been thought of simply as a particle of matter, could under the right circumstances exhibit wavelike properties. Classical mechanics and electromagnetism were based on two kinds of entity: matter and fields. In classical physics, matter consists of particles and waves are oscillations on a field. Quantum mechanics blurs the distinction between matter and field. Modern physicists are forced to concede that the universe is made up of entities that exhibit a wave–particle duality. A new representation of matter and field is needed to fully appreciate this wave–particle duality. In quantum mechanics, an electron is represented by a complex number called a wave function that depends on time and space coordinates. The wave function behaves like a classical wave displacement on a medium (e.g. on a string), exhibiting wave behaviour, interference, diffraction, etc. However, unlike a classical wave displacement, the wave function is essentially a complex quantity. Since an electron’s observable properties do not involve complex numbers, it follows that an electron’s wave function cannot itself be identified with a single physical property of the electron. The diffraction of electrons observed by Davisson and Germer revealed that, although the behaviour of the individual electrons is random and unpredictable, when a large number have passed through the apparatus, a diffraction pattern is formed whose intensity distribution is proportional to the intensity of the associated wave function. The intensity of the wave function, Ψ‎, is the square of its absolute value \|Ψ‎\|². Therefore, although an electron’s wave function itself has no physical significance, the square of its absolute value at a point turns out to be proportional to the probability of finding an electron at that point. The electron wave function must satisfy a wave equation based on the conservation of energy and momentum for the electron. There are two main ways of treating this wave equation: a classical or a relativistic treatment. The resulting wave equations are called eigenvalue equations because they have the same form as equations in a branch of mathematics called eigenvalue problems, i.e. $Ω Ψ = ω Ψ,$ where Ω‎ is some mathematical operation (multiplication by some number, differentiation, etc.) on the wave function ψ‎ and ω‎, called the eigenvalue in quantum mechanics, is always a real number. In such an equation the wave function is often called the eigenfunction. This form of treatment of quantum mechanics is known as wave mechanics (see also Schrödinger equation). The energy E and momentum p of an electron are associated with the frequency f and wavelength λ‎ of the electron’s wave using the expressions E=hf and p=h/λ‎. While the wave equation expresses the behaviour of the wavelike properties of a particle, it does not define the physical attributes it has as a particle. As a particle, the electron has an easily defined spatial and temporal position, not possessed by an oscillation of some kind of field, whose influence extends over a region of space and time. The incompatibility of these two views of the electron leads to the Heisenberg uncertainty principle. Heisenberg recognized that if matter had wavelike properties, the physical attributes normally associated with matter (position, momentum, kinetic energy, etc.) would have to be expressed in a statistical, rather than a deterministic, manner. This is illustrated by the electron diffraction patterns of Davisson and Germer. Individual electrons somehow fell onto the apparatus to form a pattern statistically consistent with the intensity of a wave function. It is as if the final wave function were made up of a superposition of all the possible positions that the electrons could fall onto, the waves of electrons constructively and destructively interfering to form the final diffraction pattern. It is known that a clever superposition of waves of different wavelengths can lead to a construction of a wave packet of finite extension (see Fourier analysis). However, to produce a packet that exists at a point of zero width requires an infinite number of waves to superimpose. Heisenberg realized that these packets of waves must account for the way in which matter particles, such as electrons, could retain some semblance of their particle-like qualities. However, this must also mean that there is an inherent uncertainty in position and momentum associated with electrons and indeed all particles of matter (see uncertainty principle). Since waves of different wavelength correspond to different possible momentum values of an electron, a superposition of such waves to form a particle at a point would correspond to an infinite uncertainty in the momentum of the electron. Therefore the more one knows about the position of an electron the less one will know about its momentum and vice versa. A similar uncertainty between the energy of the electron and its temporal position also exists. Quantities that are related by such an uncertainty principle are said to be incompatible. An alternative to the wave-mechanical treatment of quantum mechanics is an equivalent formalism called matrix mechanics, which is based on matrices. See also Bell’s theorem; hidden-variables theory. Chemistry A system of mechanics that was developed from quantum theory and is used to explain the properties of atoms and molecules. Using the energy quantum as a starting point it incorporates Heisenberg’s uncertainty principle and the de Broglie wavelength to establish the wave-particle duality on which the Schrödinger equation is based. This form of quantum mechanics is called wave mechanics. An alternative but equivalent formalism, matrix mechanics, is based on matrices. Chemical Engineering A branch of mechanics that is based on the quantum theory used for interpreting and understanding the behaviour of elementary particles, atoms, and molecules, which do not obey Newtonian mechanics. Electronics and Electrical Engineering The theory of atomic and nuclear systems, providing a mathematical framework for quantum theory. In 1926 Erwin Schrödinger developed a wave equation to describe the behaviour of elementary particles in materials by treating them as matter waves or de Broglie waves, following the hypothesis by de Broglie that electrons, etc., could be described both in terms of particle-like and wave-like behaviour. This wave equation, now known as the Schrödinger equation, described the motion of de Broglie waves in a given potential energy, for instance in a potential well, or inside a crystalline solid. The Schrödinger equation for the electron, for example, is: $(\frac{- ℏ^{2}}{2 m}) \nabla^{2} Ψ + V Ψ = j ℏ (\frac{\partial Ψ}{\partial t})$ where $ℏ$ is the rationalized Planck constant, m is the mass of the electron, V is the potential in which it moves, and ∇² is the Laplace operator. This is a differential equation in the quality Ψ, which is known as the wavefunction; this is a complex quality that can be thought of as a measure of the amplitude of the de Broglie wave describing the electron. Hence the square of the wavefunction is a measure of the intensity of the electron wave, or $\| Ψ (x, y, z, t) \|^{2} d x d y d z$ gives the probability of finding an electron at time t in the incremental volume element dxdydz located at (x, y, z). Solutions of the Schrödinger equation can be found analytically only for simple examples, usually by eliminating the time dependence by assuming the de Broglie waves have a typical exp(jωt) time dependence and solving the time-independent Schrödinger equation: $(\frac{- ℏ^{2}}{2 m}) \nabla^{2} ψ + V ψ = E ψ$ Now ψ is the time-independent component of the wavefunction and E is the total energy of the electron, and the equation describes the physical variation of the electron wavefunction in space. Analytical solutions of the time-independent Schrödinger equation can be used to provide valuable insight into the behaviour of electrons in atoms and solids. For example, the solution of a particle in a potential well leads to the concept of quantum numbers describing the allowed energy states in the well. This structure is known as a quantum well. By using a periodic value for the potential energy V, solutions of the Schrödinger equation are found to describe the origins of energy-band structure in crystalline solids; this is the Kronig–Penney model of energy-band structure. https://www.livescience.com/33816-quantum-mechanics-explanation.html A short introduction to quantum mechanics, with links for further reading Philosophy Quantum theory, introduced by Max Planck (1858–1947) in 1900, was the first serious scientific departure from Newtonian mechanics. It involved supposing that certain physical quantities can only assume discrete values. In the following two decades it was applied successfully to different physical problems by Einstein and the Danish physicist Niels Bohr (1885–1962). It was superseded by quantum mechanics in the years following 1924, when the French physicist Louis de Broglie (1892–1987) introduced the idea that a particle may also be regarded as a wave. The Schrödinger wave equation relates the energy of a system to a wave function: the square of the amplitude of the wave is proportional to the probability of a particle being found in a specified position. The wave function expresses the lack of possibility of defining both the position and momentum of a particle (see Heisenberg uncertainty principle). The allowed wave functions, or ‘eigenfunctions’, have ‘eigen-values’ that describe stationary states of the system. Part of the difficulty with the notions involved is that a system may be in an indeterminate state at a time, characterized only by the probability of some result for an observation, but then ‘become’ determinate (‘the collapse of the wave packet’) when an observation is made (see also Einstein-Podolsky-Rosen thought experiment, Schrödinger’s cat). It is as if there is nothing but a potential for observation or a probability wave before observation is made, but when an observation is made the wave becomes a particle. The wave-particle duality seems to block any way of conceiving of physical reality in quantum terms. In the famous two-slit experiment, an electron is fired at a screen with two slits (like a tennis ball thrown at a wall with two doors in it). If one puts detectors at each slit, every electron passing the screen is observed to go through exactly one slit. But when the detectors are taken away, the electron acts like a wave process going through both slits, and interfering with itself. A particle such as an electron is usually thought of as always having an exact position, but its wave nature ensures that the amplitude of its waves is not absolutely zero anywhere (there is therefore a finite probability of it ‘tunnelling’ from one position to emerge at another). The unquestionable success of quantum mechanics has generated a large philosophical debate about its ultimate intelligibility and its metaphysical implications. The wave-particle duality is already a departure from ordinary ways of conceiving of things in space, and its difficulty is compounded by the probabilistic nature of the fundamental states of a system as they are conceived in quantum mechanics. Philosophical options for interpreting quantum mechanics have included variations of the belief that it is at best an incomplete description of a better-behaved classical underlying reality (Einstein), the Copenhagen interpretation according to which there are no objective unobserved events in the micro-world (Niels Bohr and W. K. Heisenberg, 1901–76), an ‘acausal’ view of the collapse of the wave packet (J. von Neumann, 1903–57), and a ‘many worlds’ interpretation in which time forks perpetually towards innumerable futures, so that different states of the same system exist in different parallel universes (H. Everett). In recent years the proliferation of subatomic particles (there are 36 kinds of quark alone, in six flavours and three colours) has prompted physicists to look in various directions for unification. One avenue of approach is superstring theory, in which the four-dimensional world is thought of as the upshot of the collapse of a ten-dimensional world, with the four primary physical forces (gravity, electromagnetism, and the strong and weak nuclear forces) becoming seen as the result of the fracture of one primary force. While the scientific acceptability of such theories is a matter for physics, their ultimate intelligibility plainly requires some philosophical reflection. See also Bell’s theorem.
随便看	Richter, Burton Richter, Charles Francis Richter, Charles Francis (1900–1985) Richter denudation slope Richter scale rich text format Richthofen, Manfred, Freiherr von (1882–1918) ricin Ricker pulse rickets rickettsia Ricoeur, Paul (1913–2005) Riddle, Oscar Ride, Sally (1951–2012) ridge ridge and furrow ridge-and-ravine topography ridge and runnel ridge crest ridged waveguide ridge-push ridge regression riding the stack ridit Ridley, Nicholas (1500–55)