Quantum Physics Revealed As Non-Mysterious This is one of several shortened indices into the Quantum Physics Sequence. Hello! You may have been directed to this page because you said something along the lines of "Quantum physics shows that reality doesn't exist apart from our observation of it," or "Science has disproved the idea of an objective reality," or even just "Quantum physics is one of the great mysteries of modern science; no one understands how it works." There was a time, roughly the first half-century after quantum physics was invented, when this was more or less true. The series of posts indexed below will show you - not just tell you - what's really going on down there. Some optional preliminaries you might want to read: Reductionism: We build models of the universe that have many different levels of description. And here's the main sequence: Quantum Explanations: Quantum mechanics doesn't deserve its fearsome reputation.
Cosmological Interpretations of Quantum Mechanics It seems that there’s now a new burgeoning field bringing together multiverse studies and interpretational issues in quantum mechanics. Last year Aguirre, Tegmark and Layzer came out with with Born in an Infinite Universe: a Cosmological Interpretation of Quantum Mechanics, which claimed: This analysis unifies the classical and quantum levels of parallel universes that have been discussed in the literature, and has implications for several issues in quantum measurement theory… the analysis suggests a “cosmological interpretation” of quantum theory in which the wave function describes the actual spatial collection of identical quantum systems, and quantum uncertainty is attributable to the observer’s inability to self-locate in this collection. Our framework provides a fully unified treatment of quantum measurement processes and the multiverse. We conclude that the eternally inflating multiverse and many worlds in quantum mechanics are the same.
EPR paradox Albert Einstein The EPR paradox is an early and influential critique leveled against the Copenhagen interpretation of quantum mechanics. Albert Einstein and his colleagues Boris Podolsky and Nathan Rosen (known collectively as EPR) designed a thought experiment which revealed that the accepted formulation of quantum mechanics had a consequence which had not previously been noticed, but which looked unreasonable at the time. The scenario described involved the phenomenon that is now known as quantum entanglement. According to quantum mechanics, under some conditions, a pair of quantum systems may be described by a single wave function, which encodes the probabilities of the outcomes of experiments that may be performed on the two systems, whether jointly or individually. At the time the EPR article discussed below was written, it was known from experiments that the outcome of an experiment sometimes cannot be uniquely predicted. History of EPR developments Einstein's opposition
A tale of two qubits: how quantum computers work Quantum information is the physics of knowledge. To be more specific, the field of quantum information studies the implications that quantum mechanics has on the fundamental nature of information. By studying this relationship between quantum theory and information, it is possible to design a new type of computer—a quantum computer. A largescale, working quantum computer—the kind of quantum computer some scientists think we might see in 50 years—would be capable of performing some tasks impossibly quickly. To date, the two most promising uses for such a device are quantum search and quantum factoring. Although quantum search is impressive, quantum factoring algorithms pose a legitimate, considerable threat to security. Quantum computers are fundamentally different from classical computers because the physics of quantum information is also the physics of possibility. Single qubits. Pairs of qubits. Quantum physics 101. How do they work? Is the polarization horizontal or vertical?
Yves Couder In the first decades of the 20th century, physicists hotly debated how to make sense of the strange phenomena of quantum mechanics, such as the tendency of subatomic particles to behave like both particles and waves. One early theory, called pilot-wave theory, proposed that moving particles are borne along on some type of quantum wave, like driftwood on the tide. But this theory ultimately gave way to the so-called Copenhagen interpretation, which gets rid of the carrier wave, but with it the intuitive notion that a moving particle follows a definite path through space. Recently, Yves Couder, a physicist at Université Paris Diderot, has conducted a series of experiments in which millimeter-scale fluid droplets, bouncing up and down on a vibrated fluid bath, are guided by the waves that they themselves produce. The wave-particle duality is best illustrated by a canonical experiment in quantum mechanics that’s generally referred to as the two-slit, or two-hole, experiment. Scaling up
Applications Gravitation quantique à boucles - LQG - Loop Quantum Gravity - Gravitation quantique La gravitation quantique à boucles est l'une des principales voies de recherche concernant le problème de l'élaboration d'une théorie capable de décrire l'aspect quantique de la gravitation. Il faut en effet une théorie quantique de la gravitation lorsque l'on veut comprendre la naissance de l'univers et ce qui se passe à l'intérieur des trous noirs. Dans le cadre de la relativité générale classique, il apparaît alors dans ces situations des singularités avec des divergences de certaines quantités physiques indésirables. Le sujet de la gravitation quantique est extrêmement vaste et il faudrait probablement des centaines de pages pour lui rendre justice. La cosmologie quantique En résumé, on cherche à appliquer les règles de quantification standards dites canoniques aux équations d’Einstein, ce qui veut dire qu’on cherche à mettre ces dernières sous une forme dite hamiltonienne bien connue avec la mécanique analytique. décrit par une équation de Klein-Gordon avec un potentiel V( ).
Relationship between string theory and quantum field theory Many first principles in quantum field theory are explained, or get further insight, in string theory: Note: formally, gauge symmetries in string theory are (at least in most cases) a result of the existence of a global symmetry together with the profound gauge symmetry of string theory, which is the symmetry of the worldsheet under a local change of coordinates and scales. Quantum game theory Quantum game theory is an extension of classical game theory to the quantum domain. It differs from classical game theory in three primary ways: Superposed initial states,Quantum entanglement of initial states,Superposition of strategies to be used on the initial states. This theory is based on the physics of information much like quantum computing. Superposed initial states Entangled initial states The set of qubits which are initially provided to each of the players (to be used to convey their choice of strategy) may be entangled. Superposition of strategies to be used on initial states The job of a player in a game is to choose a strategy. Multiplayer games Introducing quantum information into multiplayer games allows a new type of equilibrium strategy which is not found in traditional games. See also References Notes Bibliography External links
Quantum entanglement Quantum entanglement is a physical phenomenon that occurs when pairs or groups of particles are generated or interact in ways such that the quantum state of each particle cannot be described independently – instead, a quantum state may be given for the system as a whole. Such phenomena were the subject of a 1935 paper by Albert Einstein, Boris Podolsky and Nathan Rosen, describing what came to be known as the EPR paradox, and several papers by Erwin Schrödinger shortly thereafter. Einstein and others considered such behavior to be impossible, as it violated the local realist view of causality (Einstein referred to it as "spooky action at a distance"), and argued that the accepted formulation of quantum mechanics must therefore be incomplete. History However, they did not coin the word entanglement, nor did they generalize the special properties of the state they considered. Concept Meaning of entanglement Apparent paradox The hidden variables theory
Matrix mechanics Matrix mechanics is a formulation of quantum mechanics created by Werner Heisenberg, Max Born, and Pascual Jordan in 1925. In some contrast to the wave formulation, it produces spectra of energy operators by purely algebraic, ladder operator, methods. Relying on these methods, Pauli derived the hydrogen atom spectrum in 1926, before the development of wave mechanics. Development of matrix mechanics In 1925, Werner Heisenberg, Max Born, and Pascual Jordan formulated the matrix mechanics representation of quantum mechanics. Epiphany at Helgoland In 1925 Werner Heisenberg was working in Göttingen on the problem of calculating the spectral lines of hydrogen. "It was about three o' clock at night when the final result of the calculation lay before me. The Three Fundamental Papers After Heisenberg returned to Göttingen, he showed Wolfgang Pauli his calculations, commenting at one point: In the paper, Heisenberg formulated quantum theory without sharp electron orbits. W.