Hidden variable theory Albert Einstein, the most famous proponent of hidden variables, objected to the fundamentally probabilistic nature of quantum mechanics,[1] and famously declared "I am convinced God does not play dice".[2] Einstein, Podolsky, and Rosen argued that "elements of reality" (hidden variables) must be added to quantum mechanics to explain entanglement without action at a distance.[3][4] Later, Bell's theorem would suggest (in the opinion of most physicists and contrary to Einstein's assertion) that local hidden variables of certain types are impossible. The most famous nonlocal theory is de Broglie-Bohm theory. Motivation[edit] Under the orthodox Copenhagen interpretation, quantum mechanics is nondeterministic, meaning that it generally does not predict the outcome of any measurement with certainty. In other words, it is conceivable that the Copenhagen interpretation of quantum mechanics is an incomplete description of nature. "God does not play dice"[edit] Bohr-Einstein debates[edit] .

Hong–Ou–Mandel effect Quantum-mechanical description[edit] Physical description[edit] When a photon enters a beam splitter, there are two possibilities: it will either be reflected or transmitted. The relative probabilities of transmission and reflection are determined by the reflectivity of the beam splitter. Here, we assume a 50:50 beam splitter, in which a photon has equal probability of being reflected and transmitted. Figure 1. Since the state of the beam splitter does not "record" which of the four possibilities actually happens, Feynman's rule dictates that we have to add all four possibilities at the amplitude level. Mathematical description[edit] Consider two optical modes a and b that carry annihilation and creation operators , and . where is a single-photon state. Unitarity of the transformation now means unitarity of the matrix. When two photons enter the beam splitter, one on each side, the state of the two modes becomes Since the commutator of the two creation operators and . Figure 2. by: If

When the multiverse and many-worlds collide - physics-math - 01 June 2011 Read full article Continue reading page |1|2 Editorial: "God deserves a cosmological explanation" TWO of the strangest ideas in modern physics - that the cosmos constantly splits into parallel universes in which every conceivable outcome of every event happens, and the notion that our universe is part of a larger multiverse - have been unified into a single theory. This solves a bizarre but fundamental problem in cosmology and has set physics circles buzzing with excitement, as well as some bewilderment. The problem is the observability of our universe. Cosmologists reconcile this seeming contradiction by assuming that the superposition eventually "collapses" to a single state. This problem is captured in the famous thought experiment of Schrödinger's cat. Physicists call this process "decoherence". In the case of something as large as a cat, that may be possible in Schrödinger's theoretical sealed box. New Scientist Not just a website! More From New Scientist More from the web

Ensemble interpretation The ensemble interpretation, or statistical interpretation of quantum mechanics, is an interpretation that can be viewed as a minimalist interpretation; it is a quantum mechanical interpretation that claims to make the fewest assumptions associated with the standard mathematical formalization. At its heart, it takes to the fullest extent the statistical interpretation of Max Born for which he won the Nobel Prize in Physics.[1] The interpretation states that the wave function does not apply to an individual system – or for example, a single particle – but is an abstract mathematical, statistical quantity that only applies to an ensemble of similarly prepared systems or particles. Probably the most notable supporter of such an interpretation was Albert Einstein: To date, probably the most prominent advocate of the ensemble interpretation is Leslie E. Ballentine, Professor at Simon Fraser University, and writer of the graduate-level textbook "Quantum Mechanics, A Modern Development".[3]

David Deutsch David Elieser Deutsch, FRS (born 1953 in Haifa, Israel) is a British physicist at the University of Oxford. He is a non-stipendiary Visiting Professor in the Department of Atomic and Laser Physics at the Centre for Quantum Computation (CQC) in the Clarendon Laboratory of the University of Oxford. He pioneered the field of quantum computation by formulating a description for a quantum Turing machine, as well as specifying an algorithm designed to run on a quantum computer.[2] He is a proponent of the many-worlds interpretation of quantum mechanics. Career[edit] In the Royal Society of London's announcement that Deutsch had become a Fellow of the Royal Society (FRS) in 2008, the Society described Deutsch's contributions thus:[3] He is currently working on constructor theory, an attempt at generalizing the quantum theory of computation to cover not just computation but all physical processes.[4] Popular science books[edit] The Fabric of Reality[edit] There are "four strands" to his theory:

Calculating Water Footprints: How Much Water in Your Food? The environmental impact of food production in terms of contribution to climate change is well documented. Fertilizer use, soil degradation, and transportation from far flung farms to the table are all sources of greenhouse gas emissions. However, food production also has a steep water footprint. In 2009, the Food Ethics Council (FEC) declared in a report that food products should come with water footprint information in addition to carbon information. As a general rule of thumb, crops like sugar and vegetables are more water-intensive than cereals. Another recently released report by WRAP and WWF examined how much water is wasted in the UK when food is thrown away. The report focuses on the water and carbon footprint of wasted household food and drink in the UK for the first time. According to the Water Footprint Network the water footprint of US citizens is 2840 cubic meter per year per capita. Scroll down to see comments.

Objective collapse theory Objective collapse theories are an approach to the interpretational problems of quantum mechanics. They are realistic, indeterministic and reject hidden variables. The approach is similar to the Copenhagen interpretation, but more firmly objective. The most well-known examples of such theories are: Compared to other approaches[edit] Collapse theories stand in opposition to many-worlds interpretation theories, in that they hold that a process of wavefunction collapse curtails the branching of the wavefunction and removes unobserved behaviour. Variations[edit] Objective collapse theories regard the present formalism of quantum mechanics as incomplete, in some sense. Collapse is found "within" the evolution of the wavefunction, often by modifying the equations to introduce small amounts of non-linearity. Objections[edit] The fact that these theories seek to extend the formalism is considered as violation of the principle of parsimony by some. GRW collapse theories have unique problems.

David Deutsch (Wissenschaftler) David Deutsch (* 1953 in Haifa ) ist ein israelisch-britischer Physiker auf dem Gebiet der Quanteninformationstheorie . Leben [ Bearbeiten ] Deutsch studierte Mathematik und Physik in Cambridge , Oxford und Austin und ist seit 2009 Inhaber eines Lehrstuhls an der Universität Oxford . Deutsch ist einer der bekanntesten Vertreter der sogenannten Viele-Welten-Interpretation der Quantenmechanik. Seine Analyse von Zeitreisen und damit verbundenen logischen Problemen kommt zu dem Vorschlag, dass dabei zwangsläufig nicht nur in der Zeit , sondern auch in ein "Paralleluniversum" gereist werden müsste; der Zeitreisende, welcher in die Zeitmaschine steigt, und jener, welcher aus dieser aussteigt, wäre dabei nicht identisch. Sein Arbeitsstil ist eigenwillig, obwohl er ein eigenes Büro am mathematischen Institut hat, arbeitet er zu Hause. Nach ihm ist der Deutsch-Jozsa-Algorithmus benannt. Literatur [ Bearbeiten ] David Deutsch: The Fabric of Reality. Weblinks [ Bearbeiten ]

Food and water for the poor -- not political lies via MD, GG and MS, I read an interesting interview with the Chairman of Nestle in which he says: There is no market for how that water is allocated and used. The result is waste, overuse and misuse of the water we have. If we don't do something about that, Mr. Brabeck-Letmathe fears, we will soon run ourselves dry.[snip]"If oil becomes scarce," he notes, "the oil price goes up. He makes two important points (that I have made many times on this blog and in my book). First, political interference has distorted food markets (via artificial stimulation of demand for biofuels and artificial blockages on GMOs), which is bad for farmers and the poor but good for food companies with political connections. Second, we need better markets for water, to ensure that it goes to highest and best use instead of political cronies with little need to be efficient (let alone care for the environment, human rights, etc.)

Copenhagen interpretation The Copenhagen interpretation is one of the earliest and most commonly taught interpretations of quantum mechanics.[1] It holds that quantum mechanics does not yield a description of an objective reality but deals only with probabilities of observing, or measuring, various aspects of energy quanta, entities that fit neither the classical idea of particles nor the classical idea of waves. The act of measurement causes the set of probabilities to immediately and randomly assume only one of the possible values. This feature of mathematics is known as wavefunction collapse. The essential concepts of the interpretation were devised by Niels Bohr, Werner Heisenberg and others in the years 1924–27. According to John Cramer, "Despite an extensive literature which refers to, discusses, and criticizes the Copenhagen interpretation of quantum mechanics, nowhere does there seem to be any concise statement which defines the full Copenhagen interpretation. Background[edit] Origin of the term[edit] 1. .

Consistent histories In quantum mechanics, the consistent histories approach is intended to give a modern interpretation of quantum mechanics, generalising the conventional Copenhagen interpretation and providing a natural interpretation of quantum cosmology.[1] This interpretation of quantum mechanics is based on a consistency criterion that then allows probabilities to be assigned to various alternative histories of a system such that the probabilities for each history obey the rules of classical probability while being consistent with the Schrödinger equation. In contrast to some interpretations of quantum mechanics, particularly the Copenhagen interpretation, the framework does not include "wavefunction collapse" as a relevant description of any physical process, and emphasizes that measurement theory is not a fundamental ingredient of quantum mechanics. Histories[edit] A homogeneous history (here labels different histories) is a sequence of Propositions specified at different moments of time is true at time

Quantum logic Quantum logic can be formulated either as a modified version of propositional logic or as a noncommutative and non-associative many-valued (MV) logic.[1][2][3][4][5] Quantum logic has some properties which clearly distinguish it from classical logic, most notably, the failure of the distributive law of propositional logic: p and (q or r) = (p and q) or (p and r), where the symbols p, q and r are propositional variables. To illustrate why the distributive law fails, consider a particle moving on a line and let p = "the particle has momentum in the interval [0, +1/6]" q = "the particle is in the interval [−1, 1]" r = "the particle is in the interval [1, 3]" (using some system of units where the reduced Planck's constant is 1) then we might observe that: p and (q or r) = true in other words, that the particle's momentum is between 0 and +1/6, and its position is between −1 and +3. (p and q) or (p and r) = false Thus the distributive law fails. Introduction[edit] Projections as propositions[edit]

De Broglie–Bohm theory The de Broglie–Bohm theory, also known as the pilot-wave theory, Bohmian mechanics, the Bohm or Bohm's interpretation, and the causal interpretation, is an interpretation of quantum theory. In addition to a wavefunction on the space of all possible configurations, it also includes an actual configuration, even when unobserved. The evolution over time of the configuration (that is, of the positions of all particles or the configuration of all fields) is defined by the wave function via a guiding equation. The evolution of the wave function over time is given by Schrödinger's equation. The theory is named after Louis de Broglie (1892–1987) and David Bohm (1917–1992). The de Broglie–Bohm theory is explicitly nonlocal: the velocity of any one particle depends on the value of the guiding equation, which depends on the whole configuration of the universe. The theory is deterministic. Overview[edit] De Broglie–Bohm theory is based on the following postulates: Where is the momentum operator. . .

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