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Monday, April 9, 2012

Quantum world - non locality a signal to non duality.

 source: http://en.wikipedia.org/wiki/Quantum_entanglement

Quantum Superposition - Observer is not independent of what is being Observed and we are all connected

Quantum superposition is a fundamental principle of quantum mechanics. It holds that a physical system -- such as an electron -- exists partly in all its particular, theoretically possible states (or, configuration of its properties) simultaneously; but, when measured, it gives a result corresponding to only one of the possible configurations (as described in interpretation of quantum mechanics).

The principle of quantum superposition states that if a physical system may be in some configuration—an arrangement of particles or fields—and if the system could also be in another configuration, then it is in a state which is a superposition of the two, where the amount of each configuration that is in the superposition is specified by a complex number.

Wave function collapse

In quantum mechanics, wave function collapse (also called collapse of the state vector or reduction of the wave packet) is the phenomenon in which a wave function—initially in a superposition of several different possible eigenstates—appears to reduce to a single one of those states after interaction with an observer. In simplified terms, it is the reduction of the physical possibilities into a single possibility as seen by an observer.

In general, quantum systems exist in superpositions of those basis states that most closely correspond to classical descriptions, and, when not being measured or observed, evolve according to the time dependent Schrödinger equation, relativistic quantum field theory or some form of quantum gravity or string theory, which is process (2) mentioned above. However, when the wave function collapses (process (1)), from an observer's perspective the state seems to "leap" or "jump" to just one of the basis states and uniquely acquire the value of the property being measured, e_i, associated with that particular basis state. After the collapse, the system begins to evolve again according to the Schrödinger equation or some equivalent wave equation.

Measurement problem

The measurement problem in quantum mechanics is the unresolved problem of how (or if) wavefunction collapse occurs. The inability to observe this process directly has given rise to different interpretations of quantum mechanics, and poses a key set of questions that each interpretation must answer. The wavefunction in quantum mechanics evolves according to the Schrödinger equation into a linear superposition of different states, but actual measurements always find the physical system in a definite state. Any future evolution is based on the state the system was discovered to be in when the measurement was made, meaning that the measurement "did something" to the process under examination. Whatever that "something" may be does not appear to be explained by the basic theory.
To express matters differently (to paraphrase Steven Weinberg), the wave function evolves deterministically – knowing the wave function at one moment, the Schrödinger equation determines the wave function at any later time. If observers and their measuring apparatus are themselves described by a deterministic wave function, why can we not predict precise results for measurements, but only probabilities? As a general question: How can one establish a correspondence between quantum and classical reality?

 


 

Quantum entanglement

Quantum entanglement occurs when particles such as photons, electrons, molecules as large as "buckyballs",[1][2] and even small diamonds[3][4] interact physically and then become separated; the type of interaction is such that each resulting member of a pair is properly described by the same quantum mechanical description (state), which is indefinite in terms of important factors such as position,[5] momentum, spin, polarization, etc.
According to the Copenhagen interpretation of quantum mechanics, their shared state is indefinite until measured.[6] Quantum entanglement is a form of quantum superposition. When a measurement is made and it causes one member of such a pair to take on a definite value (e.g., clockwise spin), the other member of this entangled pair will at any subsequent time[7] be found to have taken the appropriately correlated value (e.g., counterclockwise spin). Thus, there is a correlation between the results of measurements performed on entangled pairs, and this correlation is observed even though the entangled pair may have been separated by arbitrarily large distances.[8]
This behavior is consistent with quantum mechanical theory and has been demonstrated experimentally, and it is accepted by the physics community. However there is some debate[9] about a possible underlying mechanism that enables this correlation to occur even when the separation distance is large. The difference in opinion derives from espousal of various interpretations of quantum mechanics.

Quantum Entanglement - The Weirdness Of Quantum Mechanics


 

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