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Topic: Measurement (quantum mechanics)

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In the News (Tue 25 Jun 19)

  Quantum Theory - Mechanics - Crystalinks
Quantum mechanics is a fundamental branch of theoretical physics that replaces Newtonian mechanics and classical electromagnetism at the atomic and subatomic levels.
Quantum mechanics is a more fundamental theory than Newtonian mechanics and classical electromagnetism, in the sense that it provides accurate and precise descriptions for many phenomena that these "classical" theories simply cannot explain on the atomic and subatomic level.
During a measurement, the probability that a system collapses from a given initial state to a particular eigenstate is given by the square of the absolute value of the probability amplitudes between the initial and final states.
www.crystalinks.com /quantumechanics.html   (4216 words)

 Wikinfo | Quantum mechanics   (Site not responding. Last check: 2007-10-12)
Quantum mechanics or quantum physics is a physical theory formulated in the first half of the twentieth century which successfully describes the behavior of matter at small distance scales.
The quantum field theory describing electromagnetism is quantum electrodynamics; it is, at least in principle, capable of explaining chemical interactions as well as the interaction of matter and electromagnetic radiation.
The quantum field theory describing the strong nuclear force is quantum chromodynamics, which describes the interactions of the subnuclear particles: quarks and gluons.
wikinfo.org /wiki.php?title=Quantum_mechanics   (1644 words)

 Theory: Quantum Mechanics (SLAC VVC)
Quantum mechanics is the description of physics at the scale of atoms, and the even smaller scales of fundamental particles.
Quantum theory is the language of all particle theories.
The rule for probability in quantum mechanics is that probability is the square of the absolute value of the relevant probability amplitude.
www2.slac.stanford.edu /vvc/theory/quantum.html   (1067 words)

 Measurement in Quantum Theory (Stanford Encyclopedia of Philosophy)
The problem of measurement in quantum mechanics arises out of the fact that several principles of the theory appear to be in conflict.
In particular, the dynamic principles of quantum mechanics seem to be in conflict with the postulate of collapse.
quantum mechanics: the role of decoherence in
plato.stanford.edu /entries/qt-measurement   (3929 words)

 Relational Quantum Mechanics   (Site not responding. Last check: 2007-10-12)
Relational quantum mechanics is an interpretation of quantum theory which discards the notions of absolute state of a system, absolute value of its physical quantities, or absolute event.
The difficulty in the interpretation of quantum mechanics derives from the fact that the theory was first constructed for describing microscopic systems (atoms, electrons, photons) and the way these interact with macroscopic apparatuses built to measure their properties.
The move proposed by the relational interpretations of quantum mechanics has strong analogies with these, but is, in a sense, a longer jump, since all physical events and the entirety of the contingent properties of any physical system are taken to be meaningful only as relative to a second physical system.
www.seop.leeds.ac.uk /archives/spr2003/entries/qm-relational   (5177 words)

 Measurement in quantum mechanics FAQ   (Site not responding. Last check: 2007-10-12)
The quantum measurement process happens ``when'' the transaction (OW sent - CW received - standing wave formed with probability \\Psi \\Psi*) is finished - and this happens over a space-time interval; thus, one cannot point to a time of collapse, only to an interval of collapse (consistent with relativity).
If quantum theory is true, there are cases in which the results of the measurements A will depend on the setting of the knob b and/or the results of the measurements in B will depend on the setting of the knob a.[1] It is logically possible to deny CFD and thus to avoid Eberhard's proof.
The predications of quantum field theory are the same in any frame of reference but the mechanisms that generate nonlocal effects must operate in an absolute frame of reference.
omicron.felk.cvut.cz /FAQ/articles/a296.html   (4533 words)

At it's most basic, the framework of quantum mechanics consists of an experimentally unobservable wave (the effects of which can be calculated) which can be manipulated in various ways.
When wave mechanics was first conceived it was thought that the wavefunction represented the actual position of, say, the electron in the atom.
The quantum system has expanded from being merely a radioactive particle with a given chance of decaying into a box with a cat in a superposition of alive/dead states in it.
interconnected.org /matt/archive/quantum/quantum.html   (877 words)

 Quantum Worlds notes session 4
After measurement, the quantum wave becomes the quantum wave that is associated with the particular value of the observed quantity that I found.
If we describe a device measuring the velocity of a particle in terms of the mathematics of quantum mechanics (basically this is done by describing the device itself in terms of a quantum wave), we find that the device wave is decomposed along with the particle wave.
The quantum wave of the second particle, however, cannot possibly reflect this knowledge of both position and velocity according to the rules of quantum mechanics.
homepage.mac.com /stevepur/physics/qw/qw.4.html   (2201 words)

 Measurement in quantum mechanics - Wikipedia, the free encyclopedia
The framework of quantum mechanics requires a careful definition of measurement, and a thorough discussion of its practical and philosophical implications.
The process in which a quantum state becomes one of the eigenstates of the operator corresponding to the measured observable is called "collapse", or "wavefunction collapse".
Until the advent of quantum decoherence theory in the late 20th century, a major conceptual problem of quantum mechanics and especially the Copenhagen interpretation was the lack of a distinctive criterion for a given physical interaction to qualify as "a measurement" and cause a wavefunction to collapse.
en.wikipedia.org /wiki/Measurement_in_quantum_mechanics   (1852 words)

 [No title]   (Site not responding. Last check: 2007-10-12)
This postulate captures the central point of quantum mechanics--the values of dynamical variables can be quantized (although it is still possible to have a continuum of eigenvalues in the case of unbound states).
Earlier in the interpretation of quantum mechanics, it appeared that the problem of measurement could only be solved by introducing some basic notion of an observer, presumably a conscious observer.
Copenhagen) Interpretation of QM says that the very act of sentient measurement determines the outcome of the measurement in the quantum (microcosmic) realm.
www.lycos.com /info/quantum-mechanics--measurement.html   (293 words)

 Quantum Dynamical Systems: Continuous Quantum Measurement   (Site not responding. Last check: 2007-10-12)
Since in quantum mechanics measurement creates an irreducible disturbance on the observed system, and we do not wish to disturb the system unduly, the desired measurement process must yield a limited amount of information in a finite time.
In this project, aside from understanding such fundamental issues as quantum chaos, our aim is to further develop the theory of continuous measurement and apply it to systems of future technological importance such as in atom and quantum optics and quantum nanomechanics.
The top panel on the right shows an example of a localized quantum trajectory situation for the particle position distribution as a function of position of a driven Duffing oscillator (strong measurement, 'classical' range of parameters, green curve) versus a nonlocalized one (weak measurement, 'quantum' range of parameters, red curve).
t8web.lanl.gov /people/salman/icp/cqm.html   (1236 words)

 Quantum Mechanics: Psi: Physics
A typical quantum mechanics problem would thus run as follows: You start with a particle in an unknown state subject to a known set of forces, such as an electron in an electromagnetic field.
Quantum mechanically, the state of a particle is much more complicated, so you might think you would need many more measurements to determine the full wavefunction of a particle.
In quantum mechanics lingo these two states are said to be degenerate with respect to kinetic energy, which just means they have the same kinetic energy eigenvalue.
www.ncsu.edu /felder-public/kenny/papers/psi.html   (11440 words)

 Quantum Mechanics Introduction: Physics
Measurements of big things, roughly meaning anything much bigger than an atom, will seem to produce classical results because the quantum mechanical results (eg interference fringes) are too small to detect.
Quantum mechanics says that these two statements are definitively different, and the intuitive one (the cat is either alive or dead, and we just don't know until we look) is wrong.
Quantum mechanical laws generally only have measurable effects when applied to things that are too small to see, so we never evolved an understanding of them, so they seem bizarre.
www.ncsu.edu /felder-public/kenny/papers/quantum.html   (7642 words)

 Todd's Quantum Intro
Plus, it is much easier to use than either quantum mechanics or relativity (each of which require an extensive amount of math).
This is one of the most interesting phenomena to arise from quantum mechanics; without it computer chips would not exist, and a 'personal' computer would probably take up an entire room.
Quantum mechanics, however, says that there is a small probability that the ball could go right through the wall (without damaging the wall) and continue its flight on the other side!
www.hi.is /~hj/QuantumMechanics/quantum.html   (2242 words)

 Heisenberg - Quantum Mechanics, 1925-1927: The Uncertainty Relations: Further Reading   (Site not responding. Last check: 2007-10-12)
Todd's Intro to Quantum Mechanics A well-illustrated introduction.
Measurement in Quantum Mechanics FAQ summary on the measurement problem.
Philosophy of the Uncertainty Principle Technical discussion from Stanford's Encyclopedia of Philosophy; see also their Quantum Mechanics article for advanced students.
www.aip.org /history/heisenberg/p08r.htm   (256 words)

 Quantum Mechanics Measurement Problem tackled by Computer Simulation
This is the quantum mechanics measurement problem looked at from the point of view of computer simulation.
Quantum mechanics and computer simulation may separately have a formidable reputation, but this website would not exist but for a single simple idea.
You are warned that for the quantum mechanical many-body problem, we may not be able to do any better than an exponential-time algorithm, assuming that we achieve anything at all.
ourworld.compuserve.com /homepages/anima/quantum.htm   (989 words)

 The mathematics of measurement - Advanced Physics Forums
the act of measurement is actually averaging the behavior of the desired observable.
The trace operation, which is done with different \"weights\" on the wave function, which can be considered as the operators, is what gives the collapse of the wavefunction (or split into multiple universes, for that matter).
The mechanism of collapse is a highly-charged, poorly-understood subject.
www.advancedphysics.org /forum/showthread.php?t=752   (440 words)

 Measurement in quantum mechanics FAQ: The measurement problem   (Site not responding. Last check: 2007-10-12)
Measurement in quantum mechanics FAQ: The measurement problem
The formulation of QM describes the deterministic unitary evolution of a wave function.
Bell, Speakable and unspeakable in quantum mechanics, Cambridge University Press, 1987.
www.mtnmath.com /faq/meas-qm-2.html   (436 words)

 Re: measurement in quantum mechanics   (Site not responding. Last check: 2007-10-12)
On 28 May 2004 16:06:28 -0400, alistair@goforit64.fsnet.co.uk (alistair) wrote: >But if two observers in relativity measure the mass of an object are >they creating something analagous to a superposition of states by >defining >the mass with two unique values simultaneously (presumably no >superposition would exist until two measurements of the mass have been >made)?
Measurements, as a rule, would create mixtures rather than superpositions.
Next by thread: Re: measurement in quantum mechanics
www.lns.cornell.edu /spr/2004-05/msg0061473.html   (90 words)

 Further Reading on the Quantum Mechanics Measurement Problem   (Site not responding. Last check: 2007-10-12)
Ronald Hurst is also interested in the computer simulation of quantum mechanics, pursuing an idea first suggested by Louis de Broglie (which is a second idea of De Broglie's and different from the De Broglie-Bohm Interpretation).
John Cramer has proposed the Transactional Interpretation of quantum mechanics.
Quantum-D is a newsgroup dedicated to the interpretation of quantum mechanics, at:
ourworld.compuserve.com /homepages/anima/further.htm   (177 words)

 Physics 429, Quantum Mechanics Sites   (Site not responding. Last check: 2007-10-12)
There are a great number of large number of sites on the WWW about Quantum Mechanics.
(An Google search on the keyword "Quantum" yielded over 4,190,00 sites.) Some are good and some are, well, really bad.
Below are listed a few you might find interesting or helpful.
www.cord.edu /faculty/luther/physics429/qmsites.html   (87 words)

Try your search on: Qwika (all wikis)

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