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You are touching upon the measurement problem in quantum mechanics. The wave-function changes in two distinct manners: Unitary evolution by the Hamiltonian in the Schrodinger equation. Non-unitary measurement by Born's rule, i.e. what is often called "collapse of the wave-function." To many people, the latter remains puzzling, though this is a ...

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Basically any measurement is on wave function |ψ⟩ is done by operator X such that X|ψ⟩ results observable x with some probability. is not entirely correct. In quantum mechanics a system is described by a state $|\psi\rangle\in\mathcal{H}$ and a set of self-adjoint operators $A_1,\ldots,A_n$ representing the observables that we want to measure. Moreover, ...

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When a quantum mechanical object is subjected to a measurement its wavefunction has to be coupled to a measurement device. That coupling will change both the wavefunction of the object and the wavefunction of the measurement device (as well as the wavefunction of the environment!). It is important to understand that a measured quantum object is not the same ...

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What is a wave function? It is the solution of a quantum mechanical equation ( with the appropriate potentials),on which boundary conditions are imposed to make it specific to a system . $|\psi\rangle$ by itself is not independent of the environment the way that the operators X are. Thus the answer depends on the system under consideration. I like ...

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All evolution in Quantum Mechanics is done by the Hamiltonian. However, measurements of an operator result in a single eigenvalue, and the wavefunction collapses (As to how, why, etc, it is unknown as of now, Copenhagen is the most common interpretation) to an eigenstate of the operator measured with the same eigenvalue. Specifically, it collapses to the ...

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The answer to this question depends on if the user thinks there is a wave function collapse. If there is a wave function collapse, the classical object can be thought of as a collapsed wave function, but there are a lot more than just saying if there is a wave function collapse, the classical objects exist because of the collapse. There is fundamental ...

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Experimental data up to now have established that the underlying level of nature is quantum mechanical, i.e. described by the theory of quantum mechanic.s. This theory makes accurate predictions for dimensions commensurate with h_bar Classical mechanics describes set ups where h_bar, whose value is of order 10^-34 joulesecond , is essentially zero due to ...

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If you have a quantum state in which more than one of the possible outcomes of a particular measurement has non-zero amplitude (an unsharp state, as opposed to a sharp state in which there is only one outcome), then the MWI says that there will be multiple versions of you, and each version will see one possible outcome. In the standard (non-MWI) way of ...

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In non relativistic quantum mechanics you have a partial differential equation like the Schrödinger equation. The solutions are called wavefunctions. It is similar to Maxwell's equations in that if you provide the values at one time you can get the values at a later time. Unlike Maxwell the values you need to provide are complex and unlike Maxwell you need ...

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