Conceptual Basis of the measurement problme

[Anonymous No.5164178]

Hello /sci/entists,
I would like to discuss the Quantum Measurement problem. Hopefully, the discussion will be based more on the conceptual understanding of QM, so it would be advisable to any unfamiliar to the topic to read the links below. Any further sources and perspectives are welcome.

http://en.wikipedia.org/wiki/Glossary_of_elementary_quantum_mechanics

http://en.wikipedia.org/wiki/Quantum_decoherence

http://en.wikipedia.org/wiki/Measurement_problem

http://en.wikipedia.org/wiki/Quantum_Zeno_effect

[Anonymous No.5164190]

>quoting decoherence in the OP
Well thank you, that's doing it right for once!

Gotta go, can't take part in this, but I have to say the recent papers of Roland Omnès are stellar.
Also they are very clear and an easy read.

See for example
Decoherence and Wave Function Collapse, Foundations of Physics
Volume 41, Number 12 (2011)

[Anonymous No.5164193]

Why is hitler in that image OP?

[Anonymous No.5164198]

A question on superposition:

The first question I have is this: Can we truly say that a particle is in a "superposition" rather than a definite position at any time? Isn't the superposition the totality of probabilities that an observable will be in a given state? If so, then each particle is only ever in a definite state and our problem is epistemic, and superposition refers only to the probability of finding X to be in a specific state. We could then claim that the particle is in a definite state, and superposition represents only our lack of knowledge as to what that state is.

[Anonymous No.5164234]

>>5164198
Sure, this is proven by Young's experiment.
Maybe you know it already: pit a lightbulb in front of a screen with a sheet in between. Make two holes in the sheet.
On the screen you will see an interference pattern. This illustrate the wave nature of light. If you block one hole, you get no pattern.

What does this has to do with superposition?
Well know instead of a light bulb, use a pulsed light device which sends out photons one at a time. Let the experiment run with a few million photons all sent separately. Use a photographic plate as a screen.

You will find that the shape drawn by the photons is an interference pattern. This shows that the photon wavefunction has interfered with itself. This couldn't happen if the photon was just a particle at one position, since it would go through one of the hole and not the other.

[Anonymous No.5164371]

The easy way to deal with it:

(using the Heisenberg picture)
choose one initial state <span class="math">|\psi\rangle[/spoiler] for your universe
choose an orthonormal set of possible final states <span class="math">\{|\phi_i\rangle\}[/spoiler] for your universe
probability of a particular final state <span class="math">|\phi_i\rangle[/spoiler] is given by <span class="math">|\langle \phi_i|\psi\rangle|^2[/spoiler]
given that the final state is <span class="math">|\phi_i\rangle[/spoiler], the value of the quantity described by the operator A is given by what people call its "weak value": <span class="math">\langle \phi_i|A|\psi\rangle/\langle \phi_i|\psi\rangle[/spoiler]

Two-state interpretations have a simplicity competitive with many-worlds interpretations without many-worlds' conceptual problems.

[IQ fundie !!8XTTCUzK2no No.5165233]

Measurements are expressed as sets of projectors onto the eigenvectors of an observable. There is no "measurement problem", and there hasn't been one since the Copenhagen school made their (phenomenologically successful) assumptions about how macroscopic objects come about from microscopic laws.

What is there *conceptually* to discuss?

[Anonymous No.5165247]

>>5164198
No its not a flaw in the math, or a veil we need to move in order too see or something like that.

Its real. It does not have a distinct state until we interact with it (directly or through any number of links)

[Anonymous No.5165281]

>>5165247
This.

The idea of a (local) hidden variable that we can't see is incompatible with quantum mechanics.

[Anonymous No.5165303]

>>5164198
shut up and calculate

[Anonymous No.5165306]

[Anonymous No.5165404]

>>5165303
This was actually not said by Feynman, but by Mermin.

[Anonymous No.5165454]

>>5165306
Ohh god.......

btw Schrodinger looks dapper in every photo, that man had class.

[Anonymous No.5165655]

>>5165404
I don't think he woulda said it either

[Anonymous No.5166432]

>>5165281
I assume you can cite papers that demonstrate complete restriction on hidden variables?

[Anonymous No.5166541]

>>5165655
According to wikipedia he said "If I were forced to sum up in one sentence what the Copenhagen interpretation says to me, it would be 'Shut up and calculate!'"

[Anonymous No.5166816]

>>5166432
You can refer to the EPR (Einstein-Podolsky-Rosen) paper, which claims that QED is incomplete.

[Anonymous No.5166828]

>>5166432
A. Aspect et al., Experimental Tests of Realistic Local Theories via Bell's Theorem, Phys. Rev. Lett. 47, 460 (1981)

[Anonymous No.5166854]

Does anybody know how, or what software was used to convert grayscale into full color like in OP's pic?