Under what conditions will wave functions collapse in double slit experiments?

[AlonsoMcLaren]

1. Will wave functions collapse in a photon double-slit experiment after we place a detector at one of its slits and detect one photon?

2. Will wave functions collapse in a photon double-slit experiment after we detect a photon on the screen?

3. Will wave functions collapse in an electron double-slit experiment after we place a detector at one of its slits and detect one electron?

4. Will wave functions collapse in an electron double-slit experiment after we detect an electron on the screen?

 

[xts]

In most commonly accepted Bohr's (Copenhagen) interpretation:
1. Yes.
2. Yes.
3. Yes.
4. Yes.
At Copenhagen: 'detection' <=> 'collapse', but don't try to ask Danes for too precise definition of 'detection'. They used to keep common sense.

In some other interpretations the answer may be 4 * 'No'.

In yet another the answer may be: 'the question is meaningless'. (I am closest to that one, although I often use common-sense-Copenhagen approach, especially if I am supposed to calculate something rather than disputing metaphysics of 'collapse')

Try to answer only one question: 'how may you tell if the wavefunction is collapsed or not'?
Propose experimental test.

 

[Ken G]

Yes, I would say the answer is "yes" to all 4 questions in any interpretation where "collapse" is included in the description. Collapse just means the replacement of indefiniteness with definiteness. Note that whenever this happens, something else that used to be definite is now indefinite, so what we mean by "collapse" very much exposes our choices for how we are talking about the particle, and our motivation for doing the experiment. Hence collapse is not so much an interpretation of the theory of quantum mechanics, as it is an interpretation of our roles as observers.