Evolving wrote:
“The system behaves as if…”; “the neutrons behave as if…”. The whole particle passes, as ever, through the apparatus, in its indeterminate state, with all the information that its wave function contains. When the weak measurement is performed on the post-selected neutrons at the other end of the apparatus, it is “as if” the information regarding the neutron’s spin were spatially separated from the information regarding its location; but that is a quirk of the method of measurement. It is interesting, and potentially useful, as the paper says, because it allows the possibility of observing the particle without the distraction of its magnetic moment, which for the purpose of the measurement has temporarily been parked elsewhere.

Evolving wrote:I’d encourage you to look at equation 2 in the paper; Cali linked to it here:

http://www.rationalskepticism.org/physi ... l#p2053443

The equation shows the wave function after the particle has entered the beam splitter. I don’t know how to make it clearer that the information on location and on spin is present along both paths.

Evolving wrote:
“The system behaves as if…”; “the neutrons behave as if…”. The whole particle passes, as ever, through the apparatus, in its indeterminate state, with all the information that its wave function contains. When the weak measurement is performed on the post-selected neutrons at the other end of the apparatus, it is “as if” the information regarding the neutron’s spin were spatially separated from the information regarding its location; but that is a quirk of the method of measurement. It is interesting,and potentially useful, as the paper says, because it allows the possibility of observing the particle without the distraction of its magnetic moment, which for the purpose of the measurement has temporarily been parked elsewhere.

Evolving wrote:I’d encourage you to look at equation 2 in the paper; Cali linked to it here:

http://www.rationalskepticism.org/physi ... l#p2053443

The equation shows the wave function after the particle has entered the beam splitter. I don’t know how to make it clearer that the information on location and on spin is present along both paths.

Evolving wrote:I repeated it because I suspected you might have overlooked my invitation to consider equation 2, since you haven't said anything about it.

This is surprisingly hard work. If you have a good reason to suspect that the Vienna group blundered, then I'd really like to know what that reason is.

Evolving wrote:I repeated it because I suspected you might have overlooked my invitation to consider equation 2, since you haven't said anything about it.

This is surprisingly hard work. If you have a good reason to suspect that the Vienna group blundered, then I'd really like to know what that reason is.

Evolving wrote:I understand that you think this may have gone wrong with the experiment. As a matter of theory, however, do you agree that equation 2 indicates that, in the view of the experimenters, the whole wave function, location and spin, passes along both paths?

A surprising effect originating from pre- and postselection of a system is the ability to ‘separate’ the location of a system from one of its properties23, 24, 25, 26 as suggested by the Cheshire Cat story in Alice in Wonderland:

kennyc wrote:

Evolving wrote:I repeated it because I suspected you might have overlooked my invitation to consider equation 2, since you haven't said anything about it.

This is surprisingly hard work. If you have a good reason to suspect that the Vienna group blundered, then I'd really like to know what that reason is.

You know David has a mind the size of a planet and is light years beyond any known physicist. Why would anyone argue with him?

The neutrons behave as if particle and magnetic property are spatially separated while travelling through the interferometer

The measurements suggest that for the successfully postselected ensemble (only the O-detector) the neutrons’ spin travels along path I.

Suppose that we simultaneously insert detectors for ΠR , ΠL and σz . (Since ΠR and σz commute, their ordering in the
(R)
right arm does not matter.) What we see now is that whenever σz indicates net angular momentum, ΠR yields the value 1,
(R)
indicating that the photon in fact went through the right arm; whenever σz does not indicate angular momentum, ΠR yields
the value 0, indicating that the photon went through the left arm. The paradox thus evaporates. This is the standard resolution of
such counterfactual paradoxes in quantum mechanics: measurements disturb each other 1 therefore the conclusions drawn from
separate measurements do not hold when measurements are performed simultaneously. Hence one is tempted to conclude that
the paradox is nothing other than an optical illusion.

In the next section, however, we will show that there really is a Cheshire"
Cat and it is not an optical illusion. But doing so requires a subtler method.
III.
WEAK MEASUREMENTS

Evolving wrote:In the language that you quote, they put the word "separate" into inverted commas, and take pains to say things like

The neutrons behave as if particle and magnetic property are spatially separated while travelling through the interferometer

.

In other words they are not claiming that the property has really been separated from the particle: it merely appears to have been, and is an interesting effect of the method of measurement.

One has to read carefully, because they are not always equally careful; at one point they say, for instance:

The measurements suggest that for the successfully postselected ensemble (only the O-detector) the neutrons’ spin travels along path I.

I take it that we have to interpret the word "suggest" as the equivalent of "behave as if" - because if they meant here that the spin actually does travel along path I, they would be contradicting what they say in the remainder of the paper.

DavidMcC wrote:

kennyc wrote:

Evolving wrote:I repeated it because I suspected you might have overlooked my invitation to consider equation 2, since you haven't said anything about it.

This is surprisingly hard work. If you have a good reason to suspect that the Vienna group blundered, then I'd really like to know what that reason is.

You know David has a mind the size of a planet and is light years beyond any known physicist. Why would anyone argue with him?

I suppose you think that anything some researchers publish must be just fine and dandy, right?
I am not claiming toi have a brain the size of a planet, but I do have some professional experience of experiments that need coincidence detection, so I know what am talking about, unlike you, it seems.

Evolving wrote:I do have a brain the size of a planet and I am feeling very depressed.