Miss-Interpreting Quantum Collapse.

[BillyJoe]

In fact why don't we all try to re-write the passage in question, they way she should have put it and see if we can come up with something that couldn't be criticised?

I was thinking the same thing.

I think the author failed miserably in her attempt to explain this to a lay audience.
The only ones who seem to have accepted what she has said, are those amongst us who are either physicists or students of physics and, even then, they've had to forgive her extremely messy phraseology.
(I'm sorry, "turning on the light" and "messing up the result" just don't cut it)

The first thing we need to do is to zero in on what exactly it is we are trying to explain and perhaps I'll give that a go first:

Pseudoscientist say that experiments in quantum physics demonstrate that the mind of the observer can shape reality. In other words, that we can change reality with our minds.

This is, of course, a simple misunderstanding of the experiment in question. The experiment we are talking about is, of course, the double slit experiment. Essentially what happens here is that if electrons pass unimpeded from source, through the double slit, to the photographic plate they will form an interference pattern on the plate. If detectors are placed at the slits to detect the passage of electrons, the interfernce pattern changes to a scatter pattern.

That's it, pure and simple

Note that there is no "observer" in that account.
So where does the observer come in?
...it is simply a metaphor for the detection device!

Physicists describe the above by saying: "when we observe which slit the electron passes through, we change the result!"
Pure metaphor.
They don't actually observe which slit the electron passes through - they put detectors there! They could set up the experiment and then go to sleep, lapse into a coma, or die, and the same result would occur. Or they could stay there watching the experiment unfold and they would still get the same result. They could concentrate their minds as hard as they like to try to change the result but it will make no difference - they will get an interference pattern if the detectors are turned off and a scatter pattern if the detectors are turned on.
The observer plays no role at all. He is irrelevant.

How to put this simply?

I think we need to explain it in terms of that metaphor.
Something along the lines of:

Quantum physicists say that the result of their experiments change when they "observe" them. But this is pure metaphor. By "observe" they simply mean that they "turn the detectors on". That's all. In other words, their experimental set up includes devices that detect the presence of electrons and, if they switch them off, they get one pattern and, if they switch them on, they get a different pattern. That's it.

 

[Robin]

How to put this simply?

I think we need to explain it in terms of that metaphor.
Something along the lines of:

Quantum physicists say that the result of their experiments change when they "observe" them. But this is pure metaphor. By "observe" they simply mean that they "turn the detectors on". That's all. In other words, their experimental set up includes devices that detect the presence of electrons and, if they switch them off, they get one pattern and, if they switch them on, they get a different pattern. That's it.

That is good. I am still working on mine.

 

[dlorde]

Can we say that what is commonly called the 'observer' is 'just' a measuring device, and that, in principle, anything that directly or indirectly interacts with the particles concerned could equally be viewed as a measuring device?

I seem to recall having a similar problem with the concept of 'observer' when discussing Einstein's thought experiments on relativity (trains moving through stations, etc). The other party in the thread continually referred to what the observer 'understood' by the described events, rather than simply what they observed. He had difficulty understanding that a mechanical device could be an observer in this context.

 

[Fredrik]

Can we say that what is commonly called the 'observer' is 'just' a measuring device, and that, in principle, anything that directly or indirectly interacts with the particles concerned could equally be viewed as a measuring device?

It needs to be a physical system with macroscopically distinguishable states. (States you can tell apart just by looking at them, and that won't be significantly disturbed by the fact that you're looking at them). A single atom can't be an observer, but a particle detector can.

To understand measurements, we need to understand something about correlations between subsystems. For example, a Stern-Gerlach apparatus that's designed to measure the spin component along the z axis of a spin-1/2 particle uses a magnet to split a beam of particles into two. After passing the magnet, the particles in the left beam are all in the "spin up" state and the particles in the right beam are all in the "spin down" state. If you send a single particle (with a suitably prepared spin state) through the device, its state will be a superposition of the two alternatives |position:left>|spin:up> + |position:right>|spin:down>. The fact that there's no |position:left>|spin:down> state in the superposition means that if we get a signal from the detector on the left, we know that the spin is in the "up" state, and the fact that there's no |position:right>|spin:up> state in the superposition means that if we get a signal from the detector on the right, we know that the spin is in the "down" state. So we measure the spin by first correlating position states with spin state, and then actually measuring the position.

In this example, the spin and the position can be thought of as two subsystems (of the system we call a "particle"), as if they were actually different physical objects, and the specific form of the superposition is then considered a correlation between subsystems. The magnet has "correlated" the classical states of the position with the classical states of the spin.

The magnet clearly interacts with the system, but this interaction isn't considered a measurement. It's a type of state preparation that's often called a premeasurement. So what's an actual measurement? That too is an interaction that correlates classical states of subsystems, but it's only considered a measurement when the states of the "specimen" (the system being "measured") are being correlated with macroscopically distinguishable states of another subsystem. If an unstable particle decays into a particle-antiparticle pair that flies off in opposite directions, their momentum states are correlated, but that clearly doesn't mean that they have been measured. If on the other hand, the spin states of a silver atom (that's the type of spin-1/2 particles used in the original Stern-Gerlach experiment) get correlated with, let's say the position of a pointer built into an electronic device that's hooked up to the detector (imagine that the pointer starts out pointing straight up, and turns to the left if it gets a signal from the left detector, and turns to the right if it gets a signal from the right detector), then the spin state has been measured.

So why are the states of some systems "macroscopically distinguishable" while the states of other systems aren't? The difference between these two types of systems is that the ones with macroscopically distinguishable states are interacting strongly with their environments. In order to preserve a quantum superposition, it's necessary to keep the system isolated from its environment. The more the system interacts with the environment, the more information about its state becomes available in the environment. It may be practically impossible to retrieve that information (say information about the position of your computer monitor from the state of the air in your room), but all it takes to turn a superposition |A>+|B> into "either |A> or |B>", is that such information exists somewhere.

I think decoherence (the branch of quantum mechanics that deals with the effects of interactions with the environment), also explains why the states I called "macroscopically distinguishable" are stable, in the sense that they can be measured without being significantly disturbed, but I don't know exactly how. (I know a little, but I don't know it well enough to attempt an explanation).

 

[dlorde]

It needs to be a physical system with macroscopically distinguishable states. ...<detailed explanation>

Thank you for that - I think that's more or less what I had in mind (in a simpler form), but there's some food for thought there.