Miss-Interpreting Quantum Collapse.

[Schneibster]

Ah, I see. Just making sure you really get it!

 

[BillyJoe]

This is an assertion without evidence. Quantum mechanics does not distinguish "observers" from any other kind of interaction.

But the author seems to be doing away with observers altogether by putting it all down to interfering "particles".

Yes. And there's no actual reason to assume otherwise [that the observer has no effect over and above the affect of the interacting particles].

Then where is the distinguishing characteristic between quantum physics and classical physics if it is all just "interacting particles" - by which, in this context, we mean "the actual measurement interfering with the result"?

Good for her. We can do with a little less talk about the "mystery" of quantum mechanics. Especially when the "mystery" only ever happens at stages where we can't keep doing the calculations for purely practical reasons.

So you don't see anything "mysterious" in the double-slit experiment? (see above)
It's all just common sense?

"Collapse" is like the man behind the curtain in the Wizard of Oz: we can only believe it happens in cases where we can't watch it happen.

Sorry I don't understand this sentence. In any case, this is an interpretation of what happens and is not really important compared to what actually happens.

I disagree. Collapse of the wave function (meaning a discontinuous change in the quantum state of the system, rather than a continuous time evolution of the system according to the Schrodinger equation) is simply not necessary to explain any experimental results.

No, there are other equally valid interpretations. But the point was that the observer does play a role. You disagree but you haven't stated why.

 

[fls]

I don't think we are.

Perhaps, in order to avoid confusion with the meanings of the words we use, we need an example that demonstrates that it is the actual observation that causes the collapse of the wave function, and that it cannot be put down to the simple interaction of particles.

It's the double-slit experiment of course!

If you send a stream of electrons from a source towards a photographic plate with a wall containing two slits or holes between the source and the plate, an interference pattern typical of waves results. If the electrons are emitted one at a time, the same wave interference pattern results. It's as if the electron departs the source as a particle and arrives at the plate as a particle, but travels through the slits as a wave. The wave passes through both slits and forms an interference pattern on the plate.

Now, suppose we place detectors at the holes. What happens then? Well, as you know, the wave interference pattern disappears and, instead, we have a pattern that we would expect if particles were passing through the holes. The electron leaves the source as a particle, travels towards the hole as a wave, and arrives at the hole as a particle. You might say that the act of detecting/measuring the arrival of the wave at the hole collapses it to a particle. In other words, it's all caused by interacting particles.

But now, suppose we place a detector at only one of the holes. What happens now? Again a pattern typical of particles passing through the holes is obtained. But, if a million particles pass through the holes, 500,000 pass through the hole where there is no detector. There are no particles interfering with these 500,000 electrons, yet they all behave like particles instead of waves.

Therefore, the effect cannot not be just due to the interaction of particles as claimed by the author of that article, but by the observation itself. Or, at the very least, something other than just the interaction of particles. If it was just interacting particles, how would it be any different from classical physics.

Okay, so we (you, me and the author of the article) are all talking about the same thing but merely describing it in different ways. Unless you think that the placement of a single detector only eliminates the interference pattern if a human eventually becomes aware of the results (an interpretation that (afaict) is impossible to distinguish). She did not state that the effect is just due to the interaction of particles. You simply chose to interpret it that way. Whether you call it observation or measurement, in order to gather a specific kind of information, we need to interact in some way with what we want to measure or observe - to "shine a light on it". At a quantum level, the process of measurement then interferes with what we can know, in the way that has already been described by others. Yes, it is "spooky" that we can know something about quanta/wavicles/wave-particles that we don't actually interact with, but that doesn't mean that the means of observing or measuring requires a conscious observer (her point), or that the outcome is pre-determined by the means of interacting (your point). And both of these points counteract the idea that QM confirms that human consciousness creates reality as claimed in "The Secret".

I'm not going to argue with whether or not you wish to interpret her statement as necessarily meaning that it is the direct interaction of photons with the particles (as a particular example) that gives us information and therefore her statement is utter rubbish. I simply was looking for confirmation that that was what you were doing.

Linda

 

[Pragmatist]

It seems rather late in this thread to be making this point, but I don't think it's been made explicit thus far...

The OP cites an example where someone has got into the classic muddle between the simple idea that observation disturbs that which is being observed, which is trivial and does not really related to QM, and the uncertainty that is embodied in the Heisenberg relations which means that a combination certain pairs of parameters cannot be measured beyond a certain level of precision even in principle and also that the closer one confines one member of that pair to a certain value the less well-defined is the other. The latter is QM uncertainty (as I understand it and can briefly express it) the former is just an issue of experimental design (though I suppose it meets QM uncertainty in the limit).

BSM, the idea of observation disturbing the object is very much a part of QM. This is covered as one aspect of Bohr's complementarity. And Heisenberg himself fully supported that idea. To prove it, please look at Heisenberg's and Schrodinger's original writings, for example in Heisenberg's Physics and Philosophy, 1958, Chapter 3, he says:

It has been said that the atom consists of a nucleus and electrons moving around the nucleus; it has also been stated that the concept of an electronic orbit is doubtful. One could argue that it should at least in principle be possible to observe the electron in its orbit. One should simply look at the atom through a microscope of a very high revolving power, then one would see the electron moving in its orbit. Such a high revolving power could to be sure not be obtained by a microscope using ordinary light, since the inaccuracy of the measurement of the position can never be smaller than the wave length of the light. But a microscope using ~~-rays with a wave length smaller than the size of the atom would do. Such a microscope has not yet been constructed but that should not prevent us from discussing the ideal experiment.

Is the first step, the translation of the result of the observation into a probability function, possible? It is possible only if the uncertainty relation is fulfilled after the observation. The position of the electron will be known with an accuracy given by the wave length of the y-ray. The electron may have been practically at rest before the observation. But in the act of observation at least one light quantum of the y-ray must have passed the microscope and must first have been deflected by the electron. Therefore, the electron has been pushed by the light quantum, it has changed its momentum and its velocity, and one can show that the uncertainty of this change is just big enough to guarantee the validity of the uncertainty relations. Therefore, there is no difficulty with the first step.

Later in the same text he says this, which relates directly to the issue under discussion:

The observation itself changes the probability function discontinuously; it selects of all possible events the actual one that has taken place. Since through the observation our knowledge of the system has changed discontinuously, its mathematical representation also has undergone the discontinuous change and we speak of a 'quantum jump'. When the old adage 'Natura non facit saltus' is used as a basis for criticism of quantum theory, we can reply that certainly our knowledge can change suddenly and that this fact justifies the use of the term 'quantum jump'.

Therefore, the transition from the 'possible' to the 'actual' takes place during the act of observation. If we want to describe what happens in an atomic event, we have to realize that the word 'happens' can apply only to the observation, not to the state of affairs between two observations. It applies to the physical, not the psychical act of observation, and we may say that the transition from the 'possible' to the 'actual' takes place as soon as the interaction of the object with the measuring device, and thereby with the rest of the world, has come into play; it is not connected with the act of registration of the result by the mind of the observer. The discontinuous change in the probability function, however, takes place with the act of registration, because it is the discontinuous change of our knowledge in the instant of registration that has its image in the discontinuous change of the probability function.

Heisenberg's "quantum jump" in this context is of course the "waveform collapse".

 

[Pragmatist]

Fine, then I'll prove you're a fool instead of just implying it.

Do me a favor though; try to avoid looking like even more of one when I'm done by making more accusations of ad hominem attacks.

Well, there's a fine example of cognitive dissonance!

"To put it in crudely simplistic terms, as soon as the scientist switches on the light to see what’s going on, other particles, like photons, get in the way. It is the photons that are responsible for messing up the results, not the thoughts of the experimenter."

This statement is factually incorrect. It is not the means of measurement that make it impossible to determine the values of conjugate variables. They are inherently indeterminate; this is a basic characteristic of quanta, the nature of reality in the quantum realm, not an effect of measurement. Period.

So, show where she is specifically referring to "determining the values of conjugate variables."

 

[wipeout]

Therefore, the effect cannot not be just due to the interaction of particles as claimed by the author of that article, but by the observation itself. Or, at the very least, something other than just the interaction of particles. If it was just interacting particles, how would it be any different from classical physics.

In quantum physics, a particle's possible histories can interfere with each other unless the particle interacts with other particles and becomes correlated ("entangled") with them to the extent that its possible histories decohere and become seperate, non-interfering possibilities. We then find one possibility occurs. The other may have occured in a different reality, nobody knows. There is no collapse of the wave function needed. It's a mathematical shortcut that helps calculations and screws up everything else.

What all that just means is that a particle is naturally fuzzy but other particles can absorb its fuzziness and make it clear. Which is nice.

 

[Ziggurat]

Then where is the distinguishing characteristic between quantum physics and classical physics if it is all just "interacting particles" - by which, in this context, we mean "the actual measurement interfering with the result"?

The Schrodinger equation is not classical. But it is completely deterministic. There's no need to look beyond it to find the difference between classical mechanics and quantum mechanics, and it does not contain any notion of "collapse" or "observer".

So you don't see anything "mysterious" in the double-slit experiment? (see above)
It's all just common sense?

"Mysterious" and "common sense" are not antonyms. It is most certainly not common sense in terms of it matching our every-day experience with the world. But neither is it mysterious in the sense that there's some step in the process which we cannot fathom, which MUST happen any time you want to privilege an "observer" in a measurement process.

No, there are other equally valid interpretations.

There's no need for the "no" starting this sentence. Collapse is never necessary to explain any experiment. That statement does not mean collapse is not possible. It only suggests that we not bother with it since we don't need it. Occam's razor is not a proof that more complex explanations are wrong.

But the point was that the observer does play a role. You disagree but you haven't stated why.

Because nobody can even define an observer except by hand waving arguments about either macroscopic systems (ie, something we can't model quantum mechanically for purely practical reasons) or conciousness. And none of these concepts of observer (as distinct from other interactions) enter into the Schrodinger equation in any way. That means that they all require some step which violates the Schrodinger equation, but only ever at steps in the process where we can't watch it being violated. Isn't that strange?

 

[BillyJoe]

She did not state that the effect is just due to the interaction of particles. You simply chose to interpret it that way.

This is what she says:

"To put it in crudely simplistic terms, as soon as the scientist switches on the light to see what’s going on, other particles, like photons, get in the way. It is the photons that are responsible for messing up the results."

It seems pretty clear to me that she IS saying that the effect is JUST due to the interaction of particles (unless "crudely simplistic terms" means that she is actually simplifiying it to the point of it being false). But, if she is not saying that the effect is JUST due to the interaction of particles, what else is she saying (or implying) (or leaving unsaid)?

Unless you think that the placement of a single detector only eliminates the interference pattern if a human eventually becomes aware of the results (an interpretation that (afaict) is impossible to distinguish).

Let's just say that I'm becoming less certain about the role of "the observer" but more certain that it's not just "interacting particles".
But, if you are correct in saying that she is not saying it's just interacting particles, I guess I have no argument. On the other hand there are others here who are saying the opposite - that she IS saying that it's JUST interacting particles and that she IS correct in saying this!

Whether you call it observation or measurement, in order to gather a specific kind of information, we need to interact in some way with what we want to measure or observe - to "shine a light on it". At a quantum level, the process of measurement then interferes with what we can know, in the way that has already been described by others.

Your "in some way" must be pretty broard to encompass the situation where no particle is actually interfered with. I am talking, of course, about when the particle travels through one slit while the detector fails to detect (and therefore interact with) a particle at the other slit.

Yes, it is "spooky" that we can know something about quanta/wavicles/wave-particles that we don't actually interact with, but that doesn't mean that the means of observing or measuring requires a conscious observer

Yes, I'm becoming a little fuzzier on that point.

...but that doesn't mean that the means of observing or measuring requires a conscious observer (her point), or that the outcome is pre-determined by the means of interacting (your point).

She was making the point that not only can consciousness not shape reality, it does not even affect the outcome of quantum events. Of course, if it can't do the second, it certainly can not do the first. My point (of view) was that consciousness can affect quantum events by causing the wave function to collapse, but that it cannot shape reality because it cannot control the purely random nature of the collapse.

...or that the outcome is pre-determined by the means of interacting (your point).

Okay, what you are saying is that the experimental set-up determines what the outcome will be: If the experiment is set it up with no detectors, we get an interference pattern. If we set it up with detectors at both slits, we get a particle scatter pattern. If we set it up with a detector at only one slit, we get a particle scatter pattern. But I wonder why it happens in the third set-up when half the time nothing is being detected and no particles are interacting but the same interference pattern results as in the second set-up. If it's not interacting particles, what is it? I'm not happy to just leave it with "it's just that expereimental set-up, unless I really have to)

And both of these points counteract the idea that QM confirms that human consciousness creates reality as claimed in "The Secret".

Yes, this was not the point of disagreement.

 

[Ziggurat]

She was making the point that not only can consciousness not shape reality, it does not even affect the outcome of quantum events. Of course, if it can't do the second, it certainly can not do the first. My point (of view) was that consciousness can affect quantum events by causing the wave function to collapse, but that it cannot shape reality because it cannot control the purely random nature of the collapse.

This viewpoint isn't disprovable, but it's quite problematic. As you probably realize, it privileges something (conciousness) which we can't define in any rigorous sense. And it's unnecessary as well. While collapse of the wave function is useful as a practical matter, it is not contained within quantum mechanics, and we only resort to it in cases where our calculations are incomplete. The simpler explanation, therefore, is that collapse as such (meaning a non-deterministic change in the quantum state of the system) never happens at all, and that the apparent effect observed is merely the deterministic interaction of the quantum state of the system with a random initial quantum state of our measurement apparatus.

 

[BillyJoe]

The Schrodinger equation is not classical. But it is completely deterministic. There's no need to look beyond it to find the difference between classical mechanics and quantum mechanics, and it does not contain any notion of "collapse" or "observer".

Okay, I have always been a little uneasy with the concept of consciousness causing the collapse of the wave function. If they are really not required, it would certainly make it all sound a little less mysterious.

It is most certainly not common sense in terms of it matching our every-day experience with the world. But neither is it mysterious in the sense that there's some step in the process which we cannot fathom...

Did you say "we"? May you can fathom it but I must confess to being completely out of my depth!
But, seriously, how do you account for the outcome with the detector at only one slit?

Because nobody can even define an observer...or conciousness.

You mean whether an ant is conscious enough to do it, or a bacteria, or a sophisticated robot? I would certainly see that as problematic if that's what you mean.

 

[BillyJoe]

This viewpoint isn't disprovable, but it's quite problematic. As you probably realize, it privileges something (conciousness) which we can't define in any rigorous sense. And it's unnecessary as well. While collapse of the wave function is useful as a practical matter, it is not contained within quantum mechanics, and we only resort to it in cases where our calculations are incomplete. The simpler explanation, therefore, is that collapse as such (meaning a non-deterministic change in the quantum state of the system) never happens at all, and that the apparent effect observed is merely the deterministic interaction of the quantum state of the system with a random initial quantum state of our measurement apparatus.

Okay, but I'm still having trouble with the double slit single detector scenario. If the system detects/interacts with only half of the particles/waves, why don't we see a mixture of interference and particle scatter patterns on the plate?

 

[Pragmatist]

She was making the point that not only can consciousness not shape reality, it does not even affect the outcome of quantum events. Of course, if it can't do the second, it certainly can not do the first. My point (of view) was that consciousness can affect quantum events by causing the wave function to collapse, but that it cannot shape reality because it cannot control the purely random nature of the collapse.

As Ziggurat already pointed out, we have no clear definition of what consciousness even is. So any claim that it can have specific effects on quantum systems must be solely the result of speculative conjecture rather than any clearly derived formulation.

Okay, what you are saying is that the experimental set-up determines what the outcome will be: If the experiment is set it up with no detectors, we get an interference pattern. If we set it up with detectors at both slits, we get a particle scatter pattern. If we set it up with a detector at only one slit, we get a particle scatter pattern. But I wonder why it happens in the third set-up when half the time nothing is being detected and no particles are interacting but the same interference pattern results as in the second set-up. If it's not interacting particles, what is it? I'm not happy to just leave it with "it's just that expereimental set-up, unless I really have to)

It's obvious that any interference pattern in the case of 2 slits cannot be solely due to the particle or any specific property of it - because in the absence of the slits it doesn't happen.

So the key to the whole thing has to be the interaction of the particle with the slits. In other words, we need to take specific physical properties of the slits into account as well. Unfortunately most commentators simply gloss over the slits themselves and thereby lose something of the significance of the whole. The slits are not just "holes" or empty space, they are actual cavities in real materials.

If you map the physical geometry of the actual slits (sans particle) into momentum space via a Fourier transform, you get an interesting shape. If you use polar coordinates and define a mid point between the slits as the origin, the momentum space mapping of the slits appears like an antenna radiation pattern overlayed on the slits. If you then draw straight lines through the lobes of maximum intensity of that pattern and project them on to a distant screen, what you get is identical in form to the interference pattern for the particles. This clearly shows that the interference pattern is intimately related to the slits themselves as much as the particle. Here is a graphic similar to what I am talking about: http://www.bbwexchange.com/glossary/lobe2.gif

Of course classical wave theory recognises a contribution from the slits in that the size and spacing of the slits obviously changes the interference pattern, but - and this part is just my personal opinion rather than established scientific fact - what I am suggesting goes a little further than that. My departure from simple wave theory is that I believe that the slit interference pattern is somewhat independent from the particle.

When you put a detector in place to see which slit a particle went through, then of course the detector will interfere with the particle. But - here is the interesting thing to consider - does it (the detector) also "interfere" with the slits in some way independently of the particle? It's an interesting question. I can't identify a single clear mechanism by which the two would "interfere" with each other (i.e. detector and slits) but, if the two are made of real materials (the detector and the slits) and if they are not both at absolute zero then there has to be at least the possibility of some sort of electromagnetic (not to mention gravitational) interaction between the two at the very least. And, if we take the momentm space transform of the slits and detector together then obviously the pattern in momentum space will change too. So perhaps the answer to the question is not that the detector changes the particles, but rather that the presence of the detector intimately changes the geometry of the slits, or perhaps of quantum fields in space around the slits. And if that is the case, it follows that the interaction of the particle with the slits will change too, and in turn that the interference pattern must also be affected.

Anyway, that's not an authoritative answer but maybe it gives some food for thought.

On a more "official" level, it's not too difficult to show mathematically that any detector must influence a particle in a way that either is below the "limits" of the Heisenberg uncertainty (and thus leaves us in the dark about the particle to some significant extent) - or that if the influence is sufficient to resolve whatever is being measured (i.e. greater than the uncertainty limit) then the influence must radically deflect the particle to an extent where we can't reasonably expect the interference pattern to remain intact.

 

[Ziggurat]

Okay, but I'm still having trouble with the double slit single detector scenario. If the system detects/interacts with only half of the particles/waves, why don't we see a mixture of interference and particle scatter patterns on the plate?

First off, interference patterns only emerge after repeated measurements. With that in mind, here's my interpretation: a detector on one slit will interact with the component of the wave function passing through that slit, and will create a phase difference between that component and the component going through the unmonitored slit. Because the detector is in a random initial state, the phase shift will also be random. We can therefore expect that the two components WILL interfere, but their interference will be randomly determined each time by the quantum state of our detector. The net result is no visible interference pattern. We cannot distinguish between no interference pattern and an average over all interference patterns caused by this random phase shift.

 

[wipeout]

Therefore, the effect cannot not be just due to the interaction of particles as claimed by the author of that article, but by the observation itself. Or, at the very least, something other than just the interaction of particles. If it was just interacting particles, how would it be any different from classical physics.

The modern view goes a little like this...

A) When an electron goes through the two slit experiment in a vacuum, its possible histories will interfere with each other. The electron has then no single history and has therefore gone through both slits at the same time.

or

B) When an electron goes through the two slit experiment in a gas, its possible histories lose the ability to interfere with each other as they become different when the electron becomes correlated ("entangled") with the particles of the gas it interacts with in either possible journey. This means the two possible histories of the electron seperate into distinct possible events. And one of these occurs. A measuring device, observer, etc. would act just like the gas.

This effect in B is called decoherence.

The question about B is that if the history which doesn't happen occurs in another reality or if there is some unknown physical thing chosing which occurs or if nature is just simply random. Nobody knows.

In short, particles are naturally fuzzy about what they're up to but particle interactions absorb the fuzziness.

 

[fls]

This is what she says:

"To put it in crudely simplistic terms, as soon as the scientist switches on the light to see what’s going on, other particles, like photons, get in the way. It is the photons that are responsible for messing up the results."

It seems pretty clear to me that she IS saying that the effect is JUST due to the interaction of particles (unless "crudely simplistic terms" means that she is actually simplifiying it to the point of it being false). But, if she is not saying that the effect is JUST due to the interaction of particles, what else is she saying (or implying) (or leaving unsaid)?

How about....it is the act of looking at something that constrains/creates the result (e.g. removes the possibility of interference, determines the variable being measured (which determines what can't be measured), directly changes the result as in the absorption of a photon, etc.)?

Let's just say that I'm becoming less certain about the role of "the observer" but more certain that it's not just "interacting particles".
But, if you are correct in saying that she is not saying it's just interacting particles, I guess I have no argument. On the other hand there are others here who are saying the opposite - that she IS saying that it's JUST interacting particles and that she IS correct in saying this!

I don't really think that is what they are saying, but I'm pretty sure that I don't want to speak for others that are actually here (it's bad enough that I am attempting to speak for Ms. Hansen ).

Your "in some way" must be pretty broard to encompass the situation where no particle is actually interfered with. I am talking, of course, about when the particle travels through one slit while the detector fails to detect (and therefore interact with) a particle at the other slit.

Yes.

She was making the point that not only can consciousness not shape reality, it does not even affect the outcome of quantum events. Of course, if it can't do the second, it certainly can not do the first. My point (of view) was that consciousness can affect quantum events by causing the wave function to collapse, but that it cannot shape reality because it cannot control the purely random nature of the collapse.

Yes.

Okay, what you are saying is that the experimental set-up determines what the outcome will be:

Not really. I was saying the same thing that you just said - that the experimental set-up may tell us which particles have gone through the first slit, but as each particle is fired at the slits, it does not control whether that particle goes through the first slit (it just tells us whether it did after the fact).

If the experiment is set it up with no detectors, we get an interference pattern. If we set it up with detectors at both slits, we get a particle scatter pattern. If we set it up with a detector at only one slit, we get a particle scatter pattern. But I wonder why it happens in the third set-up when half the time nothing is being detected and no particles are interacting but the same interference pattern results as in the second set-up. If it's not interacting particles, what is it? I'm not happy to just leave it with "it's just that expereimental set-up, unless I really have to)

It's the elimination of the possibility of interference. The particles going through the second slit may not be interacting, but they cannot interfere with themselves (by also going through the first slit) without being detected.

Yes, this was not the point of disagreement.

That was kinda my whole point.

Linda

 

[Schneibster]

Let's just say that I'm becoming less certain about the role of "the observer" but more certain that it's not just "interacting particles".

There is a subtlety here that is worth mentioning.

Detection depends on a quantum interaction, all types of which are mediated by the exchange of quanta. In other words, all your instruments are made of quanta, and interact with quanta via the exchange of quanta. Decoherence is the idea that when these interactions occur, whatever it is that "happens" when the wave function "collapses," happens. And it doesn't matter whether anyone is looking or not, or more specifically whether the interaction is with the quanta of an instrument or with some other quanta that just happened to wander into the measurement area. The quanta interact, and a new wave function, based on the old one and on the interaction, must be used afterward. So the interaction merely represents the boundary between one wave function and another; it is decohered by the interaction. That's why it's called "decoherence."

From this point of view, the author might be considered to be "right;" however, it is clear that she cannot have been talking about decoherence, since she never invoked the concept, or even its precursors.

But, if you are correct in saying that she is not saying it's just interacting particles, I guess I have no argument. On the other hand there are others here who are saying the opposite - that she IS saying that it's JUST interacting particles and that she IS correct in saying this!

That was how I read it, too. But I think that the point is, she never made any reference to anything BUT interacting particles- specifically, she never referred to uncertainty, which is not about interacting particles, but about the parameters of quanta of which particles are merely convenient representations that are not complete.

By explicitly stating that it is the interaction with other particles that "mess up the result," she has failed to note that there are parameters that are not merely unmeasurable but have non-existent or undefined values, a far more significant "messing up of the result" than interactions with other particles; and furthermore failed to note that those interactions in and of themselves have resulted in "measurements" that have rendered some parameters unmeasurable and indeterminate, even under the wave function, which is the worst imaginable "messing up of the result."

Now, I have not seen "The Secret," nor, given her criticism, will I bother; whether her criticism of it is technically incorrect or not, it is obvious from the initial sentences of the critique that "The Secret" is another case of mysticism trying to cover itself up in quantum mechanics. To that extent, her critique is correct; however, it is important when critiquing such tripe to be strictly technically accurate, both so as not to create a false impression, and so as not to leave an opening for counter-argument based on the claim that one's explanation was false, and in this task she has failed to meet the challenge she was presented with.

It is, therefore, utter rubbish, as I stated initially.

She was making the point that not only can consciousness not shape reality, it does not even affect the outcome of quantum events. Of course, if it can't do the second, it certainly can not do the first. My point (of view) was that consciousness can affect quantum events by causing the wave function to collapse, but that it cannot shape reality because it cannot control the purely random nature of the collapse.

Again, decoherence is the idea that a conscious observer is not needed. An interaction changes the wave function forever, irreversibly. It doesn't matter whether anyone was looking or not. This idea underlies all of the successful interpretations of quantum mechanics; ones that could not accommodate it have fallen by the wayside.

Okay, what you are saying is that the experimental set-up determines what the outcome will be: If the experiment is set it up with no detectors, we get an interference pattern. If we set it up with detectors at both slits, we get a particle scatter pattern. If we set it up with a detector at only one slit, we get a particle scatter pattern. But I wonder why it happens in the third set-up when half the time nothing is being detected and no particles are interacting but the same interference pattern results as in the second set-up. If it's not interacting particles, what is it? I'm not happy to just leave it with "it's just that expereimental set-up, unless I really have to)

Another subtlety. Note that even if there is only a detector at one slit, if a photon is detected at the target but not detected at that slit, then it must have gone through the other. As soon as you can state which slit it went through, even if that is only by process of elimination, you eliminate the interference.

 

[JoeTheJuggler]

Back to the O.P.: I think the criticism of "The Secret" misusing quantum physics started with the right idea, but then overstated things eventually leading to the false statement "It is the photons that are responsible for messing up the results, not the thoughts of the experimenter."

What she was aiming for is that it's the act observation, and not the mental state (thoughts or intentions) of the observer that matters.

I think she could've gone much further (and may have as far as I know) by pointing out that all varieties of quantum weirdness disappear at levels bigger than an atom. So it's completely wrong to use Heisenberg's Uncertainty Principle, for example, on things like wealth and people.

I saw something on PBS once (maybe a NOVA program--I don't remember), where they had the "Quantum Cafe" where people were basically the quanta. People could go from here to there without ever existing in between, events may or may not happen in equal measure, time wouldn't work the way you normally think of it, etc. They were using it to illustrate points about quantum physics, but I found it more useful as an illustration of the absurdity of applying quantum physics to the world of human-scale events.

 

[Schneibster]

I saw something on PBS once (maybe a NOVA program--I don't remember), where they had the "Quantum Cafe" where people were basically the quanta. People could go from here to there without ever existing in between, events may or may not happen in equal measure, time wouldn't work the way you normally think of it, etc. They were using it to illustrate points about quantum physics, but I found it more useful as an illustration of the absurdity of applying quantum physics to the world of human-scale events.

I believe that that was one of the Brian Greene Elegant Universe series of programs.

 

[Ben Tilly]

After all of this discussion of uncertainty, why not interject a comment about what the Heisenberg uncertainty principle really says.

Suppose we have a function f whose square is integrable over the real line. (Meaning the function and its square are integrable and the integral is finite.) If we draw f^2 it is a curve with finite area under it. That area has a midpoint and a standard deviation.

Let's consider the Fourier Transform of f, let's call it F. It also will be a square integrable function with its own midpoint and standard deviation.

What Heisenberg proved was that the standard deviation of f times the standard deviation of F is at least a certain constant. (That minimum is achievable, and the functions that achieve it are the normal distributions.) Let's think of the function as a wave packet. It makes sense to talk about the standard deviation of f as how much the position of f is spread out and hence not well-defined. It makes sense to talk about the standard deviation of F as how much the frequency of f is spread out and hence not well-defined. Therefore Heisenberg's theorem says that the amount that the position is not defined times the amount the frequency is not defined must be at least a constant.

So far this is all a mathematical theorem about functions and Fourier transforms. What turns it into something important in physics is that there are several pairs of important quantities that are related to each other in quantum mechanics via a Fourier transform. For instance position and momentum. Or time and energy. In which context Heisenberg's theorem transforms into a statement that these pairs of quantities cannot both be precisely defined at the same time.

Note, I said defined, not measured. If they are not defined, then obviously you cannot succeed in measuring them. But it is not a failure of your measurement mechanism that is at fault, it is a mathematical fact of life that makes the task impossible.

Cheers,
Ben

 

[JoeTheJuggler]

So there's an episode of NUMB3RS where the hero explains that he'd neglected to take Heisenberg's Uncertainty Principle into account when he made a mathematical model of that week's crime pattern. He'd forgotten to take into account that the crook knew he was being observed.

I think "The Secret" is applying physics in a similar manner.