Miss-Interpreting Quantum Collapse.

[Schneibster]

One of the few errors they have made in that show.

 

[BillyJoe]

One of the few errors they have made in that show.

Are you saw they weren't just having a little joke?
I haven't seen the episode, but I believe that a real physicist advises on the show.
(Sorry, it might be a mathematician)

 

[BillyJoe]

That was kinda my whole point.

Hey, whose thread is this?
There was no disagreement about whether or not consciousness creates reality. We agreed from the outset that it cannot. Even if consciousness could cause collapse of the wave function, the outcome of this collapse is entirely random. Consciousness cannot force a particular outcome. Therefore it cannot create reality.

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.)?

I guess she could have meant that.

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 ).

In the light of subsequent post, I could go back and read their posts but...

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.

Sounds reasonable. But kinda weird as well.

 

[BillyJoe]

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."

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, thanks for the explanation. I am more than happy to do away with the conscious observer. It never really sat well with me in any case.

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."

Well, it seems we are all agreed that it's more than just "interacting particles" (although Linda feels it was implied, or could have been implied, or could have been imagined to have been implied, or something. - only joking Linda, I can't allow you to be totally one hundred percent right again )

...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.

That was my thought when I read the article - but for the wrong reason it now appears.

...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

Oops, now you're sounding like I did with the "conscious observer" thing. No wonder I get confused.

But I think I get it. The photon passes into both slits like a wave, is detected by/interacts with the detector, and passes somewhere through the two slits like a particle. Whether it passes through the bottom left hand bit of the first slit or the middle right hand bit of the second slit is purely a random result.

 

[fls]

Well, it seems we are all agreed that it's more than just "interacting particles" (although Linda feels it was implied, or could have been implied, or could have been imagined to have been implied, or something. - only joking Linda, I can't allow you to be totally one hundred percent right again )

I'm not about being one hundred percent right (especially since you and Schneibster weren't "wrong", just like I wasn't "right"). I'm about playing along and allowing others to be right.

Except when they're wrong. That's about 46.3 percent joking.

Linda

 

[JoeTheJuggler]

Are you saw they weren't just having a little joke?
I haven't seen the episode, but I believe that a real physicist advises on the show.
(Sorry, it might be a mathematician)

Maybe so--though I think it sounded serious. It may also have been a loose analogy (thinking about the "observer effect" made him realize the bad guy knew he was being studied) rather than some manner of incorporating Heisenberg's principle into the math he was doing.

Unfortunately for me, that bit was where I first tuned in, and I immediately thought, "Oh it's one of THOSE programs." (You know where you could substitute the work "magick" for "mathematics" and the episode would be pretty much the same.) From what you guys have said, it's not, and I should watch it for real.

 

[aerosolben]

OK, so let's talk about physics.

Bumping because Schneibster's post made the front page on reddit today, under the heading "Best explanation of what science, in general, is; that I have ever read":

http://www.reddit.com/r/science/comments/b18sh/ok_so_lets_talk_about_physics_best_explanation_of/

 

[dlorde]

Sounds like the quote is confusing a whole bunch of things - the common confusion of the problem of measurement (where bouncing measurement photons off the subject affects it) and uncertainty (HUP), where it's all a little blurry down there anyway, and the romantic Copenhagen interpretation of QM, where the (conscious) observer collapses the wave function and somehow 'causes' reality, and the idea that the way you set up your experiment determines what you will find (which, AIUI, Feynman covered with his 'sum over histories' approach).

I'm probably wrong too, but not as wrong as the quote

 

[BillyJoe]

"OK, so let's talk about physics." - Best explanation of what science, in general, is; that I have ever read.

Some of the commentary is really challenging:

damn, you made me read something long enough to have a scroll bar.

Worst semicolon; I've ever seen.

Now you need to read the best explanation of a semicolon ever written.

I like this one better: after I got cancer the doctor removed part of my colon.

Then it actually gets worse.

 

[schrodingasdawg]

BillyJoe, they're not interacting particles- they're interacting quanta, which aren't particles, and aren't waves, but partake of selected properties of both.

Physicists call these 'quanta' particles, and the probability amplitudes (usually) obey a linear wave equation, so they can reasonably well be (and often are) called waves.

 

[BillyJoe]

...okay, wavicles then.

 

[BillyJoe]

For reasons that can only be counted as masochistic, I have re-read this thread. Apparently this is the thread that set me straight about the nature of the observer effect in quantum physics. Yet, from my present vantage point only three years later, I have known this all along. How the mind does play tricks!

For reasons that must be undeniably masochistic, I have summarised the lessons learned:
(I am going to use "position", but the argument applies equally well to all other properties. And I am going to use the term "wavicles" to avert the confusion about particles and waves and whether they are one or the other, or a combination of both, or something else)

This thread is about three things:


The Heisenberg Uncertainty Principle (HUP)

Specifically it is about The Correct Understanding of HUP and The Common Misunderstanding of HUP.

The Common Misunderstanding of HUP is that the position of a quantum wavicle is, in principle, able to be determined precisely. However, because the only way to get this information is to fire other wavicles at the wavicle in question and, because doing so actually alters the position of that wavicle, in practice it cannot be done.
The first sentence is false.
The second sentence is true, but it is not what is referred to as the HUP.

The Correct Understanding of HUP is that the position of a wavicle cannot be determined even in principle, because the wavicle does not actually have a precise position.


The role of the Observer in Quantum Physics:

Specifically, the role of consciousness of the Observer on the outcome of quantum interactions.

The conciousness of the Observer actually plays no role at all in quantum interactions. Put another way, the result of a quantum experiment is not altered by the fact that the Observer is consciousness, but only by the way the experiment is set up. Once it is set up, the Observer may as well go to sleep, lapse into a coma, or die. It will not alter the outcome.

Of course, an Observer is a "complicated systems of interacting wavicles" and hence, if an Observer actually interferes with the experiment - hence altering its set up - the result of the experiment can change. But this is the result of the interaction between his "complicated system of interacting wavicles" and the wavicles in the experiment. And this has nothing to do with the Observer's conscious state.

A final point is that, when the Observer (that complicated systems of interacting wavicles) interacts with (the wavicles in) the quantum experiment, he certainly cannot willfully change the outcome in the direction he desires.


The authors article:

I still think the author has got it wrong:

If the author is familiar with The Correct Interpretation of HUP, she must also be familiar with The Common Misunderstanding of HUP. Therefore she would want to ensure that nothing she writes could be interpreted by any of her readers who do suffer from The Common Misunderstanding of HUP as reinforcing that misunderstanding.

My opinion is that what the author has written would indeed reinforce that misunderstanding, and my conclusion is that the author does indeed suffer from The Common Misunderstanding of HUP herself.

 

[schrodingasdawg]

I think your understanding is fine.

Edit: And I agree with your assessment of the author's misunderstanding.

 

[BillyJoe]

In that case, I hope you are a world famous quantum physicist!

 

[fls]

For reasons that can only be counted as masochistic, I have re-read this thread.

I re-read it as well - don't know if that makes you less masochistic or me more.

The authors article:

I still think the author has got it wrong:

If the author is familiar with The Correct Interpretation of HUP, she must also be familiar with The Common Misunderstanding of HUP. Therefore she would want to ensure that nothing she writes could be interpreted by any of her readers who do suffer from The Common Misunderstanding of HUP as reinforcing that misunderstanding.

My opinion is that what the author has written would indeed reinforce that misunderstanding, and my conclusion is that the author does indeed suffer from The Common Misunderstanding of HUP herself.

I agree. I can still recognize and sorta agree with the point I was making (that she doesn't say something that is specific enough to rule out The Correct Interpretation of HUP), but it seems more likely that her words are in reference to The Common Misunderstanding of HUP. I'm not sure this reflects well on me, though. It suggests that over the last three years, I've changed from someone who is looking for agreement to someone who is willing to be cynical.

Linda

 

[Skwinty]

I have spent the last 2 hours reading this thread.
My conclusion is that Richard Feynmann hit the nail on the head when he said" I think can safely say that nobody understands quantum mechanics"

Although he said this more than 30 years ago, it is still largely true today.
Very few people can claim to understand this topic very well.

I also think that there is a huge "mental disconnect" between "pure physics/mathematics" and "The secret/philosophy" sides of the argument.

PS What has happened to Schneibster? Why doesn't he post here anymore?

 

[Fredrik]

I don't think there's anything wrong with the quote in the OP, and I don't see anything in there that proves that she has misunderstood the uncertainty principle. She's simplifying it, but isn't that the appropriate thing to do in this type of article? Interactions will cause the apparence of collapse. For example, the double slit experiment has been performed with C70 molecules, with different values of the density of the air that the molecules must pass through. The result is that the lower the air pressure, the more the interference pattern looks like "each particle took both paths", and the higher the air pressure, the more it looks like "each particle took only one path".

If we view the molecules and the air as parts of a single quantum system, then the interactions have not collapsed the wavefunction, but they have "delocalized" the coherence of the superposition into the environment. This is what decoherence does. It makes a subsystem practically indistinguishable from being "collapsed", by moving the "quantumness" into the environment.

 

[schrodingasdawg]

In that case, I hope you are a world famous quantum physicist!

No, just a student.

My conclusion is that Richard Feynman hit the nail on the head when he said" I think can safely say that nobody understands quantum mechanics"

I think his statement was meant as a joke; if it wasn't, it's just silly. It's no more meaningful to say "no-one understands quantum mechanics" than it is to say "no-one understands classical mechanics," "no-one understands general relativity," or similar statements about any field of physics---or the other sciences, or anything else in life.

I think there is a genuine issue relating to understanding and communicating when it comes to any field of knowledge. Different people understand aspects of reality in different ways. Some people feel that they understand something when they have a rigorous set of rules for arriving at conclusions; these people would only "understand" quantum mechanics from an axiomatic approach. Others prefer to have a picture in their head, and this might cause QM to be problematic.

I myself am a bit in-between, and a picture of particles as a "wave"/"disturbance" propagating through an omnipresent medium---and wave-collapse being real---works for me. But picture is just that---a picture, a mental representation of what's going on---and without the strict set of rules for coming to conclusions, doesn't give me what I'd consider an "understanding" of QM.

I suppose another issue would be what people think of when certain words are used. Both "wave" and "particle" are adequate words to describe phenomena that occur in QM. However, some people will insist that the word particle should only refer to an object with rigid boundaries an absolute position in space, and will thus refuse to consider photons/electrons/quarks/etc. "particles", even if their understanding of the word is at odds with a great number of working physicists (such as, for instance, particle theorists).

However, these sorts of issues are not unique to QM. And to seriously insist that physicists who work everyday with QM have no understanding of it is absurd, unless your definition of "understanding" is so stringent that you can say no-one has any understanding of anything.

 

[Fredrik]

There is a fundamental difference between QM and other theories. Every theory including QM makes predictions about results of experiments, but all the classical theories are more than that. They can also be interpreted as descriptions of what actually happens between state preparation and measurement, and it's always completely obvious how to interpret the theory that way. QM seems to have many different such interpretations, and it's not at all clear that any of them is correct. They could all be wrong, which would mean that QM is just a set of rules that tells us how to calculate probabilities of possibilities.

I don't think Feynman's statement was a joke. There are of course lots of people who understand the theory, i.e. the "how to calculate" part, but no one knows how to interpret it.

 

[schrodingasdawg]

There is a fundamental difference between QM and other theories. Every theory including QM makes predictions about results of experiments, but all the classical theories are more than that. They can also be interpreted as descriptions of what actually happens between state preparation and measurement, and it's always completely obvious how to interpret the theory that way. QM seems to have many different such interpretations, and it's not at all clear that any of them is correct. They could all be wrong, which would mean that QM is just a set of rules that tells us how to calculate probabilities of possibilities.

Well, it's not really clear how classical mechanics is to be interpreted. The interpretation that the configuration of a system at any time is caused by its configuration at a prior time is the most common (probably because it's the "common sense" interpretation), but there is a more obscure teleological interpretation of classical mechanics associated with the Lagrangian formulation---i.e., the system takes the path that it does between preparation and measurement because it is "trying" (not to imply intent) to achieve its final state with the most extreme action.

Of course, one could always argue that the Lagrangian formulation of mechanics is just a mathematical trick. But either way, the "interpretation" that one makes of mechanics is metaphysical, and doesn't really affect whether someone actually understands mechanics (at least the way I understand 'understanding').

I'm not sure there's an absolutely obvious interpretation of general relativity either. Most people would agree that the theory describes the structure of space and time (rather than, say, the behavior of a tensor field defined over some fixed background), but I'm not sure it's clear whether GR implies either presentism or eternalism. Either interpretation is metaphysical, however, and choosing to believe one over the other (or neither at all) doesn't affect one's understanding of GR.

I don't think Feynman's statement was a joke. There are of course lots of people who understand the theory, i.e. the "how to calculate" part, but no one knows how to interpret it.

If someone understands the theory, then I don't see how it could be said that they don't understand the, er ... well, the field, I guess? The metaphysical interpretation isn't clear, and never can be: it's metaphysics, after all. I think understanding of the rules and how to make predictions can suffice for understanding, but I can understand being more stringent and perhaps requiring knowledge of why these rules (rather than other rules) are used and why different interpretations exist; and I can understand some people wishing to be able to form a picture in their heads. But not having a consensus on a metaphysical interpretation is a silly reason to say no-one understands a theory.