Layman's questions regarding Measurement Problem

[lauchlan]

Not sure if anyone will be able to answer these questions but it would be good if someone would give it a shot.

A friend recently explained the measurement problem to me and i thought of a few questions which he was not able to answer.

A) Do animals count as observers, and can they cause wave function collapse?

B) If i were in the same room as the experiment while observing the electrons via an observation device then as i understand it the wave function collapse will occur. But, what would happen if i were one the other side of the planet, viewing the experiment through via data stream?

C) If i am controlling the experiment but not observing observing it, will the wave function collapse occur?

D) If a computer program that was sentient observed the experiment, would the collapse occur? I know that nobody actually knows the answer to this but some theories would be great.

Thank you in advance guys.

Sorry if these questions are lame but this has really intrigued me and i can't seem to find answers to my questions due to the fact that most papers i find on the subject are written in what may as well be Greek to me.

 

[StevieTNZ]

There have been no definite experiments done to rule out explanations on how collapse occurs. It MAY be animals collapse the wave function, it MAY be our consciousness does. That's all we can say right now.

 

[homeomorphic]

It may be animals, but I think it's highly unlikely because that gives special preference to things that, from nature's point of view, don't seem to be special. An electron is an electron, whether or not it is in an animal's brain. So, if it turned out that animals collapsed the wave function, that would be very bizarre, indeed, and there is certainly no reason to believe that that is the case. However, the phenomenon of consciousness is a mysterious one that seems, at least on the face of it, to be a manifestation of nature giving animals a preferred status, so I could be wrong.

For that matter, wave function collapse seems to me to be a mere procedure for predicting the results of experiments, with no clear relation to reality, as such. What is going on behind the scenes remains a mystery.

 

[rpt]

I have read that some people argue, not only animals but all the matter around us is consciousness. This is to say that the reality existed even before the life appeared on earth.

 

[StevieTNZ]

There is also Bohm Mechanics, which 'apparently' mimics quantum predictions, except reality exists at all times, without the need for a wave function collapse.

 

[StevieTNZ]

I might also add decoherence is used by some to explain the measurement problem. Though there are many that argue decoherence does not lead to any solution of the problem.

 

[rpt]

I found the following paper on conscious observer in quantum experiment, in the Journal of Cosmology, 2011.

http://journalofcosmology.com/Consciousness135.html

Hope you would find its interesting.

 

[A. Neumaier]

A) Do animals count as observers, and can they cause wave function collapse?

Yes. Anything big enough collapses the wave function of a system observed by it.

But also a photodiode, or any other measuring device. These are far more reliable than animals,
whom to teach to measure something well is really difficult.

In physics, one usually chooses the simplest explaining set-up - so one doesn't complicate things by replacing a reliable device by something complex such as an animal or a human.

Computer programs are not observers, as the former are not material things. But if a program is in control of a measuring process the.the controlled measuring devices are observers.

 

[rpt]

StevieTNZ,

Can you explain how does the reality exist all the time without wave function collapse according to Bhorm mechanics?

 

[homeomorphic]

Yes, animals collapse the wave function. I was talking about whether conscious creatures are the ONLY things that do so, which some people have argued for.

 

[homeomorphic]

The point is that it is possible to consider a measurement as just time evolution, provided that there's some other collapse later on. So, one idea is that maybe the cut-off point where the "real" collapse happens is with conscious observers.

Also, some people don't believe in collapse at all.

 

[e.bar.goum]

rpt - I'm not sure if I'd consider something published in the Journal of Cosmology reputable. At all.

I'm uncomfortable with the idea that it requires a "consciousness" to collapse a wave-function. To me, that sounds more like pseudo-science than MWI. Photodiodes collapse wave functions, and unless your definition of consciousness is pretty broad, it's not going to include that.

The measurement problem is interesting, and I don't think it's solved by invoking consciousness.

 

[DaveC426913]

Observation is not a matter of living things at all. In a quantum sense, think of observation more like 'interaction'. Atoms can interact with other atoms. Very simplistically, this is effectively an observation.

 

[homeomorphic]

I'm uncomfortable with the idea that it requires a "consciousness" to collapse a wave-function. To me, that sounds more like pseudo-science than MWI. Photodiodes collapse wave functions, and unless your definition of consciousness is pretty broad, it's not going to include that.

I don't like the idea, myself, but see, for example Sudbury's book Quantum Mechanics and the Particles of Nature, Chapter 5. He mentions this idea there. You don't have to include photodiodes because, as I said, you can actually incorporate any measurement into Schrodinger evolution, as Sudbery explains in his book. But the catch is that it just pushes the problem somewhere else, rather than solving the problem. So, the idea was to push the problem into consciousness. Probably, whoever put forth this idea would admit that it was speculative, at best.

I don't THINK collapse has anything to do with consciousness, and there is no reason to believe it does, but it's a vague possibility.

 

[e.bar.goum]

I don't like the idea, myself, but see, for example Sudbury's book Quantum Mechanics and the Particles of Nature, Chapter 5. He mentions this idea there. You don't have to include photodiodes because, as I said, you can actually incorporate any measurement into Schrodinger evolution, as Sudbery explains in his book. But the catch is that it just pushes the problem somewhere else, rather than solving the problem. So, the idea was to push the problem into consciousness. Probably, whoever put forth this idea would admit that it was speculative, at best.

I don't THINK collapse has anything to do with consciousness, and there is no reason to believe it does, but it's a vague possibility.

Wait, what? The entire point of the measurement problem is that it cannot be encoded into Schrodinger evolution! Do you have a paper on this subject?

 

[homeomorphic]

Wait, what? The entire point of the measurement problem is that it cannot be encoded into Schrodinger evolution!

Yes, and that's why I said, it doesn't solve the problem, just pushes it somewhere else. There is a collapse, eventually, but it may happen in a later experiment.

Do you have a paper on this subject?

The place where I read about this is Sudbery. That's the only reference I know. He's not claiming that you can incorporate measurement into Schrodinger evolution, exactly. Read it and you'll see.

 

[e.bar.goum]

Yes, and that's why I said, it doesn't solve the problem, just pushes it somewhere else. There is a collapse, eventually, but it may happen in a later experiment.

The place where I read about this is Sudbery. That's the only reference I know. He's not claiming that you can incorporate measurement into Schrodinger evolution, exactly. Read it and you'll see.

Then what is he claiming? I'm just going on what you claimed he said.

I don't much fancy tracking down a book just to see a proof. And anything can be written in a book. There must be a paper on the topic, surely. Does this interpretation have a name?

 

[DaveC426913]

Then what is he claiming? I'm just going on what you claimed he said.

If one goes back to Schrodinger's poor cat in the box, one can easily imagine putting the entire contraption in a sealed box with a camera that records whether the cat is alive or dead upon opening the inner box. But this just means there are two states inside the outer box - one where the box was opened and the camera imaged a live cat, and the other where the box was opened and the camera imaged a dead cat. You've collapsed a function but you've just pushed the problem outward one box.

You could observe the experiment, check the camera recording, which would collapse it into one state or the other - but what if someone put you and the contraption in a box and did not observe you? There'd be one state where you saw a camera that detected a dead cat, and another state where you didn't. It wouldn't collapse until you were let out of the box and observed.

 

[homeomorphic]

Well, maybe I will go check it out for you, and post when I have it figured out. It's been a while since I have thought about it.

Roughly, you consider the measuring device as some huge quantum mechanical system.

I'll have to post about it later when I have time to work it out/look it up. There must be some old papers that discuss these things. The fact that it is in a book doesn't really matter. He proves what he proves.

I don't know if it has a name.

 

[e.bar.goum]

If one goes back to Schrodinger's poor cat in the box, one can easily imagine putting the entire contraption in a sealed box with a camera that records whether the cat is alive or dead upon opening the inner box. But this just means there are two states inside the outer box - one where the box was opened and the camera imaged a live cat, and the other where the box was opened and the camera imaged a dead cat. You've collapsed a function but you've just pushed the problem outward one box.

You could observe the experiment, check the camera recording, which would collapse it into one state of the other, but what if someone put you and the contraption in a box and did not observe you? There'd be one state where you saw a camera that detected a dead cat, and another state where you didn't. It wouldn't collapse until you were let out of the box and observed.

Right. Thanks. I've seen that before, it's rather obvious in formal notation. It certainly doesn't solve anything though, unless you're fond of MWI. (Which I kind of am. I blame my advanced theoretical physics lecturer for that)

homeomorphic - it's fine, DaveC has explained his argument, I've seen it before.

 

[homeomorphic]

You could observe the experiment, check the camera recording, which would collapse it into one state of the other, but what if someone put you and the contraption in a box and did not observe you? There'd be one state where you saw a camera that detected a dead cat, and another state where you didn't. It wouldn't collapse until you were let out of the box and observed.

Yeah, that's pretty much what he says, but he does the math that says that.

 

[DaveC426913]

Yeah, that's pretty much what he says, but he does the math that says that.

If one accepts the premise of the Schrodinger experiment in the first place then this "Russian doll" escalation of the experiment is a logically inescapable outcome - but having a mathematical proof doesn't hurt.

 

[A. Neumaier]

Yes, animals collapse the wave function. I was talking about whether conscious creatures are the ONLY things that do so, which some people have argued for.

Well, a photodiode may be considered to be consious of what it observes. Then the answer is yes. If consciousness refers to the kind humans (and animals?) enjoy, the answer is clearly No.

 

[A. Neumaier]

The point is that it is possible to consider a measurement as just time evolution, provided that there's some other collapse later on. So, one idea is that maybe the cut-off point where the "real" collapse happens is with conscious observers.

Also, some people don't believe in collapse at all.

There is universal agreement that collapse is _observable_ in open systems; it is an intrinsic part of the way theses systems are commonly modeled.

What is debatable is only whether it occurs in closed systems. But this is a moot question, as an observed system is never closed.

 

[A. Neumaier]

Observation is not a matter of living things at all. In a quantum sense, think of observation more like 'interaction'. Atoms can interact with other atoms. Very simplistically, this is effectively an observation.

No, not according to standard usage. A measurement/observation requires that the measurement result is irreversibly recorded (at least for some macroscopic time interval).

 

[homeomorphic]

Well, a photodiode may be considered to be consious of what it observes. Then the answer is yes. If consciousness refers to the kind humans (and animals?) enjoy, the answer is clearly No.

Not clear in the sense that I was using. I was making a distinction between "real" collapse and other collapses, which are just procedures. Of course, in this sense, it is also not clear that collapses caused by animals are "real".

It's a moot point for me because I consider collapse to be a mathematical procedure, only, so there's no "real" collapse at all. Or maybe there is a "real" collapse, but I don't care because I'm mainly concerned with predicting the results of experiments (unless I want to speculate on interpretation, just for the fun of it).

 

[homeomorphic]

There is universal agreement that collapse is _observable_ in open systems; it is an intrinsic part of the way theses systems are commonly modeled.

But we're talking about interpretation, rather than modeling. From a modeling point of view, there may be lots of collapses. But from an interpretational point of view, the question is open as to which of these, if any, are the "real" collapses.

 

[A. Neumaier]

But we're talking about interpretation, rather than modeling. From a modeling point of view, there may be lots of collapses. But from an interpretational point of view, the question is open as to which of these, if any, are the "real" collapses.

A real collapse is an observable collapse, and that happens all the time in real, open systems.

Closed systems are not observable from the outside, hence it is both irrelevant and undecidable whether or not there is a collapse.

The interpretational problems only appear if one tries to treat an observed, hence open system as a closed system, and then wonders why there are apparent problems arising from taking an idealization for the real thing.

The description by von Neumann's (who introduced consciousness into the interpretational debate) applies only to observations from outside, not to observations from inside a system, as it must be when one assumes as given a closed system, described by the Schroedinger equation. Thus the usual discussions already start from an inconsistency of the descriptions.

On the other hand, nobody seems to have a useful framework for interpreting how to observe a quantum system from inside. Thus there is currently no consistent framework to discuss the question.

 

[akhmeteli]

There is universal agreement that collapse is _observable_ in open systems

Could you please give a reference?

Thank you

 

[A. Neumaier]

Could you please give a reference?

In quantum optics, one routinely observes and analyzes quantum jumps, the most conspicuous experimental demonstrations of collapse. See, e.g.,
RG Hulet, DJ Wineland, JC Bergquist, WM Itano
Precise test of quantum jump theory
Phys. Rev. A 37, 4544 - 4547 (1988)
or
N Gisin, PL Knight, IC Percival, RC Thompson, and DC Wilson
Quantum State Diffusion Theory and a Quantum Jump Experiment
Journal of Modern Optics 40, 1663 (1993)
A much-cited paper is
MB Plenio, PL Knight
The quantum-jump approach to dissipative dynamics in quantum optics
Rev. Mod. Phys. 70, 101 - 144 (1998).

The Lindblad equations, universally used to describe the dynamics of (mixed) states of open systems have dissipative terms, which are the leftover of collapse when averaged over the quantum jumps.

 

[Eimacman]

Greetings lauchlan:

If I understand the original question, human beings or any others that I know of can not observe individual electrons directly. It requires some kind of instrumentality, and it is that instrumentality by its very nature of being able to observe the electrons causes the collapse of the wave function, not a person, life form, or apparatus, that receives the data from the instrumentality.

Therefore:

A) Do animals count as observers, and can they cause wave function collapse?

No.

B) If i were in the same room as the experiment while observing the electrons via an observation device then as i understand it the wave function collapse will occur. But, what would happen if i were one the other side of the planet, viewing the experiment through via data stream?

No, and no effect.

C) If i am controlling the experiment but not observing observing it, will the wave function collapse occur?

Possible if you are controlling the observing instrumentality, otherwise no.

D) If a computer program that was sentient observed the experiment, would the collapse occur? I know that nobody actually knows the answer to this but some theories would be great.

Again no. Only the actual observing instrumentality can cause the collapse all others would only being seeing the data from the observing instrumentality. Interpretations thereof would depend on that which was receiving the data.

 

[lauchlan]

OMG OMG OMG!


The universe really wanted me to have an answer to this question. Let me explain.

I posted this question a few days ago. I have never met a quantum physicist in my entire life and then yesterday, as i am a gas engineer, i worked in David Deutsch's house...

David Deutsch laid the foundations of the quantum theory of computation, and has subsequently made or participated in many of the most important advances in the field, including the discovery of the first quantum algorithms, the theory of quantum logic gates and quantum computational networks, the first quantum error-correction scheme, and several fundamental quantum universality results. He has set the agenda for worldwide research efforts in this new, interdisciplinary field, made progress in understanding its philosophical implications (via a variant of the many-universes interpretation) and made it comprehensible to the general public, notably in his book The Fabric of Reality.

Basically he told me that if you subscribe to the single universe idea then you could believe that consciousness collapses the wave function. But, if you subscribe to the multi universe theory then all you are seeing is a single slice of the pie, and hence one of the outcomes of the many available to the electron. Kind of like it is spread out over all the universes, but you can only see one outcome. I think that is what he meant.

Anyway, for those of you debating this and who are interested in his answer to it, you should read his book, apparently this topic is discussed at length in chapter two. Can't wait to have some time off i Jan to get through it.

Still can't believe my luck. Seriously, what are the chances, i do live in Oxford, but still. Do hope he invests in a new boiler though because the one he has is probably going to end end his life in this universe.

Thanx again for all the replies guys :)

 

[akhmeteli]

In quantum optics, one routinely observes and analyzes quantum jumps, the most conspicuous experimental demonstrations of collapse. See, e.g.,
RG Hulet, DJ Wineland, JC Bergquist, WM Itano
Precise test of quantum jump theory
Phys. Rev. A 37, 4544 - 4547 (1988)
or
N Gisin, PL Knight, IC Percival, RC Thompson, and DC Wilson
Quantum State Diffusion Theory and a Quantum Jump Experiment
Journal of Modern Optics 40, 1663 (1993)
A much-cited paper is
MB Plenio, PL Knight
The quantum-jump approach to dissipative dynamics in quantum optics
Rev. Mod. Phys. 70, 101 - 144 (1998).

The Lindblad equations, universally used to describe the dynamics of (mixed) states of open systems have dissipative terms, which are the leftover of collapse when averaged over the quantum jumps.

Thank you very much for the references. I'm still not sure though. Those references do not seem to have wordings similar to what you offer: "There is universal agreement that collapse is _observable_ in open systems" . Furthermore, everybody emphasizes that the transition from one state to another is fast, but continuous (so theoretically there is always a superposition); therefore, the only thing one can say is that under some conditions collapse can be a good approximation. No authors of your references seem to claim any experimental deviations from unitary evolution. On the other hand, unitary evolution directly contradicts strict collapse, as defined in the projection postulate. So I tend to accept the Schlosshauer's conclusion (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149)):

"no positive experimental evidence exists for physical state-vector collapse"

 

[homeomorphic]

A real collapse is an observable collapse, and that happens all the time in real, open systems.

But what does it mean for a collapse to be "observable"?

I don't know if it is the collapse itself that is observable. I would tend to think it was more like the result of the collapse. So, I see the collapse as more of a mathematical black-box, and the measurement itself (say, position of the electron is between x and y), as the "real" thing.

 

[StevieTNZ]

Wouldn't an open system still be described fundamentally by the Schrodinger equation, hence superpositions all the way?

 

[A. Neumaier]

Thank you very much for the references. I'm still not sure though. Those references do not seem to have wordings similar to what you offer: "There is universal agreement that collapse is _observable_ in open systems" .

The wording is mine, but the meaning is the same. An open system is dissipative, and dissipation is just the form an incomplete collapse takes. The equations for open systems and the equations for objective collapse http://en.wikipedia.org/wiki/Ghirardi-Rimini-Weber_theory are essentially of the same form. The main difference is that objective collapse theories believe that collapse happens at the most fundamental level, while the general theory of open systems takes its equations to be just as empirically validated rather than as fundamental, and often derives it under some plausibility assumptions (that are difficult to justify rigorously) from an underlying Schroedinger equation.

Furthermore, everybody emphasizes that the transition from one state to another is fast, but continuous

This just means that the collapse is only approximate, but to a very good approximation. The collapse in the Copenhagen interpretation also happens gradually, in the course of completing a measurement; it is instantaneous only in the unphysical idealization that a measurement takes no time.

What happens during the measurement duration is not specified by the Copenhagen interpretation, and therefore can well be continuous.

(so theoretically there is always a superposition); therefore, the only thing one can say is that under some conditions collapse can be a good approximation.

Just like all claims made in physics - I never heard even a single claim that models used in physics are accurate to infinite number of digits!

No authors of your references seem to claim any experimental deviations from unitary evolution.

The equations used for the quantitatively correct modeling of open system are without exception non-unitary. Unitary evolution is at best claimed for the much bigger, practically unobservable system composed of the actually observed system and its environment.

On the other hand, unitary evolution directly contradicts strict collapse, as defined in the projection postulate.

Well, if you take both unitary evolution and the projection postulate as absolute truth, exact to infinitely many decimal places, you get a contradiction. But it is ridiculous to regard it as that. There have been many measurements of spectroscopic energy levels, but none of them produced an exact infinite decimal expansion of a discrete eigenvalue of the Hamiltonian (normalized to ground state zero) as would be required by the Born rule as typically stated in textbooks. This shows that these postulates must be regarded as approximations.

 

[A. Neumaier]

But what does it mean for a collapse to be "observable"?

I don't know if it is the collapse itself that is observable. I would tend to think it was more like the result of the collapse. So, I see the collapse as more of a mathematical black-box, and the measurement itself (say, position of the electron is between x and y), as the "real" thing.

If you continually observe a 2-state system with eigenvalues 0 and 1 (as in the references given), and you find that the monitored variable changes randomly from 0 to 1 and back, what else are you observing than a randomly repeated collapse? If the term collapse has any meaning at all, it is this, since the Born rule asks for precisely such a behavior.

 

[A. Neumaier]

Wouldn't an open system still be described fundamentally by the Schrodinger equation, hence superpositions all the way?

An open system cannot be described by a Schroedinger equation. It is either described by a Lindblad evolution equation for the density matrix (see http://en.wikipedia.org/wiki/Lindblad_equation ) or on a more detailed level by a stochastic Schroedinger equation (with random collapses), from which one gets the Lindblad equation by averaging.

 

[StevieTNZ]

So the Lindblad equation is like a density matrix equation, which only includes partial information of the quantum system in question.

 

[homeomorphic]

If you continually observe a 2-state system with eigenvalues 0 and 1 (as in the references given), and you find that the monitored variable changes randomly from 0 to 1 and back, what else are you observing than a randomly repeated collapse? If the term collapse has any meaning at all, it is this, since the Born rule asks for precisely such a behavior.

Hmm...

Well, I will give it some thought. I can't muster a good response at the moment. Too much end of the semester pressure.

I am not a physicist by training, just a poor, helpless math grad student who dabbles in it. I have a physics grad student friend who I guess you could say is an atheist with respect to collapse (and some of that probably rubbed off on me), whereas, I am more agnostic, maybe even leaning towards it, but I'm not sure that whether you believe in collapse or not is really the issue at stake here.

We'll see if I have any time to think about quantum mechanics over the break. It's probably fairly unlikely, given the academic pressure that is on me right now (trying to graduate/publish/teaching difficulties--I'm about to explode under the pressure).

 

[akhmeteli]

Dear A. Neumaier,

Thank you very much for the reply.

The wording is mine,

That’s what I thought:-)

but the meaning is the same.

And, with all due respect, I cannot accept such unpublished (as far as I know) wording, as it’s clearly arbitrary and maybe misleading. I can also offer the following wording: “There is universal agreement that collapse is an artifact of noise”, but you don’t have to accept such wording, although the meaning is pretty much the same.

An open system is dissipative, and dissipation is just the form an incomplete collapse takes. The equations for open systems and the equations for objective collapse http://en.wikipedia.org/wiki/Ghirardi-Rimini-Weber_theory are essentially of the same form. The main difference is that objective collapse theories believe that collapse happens at the most fundamental level, while the general theory of open systems takes its equations to be just as empirically validated rather than as fundamental, and often derives it under some plausibility assumptions (that are difficult to justify rigorously) from an underlying Schroedinger equation.

Precisely:-) So my problem with your wording is that it is not clear from it that it is just “empirically validated rather than ... fundamental”, and that is why your wording may be misleading.

This just means that the collapse is only approximate, but to a very good approximation. The collapse in the Copenhagen interpretation also happens gradually, in the course of completing a measurement; it is instantaneous only in the unphysical idealization that a measurement takes no time.

As far as I understand, there are several modifications of the Copenhagen interpretation, and in some of (most popular of) them the collapse is actually defined by the projection postulate, where measurement time is not mentioned at all, as far as I know. I fully agree with your emphasis on the nonzero duration of measurement, but typically it is not mentioned at all, so there is a good chance (or a bad chance, if you wish:-)) that your wording will be taken out of context.

What happens during the measurement duration is not specified by the Copenhagen interpretation, and therefore can well be continuous.

Precisely:-), so it can well be zero in that interpretation:-)

Just like all claims made in physics - I never heard even a single claim that models used in physics are accurate to infinite number of digits!

I fully agree, but again, we need to draw the distinction between “fundamental” and “empirically validated”, in particular, “fundamental” and “empirically validated” models. Let me explain. Classical mechanics is a fundamental model, and there is no irreversibility in such a model, whereas thermodynamics is “empirically validated” in some sense, and it assumes irreversibility. Is classical mechanics accurate to infinite number of digits? Certainly not, but within classical mechanics as a model, the recurrence theorem holds, which requires accuracy to (for all practical purposes - FAPP) infinite number of digits. The same is true about quantum theory. Unitary evolution is fundamental, furthermore, there is no experimental evidence of deviations from unitary evolution. Again, within unitary evolution as a model, the quantum recurrence theorem holds, which requires accuracy to (FAPP) infinite number of digits. There is, however, an additional problem in quantum theory, as compared with classical mechanics: many people perceive collapse (e.g., projection postulate) as fundamental, whereas I think it is not fundamental, it is just an approximation, as you say.

The equations used for the quantitatively correct modeling of open system are without exception non-unitary. Unitary evolution is at best claimed for the much bigger, practically unobservable system composed of the actually observed system and its environment.

I insist, nevertheless, that “No authors of your references seem to claim any experimental deviations from unitary evolution.” If you claim such experimental deviations, please say so. (If you say that there are deviations in the presence of noise, well, I have to agree, but such a statement is pretty much tautological.) Thermodynamics is extremely useful, but its success is no evidence of deviations from (say, classical) mechanics, although thermodynamics assumes irreversibility, whereas, strictly speaking, there is no irreversibility in mechanics

Well, if you take both unitary evolution and the projection postulate as absolute truth, exact to infinitely many decimal places, you get a contradiction. But it is ridiculous to regard it as that.

I am not sure it is ridiculous, if we are talking about the fundamental level, otherwise, e.g., the recurrence theorem is ridiculous, whereas I believe it is an important result, which helps us to understand the true place of thermodynamics in physics. Similarly, “if you take both unitary evolution and the projection postulate as absolute truth, exact to infinitely many decimal places,” you obtain a useful result: the contradiction, which proves that unitary evolution and the projection postulate cannot be both absolute truth. My bet is unitary evolution is fundamental, whereas the projection postulate is not. I guess you agree at least with the latter statement, as you admit that “the collapse is only approximate”. You may say, of course, that I am nitpicking, but I don’t think so. Indeed, the Bell theorem is an extremely important result, but it does exactly what you call “ridiculous”, i.e. takes “both unitary evolution and the projection postulate as absolute truth”, as both of them are required to prove that the Bell inequalities are indeed violated in quantum theory. Approximations are not enough, as there is no such thing as “approximate nonlocality” (I consider this issue in my published article http://www.akhmeteli.org/akh-prepr-ws-ijqi2.pdf , using other people’s arguments; there are some improvements in another published article http://akhmeteli.org/wp-content/uploads/2011/08/JMAPAQ528082303_1.pdf and later preprints).

Let me emphasize that I am not trying to say that unitary evolution will agree with experimental results to infinitely many digits. I am saying that, as of today, unitary evolution is fundamental, and there is no experimental evidence of deviations from unitary evolution. If and when such deviations (e.g., objective collapse) are discovered, I will have to adapt my views accordingly.

There have been many measurements of spectroscopic energy levels, but none of them produced an exact infinite decimal expansion of a discrete eigenvalue of the Hamiltonian (normalized to ground state zero) as would be required by the Born rule as typically stated in textbooks. This shows that these postulates must be regarded as approximations.

That does not mean that unitary evolution is an approximation (as of today). While there are indeed discrete transition frequencies in elementary quantum mechanics, there are no such discrete frequencies, if you take into account natural line width (using QED).

Just a few general words in conclusion. It looks like we pretty much agree on the facts, but disagree on their interpretation. What you say may be OK at the empirical level, but this thread is about “layman’s questions”, and it seems that OP is interested in philosophical implications of quantum physics, rather than in its applications, so maybe we should discuss the fundamental level. And again, at the fundamental level, "no positive experimental evidence exists for physical state-vector collapse" (Schlosshauer)

 

[lauchlan]

and it seems that OP is interested in philosophical implications of quantum physics, rather than in its applications, so maybe we should discuss the fundamental level. And again, at the fundamental level, "no positive experimental evidence exists for physical state-vector collapse" (Schlosshauer)

Indeed you guys lost me some time ago.

Not sure if you noticed my earlier post saying that i strangely met one of the most prominent quantum physicists in the UK the other day? Anyway, it would be great if you guys could elaborate a little on the single and multi universe theory as regards wave function collapse. David seemed to explain it pretty quickly from that standpoint, though after thinking about it i am still slightly confused about something.

From a multi universe standpoint it is easy for me to understand that actually the electron is not spread out all over the place, and that when the wave function collapses we see just one of the outcomes, in our one slice/dimension.

But regardless of weather or not there is one or many universes, our observing the electron in this universe still does something to it? And it is this this that i don't understand.

I am not interested in the philosophical implications of this effect, but just really interested in what i perceive as reality and trying to understand more about it. Also, it seems to me that what we do here must affect other dimensions because let's say for example sake that there are 100 dimensions with 100 options for the electron to choose from, well if we do something here and it uses on of its options in our dimension, then that means it only has ninety-nine options left. So if its potential is checked in those dimensions then it would now be 99 instead of 100? Meaning it has been affected there too. Would be great if you could shed some light on this.

I have to say thank you again for your discussion here. Being an engineer most of this is above my station but i have managed to hang on by a thread and think i understand a lot of what you guys have shared.

 

[thedeester1]

Ill spell it out...You put a cat in a box...No matter what experiment you perform it will become agitated due to claustrofobia!


All experiments with cats prove is that they hate boxes! if they are put in them...On the other hand a cat will sleep in a box at every given opportunity...unless you put it in the box yourself...go figure that...:)

 

[lauchlan]

Sorry but i don't understand what you are saying?

Putting cats in boxes? Maybe i can't read because if that is "spelling it out" then clearly i don't know my ABCs.

 

[A. Neumaier]

And, with all due respect, I cannot accept such unpublished (as far as I know) wording,

Wording on PF is generally unpublished unless one quotes something explicitly.

Precisely:-) So my problem with your wording is that it is not clear from it that it is just “empirically validated rather than ... fundamental”, and that is why your wording may be misleading.

Pull your own ears! You use Schlosshauers conclusions in the same unqualified way, where it is not clear from the quote that it is just fundamentally postulated rather than empirically validated. Pull your own ears!

The same is true about quantum theory. Unitary evolution is fundamental, furthermore, there is no experimental evidence of deviations from unitary evolution.

Actually, strictly speaking, there is no experimental evidence in favor of unitary evolution, as all observed processes are dissipative. It is only when you neglect dissipation that you get somenthing unitary. Thus unitarity is a purely theoretical idealization.

 

[akhmeteli]

Wording on PF is generally unpublished unless one quotes something explicitly.

I was not implying that you were breaking the PF rules. I just opined that you offered your own interpretation, and your references do not seem sufficient to warrant this interpretation, it requires a leap of faith as well. I just said I was not ready for such a leap.

Pull your own ears! You use Schlosshauers conclusions in the same unqualified way, where it is not clear from the quote that it is just fundamentally postulated rather than empirically validated.

I respectfully disagree. It is absolutely clear from the words "experimental evidence" in the quote that it is not "just fundamentally postulated". Schlosshauer's work (to a large part) is actually a review of experiments.

Pull your own ears!

I regret that I happened to irritate you. I can only assure you that I am not your enemy. However, one more personal attack like this, and I'll have to conclude that discussing anything with you is not in my best interests.

Actually, strictly speaking, there is no experimental evidence in favor of unitary evolution, as all observed processes are dissipative. It is only when you neglect dissipation that you get somenthing unitary. Thus unitarity is a purely theoretical idealization.

Then there is no experimental evidence of anything - there are always some idealizations:-) Why do I think though that unitarity's experimental status is much better than that of collapse? Because each time there is an apparent deviation from unitarity, one can always find a specific source of this deviation:
"(i) the universal validity of unitary dynamics and the superposition principle has been confirmed far into the mesoscopic and macroscopic realm in all experiments conducted thus far;
(ii) all observed ‘‘restrictions’’ can be correctly and completely accounted for by taking into account environmental decoherence effects;"
(Schlosshauer, ibid.)
On the other hand, you yourself admit that collapse is an approximation.

 

[A. Neumaier]

On the other hand, you yourself admit that collapse is an approximation.

It is exactly the same sort of approximation as unitarity. Both help to have simpler models than if one takes everything into account that affects experiments.

 

[akhmeteli]

It is exactly the same sort of approximation as unitarity. Both help to have simpler models than if one takes everything into account that affects experiments.

Again, I respectfully disagree. As of today, there are no unaccountable deviations from unitarity (on the other hand, there is no positive experimental evidence of collapse). If and when such deviations are found, we will be able to call unitarity "an approximation". And even then we won't be able to say that collapse " is exactly the same sort of approximation as unitarity", - for example, we cannot say that thermodynamics "is exactly the same sort of approximation as" (say, classical) mechanics, as thermodynamics is just a superstructure with respect to mechanics, which superstructure, strictly speaking, is in contradiction with mechanics. Boltzmann's H-theorem was a great achievement, but it is not "exactly the same sort of approximation as " mechanics, it is an approximate superstructure with respect to mechanics.

You just cannot turn a superposition into a mixture without some noise or something similar. And results of averaging over noise just cannot be as fundamental as the underlying theory.

 

[fbs7]

Ill spell it out...You put a cat in a box...No matter what experiment you perform it will become agitated due to claustrofobia!


All experiments with cats prove is that they hate boxes! if they are put in them...On the other hand a cat will sleep in a box at every given opportunity...unless you put it in the box yourself...go figure that...:)

Haha :^)