Electron indeterminism Problem

[ttn]

Can appeal to QED or more advanced QFT help at all?

No. All those fancy more sophisticated quantum theories still have a collapse postulate, and so the same dilemma still obtains. (It's hidden, though -- typical QFT texts don't even ever mention the collapse postulate, because they so-quickly move to talking exclusively about certain matrix elements such as those needed to compute scattering cross sections. But, if you want to follow along the time evolution of some state according to such a theory, you'll find that you need to collapse it at measurement events in order to get things right... for exactly the same reason this is necessary in regular non-relativistic QM.)

 

[kvantti]

Sorry for the delay, ueit. Been busy doing something else.

The uncertainty principle does not allow momentum conservation violations, it only limits predictability. If MWI is a realistic interpretation you cannot have multiple paths for the same particle unless its momentum can change at random.

The momentum of a particle doesn't change at random. The particle takes one path in one universe, other paths in other universes.
But the uncertainty principle does emerge from the path integral method. If you first observe the particle at [x1] and after time [t] you observe the particle at [x2], you know it's velocity and therefore momentum between those observations. Because of this, you can't know the position of the particle between observations at [x1] and [x2], as the uncertainty principle states. From this perspective the particle did indeed take multiple paths from [x1] to [x2], because it's position between [x1] and [x2] is completely uncertain.

A particle can only change momentum if a force is acting on it (because momentum conservation). In a double slit experiment for example the path of the particle is determined by the interactions between the particle and the charged particles in the wall (electrons and quarks), therefore it depends on the geometry of the wall. But it is possible to describe the same geometry by referring not to the places where there are charges but to the places where there is no charge (the paths you are referring). But this is only a method to make the calculations. The true reason for particle's trajectory stands in its EM interaction with other particles.

Erm, according to what theory? Your own? And how do you get the self-interference fringes of single particles, which are predicted by QM and observed in double slit experiments, from your theory?
http://physicsweb.org/articles/news/3/10/12/1

Sure you can, but the burden of proof is on you to show that such an interpretation is inevitable unless MWI is employed.

It isn't "inevitable" interpretation, it is the "simplest" one. The "judge" of which interpretation is the "simpler" is, ofcourse, the Occhams razor.

This is a good reason to reject such interpretations. However, this doesn't mean MWI wins by default. There is another possibility, that QM is incomplete and, just like thermodynamics, it is only a statistical description of a classical world.

This is true.

I see no good reason to believe that "path integral formulation gives a more fundamental insight about the behaviour of particles". It is just another way to do calculations.

Well, it is used to perform calculations in QFT, which is the most fundamental theory of reality up-to-date that has been experimentally confirmed. The path integral doesn't tell just about the behaviour of particles, but about the time-evolution of the quantum field, which other formulations do not do:

However, the path-integral formulation is also extremely important in direct application to quantum field theory, in which the "paths" or histories being considered are not the motions of a single particle, but the possible time evolutions of a field over all space.

http://en.wikipedia.org/wiki/Path_integral_formulation#Functionals_of_fields

I've read Feynman's book about a year ago, so it's not that fresh into my memory but I don't remember him claiming that the path integral is a realistic description of how nature works.

True, but if you can recall he states "I find it remarkable that nature works this way*" when he speaks about the path integral calculation method. Remember all the possible paths of a photon reflecting from a mirror and how they affect the most probable path, which is the one postulated by classical optics: the path that takes the shortest amount of time.

* translated from the finnish version of the book

I have nothing against MWI, it's just as good as the other QM interpretations. It may even be true but we'll never know it, because it's unfalsifiable. The assumption that QM is a complete description has to be challenged first.

True. Still, the MWI is used in quantum cosmology because it makes apparent "randomness" possible in the 4D block universe of relativity.

One could produce a fundamentally stochastic interpretation of thermodynamics as well. So what? I agree with you that any stochastic theory contradicts relativity but I disagree that QM is inherently stochastic or that MWI is the only way QM could be deterministic.

Well, if you figure out a way to interpret QM as deterministic description of reality without some non-local hidden variables, I'm all ears.

QM is defined on a Newtonian (or Minkowsky for QFT) background. One universe, three spatial dimensions, one time dimension. Where are these other universes coming from? They do not appear in the initial description of the system.

The MWI also starts with a single universe, but this universe is "split" into other universes all the time. The other universes come from the fact that if QM describes reality as it is, all the possible observations have an independent reality of their own, and the probability of the observation describes the proportion of the universes (of all the universes) where the observation is made.

I admit I don't understand anything from this definition. There is no such thing as an isolated system (except the universe as a whole) and what is "significant" is a matter of opinion. Just because a force is weak doesn't mean it's not significant.

A world is a net of causal connections between events, as described by relativity.

I know that, done in chemistry classes. I don't see where MWI is used here though.

The percentage also tells the proportion of the universes where the nucleus has decayed after Δt=[half-life of the nucleus], hence the proportion of universes in which the cat is dead.

So, how do you apply this convoluted explanation to Schrödinger’s cat?

You just calculate the increase of entropy assiocated with the cat and its surroundings in the box and you get the number of worlds involved in the experiment.

Is world splitting related to observation, like the "collapse" in Copenhagen interpretation or a real, physical event?

The worlds are "split" when they can't interfere with each other anymore, ie. when a quantum system decoheres. Usually single "observation" decoheres a quantum system.

 

[pibomb]

The wave function cannot exist in our 4D spacetime therefore it cannot do anything ("interfering with itself" or whatever). It's only a mathematical abstraction usefull for calculating probabilities.

The "path integral " is another way to make calculations, it doesn't describe reality. Relativity denies the possibility of faster than light travel and it applies to quantum particles too.

I don't know why I am resurrecting this argument, but what is your "interpretation" on reality? Is reality really like the one Gary Zukav describes (The Dancing Wu Li Masters), where particles are actually correlations of observables? I just want to see what people here on PF think about this absraction.

 

[ueit]

I don't know why I am resurrecting this argument, but what is your "interpretation" on reality? Is reality really like the one Gary Zukav describes (The Dancing Wu Li Masters), where particles are actually correlations of observables? I just want to see what people here on PF think about this absraction.

I didn't read that book so I cannot comment on it. My "interpretation" is something like Bohm's theory but without non-locality (where the back-reaction of the particles on the wave-function is not ignored). Unfortunately, this is pure speculation on my part.

 

[ZapperZ]

I don't know why I am resurrecting this argument, but what is your "interpretation" on reality? Is reality really like the one Gary Zukav describes (The Dancing Wu Li Masters), where particles are actually correlations of observables? I just want to see what people here on PF think about this absraction.

Oh no... no, no, no, no, no... and no!



That book is as bad as the Tao of Physics, and both of them are no better than that silly "What the *(#($#*#@ do we know?" movie. The blind extrapolation of solid physics into mysticism always results in absurdity, no matter how much one tries to rationalize it. I strongly suggest that if you want to know what QM is saying, then it is more prudent to start with QM first, and interpretation later.

Zz.

 

[ueit]

Sorry for the delay, ueit. Been busy doing something else.

Sorry, I didn't see your post, I'll try to answer now.

The momentum of a particle doesn't change at random. The particle takes one path in one universe, other paths in other universes.
But the uncertainty principle does emerge from the path integral method. If you first observe the particle at [x1] and after time [t] you observe the particle at [x2], you know it's velocity and therefore momentum between those observations. Because of this, you can't know the position of the particle between observations at [x1] and [x2], as the uncertainty principle states. From this perspective the particle did indeed take multiple paths from [x1] to [x2], because it's position between [x1] and [x2] is completely uncertain.

There are paths which are not straight even in the same world.

If the particle does not interact between x1 and x2, we know its trajectory (the line between x1 and x2) so we know both its momentum and position. If there is interaction we need more information from the system our particle interacted with.

Erm, according to what theory? Your own?

Momentum conservation.

And how do you get the self-interference fringes of single particles, which are predicted by QM and observed in double slit experiments, from your theory?

I don't have a theory, but a QM treatement of the wall could help.

It isn't "inevitable" interpretation, it is the "simplest" one. The "judge" of which interpretation is the "simpler" is, ofcourse, the Occhams razor.

Positing extra dimensions/worlds is not parsimonious because anything can be "explained" that way.

This is a good reason to reject such interpretations. However, this doesn't mean MWI wins by default. There is another possibility, that QM is incomplete and, just like thermodynamics, it is only a statistical description of a classical world.

This is true.

I'm glad we agree on this point. This is the main reason I post on this forum.

Well, it is used to perform calculations in QFT, which is the most fundamental theory of reality up-to-date that has been experimentally confirmed. The path integral doesn't tell just about the behaviour of particles, but about the time-evolution of the quantum field, which other formulations do not do

Calculus is pretty useful too. Does this mean that there are "dt"'s or "dx"'s flying around us in the real world?

I'll answer the rest tomorrow.

 

[pibomb]

Oh no... no, no, no, no, no... and no!



That book is as bad as the Tao of Physics, and both of them are no better than that silly "What the *(#($#*#@ do we know?" movie. The blind extrapolation of solid physics into mysticism always results in absurdity, no matter how much one tries to rationalize it. I strongly suggest that if you want to know what QM is saying, then it is more prudent to start with QM first, and interpretation later.

Zz.

Actually, I enjoyed that book...

Do you have any references that discuss the the philosophy and interpretations of quantum theory? A link would be most accepted...

 

[ZapperZ]

Actually, I enjoyed that book...

I never said that science fiction cannot be entertaining!

Do you have any references that discuss the the philosophy and interpretations of quantum theory? A link would be most accepted...

Well, considering that I dislike "philosophical interpretation" being put ahead of the actual learning of QM, I'm the wrong person to ask this.

I can already hear people wanting to jump all over that statement. However, notice that I didn't say that I dislike "philosophical interpretation". At some point, some people need that to pacify their curiosity in the "meaning" of some things. I just think that doing that ahead of having any understanding of the subject matter is a backward way of doing it. It leads to people thinking that things in QM are mystical and have no rules in what can and cannot happen. The result will be a bastardization of QM, as what has occurred in that silly movie.

Zz.

 

[pibomb]

I never said that science fiction cannot be entertaining!



Well, considering that I dislike "philosophical interpretation" being put ahead of the actual learning of QM, I'm the wrong person to ask this.

I can already hear people wanting to jump all over that statement. However, notice that I didn't say that I dislike "philosophical interpretation". At some point, some people need that to pacify their curiosity in the "meaning" of some things. I just think that doing that ahead of having any understanding of the subject matter is a backward way of doing it. It leads to people thinking that things in QM are mystical and have no rules in what can and cannot happen. The result will be a bastardization of QM, as what has occurred in that silly movie.

Zz.

I feel that learning some philosophy while learning Quantum mechanics makes everything more understandable. It may bastardize what you learn, but it, to me, makes it easier and more worthwhile to learn QM.

Also, can someone please respond to what they feel of the statement "Particles are actually correletions of observables; therefore, "we" paint a picture of reality."

 

[ZapperZ]

I feel that learning some philosophy while learning Quantum mechanics makes everything more understandable. It may bastardize what you learn, but it, to me, makes it easier and more worthwhile to learn QM.

Also, can someone please respond to what they feel of the statement "Particles are actually correletions of observables; therefore, "we" paint a picture of reality."

I didn't respond to this earlier because mainly the term "correlations of observables" is unknown to me as far as how it is defined. What exactly does that mean? In your learning of some philosophy of QM, do YOU know what that means, keeping in mind that "correlations" has some particular meaning in physics, such as "strongly-correlated electron systems", etc. So to me, "correlations of observables", if I were to apply it from the way I understand "correlations" and "observables" seem to indicate that ALL of the observables for a particle are correlated to each other, and the existence of these correlations is the definition of a "particle"?

That doesn't seem to make any sense to me because

1. I can measure one observable of a particle and yet, have a non-commuting observable be completely uncorrelated to that first observable.

2. So what if I make a measurement of two observables that are correlated? How does this define a particle?

3. I can make measurement of correlated observables of a system. That certainly doesn't indicate that I have "a particle". I could easily have an atom, or a superfluid, or a supercurrent, which can consist of a gazillion entities.

This is what I mean when I said that books such as the ones I mentioned often do not care, or understand, that many of the principles of physics have strict and unambiguous mathematical formalism. We can't simply put pieces of things together, such as "correlations" and "observables" without understanding the mathematics that underly these concepts. That is where it is supposed to start, whereas these books (and especially those two) start the other way. They use the words and phrases of QM but without an understanding of the mathematical description of it. Thus, they are used as in ordinary language. As I've shown above, when that occurs, it will create puzzling scenario IF you have understood QM.

Maybe you can ask the author of that book on what is meant by "correlated observables" that define a particle. It certainly isn't defined that way in a QM text.

Zz.

 

[vanesch]

Well, considering that I dislike "philosophical interpretation" being put ahead of the actual learning of QM, I'm the wrong person to ask this.

I can already hear people wanting to jump all over that statement. However, notice that I didn't say that I dislike "philosophical interpretation". At some point, some people need that to pacify their curiosity in the "meaning" of some things. I just think that doing that ahead of having any understanding of the subject matter is a backward way of doing it.

Amen to that !

(and note that Zz and I have quite different views on QM )

First learn how the machinery works. For some, that's good enough.
Then, if you feel the need for it, construct a "mental picture of reality" (an ontology) with it.

I myself am of the opinion that *in as far as QM is a good theory* the most natural interpretation that goes with it is MWI-like. I'm not of the opinion that MWI is necessarily true, but I'm rather of the opinion that if MWI is not true, that something sooner or later will have to be changed to the quantum formalism - something I don't exclude at all.
The problem is that MWI is 1) a very very strange view on things and highly unintuitive (many people simply cannot accept it just on intuitive grounds, and say: bollocks ! or some similar qualifier) and 2) that if one isn't extremely well-versed in the quantum formalism, several "apparent paradoxes" seem to appear everywhere, like some that have been touched upon in this thread (energy conservation, momentum conservation and all that).

So it is a good idea to start learning QM, with the idea: these are mathematical rules that seem to work in many circumstances in the lab...

Note that I consider Bohmian mechanics (and in as much as it exists, the transactional interpretation) as in fact interpretations of *different but empirically equivalent* formalisms, and in fact not direct competitors of "interpretations of QM". You first need to alter the mathematical formalism (mainly by introducing extra formal elements) before you can "interpret" it.

 

[pibomb]

I didn't respond to this earlier because mainly the term "correlations of observables" is unknown to me as far as how it is defined. What exactly does that mean? In your learning of some philosophy of QM, do YOU know what that means, keeping in mind that "correlations" has some particular meaning in physics, such as "strongly-correlated electron systems", etc. So to me, "correlations of observables", if I were to apply it from the way I understand "correlations" and "observables" seem to indicate that ALL of the observables for a particle are correlated to each other, and the existence of these correlations is the definition of a "particle"?

This is what I mean when I said that books such as the ones I mentioned often do not care, or understand, that many of the principles of physics have strict and unambiguous mathematical formalism. We can't simply put pieces of things together, such as "correlations" and "observables" without understanding the mathematics that underly these concepts. That is where it is supposed to start, whereas these books (and especially those two) start the other way. They use the words and phrases of QM but without an understanding of the mathematical description of it. Thus, they are used as in ordinary language. As I've shown above, when that occurs, it will create puzzling scenario IF you have understood QM.

Maybe you can ask the author of that book on what is meant by "correlated observables" that define a particle. It certainly isn't defined that way in a QM text.

Zz.

I think what the author of the book that presented this was making an interpretation off of the effects of the uncertainity principle. He describes a quantum expirament as a thing that has "a region if preparation" and "a region of measurement." What he says what happnes in between these two regions is that a particle becomes indentified as a correlartion between two observables (like production and detection). Zukav also goes one step further by saying that "particles" are relationships between observables. I think he may get some of this info from the affects of the uncertainity principle.

I am a layman to QM, so, I can't really say that I can expiramentally/mathematically prove this. It's just an interpretation of this theory. And so, you are right, a person really should learn the entire complexity of the theory before chasing after it's meaning...although I still like to learn it and poke around with it.

Thanks Zapper

 

[ZapperZ]

I think what the author of the book that presented this was making an interpretation off of the effects of the uncertainity principle. He describes a quantum expirament as a thing that has "a region if preparation" and "a region of measurement." What he says what happnes in between these two regions is that a particle becomes indentified as a correlartion between two observables (like production and detection). Zukav also goes one step further by saying that "particles" are relationships between observables. I think he may get some of this info from the affects of the uncertainity principle.

I have read that book, and so that is why I criticize it. What you said above is the very reason why, if someone has learned QM, the description get very confusing. For example, "observable" in QM has a very particular meaning. It is a mathematical operator following a very strict mathematical rule (i.e. it must be Hermitian, etc..)

Furthermore, to say something in between those two regions is nothing more than speculation, because all QM can do is tell you a result of a measurement at any particular instant. So describing what happens before then is speculative on his part. He doesn't tell that to his readers clearly and presents this as if it's a part of QM.

That has always been a problem for me with such books. They mix what is a part of the standard concept with speculations without clearly indicating the boundary. Thus, they make wild extrapolations while the readers who don't know any better are still thinking that these outrageous claim is part of QM. That stupid movie is one such example.

To me, that does more harm to QM than not knowing anything at all.

Zz.