Interpretations of Quantum Mechanics (is there a general consensus?)


by Vectronix
Tags: consensus, interpretations, mechanics, quantum
Vectronix
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#1
Feb4-12, 02:59 AM
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Hi :)

I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?
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martinbn
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#2
Feb4-12, 05:16 AM
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I don't know what most scientists believe, but I find that statement strange. I would have thought that the one thing, about the wave function, they would agree on, is that it doesn't represent a real field.
phyzguy
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#3
Feb4-12, 06:29 AM
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From my experience, I would say there is not a general consensus on this point, and most scientists seem to take the view of SUAC - Shut Up And Calculate - which means they know how to do the calculations and just don't worry too much about the interpretation.

juanrga
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#4
Feb4-12, 07:38 AM
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Interpretations of Quantum Mechanics (is there a general consensus?)


Quote Quote by Vectronix View Post
Hi :)

I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?
You would fill some money refund form
jtbell
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#5
Feb4-12, 08:14 AM
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Quote Quote by Vectronix View Post
I recently read a book
Which book?
Ken G
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#6
Feb4-12, 10:51 AM
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Not only don't I think there's a consensus on that, I'm not even sure what the statement means. A field is real if it carries energy and momentum? How does one know if a field carries energy and momentum? I would say that thinking is backward-- we don't ask if it carries energy and momentum, and then decide we think it's real, we ask if we think it's real, and then decide it carries the energy and momentum. In other words, we all know we wish to associate energy and momentum with the wavefunction, whether we regard it as real or not, so we first have to ask if we regard it is real before we can decide whether or not it "carries" that energy and momentum, instead of just "associates with" that energy and momentum. So the field is not real if it carries energy and momentum, the field carries energy and momentum if it is real.
Vectronix
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#7
Feb4-12, 04:42 PM
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Yeah, what you said makes sense, Ken. I would have thought that most scientists don't believe the wave function is real, too, martin. I may have mis-stated the part about the wave function a bit, but here's a quote from the preface of the book:

"...if someone, not a theoretical physicist and not thoroughly acquainted with modern methods of analysis, were to attempt to digest a current article dealing with nuclear forces or cosmic rays, relying for help on the available books on the subject, he would discover to his dismay that modern quantum mechanics differs radically from that which he finds in the textbooks... More confusing to him is the interpretation of a field in the new mechanics. It seems evident that what is meant is a real field possessing energy and momentum. Yet the textbooks attach a purely symbolic meaning to the wave field of a particle, picturing the field concept merely as a probability function."

...and there you have it.

Quote Quote by juanrga View Post
You would fill some money refund form
lol I got it from Borders bookstore before they went out of business, so... :P

Quote Quote by jtbell View Post
Which book?
It's called Quantum Mechanics of Particles and Wave Fields, by Arthur March.
juanrga
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#8
Feb4-12, 04:57 PM
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Quote Quote by Vectronix View Post
lol I got it from Borders bookstore before they went out of business, so... :P
Try the Book publisher then
Vectronix
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#9
Feb4-12, 05:28 PM
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hehe... Do you seriously think I should? :)
bhobba
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#10
Feb5-12, 03:58 AM
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Quote Quote by Vectronix View Post
Hi :)I recently read a book that states that most scientists believe the wave function represents a real field (i.e., one that possesses energy and momentum). I think this is part of the transactional interpretation of QM but not sure... can anyone confirm whether the book I read is right about this or not?
Most probably believe it has a real existence like say an electric field does - not as an actual field - but as something that exists out there because they think a wave-function collapse is an issue. The interpretation that probably demands it is one based on quantum decoherence for that collapse and its variants - don't know about the transactional interpretation.

I personally don't believe it does - I think its like classical probability theory - its simply a device for calculating statistical outcomes. Check out:
http://arxiv.org/pdf/quant-ph/0111068v1.pdf

Thanks
Bill
stevendaryl
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#11
Feb5-12, 09:44 AM
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There is something about the wave function that makes a completely different kettle of fish than fields such as the electric field. That is, that unlike the electric field, the wave function is not a field in the physical world. It's a field in configuration space.

The distinction is this: In the case of an electric field, I can point to a particular spot, and ask "What is the value of the electric field right there?" You cannot ask the analogous question about the wave function, because it is not a probability amplitude on points in space. To see why not, consider a two-particle wave function. In general, It would be written as (simplifying to the case of 1 spatial dimension): ψ(x1, x2), the square of which gives the probability density of finding the first particle at position x1 and the second particle at position x2. It doesn't make any sense for me to point to a particular point and ask what the value of the wave function is at that point.

I don't know what the implications of this physical-space versus configuration space distinction is for whether the wave function is "real", but it certainly shows that the wave function cannot be considered an ordinary field like the electric field.
Ken G
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#12
Feb5-12, 11:45 AM
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Yet you can point to a box in real space and ask "what is the probability of finding a particle in that box", even for multiple-particle wave functions (if the particles are distinguishable, you can also specify which type of particle you are asking about). You can also ask about correlations like "what is the probability of finding particles in both of these two boxes", and so on. So it's a more sophisticated kind of field, but it seems to me one can still imagine it "exists" in real space if one wants to. True, it is kind of a "question answering field", but then, so are they all. Does one want to attribute independent existence to question-answering fields? No less so in quantum than classical physics, it was always something of a stretch in my view!
martinbn
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#13
Feb5-12, 11:59 AM
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@ Ken_G: The point of stevendaryl is that fields are represented by mathematical object that have domain spacetime not configuration space. I thought this was so obvious, that's why I didn't even say in my post!
stevendaryl
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#14
Feb5-12, 12:43 PM
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Yet you can point to a box in real space and ask "what is the probability of finding a particle in that box", even for multiple-particle wave functions (if the particles are distinguishable, you can also specify which type of particle you are asking about). You can also ask about correlations like "what is the probability of finding particles in both of these two boxes", and so on. So it's a more sophisticated kind of field, but it seems to me one can still imagine it "exists" in real space if one wants to. True, it is kind of a "question answering field", but then, so are they all. Does one want to attribute independent existence to question-answering fields? No less so in quantum than classical physics, it was always something of a stretch in my view!
Well, I don't think there was ever any question about whether the wave function was useful for answering questions. It certainly provides information about the real world. My point is that it isn't something that resides in the real world. It isn't an object that exists in some location, nor is it a field that varies from location to location.
bohm2
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#15
Feb12-12, 09:30 AM
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I really like Matt Leifer's suggestion in this post:

Even disregarding the issue of whether the quantum state has to be ontic, Bell’s theorem already implies the same issue with simultaneity. It shows that the ontic state at B must depend on the choice of measurement at A and vice versa, and there are frames of reference in which the measurements occur in either order. There are only two possible responses to this:

1. Reject relativity at the fundamental level. Assume that there is a preferred frame of reference and have the nonlocal influences operate instantaneously in this frame. The frame will be hidden at the statistical level due to the averaging over ontic states, so you will still have Lorentz invariance at the operational level, but it means that you cannot use relativistic arguments to reason about what is happening at the ontic level, so the paradoxes do not arise. This is the solution adopted in Bohmian mechanics for example.

2. Reject one or more of the assumptions of Bell’s theorem (also assumed by PBR). For example, one could adopt a no-collapse interpretation like Everett/many-worlds, which denies the existence of ontic properties localized in spacetime, an assumption that Einstein called “separability” and that is crucial to the derivation of nonlocality. Alternatively, one could adopt one of the “neo-Copenhagen” approaches to quantum theory in which the need for an ontic state is denied. Finally, one could retain realism and single-valuedness of measurement outcomes by adopting ontologies that are not considered in the derivation of Bell’s theorem, e.g. retrocausality.

I already stated in the blog post that I like the retrocausal solution, or at least that I consider it worth investigating in more detail. This is because I prefer to retain realism, fundamental Lorentz invariance and psi-epistemicism, and it is one of the few options on the table that still has a chance of doing that. If the retrocausal program fails then I would have to drop one or more of these requirements and I fluctuate between preferring neo-Copenhagen approaches or Everett depending on whether my psi-epistemic or realist convictions are stronger on any given day. To be convinced to drop fundamental Lorentz invariance, I would have to see violations of it on the statistical level. Valentini argues that this is to be expected in the Bohmian approach for example, since the statistical washing out of nonlocal influence is analagous to being in a state of thermal equilibrium in statistical mechanics, so we should expect to see systems out of this state of equilibrium somewhere in the universe. I consider this to be a firm prediction of all such theories, and so I would need to see empirical violations of Lorentz invariance to be convinced of them.
Can the quantum state be interpreted statistically?
http://mattleifer.info/2011/11/20/ca...statistically/
ardenmann0
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#16
Feb12-12, 11:16 AM
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Gell-Mann once wrote, ‘Bohr brainwashed a whole generation of physicists into ‘believing' the Copenhagen interpretation of quantum mechanics'.
LaserMind
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#17
Feb12-12, 01:29 PM
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So a wave function is not a wave and its not a particle, its an entity of some sort in 'superposition' that spreads out in x,y,z and t. We can only find out if its 'there' by decohering it. Otherwise it is not a physical, real entity.

It behaves as though it were a 'calculation' waiting for its result (at some x,y,z and t) on decoherence. It leaves no track of its path. It simply 'arrives'. We know where it came from but have no idea of its path to its destination.

So what entity can achieve this? Something superposition is not a 'thing' - its not an object that we cannot enclose or put in a container - unless we decohere. And even then decoherence results in 'values observed'.
ardenmann0
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#18
Feb12-12, 02:38 PM
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Quote Quote by martinbn View Post
I don't know what most scientists believe, but I find that statement strange. I would have thought that the one thing, about the wave function, they would agree on, is that it doesn't represent a real field.
If it doesn't represent a real field, how can it interfere with itself in the double slit experiment?

We can't detect gravitational waves right now, but it does not mean they do not exist.
It just mean our instruments are not sensitive enough to detect them directly right now.


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