Interpretations of Quantum Mechanics

[RUTA]

When I say that QM doesn't need an interpretation, I mean the theory of quantum mechanics, not the mathematical model (Hilbert space or something mathematically equivalent), and more specifically, I mean that a theory such as the Copenhagen "interpretation" doesn't need further interpretation. I mean, we obviously need to interpret the mathematics as predictions about the results of experiments, but we don't have to interpret it ontologically as a statement about what "is" and what "really happens".

I agree.

There are two major problems with the attempts to find an ontological interpretation of QM. The first is that QM may not have an ontological interpretation that has anything to do with reality, and the second is that even if it does, there's nothing we can do to verify that the correct ontological interpretation is in fact correct.

I don't know to what extent we ever verify ontological interpretations, given under determination. As a physicist who is often chastised by philosophers for being a verificationist and empiricist, I think the value of creating new interpretations lies in their ability to suggest new theory and/or experiments.

You're describing an extreme viewpoint that I don't think many people have. (Does anyone have it?) I think it would be idiotic to refuse to use words like "particle" just because the standard model isn't verifiable. What i think we should do is to continue to say that particles exist, and try to teach as many people as possible what that statement really means. (See #100).

Here are two interpretations of QM whereby there are no "click-causing particles:"

Genuine Fortuitousness, A. Bohr & O. Ulfbeck, Rev. Mod. Phys. 67, 1-35 (1995); A. Bohr, B. Mottelson & O. Ulfbeck, Found. Phys. 34, #3, 405-417 (2004).

Relational Blockworld, Silberstein, M., Stuckey, W.M., Cifone, M., Studies in History & Philosophy of Modern Physics 39(4), 736-751 (2008); Stuckey, W.M., Silberstein, M., Cifone, M., Foundations of Physics 38(4), 348-383 (2008).

I don't know that GF leads to new experiments/theory. RBW does, but until those consequences are accepted for publication, there's nothing to discuss. [We're just now finishing a paper along those lines.]

But, again, I did not post with the intent of arguing for this particular ontological interpretation of QFT. I was simply trying to point out that we would expect to create very different experiments and look for very different data if we subscribed to a very different ontological interpretation of QFT. This strikes me as trivially true, but I'm almost as philosophically naive as the physicists I'm addressing with this claim

 

[kote]

You too associate the CI with positivism? I really don't see how the CI can be thought of as an example of positivism. As far as I can tell, positivism, or at least logical positivism (I'm not sure if there's a significant difference), requires theories to be verifiable, but the CI is a fantastic example of a theory that's falsifiable but not verifiable.

Fredrik, I think maybe we are talking about different CI's (per Demystifiers other post). Bohr talked extensively about the ontological implications of his view and how we should think of and describe reality. His desire for a verifiable concept of reality is what led to his denial of any separably objective reality at all, which he realized we could never say anything verifiable about.

Popper was a realist and objected to CI. Falsifiability was a move to weaken the criteria needed to be able to discuss a realist objective world. Also, Popper "articulated his own view of science, and his criticisms of the positivists, in his first work, published under the title Logik der Forschung in 1934 (http://plato.stanford.edu/entries/popper/" (from 1967).

Asher Peres has one relatively recent defense of CI from Popper here: http://arxiv.org/abs/quant-ph/9910078. Of course, he puts his own twist on CI as well.

Bohr also held a positivist conference at his mansion and acknowledged that reading his work as agreeing with positivism was correct. In general I would not go as far as to say Bohr was a positivist beyond in his interpretation of QM though.

Positivism = Logical Positivism = Logical Empiricism

 

[molinaro]

TI does not address the issue of "incomplete" transactions. Many photons escape to infinity, they will never find their absorbers, because the Universe is expanding and it becomes more and more transparent.

Isn't that just an assumption, that there are photons that are never absorbed?

According to TI, those that would never be absorbed, are never emitted.

 

[nikman]

... So, is the experimenter really free "to set part of the terms," i.e., free to choose detector A or B for photon 2, given that photon 1 has already contributed to its related pattern at C? Is Nature really free to give "the answer it damn well pleases" at C, given the freedom of the experimenter to choose A or B?

Here, for others who might be interested but aren't familiar with the chapter, is a brief summary by Zeilinger of said chapter (his) in the Barrow et al book you cite (Science and Ultimate Reality: Quantum Theory, Cosmology and Complexity; John D. Barrow, Paul C.W. Davies and Charles L. Harper, Jr., eds.; Cambridge Univ Press, Cambridge, 2004, pp 201-220):

http://www.dancing-peasants.com/sciphil/Why_the_Quantum.pdf

Let me pull out these two paragraphs and call them central:

"A number of experiments will be reviewed underlining these views. This will include an entangled photon delayed choice experiment where the decision whether a photon that has passed a double slit did this as a particle or a wave is delayed not only until a time after its passage through the double slit assembly but even after it has already been registered. Thus, while the observed facts, i.e. the events registered by the detectors, are not changed, our physical picture changes depending on our choice what to measure. ...

"Finally an experiment on the teleportation of an entangled photon demonstrates that the decision whether or not two photons are entangled or not again can be made at a time long after these photons have already been observed. More precisely, the quantum state we assign two photons for a time period before they have been registered depends on our future choice whether or not we then implement the Bell state measurement these two photons are entangled with. This experiment lends support to the idea that the quantum state is just a representation of our knowledge and that this knowledge changes when an observation is made. Thus the reduction of the wave packet is just a reflection of the fact that the representation of our information has to change whenever the information itself changes as a consequence of an observation."

This makes my tennis-serve analogy overly simplistic (if not arguably simpleminded) but I don't see it conflicting with Z's "two freedoms" dictum. Birgit and her particle still enjoy the same mutually dependent relationship as he expounded upthread, only with more (joak here) bells and whistles. Unless I'm missing something, which as a probability could always be closer to one than zero.

 

[DrChinese]

Isn't that just an assumption, that there are photons that are never absorbed?

According to TI, those that would never be absorbed, are never emitted.

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

 

[RUTA]

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

The computation of the transition amplitude via the path integral formalism is based on the fact that “the source will emit and the detector receive” (Feynman, 1965, 167); per Tetrode, “the sun would not radiate if it were alone in space and no other bodies could absorb its radiation” (Tetrode, 1922, 325). The path integral formalism requires both an emission event and a reception event; the formalism was motivated by the idea of treating advanced and retarded potentials equally.

Feynman, R.P. (1965). “The development of the space-time view of quantum electrodynamics” in Physics: Nobel Lectures 1963-1970, edited by G. Ekspong, World Scientific, Singapore, 1988, 155-178.

Tetrode, H. (1922). Zeitschrift für Physik 10, 317-328.

 

[QMister]

I remember there is also partial decoherence.
For me this is a proof that MWI is true.

Would you care to elaborate a little further?
How does "partial decoherence" in ANYWAY give "proof" to MWI over any other interpretation such as Bohm?
Explain exactly what you mean by that if you don't mind...

I would say that there is a soft MWI and a hard MWI. Soft MWI merely claims that the wave function satisfies the Schrodinger equation and that it never collapses. Hard MWI claims that this is enough, i.e., that no further assumptions are needed in order to interpret the wave function correctly.

For me, partial decoherence is a strong evidence for soft MWI, but not for hard MWI.
As you admit, the biggest problem of hard MWI is to explain the Born rule.
With soft MWI it is much easier, because you are allowed to assume or postulate something in addition. An example of soft MWI is the Bohmian interpretation which assumes that waves serve as pilots for pointlike particles, which allows to explain the Born rule from other postulates.

I think calling it "soft MWI" is wrong though as this "soft" version would not contain other worlds, hence MANY and WORLDS are out of the interpretation.
Or are you saying there is many worlds, just in a different way than the most prominent MW interpretation states?

 

[molinaro]

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

Take a sphere of let's say, radius 10 billion light years, centred on a light bulb. Project from the centre of that sphere out to the surface of the sphere a set of lines where each passes through each atom found within the volume of that sphere.

What kind of variation in density of points on the surface of the sphere would you expect to be traced out?

How small would those variations end up if you considered where that same set of lines intersected a sphere of volume 10 meters?

Do you still think you would notice something?

 

[Dmitry67]

I would certainly think that something would be noticable if there were directions in which there were no absorbers (based on that assumption). I think the conclusion would be that there is no such effect. I.e. if TI requires an absorber, then TI is false.

Now imagine that we are talking about neutrinos rather than photons. The universe is essentially transparent to neutrinos, even if were not quite transparent to photons.

Correct
Unless... unless there will be a BIG RIP
BIG RIP created enourmous quantities of hawking radiation from tidal horizons, effectively absorbing everything.

 

[Dmitry67]

Take a sphere of let's say, radius 10 billion light years, centred on a light bulb. Project from the centre of that sphere out to the surface of the sphere a set of lines where each passes through each atom found within the volume of that sphere.

What kind of variation in density of points on the surface of the sphere would you expect to be traced out?

How small would those variations end up if you considered where that same set of lines intersected a sphere of volume 10 meters?

Do you still think you would notice something?

Sphere of 10 billion years is literally transparent to light. Look at the night sky. It is dark!
In fact, most of the absorption occurs in our galaxy (towards its center there is 100% absorption). If a photon was lucky to escape from our galaxy, it has almost no chance of being absorbed. And the Universe is becoming less and less dense, so if it is not absorbed soon, then there will be almost no chance that it will be ever absorbed. Again, unless there will be a big rip.

Regarding your question about the variation, if varies from near 0% if you point your light towards, say, "Hubble deep field" area to 100% when you point it towards the center of our galaxy.

 

[Dmitry67]

Would you care to elaborate a little further?
How does "partial decoherence" in ANYWAY give "proof" to MWI over any other interpretation such as Bohm?
Explain exactly what you mean by that if you don't mind...

I have seen - don't find right now - decription of studies of decoherence. Sorry, I can't find it right now - have to go to work soon. In brief, they studied the "shoedinger cats state". So, what happens when you open an ideal box and look inside? You start receiving photons. Is 1 photon enough to conclude that cat is dead or alive? no. 2? not enough. 100? yes.

So they studies a small system and measured how the absorption of these photons affected the system. As I remember, after receiveing 5 photons system is significantly decoherenced (but not to 100%).

 

[Dmitry67]

Can we discuss how different interpretations can be falsified – not now, but in principle (say, after TOE is discovered). Note: I am talking about the possibility of falsification

What I know:
• TI – without BIG RIP there are no absorbers for many particles. So it has problems even now.
• MWI – has problems with Born rule, but not clear how it can be used for the subject. On the contrary, if there will be found a rigorous mathematical proof that we can derive what we see from QM formalism alone, if would be an very strong argument for MWI
• BM – Quantum Gravity can ruin it, if the very notion of particle is frame-dependent (different accelerated frames do not agree on the number of real particles constituting macroscopic events)
• Objective Collapse – not an interpretation, is directly testable
• CI?
• Others?
Any additions?

 

[QMister]

I have seen - don't find right now - decription of studies of decoherence. Sorry, I can't find it right now - have to go to work soon. In brief, they studied the "shoedinger cats state". So, what happens when you open an ideal box and look inside? You start receiving photons. Is 1 photon enough to conclude that cat is dead or alive? no. 2? not enough. 100? yes.

So they studies a small system and measured how the absorption of these photons affected the system. As I remember, after receiveing 5 photons system is significantly decoherenced (but not to 100%).

Thanks,

Looking forward to more indepth explanation.

I'm a little confused, why can't this apply to say, dBB, or ANY other objective interpretation without collapse (yes people like Gerard 't Hooft etc. is working on something)?
Remember Bohm was on of the guys discovered decoherence, and the first EVER to apply it to a interpretation: dBB, so why wouldn't this support the existence of a pilot wave and be strong evidence for dBB?

 

[molinaro]

What I know:
• TI – without BIG RIP there are no absorbers for many particles. So it has problems even now.

But isn't it true that in a cosmological constant dominated universe that all photons are absorbed at the horizon?

 

[Dmitry67]

horizon itself does not absorb anything because it is always far from an object. However, horizon generates hawking-like radiation. So universe will still be filled with the very low energy photons. And there is a very low probability that 'our' photon hits the hawking photon, completing the transaction. no matter how low the probability is, there is an infinite time for it. So I think it is true even without big rip...