Are there any empirical tests for the GRW extension of quantum mechanics?

[Question69]

Has there been so far any prediction validated in experimental outcomes that these theories make as a result of the modification of the Schrodinger equation?

 

[StevieTNZ]

Has there been so far any prediction validated in experimental outcomes that these theories make as a result of the modification of the Schrodinger equation?

As far as I'm aware, no. Though looking at macroscopic superposition states (eg 40kg mirrors) and gravity in the future, they can test models whereby gravity is the cause of wave function collapse.

 

[Question69]

As far as I'm aware, no. Though looking at macroscopic superposition states (eg 40kg mirrors) and gravity in the future, they can test models whereby gravity is the cause of wave function collapse.

And for the CSL and GRW models?

 

[StevieTNZ]

And for the CSL and GRW models?

Yes, no experiments to report that differ from quantum theory.

 

[Question69]

so the CSL and GRW models have kind of been falsified?

 

[StevieTNZ]

so the CSL and GRW models have kind of been falsified?

No. I've yet to see an experiment that's been performed and reported that conforms to one of their predictions that differ from quantum mechanics.

 

[Question69]

No. I've yet to see an experiment that's been performed and reported that conforms to one of their predictions that differ from quantum mechanics.

Yes that's what falsified means.They have made predictions that do not stand up to future scrutiny.

 

[Question69]

No. I've yet to see an experiment that's been performed and reported that conforms to one of their predictions that differ from quantum mechanics.

Also, do you believe many worlds could be the right interpretation, as we have seen no evidence(so far) of the non-linearity of the wavefunction?

 

[StevieTNZ]

Yes that's what falsified means.They have made predictions that do not stand up to future scrutiny.

As far as I know, an experiment has not been performed that tests the prediction difference between collapse theories and quantum theory.

Also, do you believe many worlds could be the right interpretation,

No. But interpretation discussions belong in the sub-forum.

 

[Question69]

Oh alright.But what technology do we need then to experiment such theories? Don't both of them say that the collapse happens due to chance, alone? At least in the DP model we know we can't test right now because we can't reach the Planck scales.

 

[physika]

Has there been so far any prediction validated in experimental outcomes that these theories make as a result of the modification of the Schrodinger equation?

Not yet, they have to get up the scale.

https://www.uibk.ac.at/newsroom/13-million-euros-for-basic-quantum-research.html.en

https://www.oeaw.ac.at/esq/home/new...t-and-markus-aspelmeyer-win-erc-synergy-grant

"This behaviour has been confirmed in milestone experiments at the scale of elementary particles, atoms and even molecules containing thousands of atoms, but not for the macroscopic domain, i.e. for solid state objects visible to the naked eye.

Together they want to explore the limits of the quantum world by positioning a solid-state object containing billions of atoms at two locations simultaneously for the first time.

In a joint effort, they will study the nanoparticles in a high vacuum, its center-of-mass motion cooled down to near absolute zero and levitating in a combination of optical, electric, and magnetic fields. “With this project, we are pushing the limits of what is technically feasible today”, adds Romero-Isart."

-------

https://cordis.europa.eu/project/id/951234

.

 

[vanhees71]

"Even after more than 100 years of their discovery, the laws of quantum physics sometimes seem in contradiction to common sense. Most prominently, the superposition principle states that a single object can behave as if it were in several places at once."
Quanten theory does not imply anything like this. It provides probability distributions for a particle's position, $$P(t,\vec{x})=\langle \vec{x}|\hat{\rho}(t)|\vec{x} \rangle,$$
where $\hat{\rho}$ is the state the particle is prepared in (written in the Schrödinger picture of time-evolution).

Indeed for a pure state $\hat{\rho}=|psi \rangle \langle \psi|$ can be given by a superposition of wave functions like
$$\psi(t,\vec{x}) \rangle=\psi_1(t,\vec{x}) + \psi_2(t,\vec{x})$$,
where $\psi_1(t,\vec{x})$ and $\psi_2(t,\vec{x})$ may be two wave packets sharply peaked around to positions $\vec{x}_1$ and $\vec{x}_2$, but that does NOT imply that the particles were at two different positions at once. It only says that the probabity distribution for the particle's position is peaked around the two positions $\vec{x}_{1/2}$. This simply implies that the particle's position is not too well determined, but it doesn't say the particles where at those "two places at once".

I hope they spend the 13 M€ for something more profound than such wrong ideas, which are indeed not only "in contradiction to common sense" but also in contradiction to quantum theory.

 

[physika]

This simply implies that the particle's position is not too well determined, but it doesn't say the particles where at those "two places at once".

I hope they spend the 13 M€ for something more profound than such wrong ideas, which are indeed not only "in contradiction to common sense" but also in contradiction to quantum theory.

that is the press release...

no the words of Markus Aspelmeyer nor Oriol Romero-Isart.

---------------

Oriol Romero-Isart:
“We want to put a nanoparticle consisting of billions of atoms into a large superposition state,”
says project coordinator Oriol Romero-Isart from the Department of Theoretical Physics at the University of Innsbruck and the Institute of Quantum Optics and Quantum Information (IQOQI) of the Austrian Academy of Sciences.

Markus Aspelmeyer
“At the scale of our planned experiment, all existing collapse models would either be ruled out or constrained to parameter regimes that render them meaningless,”
says experimental physicist Markus Aspelmeyer from the University of Vienna, who is also Scientific Director at the Institute for Quantum Optics and Quantum Information - Vienna, of the Austrian Academy of Sciences.

.

.

 

[vanhees71]

Well, I meant this a bit ironically. I'm pretty sure that they'll do very high-quality work within this project. I'm only always a bit disappointed, why people who know QT as well as the PIs of this project do, cannot write a somewhat better explanation for the public but repeat over and over again the bad popular-science writing of decades ago.

 

[physika]

Well, I meant this a bit ironically. I'm pretty sure that they'll do very high-quality work within this project. I'm only always a bit disappointed, why people who know QT as well as the PIs of this project do, cannot write a somewhat better explanation for the public but repeat over and over again the bad popular-science writing of decades ago.

Dont know if here is better explained.

https://www.quantamagazine.org/how-...orld-be-physicists-probe-the-limits-20210818/

"A quantum particle in a superposition, contrary to common belief, is not really in two (or more) states at once. Rather, a superposition means that there is more than one possible outcome of a measurement. For an object at everyday scales, described by classical physics, that makes no sense — it is either here or there, red or blue. If we can’t say which it is, that’s just because of our ignorance: We haven’t looked. But for quantum superpositions, there simply is no definite answer — the property of “position” is ill-defined."

.

 

[ohwilleke]

Well, I meant this a bit ironically. I'm pretty sure that they'll do very high-quality work within this project. I'm only always a bit disappointed, why people who know QT as well as the PIs of this project do, cannot write a somewhat better explanation for the public but repeat over and over again the bad popular-science writing of decades ago.

 

[StevieTNZ]

https://phys.org/news/2022-01-limits-quantum-mechanics.html

Full paper: https://avs.scitation.org/doi/10.1116/5.0073626

 

[DrChinese]

And for the CSL and GRW models?

OK, how would the collapse operate (in objective collapse models such as GRW and CSL) with entangled particles? You have 2 separated entangled particles in which one of them (say Alice) objectively collapses after some random time t1 which occurs BEFORE Alice encounters a measurement device. First, that leads to a violation of Bell (as you are back to an EPR-like predetermined outcomes scenario). Second, that would require an FTL effect to propagate to remote Bob. (Keep in mind that particles Alice and Bob can be entangled without ever having overlapped in ANY region of spacetime.)

Per this paper: On the (im)possibility of extending the GRW model to relativistic particles

"In conclusion there cannot be a special relativistic GRW model for entangled distinguishable particles."

My point is that these don't seem like very good candidate theories in the first place. How can collapse occur prior to an irreversible interaction ("measurement"), since you need the full context to make a testable statistical prediction that respects Bell?

 

[vanhees71]

To decohere, say two entangled photons, you don't need faster-than light propagation. It's sufficient that one of the photons interact with something else, and then usually the two photons are no longer entangled but now the larger system consisting of the two photons and the other stuff the one photon was interacting with are now entangled.

If is of course very difficult to find relativistic "objective collapse models", because you always run into trouble with causality since it's very difficult to find non-local relativistically causal models.

 

[Question69]

To decohere, say two entangled photons, you don't need faster-than light propagation. It's sufficient that one of the photons interact with something else, and then usually the two photons are no longer entangled but now the larger system consisting of the two photons and the other stuff the one photon was interacting with are now entangled.

If is of course very difficult to find relativistic "objective collapse models", because you always run into trouble with causality since it's very difficult to find non-local relativistically causal models.

I wonder in many worlds, does it make sense to ask for a branching speed?

 

[vanhees71]

Since I don't understand many worlds I can't answer that question. I've no idea, how the branching in different "worlds" should be observable and thus also no idea how to define, i.e., measure, a corresponding "speed".

 

[DrChinese]

To decohere, say two entangled photons, you don't need faster-than light propagation. It's sufficient that one of the photons interact with something else, and then usually the two photons are no longer entangled but now the larger system consisting of the two photons and the other stuff the one photon was interacting with are now entangled.

As we have discussed before: You are somewhat in denial about the meaning of entangled particles that have never shared/overlapped in spacetime - and therefore have never interacted. This (per references), like an ordinary Bell test, is something that any quantum theory or interpretation should be able to describe. It is a prediction of orthodox QM, but theories like GRW and CSL - in my opinion - lack the theoretical structure to explain these phenomena. Again, they (GRW and CSL - objective collapse which is said to occur as a function of time) would need an actual FTL signal to operate, while orthodox QM merely requires generally accepted "quantum nonlocality".

https://arxiv.org/abs/0911.1314
"Quantum systems that have never interacted can become nonlocally correlated through a process called entanglement swapping. "

https://arxiv.org/abs/1209.4191
"The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime."

So I am not saying that orthodox quantum non-locality involves any FTL signaling. I don't know what it involves any more than anyone else. But Objective Collapse theories, as I read them, are attempting to insert hypotheses that can't really address the full range of quantum behaviors. If you think they can address the experiments I reference above, I'd love to understand how.

 

[vanhees71]

In these papers, the selection made to prepare entanglement between "quantum systems that never interacted" is due to local measurements.. In the first paper in the diagram in the first column it's the joint measurement on Bob's two particles (local at his place) that enable to select ensembles representing entangled states of Alice's and Charlie's particles, although these never interacted. In the 2nd paper it's the local joint measurement of the two photons labelled with IV in Fig. 1.

I still do not see (a) any need for "objective collapse" additions, because standard local QFT explains everything without causality violations and (b) how "objective collapse" additions can be made without inducing such violations, because as you say yourself, this would imply the need for FTL signals.

Of course, if there is the possibility to check such objective collapse models one should do it (see #11). I'm pretty sure that QT will also pass this test again ;-)), but to be sure, the experiment must be done and carfully validated as usual.

 

[Question69]

In these papers, the selection made to prepare entanglement between "quantum systems that never interacted" is due to local measurements.. In the first paper in the diagram in the first column it's the joint measurement on Bob's two particles (local at his place) that enable to select ensembles representing entangled states of Alice's and Charlie's particles, although these never interacted. In the 2nd paper it's the local joint measurement of the two photons labelled with IV in Fig. 1.

I still do not see (a) any need for "objective collapse" additions, because standard local QFT explains everything without causality violations and (b) how "objective collapse" additions can be made without inducing such violations, because as you say yourself, this would imply the need for FTL signals.

Of course, if there is the possibility to check such objective collapse models one should do it (see #11). I'm pretty sure that QT will also pass this test again ;-)), but to be sure, the experiment must be done and carfully validated as usual.

That's interesting, what interpretation do you hold to?

 

[Question69]

As we have discussed before: You are somewhat in denial about the meaning of entangled particles that have never shared/overlapped in spacetime - and therefore have never interacted. This (per references), like an ordinary Bell test, is something that any quantum theory or interpretation should be able to describe. It is a prediction of orthodox QM, but theories like GRW and CSL - in my opinion - lack the theoretical structure to explain these phenomena. Again, they (GRW and CSL - objective collapse which is said to occur as a function of time) would need an actual FTL signal to operate, while orthodox QM merely requires generally accepted "quantum nonlocality".

https://arxiv.org/abs/0911.1314
"Quantum systems that have never interacted can become nonlocally correlated through a process called entanglement swapping. "

https://arxiv.org/abs/1209.4191
"The observed quantum correlations manifest the non-locality of quantum mechanics in spacetime."

So I am not saying that orthodox quantum non-locality involves any FTL signaling. I don't know what it involves any more than anyone else. But Objective Collapse theories, as I read them, are attempting to insert hypotheses that can't really address the full range of quantum behaviors. If you think they can address the experiments I reference above, I'd love to understand how.

So what do you think the likely interpretation to be true is?

 

[StevieTNZ]

So what do you think the likely interpretation to be true is?

If you wish to ask about interpretations, please start a new thread in this sub-forum: https://www.physicsforums.com/forums/quantum-interpretations-and-foundations.292/

 

[PeterDonis]

So what do you think the likely interpretation to be true is?

If you wish to ask about interpretations, please start a new thread in this sub-forum: https://www.physicsforums.com/forums/quantum-interpretations-and-foundations.292/

Even in the interpretations subforum, that question is off limits. All QM interpretations make the same predictions for all experiments, so there is no way of testing by experiment which ones are "true". The interpretations subforum is for discussion of what the different interpretations say, not for expressing opinions about which ones people think are "true". Please refer to the guidelines for the interpretations subforum.

 

[DrChinese]

As referenced: We have 2 distant spin-entangled particles (Alice and Bob) that are created from independent lasers, and have never interacted (and never exist within a common light cone).

Objective collapse: "Collapse theories avoid the measurement problem by merging the two dynamical principles of quantum mechanics in a unique dynamical description. The physical idea that underlies collapse theories is that particles undergo spontaneous wave-function collapses, which occur randomly both in time (at a given average rate), and in space (according to the Born rule). The imprecise talk of “observer” and a “measurement” that plagues the orthodox interpretation is thus avoided because the wave function collapses spontaneously."

1. An objective collapse theory states that the likelihood of entangled Alice and Bob decohering is a function of time. Presumably that elapsed time can occur before either encounters a measurement device that tests a Bell inequality. As we know, the coincidence rate is strictly dependent on the relative choice of measurements on the 2 entangled particles Alice and Bob, and nothing else. If either Alice or Bob had decohered into an unentangled state PRIOR to their measurement, the statistics would be distinctly different because one or both particles would have taken on a specific spin value at time/place of decoherence. This experiment has already been executed, so we know that cannot be.

What am I missing? Again: QM says decoherence occurs only when an irreversible measurement is performed, I don't see how this could be different in GRW or any "objective collapse" theory.

2. In swapping setups, the final 2 entangled particles Alice and Bob were at one time entangled with other particles, let's call those Chris and Dale. Under an objective collapse theory, when Chris and Dale are measured, certainly an objective collapse must have occurred for their then respective partners Alice and Bob. In orthodox QM, particles can be entangled on multiple bases (say spin and position/momentum). They can then be collapsed on individual bases, leaving the particles entangled on some bases. Or swapping can occur.

Again, for objective collapse theories: Presumably the time at which the objective collapse occurs applies to all bases, not just one - else it wouldn't be an objective collapse, would it? But that cannot be either, else swapping is not possible at all quantum entanglement would have decohered once Chris and Dale are brought together. Alice and Bob would not end up with an entangled relationship.

What am I missing? My reasoning applies equally to the hypothesis that gravity induces collapse. Time, gravity, it's doesn't make any difference. It should be obvious that the standard quantum viewpoint - that collapse occurs within the context of an irreversible measurement context - is the only explanation that fits with experiment. Bell tests to date show no dependence on time.

3. There have even been experiments performed where a photon is "stored" for an hour, and collapse does not occur. Not exactly an absolute disproof of time based objective collapse, but certainly bring the concept into question.

https://www.nature.com/articles/s41467-021-22706-y

Where is there a place for objective collapse when entanglement is brought into the picture?

 

[Question69]

As referenced: We have 2 distant spin-entangled particles (Alice and Bob) that are created from independent lasers, and have never interacted (and never exist within a common light cone).

Objective collapse: "Collapse theories avoid the measurement problem by merging the two dynamical principles of quantum mechanics in a unique dynamical description. The physical idea that underlies collapse theories is that particles undergo spontaneous wave-function collapses, which occur randomly both in time (at a given average rate), and in space (according to the Born rule). The imprecise talk of “observer” and a “measurement” that plagues the orthodox interpretation is thus avoided because the wave function collapses spontaneously."

1. An objective collapse theory states that the likelihood of entangled Alice and Bob decohering is a function of time. Presumably that elapsed time can occur before either encounters a measurement device that tests a Bell inequality. As we know, the coincidence rate is strictly dependent on the relative choice of measurements on the 2 entangled particles Alice and Bob, and nothing else. If either Alice or Bob had decohered into an unentangled state PRIOR to their measurement, the statistics would be distinctly different because one or both particles would have taken on a specific spin value at time/place of decoherence. This experiment has already been executed, so we know that cannot be.

What am I missing? Again: QM says decoherence occurs only when an irreversible measurement is performed, I don't see how this could be different in GRW or any "objective collapse" theory.

2. In swapping setups, the final 2 entangled particles Alice and Bob were at one time entangled with other particles, let's call those Chris and Dale. Under an objective collapse theory, when Chris and Dale are measured, certainly an objective collapse must have occurred for their then respective partners Alice and Bob. In orthodox QM, particles can be entangled on multiple bases (say spin and position/momentum). They can then be collapsed on individual bases, leaving the particles entangled on some bases. Or swapping can occur.

Again, for objective collapse theories: Presumably the time at which the objective collapse occurs applies to all bases, not just one - else it wouldn't be an objective collapse, would it? But that cannot be either, else swapping is not possible at all quantum entanglement would have decohered once Chris and Dale are brought together. Alice and Bob would not end up with an entangled relationship.

What am I missing? My reasoning applies equally to the hypothesis that gravity induces collapse. Time, gravity, it's doesn't make any difference. It should be obvious that the standard quantum viewpoint - that collapse occurs within the context of an irreversible measurement context - is the only explanation that fits with experiment. Bell tests to date show no dependence on time.

3. There have even been experiments performed where a photon is "stored" for an hour, and collapse does not occur. Not exactly an absolute disproof of time based objective collapse, but certainly bring the concept into question.

https://www.nature.com/articles/s41467-021-22706-y

Where is there a place for objective collapse when entanglement is brought into the picture?

The collapse happens under the context of a parameter.So for example the bigger a system is, the bigger the chance of a collapse is for that.Smaller things have a very, very low chance of collapsing.If we have a big entangled system, that will have a very big chance of collapse.

 

[PeterDonis]

The collapse happens under the context of a parameter.

Please give a specific reference for what experiments, or what predictions using only the basic math of QM or some other model that makes different experimental predictions (such as the "objective collapse" theories that modify the dynamics), you are talking about that show this. Please bear in mind that this is not the interpretations subforum, so talking about what some particular collapse interpretation says is out of bounds here.

 

[DrChinese]

The collapse happens under the context of a parameter.So for example the bigger a system is, the bigger the chance of a collapse is for that.Smaller things have a very, very low chance of collapsing.If we have a big entangled system, that will have a very big chance of collapse.

OK, I can see that objective collapse might not occur often if the parameter was "small" for a single particle. But that essentially means such theories don't explain anything useful in the quantum regime. I thought the whole point was to explain away the need for defining "observer" and "measurement". If it comes back to explaining entangled particle behavior using orthodox quantum definitions in 99% of cases, what's the point?

 

[Question69]

OK, I can see that objective collapse might not occur often if the parameter was "small" for a single particle. But that essentially means such theories don't explain anything useful in the quantum regime. I thought the whole point was to explain away the need for defining "observer" and "measurement". If it comes back to explaining entangled particle behavior using orthodox quantum definitions in 99% of cases, what's the point?

Well, wouldn't it explain those ill-defined terms? An observer here is a system of particles, and the collapse happens because you are a big system that gets entangled to the small system that is in superposition because it's not big enough.

 

[StevieTNZ]

@DrChinese - Even without introducing collapse theories, there have been challenges to the notion of "delayed choice entanglement swapping"* which is what I believe you're describing in post #28. See for example: http://philsci-archive.pitt.edu/10007/1/manuscript_final.pdf

(Egg, M. (2013). Delayed-choice experiments and the metaphysics of entanglement. Foundations of Physics, 43(9), 1124-1135.)

* and I certainly agree, alongside Bernard d'Espagnat, in private email correspondence with me that the Zeilinger et al experiment in 2012 was not delayed choice entanglement swapping. Presumably, entanglement needs to exist between the two pairs to swap, which is actually broken when measured by Alice and Bob first before a bell-state measurement occurs on the other two photons.

 

[vanhees71]

That's interesting, what interpretation do you hold to?

The minimal statistical interpretation, i.e., QT without unnecessary philosophical extensions.

 

[vanhees71]

Even in the interpretations subforum, that question is off limits. All QM interpretations make the same predictions for all experiments, so there is no way of testing by experiment which ones are "true". The interpretations subforum is for discussion of what the different interpretations say, not for expressing opinions about which ones people think are "true". Please refer to the guidelines for the interpretations subforum.

So it's forbidden to discuss about alternative ansatzes like the here discussed objective-collapse postulates?

At least I found it interesting that there is now an ERC grant for an experiment testing such postulates with a challenging experiment about the quantum behavior of massive bodies (which is obviously in reach, because otherwise the grant application wouldn't have been successful, and also this aspect is a side effect of all the gravitational-wave detectors since GEO 600 and now LIGO).