crowded quantum information

[MigL]

The absence of local realism is evident in many, if not all,  aspects of QM.
Non-locality is not needed for entanglement; nor anything else.
Relegate it to the dust-bin of history, along with the aether.

[Lorentz Jr]

10 minutes ago, MigL said:

Non-locality is not needed for entanglement; nor anything else.

Neither is non-realism. If you have non-locality, you don't need non-realism.

Quote

Relegate it to the dust-bin of history, along with the aether.

Please don't tell me what to do. Nothing about the Lorentzian interpretation of physics has been scientifically disproved.

[joigus]

4 hours ago, MigL said:

No I cannot think of any other example of non-locality.
As far as I know, no other effects require that the outcome of an event at a specific point is determined  explicitly on what happens at another point, unless there is a transfer of information.
And relativity explicitly states that information is constrained to transfer at speeds not exceeding c .

So non-locality is not just unproven yet, it is actually not needed; not even for entanglement.

+1.

2 hours ago, Lorentz Jr said:

Objective collapse of individual particle wave functions.
With the same caveat that it's possible but not proven.

Non-locality is needed if one wants to retain realism.
Non-realism is needed if one wants to retain locality.

+1.

Interesting...

[MigL]

That may apply when dealing strictly with entanglement.

But how does non-locality deal with 'Schroedinger's cat in a box' ?
Absence of local realism seems to handle it just fine.

Are you suggesting we should use non-locality for one aspect of QM, and absence of local realism for other aspects ?

[Markus Hanke]

In the quantum realm, when you talk to a wall, there is a small but non-zero probability that at least some of what you say gets through to the other side:

\[T^{-1} =1+\frac{V_{0}^{2}}{4E( E+V_{0})} sin^{2}\left(\frac{2a}{\hbar }\sqrt{2m( E+V_{0}}\right)\]

This thread here, alas, appears to be a purely classical situation.

[bangstrom]

17 hours ago, joigus said:

What do you mean???

Here's a visual aid:

Entanglement is most like your picture on the upper left where one particle is in the past light cone and the other is in the future. All of our communications, whether involving entanglement or not, is received from the past and sent to the future.

John Cramer’s Transactional Interpretation of QM is an extension of the Wheeler-Feynman approach to atomic transitions where EM signaling can be interpreted as direct and instant interaction between emitter and absorber with signals moving both forward and backward in time as a prerequisite to the transmission of energy.

Thermodynamics limits our observation of events to the emission of energy from the past and arriving in the present. In Cramer’s and similar models, there is an instant, two-way signaling between the emitter and absorber that precedes any transfer of energy which is why light always travels as if prescient of its destination.

[Lorentz Jr]

Apparently the part about Schrödinger's cat being a joke (along with the Von Neumann–Wigner interpretation) hasn't gotten through the wall.

Edited November 27, 2022 by Lorentz Jr

[bangstrom]

12 hours ago, MigL said:

The absence of local realism is evident in many, if not all,  aspects of QM.
Non-locality is not needed for entanglement; nor anything else.
Relegate it to the dust-bin of history, along with the aether.

Injecting another bit of speculation here, as if we need it, but the Lorentzian interpretation, Maxwell’s equations, and SR all work, and are easier to understand, if you consider the value of c as a dimensional constant rather than the conventional speed of light. There is no hint in Maxwell's equations that c is a speed. Instead c=1/√μo ϵo.

In this view, the value of c is a universal constant giving us the amount of time found in any given distance which is approximately one second of time for every 300,000 km of distance for all observers independent of their individual motions. The Lorentzian contractions make this possible.

"Any attempt to measure the velocity of light is … not an attempt at measuring the velocity of light but an attempt at ascertaining the length of the standard metre in Paris in terms of time-units."-Herman Bondi

Common observations should tell us that observers moving at different speeds should not view any single speed as the same for all. C has all the properties of a dimensional constant and resembles nothing like a speed.

You can’t add v to c because v is a speed and c is a constant ratio. Just as nothing can go faster than c as a ratio, nothing can go faster than the ratio of 1.6 kilometers per mile. Velocities and ratios don’t add.

It simplifies SR to think of c as a dimensional constant rather than as a speed and this view also eliminates the speed related paradoxes in SR such as the “pole and barn” thought experiment.

As for the aether, the M&M experiment was looking for the presence of an aether as evidenced by the drift of photons in a moving medium. If c is a dimensional constant and not the speed of a photon, the null result of the M&M experiment indicated that either there is no aether or there is no photon drift. I prefer the latter explanation of no photon drift and we can retain the aether.

 

[joigus]

3 hours ago, bangstrom said:

Entanglement is most like your picture on the upper left where one particle is in the past light cone and the other is in the future. All of our communications, whether involving entanglement or not, is received from the past and sent to the future.

Again, no answer. The light cone of what?

Didn't you understand that my pictures were meant to explain that two events being in the same light cone doesn't mean anything? Didn't you understand that?

In my picture on the upper left, both events are in the past cone of an unspecified future event that plays no role in an EPR situation.

So "in the same light cone" specifies nothing.

1 hour ago, bangstrom said:

There is no hint in Maxwell's equations that c is a speed. Instead c=1/√μo ϵo.

Except that it is obviously a speed from dimensional grounds. Not only that; if you assume no sources (or being far away from sources) the meaning as a speed becomes even more obvious (can something be "more" obvious...?). The reason is that Maxwell's equations become wave equations for either E, B (or the scalar and vector potentials) and 1/sqrt(mu_naughtxepsilon_naught) being the phase velocity of the waves in the vacuum.

 

13 hours ago, Lorentz Jr said:

Neither is non-realism. If you have non-locality, you don't need non-realism.

The problem is non-locality is much, much harder to accomodate to everything else we know than non-realism.

The projection postulate is non-local, but it is in a way not to produce any measurable non-local consequences whatsoever. The "founding fathers" of QM were not stupid.  

The problem is: What makes quantum superpositions not to live forever, and anything like "classical data" become necessary to describe the evolution of the state? IOW: What in the quantum state carries along these "classical data" (the outcomes of measurements)? In still other words: How do we accomodate in the quantum formalism the fact that one or many of the evolving components of the quantum state suddenly become irrelevant? We should do this in a way that preserves unitarity, linearity, and locality. Seems like an impossible task.

Linearity is probably the most suspect of all...

[MigL]

8 hours ago, Lorentz Jr said:

Apparently the part about Schrödinger's cat being a joke

It may be an example brought to an absurd level, but it illustrates perfectly that QM says there is no reality until an observation/interaction is made.
Which side of the wall are you on ?

One thing I've always wondered about, and maybe you more learned gentlemen can offer some guidance ...
If I produce two entangled particles, and somehow manage to 'steer' them towards each other such that they interact ( only ) with each other, is entanglement lost ?

[joigus]

2 minutes ago, MigL said:

If I produce two entangled particles, and somehow manage to 'steer' them towards each other such that they interact ( only ) with each other, is entanglement lost ?

Good question.

Highly depends on the nature of the interaction bringing them up together, as well as the way in which they interact with each other. If you accelerate the hell out of them, they start to emit radiation, and they finally collide and perhaps radiate some more, you can rest assured they will lose quantum coherence and no longer be entangled.

Entanglement is generally produced under conditions of very ordered, very tidy, local interaction, and particles are brought to a ground state of some kind, or perhaps particles emanate from a coherent source, like in SPDC.

The take-home idea is: Almost anything you do in a careless way will break quantum coherence.

That's my "analysis." Let's see what other people think.

[Lorentz Jr]

47 minutes ago, MigL said:

QM says there is no reality until an observation/interaction is made.

Quantum mechanics says nothing about reality beyond probabilities of measurement outcomes. Only specific interpretations of QM say anything more.

[joigus]

47 minutes ago, Lorentz Jr said:

Quantum mechanics says nothing about reality beyond probabilities of measurement outcomes. Only specific interpretations of QM say anything more.

It does say something beneath: Amplitudes. Are amplitudes physical? Are they just a tool?

[Lorentz Jr]

46 minutes ago, joigus said:

Are amplitudes physical? Are they just a tool?

Quantum mechanics says nothing about that. Only specific interpretations of QM say anything more.

EDIT: Or, alternatively, amplitudes (squared) are just probability densities of measurement outcomes. The theory itself doesn't say anything about whether wave functions are "physical", or even what that would mean.

Edited November 27, 2022 by Lorentz Jr

[joigus]

12 hours ago, Markus Hanke said:

This thread here, alas, appears to be a purely classical situation.

LOL. I had to read it again to get your drift. +1

[geordief]

5 hours ago, joigus said:

Good question.

Highly depends on the nature of the interaction bringing them up together, as well as the way in which they interact with each other. If you accelerate the hell out of them, they start to emit radiation, and they finally collide and perhaps radiate some more, you can rest assured they will lose quantum coherence and no longer be entangled.

Entanglement is generally produced under conditions of very ordered, very tidy, local interaction, and particles are brought to a ground state of some kind, or perhaps particles emanate from a coherent source, like in SPDC.

The take-home idea is: Almost anything you do in a careless way will break quantum coherence.

That's my "analysis." Let's see what other people think.

Could they just  meet again under the influence of gravity?

Their trajectory could be altered if  either  or both of them went close enough to a small black hole 

I imagine entanglement would be lost when they met again

Edited November 27, 2022 by geordief

[joigus]

13 minutes ago, geordief said:

Could they just  meet again under the influence of gravity?

Their trajectory could be altered if  either  or both of them went close enough to a small black hole 

I imagine entanglement would be lost when they met again

Under most typical scattering scenarios gravity is far too weak to be of any significance. If you try to collide particles at an energy high enough, and with an impact parameter --closeness of approaching particles-- close enough to produce a BH, I don't think ordinary QM is sufficient to deal with it. I don't know how to deal with that situation, TBH. I do know enough to guess --if not to know-- that any outgoing state would come out as a mixed state --if Hawking and Bekenstein are right--, which means, coherence would be lost. Maybe @Markus Hanke wants to take this up with more precise information. He seems to be on fire lately.  

[geordief]

37 minutes ago, joigus said:

Under most typical scattering scenarios gravity is far too weak to be of any significance. If you try to collide particles at an energy high enough, and with an impact parameter --closeness of approaching particles-- close enough to produce a BH, I don't think ordinary QM is sufficient to deal with it. I don't know how to deal with that situation, TBH. I do know enough to guess --if not to know-- that any outgoing state would come out as a mixed state --if Hawking and Bekenstein are right--, which means, coherence would be lost. Maybe @Markus Hanke wants to take this up with more precise information. He seems to be on fire lately.  

I don't think I that was what I had in mind regarding the  BHs

I just meant that one or both of the particles could encounter  a BH along their trajectory and undergo   gravitational slingshots that would take them on collision course with their  entangled partner.

I guess that circumstance might  be impossible to prodjects uce except  by chance  and more or less impossible in the lifetime of our universe.

So maybe not even a thought experiment.

 

In any event any entanglement that had lasted to that point would be broken(by  those last remaining objects  in the universe )

[bangstrom]

On 11/27/2022 at 5:06 AM, joigus said:

Again, no answer. The light cone of what?

Again, a light cone can be about whatever you choose to illustrate. They were your light cones and I didn't see any that quite resembled entanglement.

Entanglement would be slightly more difficult to illustrate with a light cone than ordinary events because it would usually require two or more separate but overlapping light cones to illustrate and I have never seen it done.

On 11/27/2022 at 5:06 AM, joigus said:

Didn't you understand that my pictures were meant to explain that two events being in the same light cone doesn't mean anything? Didn't you understand that?

You didn’t explain that was your intention and I still don’t understand what you mean. An illustration of entanglement should require at least two world lines, one for each particle, and each particle would need to stay within its respective light cone.

Your illustration on the upper left “most” resembled entanglement but none of them made sense as representative of entanglement.

On 11/27/2022 at 5:06 AM, joigus said:

In my picture on the upper left, both events are in the past cone of an unspecified future event that plays no role in an EPR situation.

In your picture on the upper left, I see one one event in the future and one in the past but no world lines for the entangled particles

Entanglement violates the EPR situation in that one entangled particle can interact with its partner(s) instantly as if the they were side-by-side. Entangled particles need no physical connection to interact- not even light. It is instant action at a distance that violates the EPR.

Your illustration on the upper left “most” resembled entanglement but none of them made sense to me as representative of entanglement.

On 11/27/2022 at 5:06 AM, joigus said:

 So "in the same light cone" specifies nothing.

 "In the same light cone" means that one particle, usually an electron, can interact instantly with any other similar particle within the same light cone provided that conditions between the two permit.

This is possible in QM but not in classical physics so that is a major contrast between the two and I wouldn’t call it “nothing.”

In the the classical situation, one particle can only interact with another either directly or through some physical interaction. QM needs no physical interaction.

 

 

On 11/27/2022 at 5:06 AM, joigus said:

Except that it is obviously a speed from dimensional grounds. Not only that; if you assume no sources (or being far away from sources) the meaning as a speed becomes even more obvious (can something be "more" obvious...?). The reason is that Maxwell's equations become wave equations for either E, B (or the scalar and vector potentials) and 1/sqrt(mu_naughtxepsilon_naught) being the phase velocity of the waves in the vacuum.

The value of c works perfectly well as a universally observed dimensional constant and it behaves nothing like a speed. Just because c is the ratio of distance over time doesn’t mean it is a speed, and since c=d/t is a constant, that should be our first clue that c isn’t a speed.

The determinations of the magnetic permeability and the electro permittivity in Maxwell’s equations are static tests and their combination is a constant for the vacuum. They are speed in the dimensional sense but they are not speeds in the sense of something moving.

Edited November 28, 2022 by bangstrom
moved a disjointed sentence

[Lorentz Jr]

1 hour ago, bangstrom said:

"In the same light cone" means that one particle, usually an electron, can interact instantly with any other similar particle within the same light cone provided that conditions between the two permit.

This entire sentence is utter nonsense. 

• Nothing about relativity allows instantaneous interactions.
• Nothing about relativity says anything about particles having to be "similar" in any way.
• Every light cone is defined by either an event or some other specified point in spacetime, and no light cone that isn't defined by an interaction involving one of the particles in question (which would be necessary for them to be "in the same light cone") can be relevant to their mutual interactions.
• If two particles "interact instantaneously", that means whatever changes occur to the particles are outside of each other's light cones.

Edited November 28, 2022 by Lorentz Jr

[joigus]

52 minutes ago, bangstrom said:

Again, a light cone can be about whatever you choose to illustrate. They were your light cones and I didn't see any that quite resembled entanglement.

Entanglement would be slightly more difficult to illustrate with a light cone than ordinary events because it would usually require two or more separate but overlapping light cones to illustrate and I have never seen it done.

On 11/27/2022 at 12:06 PM, joigus said:

Didn't you understand that my pictures were meant to explain that two events being in the same light cone doesn't mean anything? Didn't you understand that?

You didn’t explain that was your intention and I still don’t understand what you mean. An illustration of entanglement should require at least two world lines, one for each particle, and each particle would need to stay within its respective light cone.

Your illustration on the upper left “most” resembled entanglement but none of them made sense as representative of entanglement.

On 11/27/2022 at 12:06 PM, joigus said:

In my picture on the upper left, both events are in the past cone of an unspecified future event that plays no role in an EPR situation.

In your picture on the upper left, I see one one event in the future and one in the past but no world lines for the entangled particles

Entanglement violates the EPR situation in that one entangled particle can interact with its partner(s) instantly as if the they were side-by-side. Entangled particles need no physical connection to interact- not even light. It is instant action at a distance that violates the EPR.

Your illustration on the upper left “most” resembled entanglement but none of them made sense to me as representative of entanglement.

On 11/27/2022 at 12:06 PM, joigus said:

 So "in the same light cone" specifies nothing.

 "In the same light cone" means that one particle, usually an electron, can interact instantly with any other similar particle within the same light cone provided that conditions between the two permit.

This is possible in QM but not in classical physics so that is a major contrast between the two and I wouldn’t call it “nothing.”

In the the classical situation, one particle can only interact with another either directly or through some physical interaction. QM needs no physical interaction.

Again: "In the same light cone" doesn't mean anything. I've shown you two distinct cases of events; a couple of them were space-like separated; the other two were time-like separated. In both cases, you can make them be either in the same light cone, or in different light cones, at will. It's painfully obvious you didn't understand.

Now rinse, and repeat. Sometimes, understanding something is a whole shampooing experience, as @iNow shrewdly suggested. Keep practicing.

56 minutes ago, bangstrom said:

The value of c works perfectly well as a universally observed dimensional constant and it behaves nothing like a speed. Just because c is the ratio of distance over time doesn’t mean it is a speed, and since c=d/t is a constant, that should be our first clue that c isn’t a speed.

The determinations of the magnetic permeability and the electro permittivity in Maxwell’s equations are static tests and their combination is a constant for the vacuum. They are speed in the dimensional sense but they are not speeds in the sense of something moving.

Your lack of understanding of basic physics is appalling. Epsilon and mu naught are not independent properties of space; the product of both is. The unit of charge can be independently chosen without any epsilon naught. In fact, in the cgs-unit system, there is no epsilon naught, and the basic unit of electric charge can be defined with dimensions of M^1/2L^3/2T^-1.  If you use such classic books as Landau-Lifshitz, you'll see they only use dimensionful electric charge units. I know the topic to be confusing to some people, that's why I once won a bet on this particular question. The bet was about how you can --if you want-- actually define the unit of electric charge in terms of mass, length, and time.

Modern quantum field theory uses dimensionless electric charge. It's an option, and it all depends on definitions.

But --and here's the essence of your misunderstanding of this particular question-- because in this universe magnetic fields are produced only as a consequence of changing electric fields, this activation of the magnetic field requires the propagation of something to be iniciated. The other constant thus becomes a measured value, which is essentially a speed. The workings of electric circuits critically depend on this speed. Here's a good Veritasium video that will make you understand this concept. It's highly imbued in physical intuition, and I highly recommend it:

Good luck!

[MigL]

I don't know how we got on the subject of light cones, and I don't want to re-read to find out.

Essentially light cones define which points in space-time have been, are, and will be, in causal contact with an event.
Causal contact has a very specific meaning in Physics, and is subject to the speed of light, c .It implies cause and effect, the very things Bangstrom is arguing against, as non-locality requires an 'effect' before information about the 'cause 'can reach that point
The 'slope' of the light cone itself is c , and separates time-like ( causal ) from space-like ( non-causal or superluminal ) events in space-time.

"Cause and effect, my love"
The Merovingian, from The Matrix Reloaded

[joigus]

20 hours ago, geordief said:

I don't think I that was what I had in mind regarding the  BHs

Sorry if I misunderstood. If they got close to a BH, and they get captured in it, according to the HB* picture of it, they would be re-emitted in the form of thermal radiation, which means they would no longer be entangled. A BH is not a good entanglement-producing machine, as it has an entropy associated to its surface. This entropy is not entanglement entropy, it's a further scrambling of information than what entanglement entropy represents.

This is all a bit dicey though. Not everybody agrees on what the HB picture of BH's is telling us.

* Hawking-Beckenstein

[geordief]

2 hours ago, joigus said:

Sorry if I misunderstood. If they got close to a BH, and they get captured in it, according to the HB* picture of it, they would be re-emitted in the form of thermal radiation, which means they would no longer be entangled. A BH is not a good entanglement-producing machine, as it has an entropy associated to its surface. This entropy is not entanglement entropy, it's a further scrambling of information than what entanglement entropy represents.

This is all a bit dicey though. Not everybody agrees on what the HB picture of BH's is telling us.

* Hawking-Beckenstein

No ,I didn't mean for them to get captured by  a BH or BHs but to get slingshotted by it or them  into each others' path.

 

Totally incredible,I know 😉

[joigus]

20 minutes ago, geordief said:

No ,I didn't mean for them to get captured by  a BH or BHs but to get slingshotted by it or them  into each others' path.

 

Totally incredible,I know 😉

Not that incredible. It's thinkable. If particles got very close to a small BH, their accelerations would be considerably big at the point of being slingshotted, and they would probably emit radiation --synchrotron radiation-- if they're charged. So my guess is they would easily lose quantum coherence. Small BH's exert huge tidal forces too.

Photons are a different matter. If you use very long-wavelength photons (bigger than the BH's Schwarzschild radius), for all I know, you can get them to scatter off BH's quite easily. Would that break quantum coherence? I don't know. But my guess is yes, easily.

Generally speaking, if I wanted to keep quantum coherence, the last thing I would try to do is to get my system anywhere close to a black hole and make it scatter off it. Black holes are notorious sources of entropy, and what you want is to keep things orderly. You also want to keep them as free as possible form very strong interactions.

Maybe @Markus Hanke has better guidance to offer on this idea. It wouldn't surprise me if he has.