Are Quantum Entities in Macro Sized Objects Entangled?

[Robert Friz]

Hi. This is my first posting on the Physics Forum so please forgive any issues as a result. I am a (reasonably educated) lay person with a strong physics interest with extensive readings -- so please be patient with my questions. :-> My questions and interest in these issues are sincere.

I have not seen a definitive statement in print that quantum entities* that are a part of a macro-sized object (e.g. the atoms in a photon detector) are entangled as a part of that macro-sized object. If this is so, due to the mass entanglement of its quantum components, the macro object will (I believe) have a single waveform as one of its characteristics.

In experiments such as the two-slit experiment, we all know that interference patterns occur until the observer tries to measure the path* of the quantum entity (e.g. a photon), and when a detector is introduced the interference pattern ceases to exist. Ostensibly, this is because the act of measurement interferes with the waveform of the quantum entity, but we all also know that this supposition is at the heart of the "measurement problem" debate.

I have not seen in print the possibility that the "measurement problem" is due to the waveform of the macro (fully entangled) object becoming entangled with the waveform of the quantum entity. Should this occur, the waveform entanglement would therefore determine the state* of the quantum entity by virtue of the state of the macro object, creating a definite position of the quantum entity and eliminating the interference pattern. The entanglement would occur when the probabilities of each of the waveforms are non-zero* at points in space-time in a location I call the "waveform overlap zone" between the macro object and the quantum entity.

Has anyone seen a discussion about this scenario in print? If so, how would the suggested entanglement of the two associated waveforms suggested above impact the "measurement problem", which continues to be one of the hottest discussions in physics?

Thank you for your help and consideration,

Bob Friz

* The definition and even the usage of each of the starred words is of course up for significant discussion.

 

[PeroK]

I'm surprised you haven't come across the idea that the apparatus gets entangled with the particle it's measuring. For example, take a look at Sean Carroll's blog:

http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/

 

[Robert Friz]

I'm surprised you haven't come across the idea that the apparatus gets entangled with the particle it's measuring. For example, take a look at Sean Carroll's blog:

http://www.preposterousuniverse.com...ion-of-quantum-mechanics-is-probably-correct/

Thank you for your reply! My first...

I have read some of Sean Carroll's work, and perhaps because I cannot accept the Many Worlds approach I overlooked his statement that the apparatus gets entangled with the particle. My bad.

If the apparatus gets entangled with the particle, then why is the "measurement problem" still an issue? Should not the "state" of the apparatus determine the "state" of the particle due to the entanglement?

Your help is deeply appreciated.

Bob

 

[PeroK]

Thank you for your reply! My first...

I have read some of Sean Carroll's work, and perhaps because I cannot accept the Many Worlds approach I overlooked his statement that the apparatus gets entangled with the particle. My bad.

If the apparatus gets entangled with the particle, then why is the "measurement problem" still an issue? Should not the "state" of the apparatus determine the "state" of the particle due to the entanglement?

Your help is deeply appreciated.

Bob

For example, our experience of the universe does not reveal entanglement directly at the macroscopic level. In MWI, with entanglement after entanglement and seemingly nothing ever getting resolved, somehow a single coherent version of the universe emerges.

The Copenhagen collapse is cleaner. The universe settles on one of many possibilities. But, that raises the problem of the special status of a "measurement".

 

[Robert Friz]

For example, our experience of the universe does not reveal entanglement directly at the macroscopic level. In MWI, with entanglement after entanglement and seemingly nothing ever getting resolved, somehow a single coherent version of the universe emerges.

The Copenhagen collapse is cleaner. The universe settles on one of many possibilities. But, that raises the problem of the special status of a "measurement".

Thanks. Cogitating...

 

[DarMM]

If the apparatus gets entangled with the particle, then why is the "measurement problem" still an issue? Should not the "state" of the apparatus determine the "state" of the particle due to the entanglement?

You'd wish so, but it doesn't. After the interaction that entangles them, the wavefunction for the device-particle system still has terms for each outcome, not one unique outcome.

 

[Robert Friz]

Thanks. However, I am struggling with "terms for each outcome" when there is only one outcome once the measurement is initiated. Can you help a 73 year old brain untangle this conundrum? Much appreciated...

 

[DarMM]

Thanks. However, I am struggling with "terms for each outcome" when there is only one outcome once the measurement is initiated. Can you help a 73 year old brain untangle this conundrum? Much appreciated...

Just to help, when you say "initiated" do you mean when the measurement starts, i.e. before it is completed with the device showing you a reading. Or do you just mean "once the measurement happens"?

 

[Robert Friz]

I appreciate you helping me peel this onion :-> . I THINK I meant 'once the measurement happens". I am aware of experiments where the measurement device changes (John Wheeler's delayed choice experiment) and I did not mean to refer to that, if that's what you meant by the first part of your question.

Rapidly becoming a novice,
Bob Friz

 

[DarMM]

Yeah so after it happens QM has terms for every outcome, even though only one outcome is actually seen, i.e. it has a term like "Device reports up and particle is spin up" and "Device is down and particle is spin down", this contrasts with the actual observation of only one outcome. That's the measurement problem.

 

[DrChinese]

In experiments such as the two-slit experiment, we all know that interference patterns occur until the observer tries to measure the path* of the quantum entity (e.g. a photon), and when a detector is introduced the interference pattern ceases to exist. Ostensibly, this is because the act of measurement interferes with the waveform of the quantum entity...

The measurement device itself need not provide ANY kind of disturbance to cause the interference to disappear. This is easily seen if you place polarizers over each slit of the 2 slits. If the polarizers are parallel, there is interference. If the polarizers are crossed, there is no interference. Either way, there is exactly 1 polarizer in front of 1 slit, so it's physical presence is NOT the critical factor.

http://sciencedemonstrations.fas.ha...-demonstrations/files/single_photon_paper.pdf

I would not use the term "entanglement" in this situation (as you do in the OP) because I don't think it clarifies anything.

 

[Robert Friz]

Please let me know if you get tired of / bored with this thread, but I still have questions. Thanks if your interest and time allows for continued dialog.

"QM... has a term like 'device reports up and particle... is spin down;" sounds like the theoretical solution to Schrodinger equations (unfortunately above my pay grade), whereas the outcome is a physical result. I'm trying to wrap my head around why, if the device-particle system is entangled, whether the very fact of entanglement "solves" the equations due to the state of the device portion of the system.

I have fallen in with the school of thought that theories cannot be proven correct, only that the theory remains viable when experimental evidence universally supports the theory. The coronary is that a theory can be proven wrong by experimental evidence that does not support the theory. Along this vein, is there evidence that causality is not in effect when a device-particle system "selects" an outcome from all the possible outcomes? Some thoughts:

Causality above depends on knowing the "state" of the device that, when entangled with the particle, determines a specific outcome. I excelled at multiple choice problems, but I am baffled by the following choices. Please select one, or more, if appropriate. :->

a. The observer does not know the state of the device, that when entangled with the particle, determines a specific outcome, but that state could be determined at some point in the future as QM continues to evolve.

b. The observer does not know the state of the device... and can never know that state due to the weirdness of QM, except via observation of the end-state of the particle and working backwards due to entanglement.

c. There is proof that there is zero causality between the initiation of the device-particle entanglement and the outcome, but the mechanism could be determined at some point in the future as QM continues to evolve.

d. There is proof that there is zero causality between the... and the outcome, but the mechanism cannot ever be determined due to the weirdness of QM and the Copenhagen Interpretation is correct (this is definitely not my favorite answer).

e. Your author (me) has no clue about this whole subject, and should have started this discovery journey when 20 and a physics major in college. I can handle this choice, should it be your preference.

Thanks again for your help!

 

[Robert Friz]

The measurement device itself need not provide ANY kind of disturbance to cause the interference to disappear. This is easily seen if you place polarizers over each slit of the 2 slits. If the polarizers are parallel, there is interference. If the polarizers are crossed, there is no interference. Either way, there is exactly 1 polarizer in front of 1 slit, so it's physical presence is NOT the critical factor.

http://sciencedemonstrations.fas.ha...-demonstrations/files/single_photon_paper.pdf

I would not use the term "entanglement" in this situation (as you do in the OP) because I don't think it clarifies anything.

Thanks for your help! As a followup question, in a device-particle system, do the waveforms of each "overlap" with the other? If so, that alone constitutes disturbance. I am aware of the polarized experiments, including John Wheeler's delayed choice experiment. However, if the waveforms of the device(s) overlap with the waveform of the particle as it departs its origin, then the particle and the devices are linked from the outset and a change in the devices will also be "known" to the particle.

Still struggling to understand, as perhaps we all are regarding the weirdness of QM, I remain

Bob Friz

 

[DrChinese]

Along this vein, is there evidence that causality is not in effect when a device-particle system "selects" an outcome from all the possible outcomes?

Well, to date no one has ever seen the slightest hint of a "cause" of a particular outcome when the quantum expectation value is between 0% and 100%. So I would call that an article of faith on your part, if you choose to believe something there is no evidence for.

I might point you to the theory of Bohmian Mechanics, which posits a mechanism for how that could occur (it is fully deterministic in principle). Although you might not like its major tenet: Instantaneous action at a distance.

 

[DrChinese]

Thanks for your help! As a followup question, in a device-particle system, do the waveforms of each "overlap" with the other? If so, that alone constitutes disturbance. I am aware of the polarized experiments, including John Wheeler's delayed choice experiment. However, if the waveforms of the device(s) overlap with the waveform of the particle as it departs its origin, then the particle and the devices are linked from the outset and a change in the devices will also be "known" to the particle.

If your idea were correct, how is it that all of the rest of the apparatus in the room has no effect on the interference/non-interference? Objectively, all of the kinds of "disturbances" you mention can be ruled out unless there is instantaneous action at a distance. See my other post about that.

 

[Robert Friz]

Well, to date no one has ever seen the slightest hint of a "cause" of a particular outcome when the quantum expectation value is between 0% and 100%. So I would call that an article of faith on your part, if you choose to believe something there is no evidence for.

I might point you to the theory of Bohmian Mechanics, which posits a mechanism for how that could occur (it is fully deterministic in principle). Although you might not like its major tenet: Instantaneous action at a distance.

Grin -- no, I don't believe in theories for which there is no evidence. I am seriously aware that "no" is a valid answer to science questions. Thanks for your help!

PS -- I am not a follower of Bohmian Mechanics, but am aware of same... As you may surmise, I am also not a follower of Copenhagen Interpretation (of which there are a number), and therein lays the struggle with the "measurement problem."

Ciao

Bob

 

[Robert Friz]

If your idea were correct, how is it that all of the rest of the apparatus in the room has no effect on the interference/non-interference? Objectively, all of the kinds of "disturbances" you mention can be ruled out unless there is instantaneous action at a distance. See my other post about that.

I agree that other apparatus may have an effect on the interference/non-interference. For that to happen, the wave function probability for the other apparatus needs to be non-zero at the site (wherever that is) of the particle. Interesting thoughts you raise! I am either inadequate to reply, or only marginally so...

Ciao

 

[Nugatory]

For that to happen, the wave function probability for the other apparatus needs to be non-zero at the site (wherever that is) of the particle.

This and some of the things that you've written above suggest that you have a basic misunderstanding of how quantum systems that include more than a single particle work.

When we have a quantum system that contains more than one one particle (maybe just a second particle, maybe a macroscopic measuring instrument composed of an enormous number of particles, maybe the entire rest of the universe) there is still only one wave function. Thus there's no such thing as a "wave function probability for the other apparatus" nor the "wave function overlap" you mention in the first post of this thread. Instead we have a single quantum system with one wave function, and its multiple terms correspond to different possible measurement outcomes, not different particles in the system. The multi-particle nature is all captured in the Hamiltonian of the system; Schrödinger's equation $H\psi=i\hbar\frac{\partial\psi}{\partial t}$ is an equation for one function $\psi$ whether the Hamiltonian includes terms for multiple particles or just one.

It is true that we often speak of the wave function of a single particle, or of a subset of the quantum system (otherwise we'd be working with the wave function of the universe all the time and even in the simplest problems). However, when we do this we're making an approximation, choosing to ignore terms in the Hamiltonian that are small enough to safely neglect. We cannot just add solutions that we find that way: the wave function of a quantum system that includes a particle and a detector is not the sum of the solutions for the isolated detector and the isolated particle. In fact, these three wave functions are elements of different Hilbert spaces, so adding them to get interference or overlap at a point is like expecting the sum of some number of apples and some number of oranges to be some number of bananas.

 

[Robert Friz]

This and some of the things that you've written above suggest that you have a basic misunderstanding of how quantum systems that include more than a single particle work.

When we have a quantum system that contains more than one one particle (maybe just a second particle, maybe a macroscopic measuring instrument composed of an enormous number of particles, maybe the entire rest of the universe) there is still only one wave function. Thus there's no such thing as a "wave function probability for the other apparatus" nor the "wave function overlap" you mention in the first post of this thread. Instead we have a single quantum system with one wave function, and its multiple terms correspond to different possible measurement outcomes, not different particles in the system. The multi-particle nature is all captured in the Hamiltonian of the system; Schrödinger's equation $H\psi=I\hbar\frac{\partial\psi}{\partial t}$ is an equation for one function $\psi$ whether the Hamiltonian includes terms for multiple particles or just one.

It is true that we often speak of the wave function of a single particle, or of a subset of the quantum system (otherwise we'd be working with the wave function of the universe all the time and even in the simplest problems). However, when we do this we're making an approximation, choosing to ignore terms in the Hamiltonian that are small enough to safely neglect. We cannot just add solutions that we find that way: the wave function of a quantum system that includes a particle and a detector is not the sum of the solutions for the isolated detector and the isolated particle. In fact, these three wave functions are elements of different Hilbert spaces, so adding them to get interference or overlap at a point is like expecting the sum of some number of apples and some number of oranges to be some number of bananas.

Thank you for your patience and for your very thorough explanation that helps me. I am hobbled by a lack of the math, but am struggling to understand the subject via lay reading. I am not unhappy about my misunderstandings; my best work has come from adversity or being wrong the first time. That is science, no? Again, thanks for your help.

 

[Nugatory]

. I am hobbled by a lack of the math,

It is, unfortunately, impossible to understand QM without the math. It's somewhat like trying to study Tolstoy when you're a native English speaker - there's only so far you can go with translations before you have to learn Russian - except worse because the gap between natural language and math (the language of physics) - is greater than the gap between Russian and English.

You might try Giancarlo Ghirardi's book "Sneaking a look at god's cards"; it does a good job of presenting the essential concepts to someone who lacks the math background to get through a college-level QM textbook.

 

[Robert Friz]

It is, unfortunately, impossible to understand QM without the math. It's somewhat like trying to study Tolstoy when you're a native English speaker - there's only so far you can go with translations before you have to learn Russian - except worse because the gap between natural language and math (the language of physics) is greater than the gap between Russian and English.

You might try Giancarlo Ghirardi's book "Sneaking a look at god's cards"; it does a good job of presenting the essential concepts to someone who lacks the mathbackground to get through a college-level QM textbook.

Thanks!

 

[StevieTNZ]

As posted in another thread, you may find this thread helpful in your understanding quantum mechanics obeyed by macroscopic systems -- https://www.physicsforums.com/threads/experiments-probing-the-macroscopic-limits-of-qm.903867/

I also endorse reading 'Sneaking a Look at God's Cards' to help get you started.

 

[A. Neumaier]

macro object will (I believe) have a single waveform as one of its characteristics.

In practice, macroscopic objects are always modeled by density operators (i.e., mixed states), never by wave functions. In any interpretation that thinks that the state represents knowledge (rather than is objective, observer-independent), it must be so even fundamentally, since we cannot know all microscopic details of a macroscopic object. Thus treating a macroscopic body in terms of a single wave function (as in some discussions of the foundations) is something very questionable.