Does entanglement synchronization change with distance in general relativity?

[SchrodingersRat]

Hi everyone, this is my first post.

As anyone interested in physics I am somewhat familiar with the concept of entanglement. Also I have read that contrary to what most people think about this phenomenon, the particles involved are not always exactly synchronized but one can actually seem to be ahead of the other in time (time in the sense of what you measure with a clock). This would be hard to explain in a Newtonian-like formulation of physics but as they say this is not necessarily a problem with GR.

A question I have thought about regarding this, and one I am sure someone would have come up with an experiment to test, is how this effect changes with distance. That is, does the degree of de-synchronization compared to clocks increase linearly with distance? And are there other factors that can affect this behavior?

Also, is the de-synchronization different for every entangled particle pair or is there some form of correlation in every pair with roughly the same two positions? The first would seem to fit better with the rest of modern physics, but I my knowledge of QM is not that deep yet.

 

[PeroK]

Hi everyone, this is my first post.

As anyone interested in physics I am somewhat familiar with the concept of entanglement. Also I have read that contrary to what most people think about this phenomenon, the particles involved are not always exactly synchronized but one can actually seem to be ahead of the other in time (time in the sense of what you measure with a clock).

I have no idea what you mean by this. A system of particles in an entangled state is described by a single state that cannot be decomposed into a separate state for each particle.

 

[DrChinese]

Hi everyone, this is my first post.

A question I have thought about regarding this, and one I am sure someone would have come up with an experiment to test, is how this effect changes with distance. That is, does the degree of de-synchronization compared to clocks increase linearly with distance? And are there other factors that can affect this behavior?

Also, is the de-synchronization different for every entangled particle pair or is there some form of correlation in every pair with roughly the same two positions? The first would seem to fit better with the rest of modern physics, but I my knowledge of QM is not that deep yet.

Entangled systems are not "synchronized" as you imagine. They follow a set of rules that can be difficult to understand for the beginner. Generally: time and distance are not factors. Interaction with other quantum particles or systems is a factor. Entanglement can be full (maximal) or partial. Entanglement can occur on some bases (such as spin) but not on others (such as momentum). And entanglement can be between 2, 3, or more particles.

There are literally thousands of experiments in the canon on entanglement.

 

[PeterDonis]

Hi everyone, this is my first post.

Hi, and welcome to PF!

the particles involved are not always exactly synchronized but one can actually seem to be ahead of the other in time

It would help if you could give some specific references to where you have read this.

However, I suspect what you are referring to is descriptions of experiments on pairs of entangled particles in which measurements are made on the particles at spacelike separated events--that is, it would be impossible for a light signal to travel from one measurement to the other. For spacelike separated measurements, their time ordering is frame-dependent--they can happen at the same time in one frame, but in other frames measurement A can happen before measurement B, or measurement B can happen before measurement A.

What this means from a physics perspective is not that the particles or the measurements on them get "desynchronized", but that the time ordering of the measurements cannot matter--in other words, the measurement results cannot depend on the order in which the measurements are made. (In more technical language, physicists will say that the measurements must commute.) That puts strong constraints on the types of physical models that can match the experimental results.

 

[SchrodingersRat]

Hi, and welcome to PF!


It would help if you could give some specific references to where you have read this.

However, I suspect what you are referring to is descriptions of experiments on pairs of entangled particles in which measurements are made on the particles at spacelike separated events--that is, it would be impossible for a light signal to travel from one measurement to the other. For spacelike separated measurements, their time ordering is frame-dependent--they can happen at the same time in one frame, but in other frames measurement A can happen before measurement B, or measurement B can happen before measurement A.

What this means from a physics perspective is not that the particles or the measurements on them get "desynchronized", but that the time ordering of the measurements cannot matter--in other words, the measurement results cannot depend on the order in which the measurements are made. (In more technical language, physicists will say that the measurements must commute.) That puts strong constraints on the types of physical models that can match the experimental results.

I feel a bit stupid now, but I don´t remember where I read this except that it was on the internet. Are you saying that there is not desynchronization but rather that it is not possible to determine in which order the measurements were made? Also I know that there is a phenomenon referred to as time-like quantum entanglement, could you tell briefly how it works and how it relates to regular entanglement?

 

[PeroK]

I feel a bit stupid now, but I don´t remember where I read this except that it was on the internet. Are you saying that there is not desynchronization but rather that it is not possible to determine in which order the measurements were made? Also I know that there is a phenomenon referred to as time-like quantum entanglement, could you tell briefly how it works and how it relates to regular entanglement?

In Special Relativity there is no absolute time. In particular, there is no universal simultaneity. Events that happen in the same place have a definite order. Events may however be "spacelike" separated, which means they have no definite order. It makes no sense to say which one absolutely happened first.

 

[SchrodingersRat]

I know that you cannot measure absolute time in relativistic physics. But by desynchronization I mean what could be described as how close a "spacelike" separation is to being a "lightlike" separation.

 

[SchrodingersRat]

Actually I found an article that answered these questions nicely. I´m sorry for taking up people´s time.

 

[FactChecker]

Actually I found an article that answered these questions nicely. I´m sorry for taking up people´s time.

If possible, can you please post a link to the article so others who have the same question can understand.
I am just a casual amateur and would appreciate it.

 

[bhobba]

Actually, I would say entanglement is an easier concept to understand in Quantum Field Theory (QFT). It's just an excitation of the underlying quantum field that permeates all space of two particles. The 'configuration' of such an excitation can be localised or spread across a large volume, just as a single particle can do the same. Until measurement, the particles are viewed as a single excitation rather than as two individual excitations, each of a single particle. When measured (i.e., interacting with something we call a measuring device), that tells us about a single particle, it becomes two separate excitations.

 

[pines-demon]

Actually, I would say entanglement is an easier concept to understand in Quantum Field Theory (QFT). It's just an excitation of the underlying quantum field that permeates all space of two particles. The 'configuration' of such an excitation can be localised or spread across a large volume, just as a single particle can do the same. Until measurement, the particles are viewed as a single excitation rather than as two individual excitations, each of a single particle. When measured (i.e., interacting with something we call a measuring device), that tells us about a single particle, it becomes two separate excitations.

While I like this, it is not like if I can picture it better, because even with a classical field in mind I cannot get a sense of how it violates Bell inequalities.

 

[jeffn1]

Would the statement that the two entangled particles retain the same relationship to their underlying quantum field be consistent with your view? To me, that is a nice explanation for quantum entanglement without any issues about faster than speed of light communication, etc.

 

[PeroK]

Would the statement that the two entangled particles retain the same relationship to their underlying quantum field be consistent with your view? To me, that is a nice explanation for quantum entanglement without any issues about faster than speed of light communication, etc.

It would help if you replied to the post and statement that you are referring to.

That said, it's not clear to me how QFT makes any fundamental difference in terms of "explaining" entanglement and "non-locality". It's mathematically more sophisticated and a more general formulation of QM, but the fundamental issue of "non-locality" remains.

Basic QM is non-relativistic. The Schrodinger equation is explicitly not covariant. A particle can be found outside its future light-cone. QFT fixes that by incorporating SR, recognising that particles are not fundamental and embedding the maximum speed of causality into its mathematical structure.

Entanglement, however, is about correlation of measurements (not causation). As far as QFT is concerned, space-like separated measurements commute (i.e. do not depend on each other). That is mathematically compatible with space-like separated measurements on an entangled system being correlated. That remains bound up in the concept of an entangled (non-local) state. A two-particle wave-function has been replaced by a quantum field, but fundamentally the subtle distinction between causation and correlation remains.

 

[jeffn1]

It would help if you replied to the post and statement that you are referring to.

That said, it's not clear to me how QFT makes any fundamental difference in terms of "explaining" entanglement and "non-locality". It's mathematically more sophisticated and a more general formulation of QM, but the fundamental issue of "non-locality" remains.

Basic QM is non-relativistic. The Schrodinger equation is explicitly not covariant. A particle can be found outside its future light-cone. QFT fixes that by incorporating SR, recognising that particles are not fundamental and embedding the maximum speed of causality into its mathematical structure.

Entanglement, however, is about correlation of measurements (not causation). As far as QFT is concerned, space-like separated measurements commute (i.e. do not depend on each other). That is mathematically compatible with space-like separated measurements on an entangled system being correlated. That remains bound up in the concept of an entangled (non-local) state. A two-particle wave-function has been replaced by a quantum field, but fundamentally the subtle distinction between causation and correlation remains.

Thank you for your thoughtful response. I was responding to Bhobba's statement ("I would say entanglement is an easier concept to understand in Quantum Field Theory (QFT)....", quoted more fully, below). He seems to think that QFT does help explain entanglement, and that seems to make sense to me:

Actually, I would say entanglement is an easier concept to understand in Quantum Field Theory (QFT). It's just an excitation of the underlying quantum field that permeates all space of two particles. The 'configuration' of such an excitation can be localised or spread across a large volume, just as a single particle can do the same. Until measurement, the particles are viewed as a single excitation rather than as two individual excitations, each of a single particle. When measured (i.e., interacting with something we call a measuring device), that tells us about a single particle, it becomes two separate excitations.

 

[pines-demon]

What do you actually get from QFT in terms of entanglement? You can use relativistic QM (without going into field theory) and you still add nothing to the issue. So it is not relativity that is doing the work here. Is it the idea that you can replace two particles by a single space-encompassing field?

 

[jeffn1]

What do you actually get from QFT in terms of entanglement? You can use relativistic QM (without going into field theory) and you still add nothing to the issue. So it is not relativity that is doing the work here. Is it the idea that you can replace two particles by a single space-encompassing field?

Yes, the concept I would throw out is that, perhaps, the entangled particles retain their same relationship to their underlying (and non-local) quantum field. So, even when they are separated by billions of miles, their spins (for example) would retain the same relationship to their underlying quantum field. So, as a result of this, the spins of the two entangled particles would continue to be correlated.

I do not know if Bhobba was saying the same thing. But, I have not read much content that views entanglement as related to QFT. So, his comment stood out to me. (I have occasionally read some materials that seem to suggest this, but nothing very concrete.)

 

[jeffn1]

At the risk of speaking well above my pay grade, I think that is a pretty central question when it comes to entanglement of two particles millions of miles apart. I think there is evidence that measuring/collapsing/detecting the local particle has an immediate effect (faster than the speed of light) on the entangled particle millions of miles away (but this correlation is only observed when the non-local particle is measured; the nonlocal particle does not spontaneously do anything when the local particle is measured.) [Keep an eye out, someone with more knowledge than my might clarify or correct my statement.]

 

[PeterDonis]

I think there is evidence that measuring/collapsing/detecting the local particle has an immediate effect (faster than the speed of light) on the entangled particle millions of miles away

No, there isn't, because of this:

(but this correlation is only observed when the non-local particle is measured; the nonlocal particle does not spontaneously do anything when the local particle is measured.)

QM satisfies what's called the "no signaling theorem", which is the mathematical version of what you state here: that if particle A and particle B are entangled, and you measure particle A, there is no observable effect on particle B. And that means it's impossible to have evidence of any "immediate effect (faster than the speed of light)". Any apparent effect in the theory is an artifact of a particular formulation that doesn't take into account how the correlations are actually observed.

 

[jeffn1]

No, there isn't, because of this:


QM satisfies what's called the "no signaling theorem", which is the mathematical version of what you state here: that if particle A and particle B are entangled, and you measure particle A, there is no observable effect on particle B. And that means it's impossible to have evidence of any "immediate effect (faster than the speed of light)". Any apparent effect in the theory is an artifact of a particular formulation that doesn't take into account how the correlations are actually observed.

But, Peter, if the nonlocal particle is measured before the the speed of light would allow a signal, don't the observed correlations strongly suggest that the measurement of the local particle affected the nonlocal particle faster than the speed of light? (I do want to note that I appreciate that you take the time to respond to my posts. Thx!).

 

[PeterDonis]

if the nonlocal particle is measured before the the speed of light would allow a signal, don't the observed correlations strongly suggest that the measurement of the local particle affected the nonlocal particle faster than the speed of light?

No. The fact that the measurements happen to be spacelike separated in a particular case is actually a red herring. If you do the math, you will realize that the correlations are the same regardless of the spacetime relationship of the two measurements! In other words, we have two entangled particles, A and B, and we make measurements on them that show correlations that violate the Bell inequalities. (That last qualification is necessary to make sure that any kind of "classical" model is ruled out.) And the correlations are the same whether we measure A first and then B (i.e., measurements timelike separated with A in the past of B), or B first and then A, or A and B are measured at spacelike separated events so there is no invariant fact of the matter about which one happens first.

What all this tells is that, whatever is going on in these experiments, it cannot be something simple like "the measurement of one particle affects the other". If measuring A affects B, we would expect such an effect not to happen if B is measured before A instead of after. But that's not the case for these experiments; the "effect" happens even if we measure B first. In such a case we would more naturally say that measuring B affects A: but that would make that case different from the case where measuring A affects B, and, again, in the actual correlations there is no difference. (And of course if the measurements are spacelike separated, so there is no invariant fact of the matter about which one happens first, it doesn't make sense to talk of either measurement "affecting" the other, at least not with our normal intuitive meaning of those words.)

In short, there is no ordinary language description we can give to these experiments that (a) matches our ordinary language intuitions, and (b) matches the actual QM math and the experimental results that confirm it. We're simply in new territory here, which is why QM interpretations are still a matter of dispute more than a century after QM was first developed. As Richard Feynman said, you have to resist the temptation to keep asking "How can it be like that?" because nobody knows how it can be like that.

 

[jeffn1]

In such a case we would more naturally say that measuring B affects A: but that would make that case different from the case where measuring A affects B, and, again, in the actual correlations there is no difference. (And of course if the measurements are spacelike separated, so there is no invariant fact of the matter about which one happens first, it doesn't make sense to talk of either measurement "affecting" the other, at least not with our normal intuitive meaning of those words.)

I need to look into this more. My intuition would be that the entangled particles are in a state of flux before either is measured/detected/collapsed/branched off. Once either particle is measured, the state of flux "stops" for both particles. So, the measurement of either particle sort of "settles" the measured state for both particles.

But, I like to think I am thoughtful enough to realize I do not have necessary depth of knowledge to engage fully. I will continue to think about your post and perhaps play around with Gemini and see what AI says in response to my prompts. Sincere thanks for engaging with me.:)

 

[PeterDonis]

My intuition

Nobody's intuitions are worth much here. That's a big part of what Feynman meant when he said nobody knows how it can be like that.

Intuitions can be retrained, at least to an extent, but that requires taking the time to become thoroughly familiar wth the math of QM and how it makes predictions.

the entangled particles are in a state of flux before either is measured/detected/collapsed/branched off. Once either particle is measured, the state of flux "stops" for both particles. So, the measurement of either particle sort of "settles" the measured state for both particles.

This is all just words. At best it amounts to a rudimentary attempt at a QM interpretation--but discussion of QM interpretations belongs in the interpretations subforum, and should be based on interpretations that are already in the published literature. Trying to roll your own is not going to work out well, and in any case personal speculation is off limits here.

perhaps play around with Gemini and see what AI says

Please be aware that, first, AI is generally not a valid reference here at PF, and second, asking AI questions is generally not a good way to learn physics, particularly with a subject like QM. You need to be looking at textbooks (my personal first recommendation is Ballentine, but there are others) and peer-reviewed papers.