non locality ?

[interested]

Are  non local interactions fact or fiction, or is the jury still out.

If I google for proof of non locality and it is everywhere, then I google for explanations of non locality using standard theory and I find it.

[Eise]

53 minutes ago, interested said:

Are  non local interactions fact or fiction, or is the jury still out.

Fiction. But there are non-local correlations. 

[swansont]

4 hours ago, interested said:

Are  non local interactions fact or fiction, or is the jury still out.

If I google for proof of non locality and it is everywhere, then I google for explanations of non locality using standard theory and I find it.

Do these links actually have valid explanations, or are you just counting google hits on the search parameters, which just happen to have those words but do not actually provide support? (or are crackpot sites)

[interested]

6 hours ago, Eise said:

Fiction. But there are non-local correlations. 

Are you contradicting your self, please explain "but their are non local correlations"

2 hours ago, swansont said:

Do these links actually have valid explanations, or are you just counting google hits on the search parameters, which just happen to have those words but do not actually provide support? (or are crackpot sites)

As examples here is a link to a paper demystifying none locality https://arxiv.org/ftp/arxiv/papers/1205/1205.4636.pdf concluding non locality is basically nonsense, and then here is another link claiming non locality is a proven fact https://phys.org/news/2015-11-nist-team-spooky-action-distance.html, and then here is another explaining it via another dimension https://arxiv.org/ftp/quant-ph/papers/0307/0307117.pdf . As you are aware I am easily confused. Are any of the papers on none locality based on provable fact, or is it just a case of physicists having a laugh. 

Do you think non locality is fact fiction or is still not 100% clear.

 

[Strange]

12 minutes ago, interested said:

Are you contradicting your self, please explain "but their are non local correlations"

You asked about non-local interactions.

Non-locality is a real thing, but it does not allow communication of information or interactions to take place non locally (i.e. faster than light).

p.s. the first and last of your links look fairly bogus to me 

[interested]

16 minutes ago, Strange said:

You asked about non-local interactions.

Non-locality is a real thing, but it does not allow communication of information or interactions to take place non locally (i.e. faster than light).

p.s. the first and last of your links look fairly bogus to me 

Thanks for that. Someone recommended using arxiv in my searches when looking for detailed papers.

Does the second link above have a consensus https://phys.org/news/2015-11-nist-team-spooky-action-distance.html or does anyone else have a differing opinion

[swansont]

1 hour ago, interested said:

Are you contradicting your self, please explain "but their are non local correlations"

As examples here is a link to a paper demystifying none locality https://arxiv.org/ftp/arxiv/papers/1205/1205.4636.pdf concluding non locality is basically nonsense, and then here is another link claiming non locality is a proven fact https://phys.org/news/2015-11-nist-team-spooky-action-distance.html, and then here is another explaining it via another dimension https://arxiv.org/ftp/quant-ph/papers/0307/0307117.pdf . As you are aware I am easily confused. Are any of the papers on none locality based on provable fact, or is it just a case of physicists having a laugh. 

Do you think non locality is fact fiction or is still not 100% clear.

 

You ask for examples and then provide link to them.

as Strange notes, you asked about interactions. Entanglement does not rely on interactions being nonlocal. The correlations, however, are, just as Eise said.

[Mordred]

Non locality is related to spacetime. It is more often based on Einstein locality. In essence on field treatments with your 4d spacetime coordinates (including time) it is the interactions that occur between both the field and particle within a specified unit of time. Typically it will be the neighboring 4d coordinate to a coordinate being measured. (keep in mind 4d) so past and future events are non local to present events.

 In quantum correlstions non local are previous interactions that have occurred that affect current local measurements.  Ie when the entangled particle pair is created is non local to the local spacetime region at time of measurement within the locality of the detectors

Edit a more accurate definition of Einstein locality is as follows

if two events are outside each others’ light cones there cannot be any causal connection between them.

Edited April 21, 2018 by Mordred

[interested]

Thank you all for the answers

In simple terms, trying to summarize. Are you all stating that, if two entangled particles exist at opposite sides of the universe, we can not know the state of the both particles until we measure one of them, once this measurement is done we instantly know the value of the other. No magic or additional dimensions involved? 

Edited April 21, 2018 by interested

[Mordred]

Correct entanglement does not involve FTL communication its communication application of interest is encryption not FTL. There is no hidden variables or dimensions 

Edited April 21, 2018 by Mordred

[studiot]

1 hour ago, interested said:

Thank you all for the answers

In simple terms, trying to summarize. Are you all stating that, if two entangled particles exist at opposite sides of the universe, we can not know the state of the both particles until we measure one of them, once this measurement is done we instantly know the value of the other. No magic or additional dimensions involved? 

To get entangled, those particles must have been together on the same side of the universe at some time.

So how long did it take to get separated by a whole universe?

What are the chances of something happening to disentangle them in that time?

So how practical is this proposition?

[interested]

14 hours ago, studiot said:

To get entangled, those particles must have been together on the same side of the universe at some time.

So how long did it take to get separated by a whole universe?

What are the chances of something happening to disentangle them in that time?

So how practical is this proposition?

Apologies I was being lazy forming my question. I should have stated the particles are separated by an arbitrary distance. I fully recognize that entanglement is a delicate thing and particles can decohere. It was as you say not a very practical example. 

Why is it commonly thought by many that once particles are entangled moving one of the pair instantly affects the other, and that this can be done repeatedly. Ie changing the polarization or spin of one photon will change the other photon. Who put the idea out there first. I was reading about wave functions and quantum fluctuations this morning and entanglement and non locality came up yet again.

 

[studiot]

Suppose you made a coin by pressing together a tail face and a head face.

You have effectively entangled these two faces.

Now suppose you split the faces and took one to the other end of the universe, leaving the other face behind with a friend, but sealed in an envelope.

If you friend then opens the envelope he will instantly know which face you have taken, but he will not know until he opens the envelope.

This is a model of how entanglement works.

[StringJunky]

19 minutes ago, studiot said:

Suppose you made a coin by pressing together a tail face and a head face.

You have effectively entangled these two faces.

Now suppose you split the faces and took one to the other end of the universe, leaving the other face behind with a friend, but sealed in an envelope.

If you friend then opens the envelope he will instantly know which face you have taken, but he will not know until he opens the envelope.

This is a model of how entanglement works.

I can't see what use it is or that it's odd in anyway because the entangled particles were together, then separated, and when you do look the wavefunction collapses. If you could change the state at one end to change the other then that would be interesting

[swansont]

47 minutes ago, interested said:

 Why is it commonly thought by many that once particles are entangled moving one of the pair instantly affects the other, and that this can be done repeatedly. Ie changing the polarization or spin of one photon will change the other photon. Who put the idea out there first. I was reading about wave functions and quantum fluctuations this morning and entanglement and non locality came up yet again.

 

Because that misinformation is common in the popular press.

36 minutes ago, studiot said:

Suppose you made a coin by pressing together a tail face and a head face.

You have effectively entangled these two faces.

Now suppose you split the faces and took one to the other end of the universe, leaving the other face behind with a friend, but sealed in an envelope.

If you friend then opens the envelope he will instantly know which face you have taken, but he will not know until he opens the envelope.

This is a model of how entanglement works.

It's an analogy, but one very important distinction to note is that in QM, the state is not determined until a measurement is made, whcih is not something that can be modeled classically.

[studiot]

On 22/04/2018 at 12:13 PM, swansont said:

Because that misinformation is common in the popular press.

It's an analogy, but one very important distinction to note is that in QM, the state is not determined until a measurement is made, whcih is not something that can be modeled classically.

Well I don't think that is a poor analogy, though obviously every analogy is imperfect.

 

Classically if a third person places each face (without noting which is which) in a separate sealed envelope, that surely is as near as a classical model can get?

[swansont]

11 minutes ago, studiot said:

 Classically if a third person places each face (without noting which is which) in a separate sealed envelope, that surely is as near as a classical model can get?

That's probably as close as you will get. Where it fails is that there are effects of the state being undetermined that you can't recreate classically.

The other caveat is that this isn't a model of how entanglement works — I don't think anybody actually knows how it works (which would require a mechanism). It's an analogy of how it behaves.

[interested]

On 4/22/2018 at 10:01 AM, StringJunky said:

If you could change the state at one end to change the other then that would be interesting

Is that possible or  are we into pop science again. 

[Strange]

26 minutes ago, interested said:

Is that possible or  are we into pop science again. 

No it is not possible. Once you have measured the state (in order to change it) you have broken the entanglement.

[swansont]

2 hours ago, Strange said:

No it is not possible. Once you have measured the state (in order to change it) you have broken the entanglement.

In a way, it is. There are interactions that aren't measurements and thus don't break the entanglement. They amount to a unitary transformation of the states. In some treatments there are four Bell state bases, and the classical communication tells you which one to use. 

If you've entangled photon polarizations, for example, sending the photon through a half-wave plate changes the polarization to the orthogonal state, but you haven't measured it, so it's still entangled.

[Strange]

2 minutes ago, swansont said:

If you've entangled photon polarizations, for example, sending the photon through a half-wave plate changes the polarization to the orthogonal state, but you haven't measured it, so it's still entangled.

Good example. But, because you haven't measured it you can't see the change at the other end.

[interested]

23 hours ago, swansont said:

In a way, it is. There are interactions that aren't measurements and thus don't break the entanglement. They amount to a unitary transformation of the states. In some treatments there are four Bell state bases, and the classical communication tells you which one to use. 

If you've entangled photon polarizations, for example, sending the photon through a half-wave plate changes the polarization to the orthogonal state, but you haven't measured it, so it's still entangled.

Is this like taking two polarized photons and splitting them to produce two entangled pairs of photons, with known polarizations, then passing ONE of  the polarized entangled photons through another polarizing filter changing its polarization, and measuring them to compare the polarization of both the entangled pairs.  

Could entangled electrons if they are separated be affected by a magnetic field https://phys.org/news/2015-07-spin-entangled-electrons.html likewise could entangled electrons and photons be affected by polarization filters or magnetic/electrostatic fields.

PS how is an electrons spin altered, I thought all fermions had 1/2 spin https://en.wikipedia.org/wiki/Spin_(physics) 

[swansont]

32 minutes ago, interested said:

Is this like taking two polarized photons and splitting them to produce two entangled pairs of photons, with known polarizations, then passing ONE of  the polarized entangled photons through another polarizing filter changing its polarization, and measuring them to compare the polarization of both the entangled pairs.  

No. Passing a photon through a polarizer determines its polarization. It is a measurement.

32 minutes ago, interested said:

Could entangled electrons if they are separated be affected by a magnetic field https://phys.org/news/2015-07-spin-entangled-electrons.html likewise could entangled electrons and photons be affected by polarization filters or magnetic/electrostatic fields.

PS how is an electrons spin altered, I thought all fermions had 1/2 spin https://en.wikipedia.org/wiki/Spin_(physics) 

Spin orientation, not magnitude. You would change from spin up to spin down, or the reverse.

I think you can do things to change the spin orientation that does not count as a measurement.

[interested]

1 hour ago, swansont said:

I think you can do things to change the spin orientation that does not count as a measurement.

So once particles are entangled and separated one can be manipulated and not be counted as a measurement, the particles would remain entangled, and then a measurement could be taken, giving the state of the other entangled particle as soon as the measurement is taken.

Can you expand on the above statement.

[swansont]

18 minutes ago, interested said:

So once particles are entangled and separated one can be manipulated and not be counted as a measurement, the particles would remain entangled, and then a measurement could be taken, giving the state of the other entangled particle as soon as the measurement is taken.

That's correct. 

18 minutes ago, interested said:

Can you expand on the above statement.

I'm not sure what you're looking for.