Bell's theorem proof. Does it really proofs anything?

[DrChinese]

So you are saying, that after first measurement photons are not entangled any more. If so - does it matter at all that they were entangled from very beginning.

Or maybe i am just getting this wrong, but - does entanglement gives any other extra properties to photons than just that they have all same properties?

In this experiment they use that crystal to create entangled photons with same polarization and send them to Alisa and Bob. Why would it make any difference if i replace "twin-photon crystal" with "black box", which also outputs same photons, only with difference, that they are "manually created" (two "light bulbs" and bunch of polarization filters) .

?

There is a difference, and you can tell by an experiment. If you observe Alice and Bob at the same but *random* angles, the following pattern will emerge over a series of trials:

If Alice and Bob ARE entangled (PDC source), they will be 100% correlated.
If Alice and Bob are NOT entangled (black box source), they will be about 75% correlated.

Does that help? In both cases, the photon pairs are clones of each other in the sense that that have the same quantum properties. The difference is that entangled particles are in a superposition of states because the value of one or more of those quantum properties is not known. That leads to some rather unusual experimental situations as compared to particle pairs which are not in a superposition.

 

[0xDEAD BEEF]

DrChinese

regarding -
If Alice and Bob ARE entangled (PDC source), they will be 100% correlated.
If Alice and Bob are NOT entangled (black box source), they will be about 75% correlated.

But if i have blackbox, which outputs two photons (to Anna and Bob) having same polarization

+---------------- BLACKBOX -------------------|
|laser -> beam splitter -> polarizer for anna | -> anna's setup
|                      \-> polarizer for bob  | -> bob's setup
+---------------------------------------------|

Should not hey both get 100% correlated, if "polarizer for anna" is set to same value as "polarizer for bob"?

Beef
P.S. I did not like that Dr. Robert Nemiroff stuff. It was too easy, too non chalenging. Too much facts, without proof/idea behind them. And I thought education quality is bad only at my country... :)

 

[DevilsAvocado]

(Just a short temporary comeback ;)

Honestly 0xDEAD BEEF, I know communication can be hard sometimes, but it’s beyond my imagination why this doesn’t answer your question:

The "catch" (that your predefined photon polarization will never ever work), is because the relative angle between Alice & Bob can be anything between 0-360, but "your" photons doesn’t care one bit about this relative angle. The only thing that they will "respond" to is their own polarization and the setting of their own polarizer.

I.e. there is no "communication" or "link" between Alice & Bob in your "design", and this is crucial.

 

[DevilsAvocado]

P.S. I did not like that Dr. Robert Nemiroff stuff. It was too easy, too non chalenging.

Why on Earth are you asking all this questions if everything is perfectly clear to you…????

 

[0xDEAD BEEF]

Because I want to understand, not to learn. (Edit: maybe also because i want to have chat with smart people... ;) )

Regarding relative angle between Bob and Alice - IN QM experiment increasing relative angle between Bob and Alice also increased mismatch rate. Same that would happen with "predefined photon polarization".
Say - i fire two photons with 0,0 angle polarization at Bob and Alice. Bob measures at 0 angle, so he gets 1, Alice measures at 90 angle so she gets 0. If she would measure at same 0 angle, then she would get same 1. Same would applie if i would fire my photons at differen angle (like 55). At 55 Bob would get 1, Alice 0. Still mismatch!

 

[0xDEAD BEEF]

Because I want to understand, not to learn. (Edit: maybe also because i want to have chat with smart people... ;) )

Regarding relative angle between Bob and Alice - IN QM experiment increasing relative angle between Bob and Alice also increased mismatch rate. Same that would happen with "predefined photon polarization".
Say - i fire two photons with 0,0 angle polarization at Bob and Alice. Bob measures at 0 angle, so he gets 1, Alice measures at 90 angle so she gets 0. If she would measure at same 0 angle, then she would get same 1. Same would applie if i would fire my photons at differen angle (like 55). At 55 Bob would get 1, Alice 0. Still mismatch!

EDIT:
So here is what I don't like about this proof. And with don't like i mean - i don't understand it.

There are two entangled photons. Twin-photons. They are exactly same.
Now Bob and Anna does some measurements on them. That is cool. And i can not disagree with output of those measuremets, since they are what they are and what they tell us is something about those two photons being measured.
What I don't like (don't understand) is this non-locality stuff which somehow using just some "that should be so but is not so there is information exchange" functions is proven.

Furthermore - i don't understand - what is difference if these twin-photons "collapse" when hiting detector or collapse earlier.

I totaly accept output of this experiment (data), but i don't understand, how one can conclude, that there was some information exchange between photons, when they hit detectors. To me it seems, that moment, when these photons exchanged information and became equal does not matter. Say - both photons where unknown about their state, but decided simulatenosly it, when hiting Anna's or Bob's detector. Or - both photons had their state known already prior this happening. What i think (can not understand) is that in both case experiment results should be the same. But if so - how can this experiment prove non-locality. I only see experiment measuring two photons. In fact - there should be many theories explaining this behavior. Maybe those photons carry only partial information, since they vere born from single photon and so they should not carry more information, that one, who created them (one hitting PDC crystal).

I really don't see, how one can conclude non-locality (instant information exchange) from this data. Yes - i see that A, B, C case and error stuff, but somehow i don't see, how it applies to this case. More over - we are dealing eith entangled photons not with ussual ones.

Sure, i am not going to discover America, but neither i am going to accept claim, that information "got" exhanged faster than light, when there is no actual evidence of that.

Say - if Anna would change her setting, and Bob would instantly start seeing more + at output, than 0 - one would say, that two photons have exchanged information. No doubt.

Only reason why i got interested in this experiment was because of it's loud announcment, that two particles stayed connected at 27km distance. Cool, right? So i checked internet and started actually searching for this experiment to get more information and understand, how could that happen.

But now all i see is that actualy i don't see particles excganging data. What i see is same particles from very beginning and I don't see "the reason" or "the catch" why should they change, when they got measured, if that should be similar to situation, where they did not exchange anything at all (maybe ar very begining). And btw - these two particles are born at middle of crystal, as i see that (402nm laser hits crystal and somwhere in crystal 901nm twin-particles are born). They still have to travel through that crystal to find exit. And crystal cerainly wants to know their polarization before it allows them to leve (they interact with crystal).

Beef

 

[DrChinese]

DrChinese

regarding -
If Alice and Bob ARE entangled (PDC source), they will be 100% correlated.
If Alice and Bob are NOT entangled (black box source), they will be about 75% correlated.

But if i have blackbox, which outputs two photons (to Anna and Bob) having same polarization

+---------------- BLACKBOX -------------------|
|laser -> beam splitter -> polarizer for anna | -> anna's setup
|                      \-> polarizer for bob  | -> bob's setup
+---------------------------------------------|

Should not hey both get 100% correlated, if "polarizer for anna" is set to same value as "polarizer for bob"?

The answer is NO, and here is a specific example:

From your box emerges a pair of photons polarized at the same angle, which is 0 degrees. If I run each through a polarizering beam splitter set at 45 degrees, there is a 50% chance of a + and 50% of a -. But that applies independently to each. There are 4 permutations:

++
+-
-+
--

A correlation of 50%, not 100%. If you average at all angle settings (i.e. not just 45 degrees), you will actually get a 75% average.

If you did the same thing with polarization entangled photons, you would get 100% correlation. Regardless of the angle setting (as long as set the same for both Alice and Bob).

 

[DrChinese]

EDIT:
So here is what I don't like about this proof. And with don't like i mean - i don't understand it.

There are two entangled photons. Twin-photons. They are exactly same.
Now Bob and Anna does some measurements on them. That is cool. And i can not disagree with output of those measuremets, since they are what they are and what they tell us is something about those two photons being measured.
What I don't like (don't understand) is this non-locality stuff which somehow using just some "that should be so but is not so there is information exchange" functions is proven.

Furthermore - i don't understand - what is difference if these twin-photons "collapse" when hiting detector or collapse earlier.

I totaly accept output of this experiment (data), but i don't understand, how one can conclude, that there was some information exchange between photons, when they hit detectors. To me it seems, that moment, when these photons exchanged information and became equal does not matter. Say - both photons where unknown about their state, but decided simulatenosly it, when hiting Anna's or Bob's detector. Or - both photons had their state known already prior this happening. What i think (can not understand) is that in both case experiment results should be the same. But if so - how can this experiment prove non-locality. I only see experiment measuring two photons. In fact - there should be many theories explaining this behavior. Maybe those photons carry only partial information, since they vere born from single photon and so they should not carry more information, that one, who created them (one hitting PDC crystal).

I really don't see, how one can conclude non-locality (instant information exchange) from this data. Yes - i see that A, B, C case and error stuff, but somehow i don't see, how it applies to this case. More over - we are dealing eith entangled photons not with ussual ones.

Sure, i am not going to discover America, but neither i am going to accept claim, that information "got" exhanged faster than light, when there is no actual evidence of that.

Say - if Anna would change her setting, and Bob would instantly start seeing more + at output, than 0 - one would say, that two photons have exchanged information. No doubt.

Only reason why i got interested in this experiment was because of it's loud announcment, that two particles stayed connected at 27km distance. Cool, right? So i checked internet and started actually searching for this experiment to get more information and understand, how could that happen.

But now all i see is that actualy i don't see particles excganging data. What i see is same particles from very beginning and I don't see "the reason" or "the catch" why should they change, when they got measured, if that should be similar to situation, where they did not exchange anything at all (maybe ar very begining). And btw - these two particles are born at middle of crystal, as i see that (402nm laser hits crystal and somwhere in crystal 901nm twin-particles are born). They still have to travel through that crystal to find exit. And crystal cerainly wants to know their polarization before it allows them to leve (they interact with crystal).

Beef

This helps a lot to explain your view. I think I can answer a couple of things. There were 2 assumptions in the Bell derivation: a) no faster than light signaling; b) pre-existing values/formula/etc. for outcomes (since you have the perfect correlations). One of these assumptions MUST be wrong.

So take your pick. Then we are at the same place.

 

[0xDEAD BEEF]

The answer is NO, and here is a specific example:

From your box emerges a pair of photons polarized at the same angle, which is 0 degrees. If I run each through a polarizering beam splitter set at 45 degrees, there is a 50% chance of a + and 50% of a -. But that applies independently to each. There are 4 permutations:

++
+-
-+
--

A correlation of 50%, not 100%. If you average at all angle settings (i.e. not just 45 degrees), you will actually get a 75% average.

If you did the same thing with polarization entangled photons, you would get 100% correlation. Regardless of the angle setting (as long as set the same for both Alice and Bob).

Very good! Now i really start to understand more! Thank you! :)

BUUUT! :)

But what I would like to say is, that -
if normal photon has angle x, then chance of it hitting detector with angle y is determined by formula - (x < y + 45) && (x > y - 45),

So should not it be so, that (simply) twin photon's chance is deterined by slighlty different formula since it is slightly "cooler" photon? Say
(x < y + 45 + "some value more likely to be 0, but can reach 90 as well") && (x > y - 45 - "same magic value")

Beef

 

[DevilsAvocado]

Because I want to understand, not to learn. (Edit: maybe also because i want to have chat with smart people... ;) )

Ahhh! This will definitely disqualify me; I’m not smart I just repeat what really smart people have written on the subject!

Regarding relative angle between Bob and Alice - IN QM experiment increasing relative angle between Bob and Alice also increased mismatch rate. Same that would happen with "predefined photon polarization".

This is frustrating. We explain to you exactly how this works, and then you "forget" everything, and "act" as it never happened...

Check out https://www.physicsforums.com/showpost.php?p=3024599&postcount=28" and you see exactly what I mean.

This is my last sentence in this thread, guaranteed. Adios Amigo

 

[Gordon Watson]

So you are saying, that after first measurement photons are not entangled any more. If so - does it matter at all that they were entangled from very beginning.

Or maybe i am just getting this wrong, but - does entanglement gives any other extra properties to photons than just that they have all same properties?

In this experiment they use that crystal to create entangled photons with same polarization and send them to Alisa and Bob. Why would it make any difference if i replace "twin-photon crystal" with "black box", which also outputs same photons, only with difference, that they are "manually created" (two "light bulbs" and bunch of polarization filters) .

?

I am thinking that my encouragement might help us both learn something:

BUT PLEASE NOTE that I am not a physicist; ; so where I am wrong, you and I will see where we are maybe both wrong together -- and so we would both learn something valuable together.

SO: I encourage you to work on understanding your good and simple experiment (that you have in mind, as I understand it). PS: If I misunderstand, then do what follows anyway, and soon.

Here's what you can learn from the model that you have in mind AS I SEE IT:

1. Your experiment is easily done USING a source of entanglement; even easier as a thought experiment: Simply sandwich an EPRB-Bell source (black-box) between two aligned and coupled polarizers which rotate, at random, but stepwise, in unison. This gives you your black-box source -- yours is just an EPRB-Bell black-box in a bigger black-box! That seems quite OK to me.

2. Then: Do your experiment in exactly the same setting as EPRB-Bell.

3. You will find the correlation to be exactly one-half of the EPRB-Bell correlation. So get someone to teach you the really simple mathematics of what is going on -- it's just old Malus' Law, twice.

4. The one-half reduction is explained by the fact that YOUR black-box [your sandwich] has REDUCED the correlation of the paired photons that are emitted from the inner -- EPRB-Bell -- black-box. That is:

5a. YOUR black-box is delivering paired-photons with a common polarization at some random orientation; that is all.

5b. BUT the EPRB-Bell black-box delivers magnificently paired photons whose total angular momentum is zero -- they are said to be "in the spherically symmetric singlet state". Get someone to explain that to you.

5c. SO in EPRB-Bell experiments with paired-photons (typically), each photon has its total angular momentum antiparallel to its twin. That is, for any common orientation whatsoever, over the whole of the ordinary 3-space of Euclid: If you measure the polarizations of EPRB-Bell twinned photons, they are ALWAYS the same. That is a fantastic degree of correlation!

PLEASE NOTE and understand: When you measure the polarizations of YOUR twinned photons, under the same conditions, i.e., for any common orientation whatsoever, or even just do this measurement over the 2-space orthogonal to the line-of-flight axis: They are NOT ALWAYS the same.

6. You can see, therefore, that your source delivers photon-twins with much less correlation; yet YOUR overall correlation result is pretty good, at exactly one-half of EPRB-Bell.

7. Then, in my opinion, after you really understand your model and experiment and its mathematics, you have your next experiment:

8. You remove the sandwiching polarizers; you see the that correlation doubles; you understand the much tighter correlation of the paired-photons (compared to those that came from your black-box); you join the club of convinced local realists, under a free trial membership; ; you wait to be shown where you are wrong.

In the meantime, see if you can learn and understand the mathematics that yields the EPRB-Bell experimental results.

QED?

PS: You should ask someone to correct the title of your thread.

From -- Re: Bell's theorem proof. Does it really proofs anything?

To -- Re: Bell's theorem proof. Does it really prove anything?

Good luck! :!)

 

[DevilsAvocado]

Mamma Mia

 

[DrChinese]

But what I would like to say is, that -
if normal photon has angle x, then chance of it hitting detector with angle y is determined by formula - (x < y + 45) && (x > y - 45),

But the actual formula follows cos^2(theta), where theta=x-y for your example. Please notice that yours does not yield the same results. And it won't matter if one is "cooler" than the other (whatever that means) because when theta=0, there is perfect correlation.

 

[DrChinese]

Mamma Mia

Just curious if that qualifies as a sentence.

Heh heh heh.

 

[DevilsAvocado]

Just curious if that qualifies as a sentence.

Heh heh heh.

nope
no
period
and
only
two
words
that
looks
like
something
'italiano'
or
maybe
old
ABBA
on
acid

 

[0xDEAD BEEF]

But the actual formula follows cos^2(theta), where theta=x-y for your example. Please notice that yours does not yield the same results. And it won't matter if one is "cooler" than the other (whatever that means) because when theta=0, there is perfect correlation.

Hmm. Ok, so i have "tuned" my program a bit and now i get more interesting results. Thought - i doubt that i have properly implemented photon physics in my program.

So - as i now understand it -
If those two photons would not be entangled twin-photons, then (for example), when Anna has her detector at 0 angle and Bob has his at 90, then photon flying in at 45 angle could cause Anna's detector to fire 0 and Bobs detector to fire 0, since now this photon has cos^2(45) probability hitting Anna's + sames as Bob's -, so some times this 45 degree photon should cause 0 for Anna and 0 for Bob, when they have 0 vs 90 degree setup, but since experiment shows, that Anna and Bob are always correlated at 0 angle delta and always 100% uncorrelated at 90 angle delta -> this proves that something strange is going on?

EDIT:
if that non-sense text was not clear, then here is another try to explain what i meant.
So, Anna has 0 setup, Bob has 90 setup. There is photon coming in at 45 degrees angle.
Sometimes we should se:
++
--
+- (more often)
-+ (more often)

But we see only:
+-
-+

So this is strange and proves non-locality. Right?

EDIT2:
Further more. (if mine understanding above was correct) -
Now one could start patching "theory" and try to come up with new formula, so, that photon has 100% probability going one way, if delta < 45. However soon one would discover, that no mater how hard he tries, but having photon always go up, when angle < 45, means, that it always goes down, when angle > 45, so cos^2(delta) formula can only be replaced with |delta| < 45. But if one does so and creates simulation, he sees, that correlations (mismatches) should form linear graph. But we see cos, so how is that possible?

Am i right?
Beef

 

[zonde]

EDIT:
if that non-sense text was not clear, then here is another try to explain what i meant.
So, Anna has 0 setup, Bob has 90 setup. There is photon coming in at 45 degrees angle.
Sometimes we should se:
++
--
+- (more often)
-+ (more often)

But we see only:
+-
-+

So this is strange and proves non-locality. Right?

Minor point. You don't see +- and -+ more often with photon polarization at 45°. According to your description you have sometimes photons with 45° polarization sometimes with 0° or 90° and sometimes another angle. So photons with 45° polarization will not contribute to correlation but photons with 0° or 90° will always contribute to correlation. When you sum up all angles it turns out that correlation is half of the maximum.

EDIT2:
Further more. (if mine understanding above was correct) -
Now one could start patching "theory" and try to come up with new formula, so, that photon has 100% probability going one way, if delta < 45. However soon one would discover, that no mater how hard he tries, but having photon always go up, when angle < 45, means, that it always goes down, when angle > 45, so cos^2(delta) formula can only be replaced with |delta| < 45. But if one does so and creates simulation, he sees, that correlations (mismatches) should form linear graph. But we see cos, so how is that possible?

Am i right?

Yes, this is reasoning behind Bell theorem.

As a die hard local realist I would like to point out that other side of the story is experimental tests of theory that poses quite different questions.

 

[0xDEAD BEEF]

What are key points how local-realism explains these experiments?

No! My configuration was different. It was - Bob 0, Alisa 90. Photons flying in sometimes have angle 45, so they sometimes must hit ++, --, +-, -+, BUT, we only get +- and -+.

BTW - thank you guys a lot! With every reply I grow smarter and smarter! :)

Beef

 

[DevilsAvocado]

But we see cos, so how is that possible?

QM !

 

[DrChinese]

nope
no
period
and
only
two
words
that
looks
like
something
'italiano'
or
maybe
old
ABBA
on
acid

You can put pepperoni on mine. And crank up some Steely Dan.

 

[DevilsAvocado]

You can put pepperoni on mine. And crank up some Steely Dan.

HAHAHA

YES! Pepperoni + Steely Dan = makes my life worth living!

(sorry for the "sentence violation", going to jail now... )

 

[zonde]

What are key points how local-realism explains these experiments?

Photon experiments that test Bell (or CHSH) inequalities relay on so called fair sampling assumption.
The thing is that you don't detect all photons that leave beam splitter but only portion. Typically you have around 10% coincidence rate i.e. you discard 9/10 of detections because you don't have matching detection at the other side.
Idea of fair sampling assumption is that if you would detect them it would not change observed correlations.
So if you assume that detected sample of photons is biased then you have to conclude that photon tests don't prove non-locality.
And I would like to add that this is the only way out of the paradox consistent with local realism.

Btw there was another idea (so called "locality loophole") but it was disproved by experiment with fast switching polarizers.

And you can try to look here as well:
http://en.wikipedia.org/wiki/Loopholes_in_Bell_test_experiments"

No! My configuration was different. It was - Bob 0, Alisa 90. Photons flying in sometimes have angle 45, so they sometimes must hit ++, --, +-, -+, BUT, we only get +- and -+.

I guess you misunderstood me. My point was that photons flying in sometimes have 45° angle and sometimes different angle.

 

[DevilsAvocado]

Da Capo: Mamma Mia

 

[DrChinese]

1. It was - Bob 0, Alisa 90. Photons flying in sometimes have angle 45, so they sometimes must hit ++, --, +-, -+, BUT, we only get +- and -+.

2. What are key points how local-realism explains these experiments?

1. If you know that the photons coming in are polarized at 45 degrees, then they cannot be polarization entangled. And you will get: ++, --, +-, -+.

2. zonde has given a pretty good answer already. This is a very complex question and the answers tend to arouse controversy. But the short answer is that NO local realistic explanation also matches QM. In the view of zonde, local realism + fair sampling can match QM experimentally. This is far from certain (but *may* be possible). What is certain is that such local realism means that a complete sample will not agree with QM. Which follows Bell's Theorem, which essentially states:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.