Simple QM question

[Kriminal99]

Someone tell me why this scenario is different from QM with respect to its determinism...

 

I run into a government building with two time bombs set to explode at the same time. I run into a person in the building and attach one bomb such that he cannot remove it. He runs off and we both explode at the same time.

 

Or instead, I run out of some engineering lab with two gyroscopes. I give one to my accomplice and we both escape on skateboards and exhibit correlated movement patterns...

[cwes99_03]

Wow, Krim. Maybe provide some more info and a better stated question. I didn't see a question there, but maybe someone with an actual QM background understands.

[Kriminal99]

The question is, how is it known that entangled particles have not swapped something physical but unobservable (by us using current technology) that would cause their measurements to be correlated, or just have something in common that would cause their measurements to be correlated?

 

Or just another question why is it believed there are no local hidden variables in QM?

[Erasmus00]

Or just another question why is it believed there are no local hidden variables in QM?

 

In 1965, Bell wrote a seminal paper. In it, he analyzed the Einstein Podolsky Rosen paradox (a paradox regarding entangled particles). In this paper, he demonstrated that if there is some hidden variable then certain inequalities arise regarding the correlations. (I believe that paper is titled "On the E-P-R Paradox" you are welcome to read it). I beleive Griffith's intro quantum text also deals with Bell in an appendix.

 

These inequalities disagree with quantum mechanics. Hence, either quantum mechanics is wrong, or local hidden variables are wrong. Quantum mechanics has been experimentally validated time and time again.

-Will

[Kriminal99]

I was under the impression that the condradiction was either there are more than only local hidden variables, or quantum mechanics being wrong. Not that there were not any local hidden variables.

 

Meaning there were non local hidden variables.

 

But what I was asking is, why are local hidden variables not capable of explaining the correlation? I don't understand how it is impossible for measurements on two particles seperated by some amount of space to be 100% correlated through purely determinisitic means.

[sebbysteiny]

The question you are posing is,by enlarge, still at the cutting edge of science.

 

However, the basics are still capable of being understood by people like you and me.

 

Every particle is a wave and thus can be described as a wavefunction. A wavefunction contains all the terms that have been measured. However, due to Hysenburg's uncertainty principal, some measurements cannot be known when others are known, eg momentum and position. So what happens to the position of, say, an electron when you measure it's momentum exactly? It becomes a superposition of numerous position states, with each one having a probability. Thus, the electron efectively acts and behaves as if it's position wer blurred. It does not behave like it has a position, it's just we don't know it yet, it behaves as if it has all possible possitions.

 

What does this mean? An electron wave with a measured momentum, could go in one of two slits. Each slit is this a position state. When the electron passes through the slits, and you measure the electron position at a screen, you get a diffraction pattern as if every electron went through both slits at the same time and interferred with itself. However, if you try to measure which slit the electron went through, the act of making the measurement changes the wavefunction and thus the properties. The electron now behaves as if it went through one slit only so it doesn't interfear with itself and you get no diffracion pattern.

 

Young's slits is the most vivid example I can think of where a wavefunction acts not as if the unmeasured state is unknown, but as if the unmeasured state is a combination of all the possible states.

 

Entanglement is essentially the same. The electrons, before they are measured, have become coupled together. They act as if they are a combination of the two possible states, and not as if they are either one or the other but we don't know which. Thus, when you measure one of the entagled particles, you force it's quantum state and it's properties thus change. At that exact moment, the quantum state of the entangled particle also changes state and therefore it's properties.

 

Exchanging some quasi-particle between entangled particles simply does not explain why the behavior of one particle actually physically changes suddenly simply because the other particle in a different place has been measured.

[Erasmus00]

I don't understand how it is impossible...

 

I referenced the paper and Bell so that you could do your own research, and do some learning on your own. The internet is full of useful information.

 

Since you are unwilling, here is Bell's paper.

 

http://www.drchinese.com/David/Bell_Compact.pdf

 

Note that Bell himself favors a non-local hidden variables interpretation of quantum mechanics, attributed to Bohm.

 

However, this approach is unsatisfactory because such communication between remote pairs must be instantaneous, and as such would violate causality (according to relativity). Hence, any non-local variables cannot be thought of as causal.

-Will

[Kriminal99]

Exchanging some quasi-particle between entangled particles simply does not explain why the behavior of one particle actually physically changes suddenly simply because the other particle in a different place has been measured.

 

How would you know if the other particle's behavior has changed without also measuring it even if indirectly?

 

Also with the slit experiment what methods are being used to measure the momentum and the position?

 

@ Ersas People who post simply pointing to something else or referring to other people's opinions don't understand the subject sufficiently to consider what they say valid in my opinion. If they did they would just answer the question directly. If you are going to bother to post, do something other than make some "other people claim x" post.

[Erasmus00]

People who post simply pointing to something else or referring to other people's opinions don't understand the subject sufficiently to consider what they say valid in my opinion.

 

I'm of the opinion that it isn't my job to educate people too lazy to spend fifteen seconds googling. You have a world of information at your fingertips.

 

If you want to have a serious discussion about Bell's inequalities, then by all means, lets. But it isn't my job to type out the mathematical proofs and arguments you can find faster then I can type. I've linked to the paper above. Read it.

 

If you want to learn, put some effort in.

-Will

[IDMclean]

I've been struggling with this particular phenomena recently, as it is vital to my particle model. I thinking I have an Idea as to what is happening, Though I am not absolutely sure.

 

I think it may have to do with a particle swap, as you suggest, though I am unsure how to model that in such a way as to not violate Casuality, Relativity, and a few others.

[Qfwfq]

People who post simply pointing to something else or referring to other people's opinions don't understand the subject sufficiently to consider what they say valid in my opinion. If they did they would just answer the question directly. If you are going to bother to post, do something other than make some "other people claim x" post.

This is a pointless and inappropriate remark, it is perfectly legitimate to offer a source to somebody who has asked a question and the source that Will offered you is spot-on appropriate. You might choose to discuss Bell's views, or those of EPR, but there's no use criticizing someone for having linked to them.

 

In any case, the status quo is that Bell's inequalities are found to be violated, in experiments involving singlet states.

[Kriminal99]

I'm of the opinion that it isn't my job to educate people too lazy to spend fifteen seconds googling. You have a world of information at your fingertips.

 

If you want to have a serious discussion about Bell's inequalities, then by all means, lets. But it isn't my job to type out the mathematical proofs and arguments you can find faster then I can type. I've linked to the paper above. Read it.

 

If you want to learn, put some effort in.

-Will

 

If you don't want to take part in a discussion, thats absolutely fine. My point is that when someone makes statements like "it isn't my job to educate people too lazy to spend fifteen seconds googling" are trying to impact a discussion without taking any personal responsibility for the claim being made.

 

In law this tecnique is called hearsay and is not allowed because the person making the claim could be lying but could not be prosecuted for purgery because they can always just claim the person they heard say something was the one who lied instead of themselves. This would make it easy to lie in court and get away with it.

 

In a debate it is not that you are likely to be lying, but rather that you could be trying to hide a lack of understanding of the topic while still trying to make your opponent appear wrong.

 

Furthermore I have seen that when a person has a really good understanding of a subject they can and usually will explain why objections can be dealt with in a convincing manner to anyone skeptical of their claims. When a person cannot do this with minimal effort, it tells me that they do not understand their opponents specific objection or how it can be dealt with. This means that as far as that person is concerned, there is a potential problem with what they believe that they are not aware of. This is not a good sign, since the only kind of knowledge a person is capable of having is the abscence of information that contradicts that which he believes.

 

All that being said, I should mention that not even most statistics students understand the assumptions necessary for any type of statistical reasoning to work, so I wouldn't consider it likely for you to easily understand my objection. Mostly only people who have studied philosophers objections to inductive reasoning (I think Hume is the main one) or just have meditated on the subject carefully themselves for whatever reason clearly understand the limitations of inductive reasoning and statistics.

 

Alot of the time someone has an objection to something you won't really understand it because it comes from their unique perspective. But the question is does that mean you listen and try to understand it (thus reinforcing your understanding of the subject even if they turn out to be wrong) or do you just look for some least effort way to make them look wrong even though for all you know they could be right?

 

But by the way, I've already read a bunch of stuff on the subject. In fact I'm not even sure where you got the idea I hadn't.

 

This is a pointless and inappropriate remark, it is perfectly legitimate to offer a source to somebody who has asked a question and the source that Will offered you is spot-on appropriate. You might choose to discuss Bell's views, or those of EPR, but there's no use criticizing someone for having linked to them.

 

In any case, the status quo is that Bell's inequalities are found to be violated, in experiments involving singlet states.

 

I wasn't complaining that he was providing a link or information. I was addressing the manner in which he did so. The difference would be:

 

A: The following link might have useful information: link

and

B: Everyone else thinks you are wrong see look: LINK

 

The link isn't what I was talking about it was the sentence before the links.

[Erasmus00]

If you don't want to take part in a discussion, thats absolutely fine. My point is that when someone makes statements like "it isn't my job to educate people too lazy to spend fifteen seconds googling" are trying to impact a discussion without taking any personal responsibility for the claim being made.

 

You asked a question, specifically about why can't we think of quantum correlations as some sort of hidden variables. I posted a link to a mathematical proof as to why. Either quantum mechanics is right, or local hidden variables are right, they are mutually exclusive. I pointed you to the mathematical proof of this statement.

 

In law this tecnique is called hearsay...

 

Not at all, I provided you with a published scientific paper that outlines, very rigorously, the logic. This isn't hearsay, but providing the most appropriate information straight from the original thinker.

 

In a debate it is not that you are likely to be lying, but rather that you could be trying to hide a lack of understanding of the topic while still trying to make your opponent appear wrong.

 

Or maybe I find it easier to tell you where to look then to type up dozens of pages of material. Again, I will answer any questions about the Bell's proof that you may have, and continue this discussion. I am not, however, going to type up Bell's entire argument.

 

Furthermore I have seen that when a person has a really good understanding of a subject they can and usually will explain why objections can be dealt with in a convincing manner to anyone skeptical of their claims.

 

You haven't made any objections. You asked a question, I linked you to the answer and you have seemingly refused to read it.

 

All that being said, I should mention that not even most statistics students understand the assumptions necessary for any type of statistical reasoning to work...

 

First of all, you are making assumptions (that I haven't studied Hume and don't understand the foundations of statistics). I also point out that objections to statistics are completely irrelevant to this discussion. Bell's work is based on probability theory, which is quite different then statistics in its foundations.

 

Statistical arguments could potentially be made to attempt to demonstrate certain experiments aren't valid, but simply do not apply to what we are discussing.

 

I also point out that some of the basic validations of quantum mechanics do not require complicated experiments (atoms are stable, for instance, no experiment necessary).

 

But by the way, I've already read a bunch of stuff on the subject. In fact I'm not even sure where you got the idea I hadn't.

 

I got the idea from your refusal to read the sources and discuss them.

 

A discussion of Bell's inequalities can be found in nearly any quantum text (see, for instance, Griffith's introductory text) so I made the assumption someone who had read on the subject would be familiar with the idea.

-Will

[Qfwfq]

In law this tecnique is called hearsay and is not allowed because the person making the claim could be lying but could not be prosecuted for purgery because they can always just claim the person they heard say something was the one who lied instead of themselves. This would make it easy to lie in court and get away with it.

Apart from your faulty logic, this is pointless as we aren't here for a legal debate, or to the purpose of convicting anybody. It just shows you aren't here for scientific discussion. I assume that 'purgery' was meant to be perjury and not some act of purification. Hearsay doesn't enable a person to lie and get away with it, law simply distinguishes it from the witness testifying the fact itself, the difference is that between testifying X and testifying that Mr. Smith said X. It doesn't have the same significance in court.

 

In scientific debate it is common practice to give reference to previous work. I won't go into the details of the entire process here, it would be out of place, but in the specific case of you having posed a question, Will showed you the initial source of the most appropriate answer. I would add that much research has been done and is still in course but it now seems clear that Bell's inequalities are violated, there is no local realism and hidden variables couldn't clear up the interpretation of QM. If you want to discuss the details of this, after having fully gained familiarity with it, you are welcome to do so with the right kind of approach and manner. If instead you pose a question, as you did to start this thread, then respect the replies you get as required by the rules.

 

I wasn't complaining that he was providing a link or information. I was addressing the manner in which he did so. The difference would be:

 

A: The following link might have useful information: link

and

B: Everyone else thinks you are wrong see look: LINK

 

The link isn't what I was talking about it was the sentence before the links.

And this is called dodging, here on Hypography. Just compare with the words of yours I had replied to.

[Kriminal99]

You asked a question, specifically about why can't we think of quantum correlations as some sort of hidden variables. I posted a link to a mathematical proof as to why. Either quantum mechanics is right, or local hidden variables are right, they are mutually exclusive. I pointed you to the mathematical proof of this statement.

 

 

 

Not at all, I provided you with a published scientific paper that outlines, very rigorously, the logic. This isn't hearsay, but providing the most appropriate information straight from the original thinker.

 

 

 

Or maybe I find it easier to tell you where to look then to type up dozens of pages of material. Again, I will answer any questions about the Bell's proof that you may have, and continue this discussion. I am not, however, going to type up Bell's entire argument.

 

 

 

You haven't made any objections. You asked a question, I linked you to the answer and you have seemingly refused to read it.

 

 

 

First of all, you are making assumptions (that I haven't studied Hume and don't understand the foundations of statistics). I also point out that objections to statistics are completely irrelevant to this discussion. Bell's work is based on probability theory, which is quite different then statistics in its foundations.

 

Statistical arguments could potentially be made to attempt to demonstrate certain experiments aren't valid, but simply do not apply to what we are discussing.

 

I also point out that some of the basic validations of quantum mechanics do not require complicated experiments (atoms are stable, for instance, no experiment necessary).

 

I got the idea from your refusal to read the sources and discuss them.

 

A discussion of Bell's inequalities can be found in nearly any quantum text (see, for instance, Griffith's introductory text) so I made the assumption someone who had read on the subject would be familiar with the idea.

-Will

 

As I just very clearly stated in response to q, I was not addressing the fact that you posted a link but the manner in which you did it. You still do not understand what I was talking about in regards to statistics. I didn't make any assumptions, because I did not say that you did understand the assumptions inherent to all statistical reasoning or the generality problem of induction. I simply stated that I wouldn't assume that you did, nor do people often automatically understand other people's objections since people are impacted differently by different information. But as I said your responses do not indicate you have an understanding of my objection.

 

And I read the related information long ago. The only assumption I see here is your repeated assertion that I did not.

 

Apart from your faulty logic, this is pointless as we aren't here for a legal debate, or to the purpose of convicting anybody. It just shows you aren't here for scientific discussion. I assume that 'purgery' was meant to be perjury and not some act of purification. Hearsay doesn't enable a person to lie and get away with it, law simply distinguishes it from the witness testifying the fact itself, the difference is that between testifying X and testifying that Mr. Smith said X. It doesn't have the same significance in court.

 

In scientific debate it is common practice to give reference to previous work. I won't go into the details of the entire process here, it would be out of place, but in the specific case of you having posed a question, Will showed you the initial source of the most appropriate answer. I would add that much research has been done and is still in course but it now seems clear that Bell's inequalities are violated, there is no local realism and hidden variables couldn't clear up the interpretation of QM. If you want to discuss the details of this, after having fully gained familiarity with it, you are welcome to do so with the right kind of approach and manner. If instead you pose a question, as you did to start this thread, then respect the replies you get as required by the rules.

 

And this is called dodging, here on Hypography. Just compare with the words of yours I had replied to.

 

No the first line of your post is dodging. The post had nothing to do with convicting anyone. It was pointing out a general fallacy used in any kind of debate where someone tries to impact a discussion in this manner.

 

The definition of hearsay is irrelevant. I was pointing out the PURPOSE of not allowing hearsay in a courtroom, or any similar technique in any kind of debate. Why do you think it is illegal to lie in court? If you could lie with no consequence then no court would be able to collect accurate evidence from witnesses and the legal system would be useless. Hearsay is a way to circumvent this- you claim something and if its shown to be a lie you still don't get in trouble because you can just say it was the other person who lied.

 

Just like saying "Person X thinks you are false therefore you must be false" allows you to potentially have an impact on how a discussion appears and yet:

 

A) Not be able to have your claim refuted or analyzed in the current discussion because the other person is the one that made the claim not you, you just pointed to the other person's claim.

 

:hihi: Not be resposible if the other person is wrong, which means you can do it all day long without consequence. Even if the specific claim you initially point to is wrong you can just say "oh they don't know everything about it still more people disagree" and point to another claim that is not your own. You can do this all day long without consequence which wastes the time of readers and your opponent and gives a false impression to readers until each referenced claim can be refuted.

 

As I already pointed out, my response had nothing to do with the posting of a link, but rather than manner in which the link was posted. Again this is what you referred to as dodging, as I made this perfectly clear.

[sebbysteiny]

In law this tecnique is called hearsay and is not allowed because the person making the claim could be lying but could not be prosecuted for purgery because they can always just claim the person they heard say something was the one who lied instead of themselves. This would make it easy to lie in court and get away with it.

 

This isn't true. Heresay is allowed in a court of law. However it is treated as a special case and it's weight is less than normal evidence because the person making the statement cannot be brought to court for cross examination and the less direct the evidence is, the less convincing it will be. Also, you have to declare in advance if you are using hearsay. I believe the relevant chapter is CPR 25.3. Nevertheless, convincing evidence is convincing evidence even if it is hearsay.

[Qfwfq]

Krim, if you want to discuss local realism, hidden variables, Bell's inequalities and related topics, just discuss them. They are very interesting topics. But if you ask a question and someone tells you where you could find help don't get upset, if you have already familiarity with it just say so and proceed to make your points about it.

 

So, what do you think about the quantum description of things?