Bell inequality

  • Thread starter jerromyjon
  • Start date
1,228
188
I went through a paper last week about the Bell inequality and how it is incompatible with QM. Something along the lines of probability in classical regards being 1/3 but in quantum mechanics it is 1/4. It went into some basic principles of how this is determined through quantum entanglement to be 2 separate variables measured on 2 entangled particles. OK then. I file it away in the pile labeled "not fully understood". But then something doesn't sit right... wouldn't 2 variables with 2 possible values be 1/4 chance of any of the 4 possible "states" occurring? That's just classical probability.
 

Stephen Tashi

Science Advisor
6,565
990
You'll have to ask a specific question if you want a specific answer.

Why would 2 variables with two possible values have a 1/4 probability of each combination of values? Is the probability that a randomly selected person is male and not retired equal to 1/4 ?
 
1,228
188
I was trying to explain it in a simple boolean manner, 0 or 1, true or false, heads or tails fits best... 2 coins with 2 possible states. 25% both heads 25% heads/tails 25% tails/heads 25% both tails.
 

Stephen Tashi

Science Advisor
6,565
990
I was trying to explain it in a simple boolean manner, 0 or 1, true or false, heads or tails fits best... 2 coins with 2 possible states. 25% both heads 25% heads/tails 25% tails/heads 25% both tails.
That's clear. Now what is the question? Are you asking why ordinary probability theory gives an answer of 1/3 in the quantum entanglement problem? To answer that I, myself, would need to hear a statement of the entanglement problem you read about. Perhaps someone else knows the problem just from the mention of the word "entaglement".
 
1,228
188
I think I need to be a bit more organised... I read it from a link in a post here several days ago and now I can't find it. :-(
Aha! Browser history...
http://drchinese.com/David/Bell_Theorem_Easy_Math.htm
I'm going to read through it again hoping to catch what I missed or realize where I misunderstood.
 
1,228
188
I just absorbed another version found in another thread here: http://www.felderbooks.com/papers/bell.html
It makes the same case of what should be 5/9 chance turns out 50/50.

But just before reading that version I had the "aha!" moment and realised this is because entanglement gives 100% (or close to, ideally) chance of pairs being opposite spin in any 1 of the 3 axes. We can only measure 1. So then we double up pairs, and we measure 2 axes on 1 of each pair. Then when we think we can predict what the measurements of the other pair will be it turns out random?
 
1,228
188
I'm still not sure if I explained that well enough or correctly, or if the original paper by Bell? would provide any additional insight. All I am trying to do is relate what is expected locally (meaning classically as in all 3 axes in 1 particle should always be the opposite spin in all 3 axes of entangled pairs) to what truly occurs non-locally (the measurements in the other 2 axes is affected in the pair by measuring the first axis on the first particle). This is truly the gist of the inequality, is it not?
 

Nugatory

Mentor
11,946
4,460
Another very good resource for your level of understanding is this article.
 
1,228
188
I haven't finished reading it yet, but can I assume there is verification that we know for sure a singlet state that we've partnered that we can measure vectors A,B and verify we know what C is or is that inferred from Bell's Theorem exclusively?
 

atyy

Science Advisor
13,380
1,521
I don't think anyone understands your question or what article you are referring to, since there are now 3 references in the thread.
 
1,228
188
Forget it I'm good thanks for the links everyone.
 
1,228
188
Detection-Loophole-Free Test of Quantum Nonlocality, and Applications, arXiv:1306.5772)

Here's a recent proof...
 

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving

Hot Threads

Top