# Quantum entanglement ?

1. Feb 25, 2010

### tell_me_why

Quantum entanglement ????

Ok, after beating my head with numerous link on net somehow Icould not grasp the idea of quantum entaglement...all i understand is two particles somehow become co-related and then when seperated to any distance still maintain co-realation , the moment you see one the other property is defined.

Whats wrong in this..whats weird in this ..i can't understand.

Take an example ..i got 2 pens red and blue .

now i put each in box and ask my friends to take them away.

then one of my friend open box and find the pen is red so definetly the other would be blue.

also until my friend didn't open the box , either of them do not knew what color they have.

Can someone help me understanding this .....please given an example also instead of pasting me any link to internet.

2. Feb 25, 2010

### DrChinese

Re: Quantum entanglement ????

Your example is fine, but for one small detail. That was understood in 1935 when the EPR paper was written. But it is spin statistics at other angles that cause the problems. This was pointed out by Bell in 1964. The relationship is cos^2(theta) and your example will not work for some groups of angles. Usual examples are 0/120/240 degrees (a la Mermin) or 0/22.5/45/67.5 degrees (CHSH).

3. Feb 25, 2010

### Staff: Mentor

Re: Quantum entanglement ????

In order to see the "strangeness" of the outcome for entangled states in examples like the ones Dr. Chinese mentions, you really have to study one of them in detail. You shouldn't expect someone to write one of them up completely for you here, when it's been done many times elsewhere on the Web.

I like Mermin's example, myself. He published it in an article titled "Is the Moon There When Nobody Looks? Reality and the Quantum Theory." You can easily find it with a Google search for "Mermin moon". I'm pretty sure Dr. Chinese has a link to it on his Web site.

4. Feb 25, 2010

### DrChinese

Re: Quantum entanglement ????

Echoing the above... here is my website link for the Mermin example:

http://drchinese.com/David/Bell_Theorem_Easy_Math.htm

This has easy math, but as jtbell says, you need to work through an example that DOESN'T support your contention to see the issues involved.

5. Feb 26, 2010

Re: Quantum entanglement ????

You are not the only one who want to understand the REAL PHYSICAL SENSE of the term “entanglement“ : see the thread “Entanglement and Concurrence: asking for definitions”.

May be you will find it in arXiv:0706.2488v2 :-)))