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dieselpawn
2004-Mar-29, 06:45 AM
I teach physics on the high school level and was recently shocked by a lesson in one of my text books. Though I have a bachlors degree in physics and teaching, I am not very familiar with the work of John Stuart Bell. In one of the lessons of the text book, it talks of an experiemnt performed by John Stuart Bell. In the experiement, he took a molecule, split it in half and changed the rotational rate of the electrons of one of the halved molecules. Suprisingly, the rotation of the electrons in the other halved molecule matched and changed when the other was, no matter how apart the 2 halves were. This completely defied my view of physics and quantum mechanics. An instant change in both molecules would require a "cause and effect" which exceeds and contradicts Einsteins theorys. Could you please provide me with any more information on this claim?? I have searched the internet and could not find any other sources for information on the topic. :(

PhantomWolf
2004-Mar-29, 06:53 AM
It sounds like something similar to particle entanglement and probably uses a similar mechanism which under all current theory is the only thing apparently able to occur faster then c, in fact it appears to occur instantaneously regardless of distance. I have it on reasonably good authority that Einstein described the process as "spooky."


[edited to fix typo]

Diamond
2004-Mar-29, 07:56 AM
I teach physics on the high school level and was recently shocked by a lesson in one of my text books. Though I have a bachlors degree in physics and teaching, I am not very familiar with the work of John Stuart Bell. In one of the lessons of the text book, it talks of an experiemnt performed by John Stuart Bell. In the experiement, he took a molecule, split it in half and changed the rotational rate of the electrons of one of the halved molecules. Suprisingly, the rotation of the electrons in the other halved molecule matched and changed when the other was, no matter how apart the 2 halves were. This completely defied my view of physics and quantum mechanics. An instant change in both molecules would require a "cause and effect" which exceeds and contradicts Einsteins theorys. Could you please provide me with any more information on this claim?? I have searched the internet and could not find any other sources for information on the topic. :(

This is quantum entanglement.

logicboy
2004-Mar-29, 01:16 PM
I did a quick google and found this http://www.mathpages.com/home/kmath521/kmath521.htm

I hope it's of some help to you

milli360
2004-Mar-29, 02:25 PM
In one of the lessons of the text book, it talks of an experiemnt performed by John Stuart Bell. In the experiement, he took a molecule, split it in half and changed the rotational rate of the electrons of one of the halved molecules. Suprisingly, the rotation of the electrons in the other halved molecule matched and changed when the other was, no matter how apart the 2 halves were. This completely defied my view of physics and quantum mechanics. An instant change in both molecules would require a "cause and effect" which exceeds and contradicts Einsteins theorys.
I don't think that Bell ever actually did the experiment himself, did he?

Besides, you have to be careful how you interpret this. It is not the case that one particle is changed over and over and the other particle matches its changes. That is definitely not what happens. At no time during the experiment does anything "change," except to change from an indeterminate state to a determined one. Once the particles states have been determined, they no longer remain entangled. No?

George
2004-Mar-29, 04:50 PM
This completely defied my view of physics and quantum mechanics. An instant change in both molecules would require a "cause and effect" which exceeds and contradicts Einsteins theorys.

John Bell came up with a brilliant experiment which disproved the logical "cause and effect" approach Einstein believed. In measuring spin, he reasoned there were 9 possible conditions for his experiment. Einstein's theory had to be more than 50% correct for it to be true. It wasn't.

A new book out by Brian Greene (Fabric of the Cosmos) goes into detail regarding entangled particles and John Bell's logic.

btw..Welcome to the board.... =D>

milli360
2004-Mar-29, 05:04 PM
John Bell came up with a brilliant experiment which disproved the logical "cause and effect" approach Einstein believed. In measuring spin, he reasoned there were 9 possible conditions for his experiment. Einstein's theory had to be more than 50% correct for it to be true. It wasn't.
It doesn't disprove it. The EPR (Einstein-Podolsky-Rosen) paradox described the consequences of quantum mechanics, and the experiments bore out those consequences. The experiments show that there are no local hidden variables, but the experiments have not ruled out nonlocal hidden variables--but that is exactly what Einstein would have maintained.

George
2004-Mar-29, 09:40 PM
The EPR (Einstein-Podolsky-Rosen) paradox described the consequences of quantum mechanics, and the experiments bore out those consequences. The experiments show that there are no local hidden variables, but the experiments have not ruled out nonlocal hidden variables--but that is exactly what Einstein would have maintained.

Thanks for the clarification (although I do not know what non-local hidden variables would mean in this case). Regardless, it is encouraging as EPR seems to be less weird. It is interesting reading about it, but, it is over my head. It is clear Bell has received considerable credit for his ingenuity in this work.

Eta C
2004-Mar-29, 10:02 PM
To get the words from the horse's mouth you may want to check out a collection of Bell's papers that the Cambridge University Press put together. It has the great title of "Speakable and unspeakable in quantum mechanics" (http://www.amazon.com/exec/obidos/tg/detail/-/0521334950/qid=1080597554/sr=1-1/ref=sr_1_1/102-0793928-2286517?v=glance&s=books). A couple of the papers are non-technical, although most require some knowledge of physics.

dieselpawn
2004-Mar-29, 10:53 PM
Thank you everyone for your reply. Quantum entanglement, though I understand the basic principle, is still a little over my head #-o However the links and explainations provided were most helpful. The situations and lessons were alot more descriptive and educational than the brief, over-simplified version i saw in the textbook. Perhaps I'll have the opportunity to research this in grad school. I was just very surprised it was so loosely described and even appeared in a high school text book. Thanks Eta C for the link to "Speakable and Unspeakable in Quantum Mechanics", I've checked it out of the local library and found it most fascinating. :D