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Name: James
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Question:
A buddy and I got into a debate late one night while on guard duty here in Iraq. I know I have heard this somewhere but I can't seem to find the proof I need to show that I am right. The question is, do two particles created at the same moment have similar spins and do they maintain that similarity despite the distance between them? So if one were to have a spin of one "direction" and suddenly changed by an outside force its brother would respond and change its own spin even if it were on the other side of the galaxy. Now I might be mixing star trek with real science but I could swear I heard something about that back in high school physics. Thanks for any light you an shed on this.



Replies:
I think you are thinking of the concept of 'entangled' particles. Quantum physics predicts that certain particle decay events will create 'entangled particles' whereby two mirror-image particles are created, with opposite properties (e.g. momentum, spin, etc.). A weird feature of quantum physics is that the particles are identical until you observe them (they do not instantly acquire their ultimate spin state). When observe the spin of one, it coalesces into its spin state, and the other into the opposite spin state. Before the observation though, they're an equal mix of both states. Here's some more detailed info:

http://en.wikipedia.org/wiki/Quantum_entanglement

So, by observing one, you 'force' the other into one state instead of its previous 'mixed' state.

Related is the EPR Paradox (named for its 'inventors', Einstein, Podolski, and Rosen). Einstein hated this 'action at a distance'. EPR came up with a thought experiment to try to 'disprove' this crazy quantum physics. If you separate these entangled particles by a large enough distance, and then observing one causes a change in another very far away, then you have information being transmitted faster than light, they reasoned. The paradox it turns out is not one at all -- but I will let you read about that yourself...

http://scienceworld.wolfram.com/physics/Einstein-Podolsky-RosenParadox.html

,among many other sites.

Hope this helps, and THANK YOU for your service to our country.

Burr Zimmerman


James,

What you might be referring to is quantum entanglement. You can find a icely detailed article here:

http://en.wikipedia.org/wiki/Quantum_entanglement

Matt Voss



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