kyrademon: Graymouser --
Let's say an electron-positron pair is emitted from a source in a state called a spin singlet. The particles shoot off and are measured later. Whatever axis their spins are measured along, they are always found to be opposite from each other. This can only be explained if the particles are linked in some way. Amazing!
It seems like this should allow faster than light communication, which violates causality according to special relativity. But it doesn't.
Causality is preserved because there is no way to transmit messages with these particles by manipulating the spin. When you take a first measurement of one of the particles, you always have a 50% probability of measuring a positive spin and a 50% probability of measuring a negative spin on whatever axis you're looking at, completely at random. It is fundamentally impossible to influence what result you get.
So, yeah, if you measure "-x" on one you will measure always "+x" on the other, even if the particles are millions of light years apart. It's counterintuitive and strange and spooky and all that stuff. But you can't actually use it to transmit a message. On either side, it's always going to look random. It is random. Just linked.
flabdablet: If we entangle particles A and A' and then separate them physically, all we've done is set things up so that measurements involving A can be used to generate accurate predictions about the results of measurements involving A'. So if I examine A and find out something about its polarization or spin or whatever, then I can confidently predict the result you will get whenever you get around to measuring A'.This is what I don't get- unless I'm missing some key part of what you're saying, if you're saying I can:
What I cannot do with A and A' is push some kind information into A when it arrives at my measuring station that you can then extract from A' without hearing from me via some other channel. All I can do is measure properties that A (or, strictly, the A+A' entangled pair) already has, such as the response it generates in a spin or polarization detector.
[...]
The "spooky action at a distance" much beloved of popular writings on entangled photons refers to this correlation between Mars and Belgium's bit strings. It has nothing whatsoever to do with any ability to transfer other information from Mars to Belgium or vice versa; the content of the bit strings is still random.
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No. No they don't. Noooooooooooooooo.
What some physicists are suggesting is that all such mystical brain functions are aspects of one phenomenon: a subatomic but universal intelligence system that receives, integrates, and transmits information at a level much deeper than the sensory appearances of what we call space, time, and separateness. And this intelligence system, although outside space-time as we know it, manifests itself within space and time as electrons, atoms, molecules, cells, complicated critters like you and me, planets, stars, and whole galaxies.
No they aren't, no there isn't, no it doesn't. No.
Should have been published in Non Magazine.
posted by Segundus at 1:33 AM on December 5, 2010 [9 favorites]