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Beginner's Guide to Quantum Entanglement
No Fortune writes "Einstein called it 'Spooky action at a distance.' This article describes, in scientific layman's terms, how spooky action is created." From the article: "Normally the photons exit the crystal such that one is aligned in a horizontally (H) polarized light cone, the other aligned vertically (V). By adjusting the experiment, the horizontal and vertical light cones can be made to overlap. Even though the polarization of the individual photons is unknown, the nature of quantum mechanics demands they differ."
...what the hell is the matter with you anyway?
Throwing that kind of physics at us on a Saturday evening when you *know* most of us are half drunk?
Bastard.
Mod me down with all of your hatred and your journey towards the dark side will be complete!
Lord help us... but anyway, you've got be half-drunk to even start getting quantum physics. Everyone knows that... well, they do when you ask, they didn't before you asked.
in scientific layman's terms
Ah, oxymoron terms... the best kind.
+1 dugg
Is that what the geek kids are calling it these days?
"Excuse me, but you stimulate the neurons in my hypothalamus. Would you like to come over to my place and study quantum entanglement?"
Suppose you take a coin and spin it on a frictionless surface in a vacuum, so that it's perfectly balanced and doesn't wobble. In theory, it will keep on spinning at the same rate forever.
Now suppose you take a second coin, identical in all respects to the first, and start both coins spinning at the same time--but with one of them 90 degrees out of phase compared to the other, so when one is "horizontal" when viewed from above, the other is "vertical".
Finally, suppose you have a way to move the coins without affecting their rotation. Move one of the coins as far away as you like from the other.
Reach out a finger and stop one of the coins. Suppose that at the instant you stopped it, the coin was horizontal. You now know that, at that particular instant, the second coin was vertical--not because the coins somehow "communicated" with each other, but simply because they both followed the same laws of physics up until you interfered.
Granted, I'm oversimplifying tremendously, but is this a semi-reasonable explanation of why quantum entanglement has nothing to do with instantaneous communication, or do I just need to get to sleep?
I've been waiting for Teach Yourself Spooky Action in 24 hours.
:-)
It's right next to Brain Surgery for Dummies, Nuclear Power Plant Management for Complete Idiots, Intelligent Design for the Non-Intelligent, and War Planning for the GOP
Table-ized A.I.
While we are on the subject of Quantum Mechanics. Check out Caltech's website on Quantum Computers.
I would also like to put you towards HP's Research on it.
The future is quantum mechanics, no matter the subject.
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>>The comments were 50% juvenile drunken-louts-at-school level and the other 50% were people who didn't understand the question.
Exactly!!! And what is your impression of Digg comments?
Goodness, no, this is not an accurate analogy. Here's a formally equivalent analogy that should raise your suspicions:
Take two bullets and fire them in opposite directions from identical guns. If you measure the distance of bullet #1 at time t, you will find, amazingly, that bullet #2 has traveled exactly the same distance, but in the opposite direction. Hopefully that doesn't strike you as an amazing result.
What both of our thought experiments say is that if you establish a correlation in a composite system (the two bullets, or your two coins), and you expand the system without doing anything to mess the correlation up, then, amazingly (not!) the correlation will be preserved no matter how large the system gets.
What QE involves is something different: it says you can create a correlation after you have expanded the system, and in less time than it would take any kind of signal or force to cross the distance involved (in fact, instantaneously as far as anyone knows). The correlation can't be used for communication because you can only verify the results of the correlation by communicating the results of measurements on the two parts of the system, which, of course, you can only do at the speed of light.
The whole business arises from the fact that we don't yet understand what happens when the "wavefunction collapses." We know that measuring a quantum system instantly transfers it from the quantum state it was in into a new one (the one consistent with our measurement). So far as we know, this happens instantly over the entire volume that the wavefunction occupies. The problem with this is that it seems dangerously close to violating relativity, because it seems something is being transmitted instantaneously over finite, possibly large, distances.
Relativity is not yet in trouble because we have no good theory of quantum measurement, no knowledge of how a wavefunction collapses, so we can't apply the restrictions of relativity to the internal workings of the collapse. Relativity may never be in trouble, because the collapse may be an epiphenomenon, an event that seems to involve transmission of information but which really doesn't.
Here's an example of an epiphenomenon: point the world's biggest laser at the Moon and look through a telescope at the dot. Aim the laser at one side of the Moon, and then swing it over to the other side quickly. If it takes you 0.25 seconds to move the laser's aim, how long will it take the dot to "travel" across the face of the Moon? 0.25 seconds, clearly, for a "speed" of 22,000 km/s. If you can change the aim of the laser in less than about 0.15 seconds your dot will "travel" across the surface of the Moon faster than the speed of light.
But that's because nothing is really moving. The "motion" of the dot is just a fiction in your mind you create to help describe what you're seeing, because what you are seeing looks superficially similar to what you see when a real object moves. But there's no more real motion here than there is horizontal motion when a group in a stadium does "the wave". In the same way, the "transmission" of information in a QE experiment may turn out to be an epiphenomenon of a higher order, something that "looks" like transmission but really isn't.
The hidden variables theory of quantum mechanics was disproven by a physicists named John Bell. In his method, he began by assuming that these "hidden variables" existed, then, using geometric arguments and the postulates of quantum mechanics, derived a set of inequalities which showed no physical theory of local hidden variables can ever reproduce all of the predictions of quantum mechanics.
It's not intuitive at all, but Bell's argument is sound. Entanglement and action-at-a-distance is real, and not due to the system's state being pre-determined by hidden variables.
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