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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."
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?
That's a too simple description of polarization. It doesn't work that way. Take a polarizing filter and shine a light through it. Add another polarizing filter but rotate it 90 degrees from the other. The light is cut off from passing all the way through both. So far, so good. Now here's the tricky part. Take a third polarizing filter and place it in between the two previous ones. Rotate it around. WOW! At some intervals you can now see through all three! With two if you rotate the second you get total blockage when the filter is at 90 and 270 degrees from the first. You get more blockage points around the 360 degrees with the in-between third one (Extra ponts: how many?)! Strange. Add another. You get even more blockage points. (How many now?) Very strange indeed. Does the experiment account for this, the real behavior of polarizing filters and not the simplistic one in the article?
Why does one photon have to "communicate" to the other? Take two photons, one is polarized 90 degrees from the other. You don't know anything else. At some point you observe one, and now know the polarization of the other. Why is their communication taking place?
To make an analogy,say I flip a coin and don't look at it. Then I cut the coin in half between the two sides (without looking at which side is which). I take one side across town to my friend, and keep one. I have no idea which side I have until I look at it, but once I do I also know which side my friend has across town. Where's the mystery here, because I've never been able to understand why there's any spooky action at a distance?
AccountKiller
> if I send a baseball in one direction spinning topwise, while at the same isntant sending a
> baseball in another direction spinning bottomwise, their spins will be opposite and continue
> to do so, without any interaction between the baseballs.
Yes, but baseballs are not subatomic particles. Among other things, looking at which direction they're spinning hardly changes their spin at all. The traditional line of thinking is that the laws of physics are different at the macroscopic level versus the subatomic level, but I suspect the real issue is that they *apply* differently because of the certain scale-related difference. Baseballs have a much larger mass, for instance, so gravity is a real issue for them; whereas, gravity hardly has any impact on an individual electron at all. On the other hand, a baseball has an almost exactly balanced charge, so electromagnetic force has very little impact on it; whereas, for an electron, that's a fairly big deal. These forces, though, are the two we understand best; nuclear force and weak force presumably also apply rather differently to an electron versus a baseball, but I'm not sure we understand all the details.
The whole deal with information "flowing" is anchored in the Heisenberg principle. The models I have read all suppose that if we don't know the direction of a particle's spin, it's spin direction is not merely unknown to us but actually indeterminate, i.e., could go either way. I don't fully understand all the arguments for this, but it is related in some way to the wave/particle duality of light, wherein before you measure the positions of the individual photons two beams of light interact as if they were waves, creating interference patterns, but upon being measured the photons do turn out to have very specific positions.
Cut that out, or I will ship you to Norilsk in a box.