Slashdot Mirror
Quantum Theory Experiment Said to Prove "Spooky" Interactions (economist.com)
universe520 writes: Albert Einstein was troubled by how two particles can communicate with each other even if they are on opposite sides of the galaxy. Today researchers in the Netherlands have closed the final two loopholes in how quantum entanglement works. The Times reports: "The new experiment, conducted by a group led by Ronald Hanson, a physicist at the Dutch university’s Kavli Institute of Nanoscience, and joined by scientists from Spain and England, is the strongest evidence yet to support the most fundamental claims of the theory of quantum mechanics about the existence of an odd world formed by a fabric of subatomic particles, where matter does not take form until it is observed and time runs backward as well as forward."
You seem to think that these theories are meant to be taken literally. You might want to do some more reading on the subject. People much smarter than you have been thinking about this for decades.
I don't respond to AC's.
It's not intractable, but it is a challenge. (Well, not "five"; I kinda hate that expression. But "scientifically interested layman" isn't beyond reach.)
Try it this way: Quantum mechanics rules are the "real" rules of the universe: objects don't have exact positions or locations. Rather, what you get is a wave that describes the object. One way to interpret that wave is that it predicts the probability that it could be at any particular place. The total behavior of the object is the sum of those probabilities. It really is in every single place, all at once, though "more" some places than others. These waves can even cancel out. That's very much at odds with what we expect.
Here's the thing with probabilities: the more of them you add up, the more they behave like the average. That is, there's a lot of uncertainty in the roll of a 20 sided die. But you know that if you roll it a thousand times, the average is going to be very close to 10.5.
Real-world objects contain far, far, far more than a thousand objects. If you work the sum of the quantum waves for that many objects, what pops out is remarkably like plain classical physics. So, everything you see looks like ordinary physics.
But if you design your experiment carefully, you can make some of the quantummy behavior show up. The most classic one is the two-slit experiment: you restrict the particle's path to one of two places, and you get interference waves. But if you modify the experiment so that it is interacting with large-scale objects like a detector somewhere in the process, the waves vanish. (A detector is something that has large-scale changes between the particle's presence and the particle's absence.) The confusing part is that you can put the detector in places where you wouldn't expect it to have an effect, but since the particle is "everywhere", it affects it in counterintuitive waves.
Proving that for certain turns out to be tricky. The difference between "the particle really is (partly) everywhere at once" and "the particle is actually in only one place, but you can't tell" is pretty subtle. You can show it by carefully counting up "entangled particles", where the two probability waves are linked. It would be natural to think that particles were exchanging information to maintain the linkage, faster than the speed of light, but the quantum rules actually rule that out. Proving it for certain is hard, since you're talking about very tiny things and very fast speeds. We actually have been doing it for decades, but since it's so hard, there were usually loopholes. This experiment finally nails the last of them shut.
The solution to the chicken-egg problem lies in the behavior of the sums: big objects behave like you expect them to because the probability of them not doing so becomes vanishingly small. There's still some fiddly bits: that "vanishingly small" isn't quite zero and nobody exactly knows where it goes. Some say "another universe"; others (like me) just put our fingers in our ears and say "I don't know but shut up and calculate la la la".
Did you read the article? It gives a pretty good description of the experiment.
They create two electrons, A and B, completely independently, in two different, widely separated labs. They use those electrons to produce a photon each (Ap and Bp), and send those photons to a third lab. The properties of the photons will depend on the properties of the electrons, but the electrons were created independently so the properties of the photons should not be correlated with each other. In fact, if at this stage you test the electrons and photons, you find that A and B and Ap and Bp are not correlated.
That third lab entangles the photons. Then the two original labs test their electrons. Now they discover that the properties of A and B ARE correlated.
No. You're taking "observation" too literally. A better explanation is -- nothing exists in any definable state until it interacts with something else.
That's what "measurement," "observation," and "detection" generally mean -- some sensor capable of being triggered by an event was triggered... something in a quantum state interacted with something else and the wave function collapsed.
No conscious observer is required. Just stuff interacting with stuff.
Take 2 polarized filters, and measure the amount of light that gets through as a function of the angle between them. With a classical model of polarization, you'd expect it to fall directly with the angle, but instead it falls of as cos^2 of the angle.
The classical E.M. theory perfectly predicts the cos^2 term. See Malus law.
What's really weird, though, is that of you take 2 polarizing filters at right angles, such that no light gets through, then stick a third between them at a 45 degree angle, then it's as bright as one filter alone.
No, you would have less power than a single polarizer. This also very well explained by Jones calculus.