Violation of Heisenberg's Uncertainty Principle

mbone writes "A very interesting paper (PDF) has just hit the streets (or, at least, Physics Review Letters) about the Heisenberg uncertainty relationship as it was originally formulated about measurements. The researchers find that they can exceed the uncertainty limit in measurements (although the uncertainty limit in quantum states is still followed, so the foundations of quantum mechanics still appear to be sound.) This is really an attack on quantum entanglement (the correlations imposed between two related particles), and so may have immediate applications in cracking quantum cryptography systems. It may also be easier to read quantum communications without being detected than people originally thought."

Re:Magic

[Seumas]

This is exactly how I feel when it comes to quantum-anything. Especially quantum-computing, which leaves me looking at papers on it the way my cat looks at me when I ask him to do my taxes. It's one of the best examples I've encountered of anything sufficiently advanced enough being indistinguishable from magic.

Not magic

[aNonnyMouseCowered]

Most people won't consider quantum physics magic simply because it involves things that aren't experienced in everyday life. If I see a chair float in the air, I'd say it's magic because a chair suddenly floating up is contrary to my everyday experience of chairs. Familiar things behaving in unfamiliar ways, that's magic. A person being cut up and put back together is a magic trick. A medieval person might consider the Amazon Kindle magic because it resembles a book or at least a biblical tablet and yet contains the contents of thousands of books.

I'd consider quantum states magical only in so far as they produce macroscopic effects, a real-life cat that's both alive and dead. Quantum entanglement would be magical if it would allow us to develop instantaneous communication devices or, even more magical, Star Trek-style teleportation.

Re:Argh science journalism.

[osu-neko]

Only on Slashdot can you find a comment better than the article. Someone give him a modpoint.

With the proviso that the comment would be utterly incomprehensible to the target audience of the original article. "Better" is thus a relative term, and an assessment the BBC would rightfully disagree with in this case.

Re:Magic

[Americium]

Feynman's path integrals are over all space, or all paths, but are of the wave function. Bell's proof showed that any hidden variables would produce different results when measurements are taken, or Feynman's path integrals calculated. So no, hidden variables do not exist. Thinking about whether the particle is actually spin up or spin down before measurements are taken is meaningless, as quantum mechanics only give probabilities of the outcome of a measurement using the wave function to calculate these probabilities. It actually says nothing at all about the particle before measurements are taken.