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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."
Let's just get all the Walter White jokes out of the way...
I learned about it on the factual science TV show (currently honored on Google.com), Star Trek. They need a Heisenberg compensator.
"Microsoft issues yet another patch to its quantum communications system to prevent hackers from eavesdropping on encrypted signals. The updates will be issued on Tuesday, but they might not be..."
Sorry, but gray text on gray background is making my eyes bleed.
He's not only a fantastic meth cook, but a stellar physicist as well
"The difference between genius and stupidity is that genius has it's limits" - Albert Einstein
Quantum entanglement is the equivalent of magic.
"...so the foundations of quantum mechanics still appear to be sound..."
Are they sure about that? I think they fe-line to us.
I've calculated my velocity with such exquisite precision that I have no idea where I am.
that Walt Jr. can have BOTH pancakes AND cereal for breakfast?
I like microcars
So basically this "uncertainty limit" is itself uncertain.
I don't know much about quantum physics but isn't that how it's supposed to work?
Is there more truth to recursive opensource software algorithims than we previously thought?
(-1 Completely Ignorant)
Quantum "encryption" was never that. It is only quantum "modulation" and its "security" is pure conjecture, not anything actually provable in the mathematical sense as you get with real encryption. That does not hinder a log of gullible fools to hail it as the new thing. (It does have a lot of other fundamental and unsolved problems, even if it should be secure.)
Most ACs are not even worth the keystrokes to insult them. Be generically insulted by this and ignored otherwise.
the arguements are, if i measure something, it changes that something, somehow. So i measure that something weakly, which changes that something weakly, and note the changes, that i didn't?
Seems to me he confirmed that if i measure something, that i changed it. Re-enforcing the principle, and Quantifying that it occured. Wrong premmis to start with, just a reconfirmation of the principal and the affect/effect at weak levels.
"Any sufficiently advanced technology is indistinguishable from magic." -- Arthur C. Clarke
They thought they found a violation of Heisenberg's Uncertainty Principle but they weren't sure.
You are welcome on my lawn.
I'm not really sure how to feel about this.
Since I can't tell them apart, I treat all ACs as the same person.
The uncertainty on my understanding of this article is very large, that mean the uncertainty on someone else's understanding is very small. That person needs to explain it.
Q: "So, how do your Heisenberg compensators work?"
The researchers: "They work just fine, thank you."
Ezekiel 23:20
that they checked heir cables before publishing this.
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.
This article is horrible.
"The Heisenberg uncertainty principle is in part an embodiment of the idea that in the quantum world, the mere act of observing an event changes it."
That's not the Heisenberg uncertainty principle. That's just the observer effect, and it's not something peculiar to quantum mechanics. You want to measure the temperature of a system, so you stick a thermometer in there. Okay, the mercury in the thermometer absorbs a bit of heat from the system, providing you with a temperature measurement at the same time it changes the temperature of the system. If you want to measure the parameters of a particle, you stick a bubble chamber in the way, and as the particle flies through the chamber it smacks into hydrogen molecules, showing you what it's doing but also taking a different path than it would have if none of those hydrogen molecules were in the way. Big fat hairy deal.
The HUP doesn't just say that you can't simultaneously measure the position and momentum of a particle, it says that a particle *does not simultaneously possess* a well-defined position and momentum. If the particle's doing something in a system and is interacting in such a way that you can define its position to arbitrary precision, then it *does not have* a well-defined momentum for you to measure, and vice versa. Position and momentum are what are called quantum conjugate variables, and the HUP says that when you have a pair of those variables, then the product of their uncertainties is greater than or equal to a constant. There is *no state* in which that particle is even *allowed* to exist in which it possesses both a well-defined position and well-defined momentum.
A signal processing analogy, for any analog people. A particle's wavefunction carries information about its position and its momentum. Where the wave exists is where the particle actually is, and the wavelength is the particle's momentum. Take a particle whose momentum you know to the utmost precision, and graph that. Range of momentums on the x axis, probability of the particle having that momentum on the y axis. You'll get a graph that looks like a Dirac function, a value of 0 everywhere except for a single spike corresponding to the particle momentum, area under the curve of 1.
Now switch domains, change from the momentum to the position domain, this is mathmatically the same thing as changing from a time domain to a frequency domain, which means you can use your old friend the Fourier Transform.
What do you get when you do an FT of a Dirac function? You get a constant value everywhere, from -infinity to +infinity. If you know exactly where that particle is, you have no idea *where* it is, and it's not because you disturbed it in measuring it, it's because *it* has no idea where it is, a well-defined position does not exist; since the uncertainty in the momentum measurement approaches zero than the uncertainty in the position measurement has to approach infinity so that the product of those uncertainties remains greater than a constant.
The "you change the system by measuring it" is an analogy, and it's one that Heisenberg himself used to explain the HUP, but *that is not what it says*. The HUP is not a statement about the process of measuring things, it is a statement about the nature of the universe, and finding a way to improve a measuring system to reduce the disturbance it creates in the system it's measuring has nothing to do with the HUP.
So the paper says we are not sure about the uncertainty principle?
http://www.youtube.com/watch?v=0Eeuqh9QfNI : Quantum Entanglement Lectures from Leonard Susskind. It really isn't that complicated, there are a lot of people here making statements that should instead be asking questions. This series along with his series on Quantum Mechanics should help answer those questions.
> While there is a rigorously proven relationship about uncertainties intrinsic to any quantum system, often referred to as “Heisenberg’s Uncertainty Principle,” Heisenberg originally formulated his ideas in terms of a relationship between the precision of a measurement and the disturbance it must create. Although this latter relationship is not rigorously proven, it is commonly believed (and taught) as an aspect of the broader uncertainty principle. Here, we experimentally observe a violation of Heisenberg’s “measurement-disturbance relationship”
So the actual Heisenberg’s Uncertainty Principle is still as valid as ever (and of course it is because it's a mathematical consquence of the axioms of quantum mechanics), just some erroneous formulation he started out with has been shown wrong.
It's always seemed self-evident to me - if a particle is changing it's position, then it has a momentum but no fixed position
No. If it was that simple then this issue would arise already in Newtonian mechanics. A Newtonian particle with a well-defined momentum is constantly changing its position, but at any given instant in time it does have a particular position. This is just not the case in quantum mechanics; one has only a probability of finding a particle at a given point, and if it has a definite momentum then that probability is uniform over space, so it's position is completely indeterminate (in a 1D example, anyway).
if it has no momentum then it is not changing it's position, so it has a fixed position. In other words, the quality of each depends on a changing value for the other.
Again, no. Classically, a particle with a fixed momentum zero has a fixed position, but in quantum mechanics this is not possible. The best one can do is localize a particle to some region of space (i.e., "trap" it with some imposed potential, be it electric or whatever), in which case it will have a mean momentum of zero, and a mean position, but both its momentum and position are statistically distributed about this mean values (i.e., are "fluctuating" if you like, but this is also a dangerous way to think about it, because their values aren't fluctuating with time, they are in fact fundamentally uncertain at any instant of time), and the product of the widths of these distributions must be greater than some fundamental finite value, and that is the uncertainty principle.
(Read that fellow who's a prof in quantum mechanics at MIT, Seth Lloyd.)
It's about universal balance --- too many people are still unfamiliar with GFB Riemann, most unfortunately. In the present we are saddled with Fantasy Finance and Fantasy Physics, I fear.....
...that socks aren't different for left and right feet?
Is your cat named Schrodinger? And are you quite certain of how he was looking at you? (Ba-dump-duush!)
My first Journal Entry ever, in 8 years! http://slashdot.org/journal/365947/aphelion-scifi-fantasy-horror-poetry-webzine
Im a Physicist* and I find these results quite interesting.
* I'm not really a Physicist, but I do watch the Discovery Channel a lot and I read, like, half of Brian Greene's The Elegant Universe.
This sig is not paradoxical or ironic.
Can anyone who has access to the journal article inform us what value they measured for SIGAMAx*SIGMAp. The accepted theory says >= Hbar/2.
For all the fuss they're making about this impacting quantum encryption; they didn't give any numbers in the bbc article. I guess that's to be expected from popular news.