from the the-universe-is-stranger-than-you-imagine dept.
You may (or may not) have heard about the Heisenberg Uncertainty Principle:
In quantum mechanics, the uncertainty principle, also known as Heisenberg's uncertainty principle, is any of a variety of mathematical inequalities asserting a fundamental limit to the precision with which certain pairs of physical properties of a particle, known as complementary variables, such as position x and momentum p, can be known.
According to a report in ChemistryWorld, a new technique allows atomic spin properties to be measured simultaneously with greater accuracy — Atomic Spins Evade Heisenberg Uncertainty Principle:
Many seemingly unrelated scientific techniques, from NMR spectroscopy to medical MRI and timekeeping using atomic clocks, rely on measuring atomic spin – the way an atom's nucleus and electrons rotate around each other. The limit on how accurate these measurements can be is set by the inherent fuzziness of quantum mechanics. However, physicists in Spain have demonstrated that this limit is much less severe than previously believed, measuring two crucial quantities simultaneously with unprecedented precision.
Central to the limits of quantum mechanics is the Heisenberg uncertainty principle, which states that it is not possible to know a particle's position and momentum with absolute accuracy, and the more precisely you measure one quantity, the less you know about the other. This is because to measure its position you have to disturb its momentum by hitting it with another particle and observing how the momentum of this second particle changes. A similar principle applies to measuring a particle's spin angular momentum, which involves observing how the polarisation of incident light is changed by the interaction with the particle – every measurement disturbs the atom's spin slightly. To infer the spin precession rate, you need to measure the spin angle, as well as its overall amplitude, repeatedly. However, every measurement disturbs the spin slightly, creating a minimum possible uncertainty.
The alternative approach suggested by Morgan Mitchell's group at the Institute of Photonic Sciences in Barcelona, could circumvent this problem. The spin angle, they say, is in fact two angles: the azimuthal angle (like longitude on the Earth's surface) and the polar angle (like latitude). To measure the precession rate, you need only the azimuthal angle. Therefore, by loading as much uncertainty as possible into the polar angle, you can measure the two quantities you need – the azimuthal angle and amplitude of the spin – and therefore measure the spin precession rate much more accurately than previously thought possible.
Is this the harbinger of finer-grained and/or quicker MRIs?
References: G Colangelo et al, Nature, 2017, DOI: 10.1038/nature21434
(Score: 2, Informative) by Anonymous Coward on Monday April 03 2017, @04:01PM (1 child)
This isn't evading the Heisenberg Uncertainty Principle.
The journal has a decent Editor's Summary for this paper:
Also, from the paper's Intro section (my emphasis added):
(Score: 3, Interesting) by FatPhil on Monday April 03 2017, @08:34PM
> This is because to measure its position you have to disturb its momentum by hitting it with another particle and observing how the momentum of this second particle changes.
HUP applies where it applies for purely mathematical rules of definition, not *because* measurement disturbs the system. Even if there was a measurement that didn't disturb the system, the HUP would still apply. The above is often given as an easy to understand reason, but it's just another one of those lies that are told to simplify things to people who don't want to look at the equations. The waveform simply has many (possible) positions and many (possible) frequencies (which determine the momentum), you cannot accurately define one without making the other less well defined.
This seems to be a reasonable write-up: http://abyss.uoregon.edu/~js/21st_century_science/lectures/lec14.html
Great minds discuss ideas; average minds discuss events; small minds discuss people; the smallest discuss themselves
(Score: 3, Funny) by jdavidb on Monday April 03 2017, @04:28PM (2 children)
At last! We're inventing Heisenberg compensators!
ⓋⒶ☮✝🕊 Secession is the right of all sentient beings
(Score: 3, Funny) by frojack on Monday April 03 2017, @04:37PM (1 child)
And saving cats!!!
No, you are mistaken. I've always had this sig.
(Score: 5, Funny) by requerdanos on Monday April 03 2017, @05:16PM
At last! We're inventing Heisenberg compensators!
And saving cats!
Well, maybe, maybe not.
(Score: 2) by VLM on Monday April 03 2017, @05:28PM
I'm trying to mix this with Heisenberg's microscope and the traditional SN car analogy with only partial success.
Something like if you shove a car tire with a given amount of force it'll all randomly bounce about. It seems that over a long enough time period and a hard enough shove its impossible to predict where the tire will go; you've found a limit. Below that it would just sorta fall over, or a nanosecond after shoving it, it hasn't really gone anywhere random. All of heisenberg's microscope arguments apply where if you put out styrofoam bowling pins to see where the tire goes they're too mushy to be sure and if you put out hesco bastions they are so solid the tires bounce off so you have no idea where they were headed.
However if you "trick" the tire by locking it into a car suspension with a fixed camber and toe-in, then a shove is enormously more predictable. In fact now that the tire is locked down and no longer free floating, you can arrange your hesco bastions and styrofoam bowling pins to acquire a ridiculous amount of information about the location and energy in the shoved tire.
Of course this all requires you NOT look too closely at the man behind the curtain who mounted the tire in the car suspension.
There's a different form of brain fog something about dimensional compaction and/or superconductivity on the 2D event horizon of a black hole or cold superconductor pure metals (like lead) under pressure or something equally handwavy that boils down to you can game the system to force a 3-d world into conforming to a 2-d experiment resulting in 2-d levels of data gathering in our 3-d world if you avoid looking at the compaction too closely.
(Score: 2) by Justin Case on Monday April 03 2017, @06:07PM (3 children)
I understand that the precise truth is reserved for those who can read the symbols of that foreign language called "math", and the English version is necessarily watered down.
to measure [a particle's] position you have to disturb its momentum by hitting it with another particle and observing how the momentum of this second particle changes
Is is really possible to work with individual particles like that? How the hell do you hit Particle One with Particle Two when you don't know the exact location of Particle One?
How do you then measure the allegedly unmeasurable properties of Particle Two, in particular, its changing momentum, given that you can't know where it is?
It sounds like blindfolded billiards.
(Score: 3, Interesting) by JoeMerchant on Monday April 03 2017, @09:37PM (2 children)
Most of these measurements are done with millions, if not billions, of particles and summing up the result into something observable.
The progress the French lab made is (obvious now that they've demonstrated it) to focus the uncertainty into one of two degrees of freedom, thereby reducing the product. Something like: 0.5 * 0.5 = 0.25, but 0.1 * 0.9 = 0.9, so measure the 0.1 * 0.9 case and you get almost 1/4 the uncertainty.
Grossly oversimplified, of course, but who really wants to read a bunch of French guys explaining quantum physics in English?
Україна досі не є частиною Росії Слава Україні🌻 https://news.stanford.edu/2023/02/17/will-russia-ukraine-war-end
(Score: 2) by Justin Case on Monday April 03 2017, @10:51PM (1 child)
measurements are done with millions, if not billions, of particles and summing up the result
Yeah, more or less as I suspected. So why don't they say so? It is like the dual-slot photon experiment, where they say that a single photon goes through both slots. I always wondered where do you get a single photon, and how do you see it? Then came the admission that they're testing with a beam of (probably billions? of) photons.
(Score: 2) by JoeMerchant on Tuesday April 04 2017, @12:38PM
The next thing you will hear is that it's not a particle when it goes through the slot, it's a wave - can't you see the interference patterns?
Україна досі не є частиною Росії Слава Україні🌻 https://news.stanford.edu/2023/02/17/will-russia-ukraine-war-end
(Score: 2) by subs on Monday April 03 2017, @07:15PM (9 children)
Central to the limits of quantum mechanics is the Heisenberg uncertainty principle, which states that it is not possible to know a particle's position and momentum with absolute accuracy, and the more precisely you measure one quantity, the less you know about the other. This is because to measure its position you have to disturb its momentum by hitting it with another particle and observing how the momentum of this second particle changes.
No, no, no, the Heisenberg uncertainty principle isn't a measurement problem. It is a fundamental mathematical property of waves and arises out of how quantum systems behave in wave-like ways. Damn near every science news article gets these two conflated and confused.
(Score: 2) by Justin Case on Monday April 03 2017, @07:35PM (2 children)
So does this new research indicate that math is wrong?
BTW it is certainly convenient that the universe seems to be well described by math in many situations, but as far as I know the universe is under no obligation to obey someone's often flawed or incomplete formulas. Math says 1 + 1 = 2 but reality does not present us any two completely identical objects, making math an oversimplification of reality in this example.
(Score: 0) by Anonymous Coward on Monday April 03 2017, @08:22PM
No, see the first post in this article.
(Score: 2) by subs on Monday April 03 2017, @11:40PM
AC already answered your question. In short: the summary is misleading and overly confident in its proclamations.
(Score: 0) by Anonymous Coward on Monday April 03 2017, @08:13PM
You are correct withing the context of wave mechanics, and in fact you can derive classical uncertainty relationships using that approach. You can also get there from matrix mechanics using creation and annihilation operators. In fact, the hitting of particles by photons is the basis of Heisenberg's microscope [unl.edu], and it is just as informative to a general audience now as it was to Heisenberg in developing his mathematics.
(Score: 3, Funny) by aristarchus on Monday April 03 2017, @10:20PM (4 children)
property of waves and arises out of how quantum systems behave in wave-like ways. Damn near every science news article gets these two conflated and confused.
Heisenberg, or Schoedinger? One has to do with the exclusivity of velocity and position, the other with the underdetermination of phenomena until observation. One has something to do with cats, the other does not. Is this the science news conflating, or the public? I think the only way to tell would be to open the damn box, and see how fast the particles are going, with a minimum degree of uncertainty, while they are where they are.
(Score: 3, Interesting) by subs on Monday April 03 2017, @11:31PM (3 children)
Heisenberg. See this excellent video [youtube.com] for a mathematical foundation to understand why the uncertainty principle isn't the same as the measurement problem. If you're impatient, skip to 5:30 for a practical example and 9:55 for the mathematical derivation of the Uncertainty principle from basic Fourier theory.
(Score: 2) by aristarchus on Tuesday April 04 2017, @06:58AM (2 children)
Hmmm, interesting. But for the indulgence of a very old cosmologist, and possible our current generation of astrophysicists, could you explain how this is a problem of mathematics, especially concerning the Fourier reduction, and not a question of questionable metaphysical assumptions? The problem of determinism remains? Or why not.
(Score: 2) by subs on Tuesday April 04 2017, @10:39AM (1 child)
The reason the uncertainty principle has nothing to do with measurement is because it can be derived from the fundamental analysis of waves. Therefore all wave-like phenomena (such as QM's probability waves) will be subject to it. If you are a cosmologist or astrophysicist, the mathematics used in that video should be absolutely trivial, so I don't know how to describe it any more accurately to you.
(Score: 1, Informative) by Anonymous Coward on Tuesday April 04 2017, @12:05PM
I suppose the confusion comes from the historical time order of introductions of QM elements into physics. Heisenberg and uncertainty came first, probability waves came second, so it goes a little bit contrary to story-telling order to derive uncertainty principle from wave function.