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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) 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.