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posted by Fnord666 on Thursday August 02 2018, @01:29PM   Printer-friendly
from the one-way-spaghettification dept.

Observations made with ESO's Very Large Telescope have for the first time revealed the effects predicted by Einstein's general relativity on the motion of a star passing through the extreme gravitational field near the supermassive black hole in the centre of the Milky Way. This long-sought result represents the climax of a 26-year-long observation campaign using ESO's telescopes in Chile.

[...] The new measurements clearly reveal an effect called gravitational redshift. Light from the star is stretched to longer wavelengths by the very strong gravitational field of the black hole. And the change in the wavelength of light from S2 agrees precisely with that predicted by Einstein's theory of general relativity. This is the first time that this deviation from the predictions of the simpler Newtonian theory of gravity has been observed in the motion of a star around a supermassive black hole.


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  • (Score: 0) by Anonymous Coward on Thursday August 02 2018, @01:48PM (10 children)

    by Anonymous Coward on Thursday August 02 2018, @01:48PM (#716206)

    The motion of Mars matches the predictions of the epicycle model [wikipedia.org] almost perfectly. However, the epicycle model is wrong, though still useful.

  • (Score: 2) by ikanreed on Thursday August 02 2018, @01:58PM (1 child)

    by ikanreed (3164) Subscriber Badge on Thursday August 02 2018, @01:58PM (#716216) Journal

    I mean, you're welcome to indicate the places parsimony and/or coherence of general relativity could be increased without sacrificing predictive power.

    • (Score: 2) by FatPhil on Thursday August 02 2018, @11:42PM

      by FatPhil (863) <pc-soylentNO@SPAMasdf.fi> on Thursday August 02 2018, @11:42PM (#716492) Homepage
      But how did this data counter any alternative models?
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  • (Score: 2) by DannyB on Thursday August 02 2018, @02:07PM (1 child)

    by DannyB (5839) Subscriber Badge on Thursday August 02 2018, @02:07PM (#716221) Journal

    You're not thinking in circles. You're thinking in epicycles!

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    • (Score: 2) by Gaaark on Thursday August 02 2018, @03:06PM

      by Gaaark (41) on Thursday August 02 2018, @03:06PM (#716260) Journal

      and his ycles ARE epic!
      :)

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  • (Score: 2, Informative) by Anonymous Coward on Thursday August 02 2018, @03:31PM (4 children)

    by Anonymous Coward on Thursday August 02 2018, @03:31PM (#716290)

    The epicycle model is wrong, as are things that may be compared to the epicycle model. Yet as you note, we can obtain useful predictions from the epicycle model, very close to the ones actually observed, but still wrong enough to give Kepler the heebie-jeebies.

    When we look at Mars, we find that Newtonian mechanics is more correct. It gives us more accurate predictions.

    Then if we look at Mercury, we see that Newtonian mechanics is wrong and that general relativity is more correct, again giving more accurate predictions.

    Looking back on the epicycles, we find that the later theories have the advantage of being able to be correct in all the instances that the epicycles were correct. It's just that the later theories are correct for more situations than the earlier theories. Newtonian mechanics holds for everything explained by epicycles and then some. General relativity holds for everything explained by epicycles and Newtonian mechanics both and then some.

    Some smart guy had some things to say about both the flat Earth model and ball Earth model [tufts.edu]. I hope I am faithfully borrowing his ideas for this comment.

    • (Score: 2) by HiThere on Thursday August 02 2018, @05:42PM (3 children)

      by HiThere (866) Subscriber Badge on Thursday August 02 2018, @05:42PM (#716349) Journal

      IIUC the epicycle model is not wrong, exactly, it's just that to get arbitrarily close the observations requires an exponential number of epicycles. Or perhaps that's just that it can approach arbitrarily close to Newtonian mechanics.

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      • (Score: 3, Interesting) by AthanasiusKircher on Thursday August 02 2018, @06:07PM

        by AthanasiusKircher (5291) on Thursday August 02 2018, @06:07PM (#716359) Journal

        Well, the historical epicycle model is definitely wrong, because (contrary to popular belief) there were no "epicycles upon epicycles." You can read more about that in the link someone already gave above. The mathematics required to build models of epicycles upon epicycles simply didn't exist in medieval times, and there's no historical evidence that they were ever used.

        If I remember correctly, Owen Gingerich (science historian) traced the error to some ignorant 19th-century historian who didn't understand how the epicycle system worked, and mistook other aspects of the theories as "epicycles upon epicycles."

        So yes, if we build a theory of epicycles that is completely divorced from the method used historically, one can approximate motion to an arbitrary level of precision. But why would you? At best, it serves to perpetuate a scientific urban legend.

      • (Score: 1, Informative) by Anonymous Coward on Thursday August 02 2018, @06:41PM (1 child)

        by Anonymous Coward on Thursday August 02 2018, @06:41PM (#716386)

        IIUC the epicycle model is not wrong, exactly, it's just that to get arbitrarily close the observations requires an exponential number of epicycles. Or perhaps that's just that it can approach arbitrarily close to Newtonian mechanics.

        The planetary motions are essentially periodic and any periodic function on the real numbers is equal to some sum of functions of the form fₙ(t) = Aₙ sin(ωₙ t + φₙ) -- the Fourier series.

        Since are 3 spatial dimensions so we can in principle express the planetary motions as three periodic functions (one for each axis), express each of those functions as a Fourier series, and those series can be used to describe the all the motions as circles-on-circles-on-circles-on-...

        This model requires an enormous table of measured Aₙ, ωₙ and φₙ values, which makes it a bad theory (to the point where we might call this theory wrong). Contrast it with Newton's law of universal gravitation, which requires measurement of the constant G and the masses of the objects involved -- this involves much fewer assumptions and Occam's razor applies.

  • (Score: 2) by darkfeline on Thursday August 02 2018, @09:12PM

    by darkfeline (1030) on Thursday August 02 2018, @09:12PM (#716457) Homepage

    > though still useful.

    No, it isn't. Using proper elliptical equations predicts the orbits far more accurately and is also far easier to calculate.

    A model that is both less accurate and more complex is not useful. Epicycles only exist because of the blind religious devotion that the Pythagoreans had for circles.

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