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Thread: Ptolemy and Copernicus

  1. #151
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    Quote Originally Posted by wd40 View Post
    MG = Michelson-Gale experiment (relative rotation between Earth and cosmos detected)
    But relative rotation is seen all day long, so, in light of the MM exp., doesn't it mainly confirm the accuracy of interferometry more than argue that the Earth is the one rotating? If greater accuracy could be achieved, however, then it would show that the rate of rotation varies slightly. This inconstancy would favor little Earth's erratic behavior over all that stuff above.

    Presumably in the Galilean era, such results would have been interpreted as proof positive of the Geocentric model.
    I'm unsure how the MG experiment would be taken if it only shows relative rotation, or am I missing something?
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  2. #152
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    Quote Originally Posted by wd40 View Post
    Presumably in the Galilean era, such results would have been interpreted as proof positive of the Geocentric model.
    One experiment deals with orbit and the other with spin. The most straightforward interpretation in history would have been to say the MM experiment says the Earth is not orbiting but the MG experiment says it is rotating. That would have favored neither heliocentric nor geocentric, but been a rather ugly mix of the two! People would have been put into a downright tizzy, I should think.

  3. #153
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    Quote Originally Posted by George View Post
    I'm unsure how the MG experiment would be taken if it only shows relative rotation, or am I missing something?
    In that distantly pre-Relativity era, the conclusion drawn from a positive MG combined with a zero-velocity MM, would be to indicate a non-rotating non-revolving Earth. with the cosmos doing the moving round it. Airy's Failure, Fresnel drag, Bradley's aberration, Sagnac Effect and belief in an ether, all together, would have been taken in the Galilean era as proof of the Tychonic/tweaked Ptolemaic model.
    Last edited by wd40; 2018-Mar-21 at 10:40 AM.

  4. #154
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    Quote Originally Posted by wd40 View Post
    In that distantly pre-Relativity era, the conclusion drawn from a positive MG combined with a zero-velocity MM, would be to indicate a non-rotating non-revolving Earth. with the cosmos doing the moving round it. Airy's Failure, Fresnel drag, Bradley's aberration, Sagnac Effect and belief in an ether, all together, would have been taken in the Galilean era as proof of the Tychonic/tweaked Ptolemaic model.
    I think it's still hard to say just how many would favor rotation even with the positive MG result. The MG result could be interpreted in other ways such and if they leaped to the idea that the spinning universe caused such a result, and, if so, they would have guessed correctly if my limited understanding of GR is correct. More importantly, there were still the "obvious" arguments countering rotation including why our atmosphere wasn't spinning at extreme speeds, etc. Then there were the more dogmatic religious or teleological arguments that would favor the Tychonic model.
    We know time flies, we just can't see its wings.

  5. #155
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    Quote Originally Posted by wd40 View Post
    In that distantly pre-Relativity era, the conclusion drawn from a positive MG combined with a zero-velocity MM, would be to indicate a non-rotating non-revolving Earth. with the cosmos doing the moving round it. Airy's Failure, Fresnel drag, Bradley's aberration, Sagnac Effect and belief in an ether, all together, would have been taken in the Galilean era as proof of the Tychonic/tweaked Ptolemaic model.
    I don't see why you conclude a positive MG effect supports a non-revolving Earth with the cosmos doing the movement around it. I would say the MG result is moot on the issue, because it can equally be explained by a rotating ether and a rotating Earth within a stationary ether. All it does is rule out an ether that is dragged around by the Earth, so it makes the null MM result say either the Earth is not orbiting through the ether, or there is no ether. It doesn't say what is happening with spin, even for those committed to the existence of an ether. Indeed, one could ask, why would the ether follow around the distant stars, rather than the closer objects like the Sun? In other words, pinning the ether to the stars makes more sense when both are being regarded as stationary, and therefore in a special frame.
    Last edited by Ken G; 2018-Mar-21 at 08:02 PM.

  6. #156
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    Returning to the OP and the origin of Copernicus' claim that Ptolemy needed 34 circles. I have been reading Barbour's "The Discovery of Dynamics" where he describes how Ptolemy used an algorithm to produce successively more accurate approximations to the orbits of the planets.

    p 170 "Thus, the solution of Ptolemy's problem involves solution of a succession of generalised Hipparchan problems, each one leading to a better approximate solution until the observations are reproduced to realistic accuracy. Ptolemy in fact found that it was necessary to make only one or two corrections."

    From looking at the method it looks like each correction requires 2 or 3 circles to be determined along with the epicycle, so determining the orbits of all the planets to sufficient accuracy will approach the 34 that Copernicus complains of, especially given the greater accuracy of observations in Copernicus' era.

    The end of the section on Hellenistic astronomy has some interesting commentary. On Copernicus vs Aristarchus heloicentric hypotheses and the role of Ptolemy:-

    p 189 "I suspect the difference between the two men was precisely that Copernicus grasped fully the immense significance of the proposal (which was, after all, not originally his own), stated it clearly, and provided solid arguments in its support. And the reason why Copernicus could do this but Aristarchus could not is clearly at hand: all the detailed observations and analysis on which Copernicus could base his case were not available to Aristarchus; for they were made by his successors. They were the true creators of the heliocentric system; Copernicus only added the final touch.

    For the real evidence for heliocentricity was in the demonstration by Ptolemy that in all cases the the second [Kepler] inequality can be unravelled from the first and then when this is done it leaves behind in each case a first inequality characterized by essentially the same functional dependence and structure (circular motion with eccentric centre and equant). Without the solid basis that these factual data provided, the Copernican revolution would have been impossible.

    The transition from the old cosmology of Plato and Aristotle to the new astronomy of Kepler required four major steps: liberation of astronomy from the diurnal motion of the earth, liberation from the annual motion, liberation from uniformity of motion, and liberation from circularity of the motion. The first and second of these were presented almost 'on a plate' to Copernicus by the combined efforts of the ancient astronomers. The third was entirely Ptolemy's achievement. And the fourth, in some ways the least important in the historical perspective, could never have been achieved without the previous three."

    p190 "What then was left for Copernicus to do? First, he realized how the scale invariance of the Ptolemaic algorithmic procedure could be exploited to convert the geometrical similarity of the epicyclic motion into identity, that is, he postulated that all the epicyclic radii of the superior planets should be set equal to the earth-sun distance and that the same should be done for the deferents of the inferior planets. Next, he inverted the deferent and epicycle of the two inner planets. then he stretched out his hand, plucked the luminous planets from the tips of the epicyclic spokes and calmly placed them in the ghostly deferent points. Finally, he reversed the earth-sun vector. Thus he made the transition from the geoastral to the helioastral frame. The move was deft, almost cheeky; but at a fundamental level he did precious little else.

    Ptolemy built the carousel. Long after the fair-keeper has retired to bed, Copernicus came in the night, moved the linchpin, and switched on the lights. The effect was magical. Science, already stirring, woke from its millennial torpor. Copernicus's proposal is a never-ending source of fascination, bizarre in the manner he made it, incredible in the extent of its far-reaching consequences, and the parallel in science of Richard II's soliloquy on the fate of kings: the merest pinprick that finds the point on which all hinges."

  7. #157
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    Quote Originally Posted by loglo View Post
    The effect was magical.
    Judging by Goethe, Copernicus actually ended the era of Harry Potter-type 'magic':

    "But among all the discoveries and new convictions nothing may have produced greater effect on the human spirit than the doctrine of Copernicus. The world had scarcely been recognized as round and complete in itself when it was expected to relinquish the enormous privilege of being the center of the universe. A greater demand may never have been addressed to mankind. For think of all the things that went up in smoke as a result of accepting this: a second Paradise, a world of innocence, poetry and piety, the testimony of the senses, the conviction of a poetic-religious faith: it is no wonder that people did not want to give up all of this, and that they opposed such a doctrine in every way--a doctrine that justified those who accepted it in, and summoned them to a previously unknown, indeed unimagined freedom of thought and largeness of views" (H.Blumenberg, The genesis of the Copernican world p700).

    Quote Originally Posted by loglo View Post
    Science, already stirring, woke from its millennial torpor.
    One wonders how the Industrial/Scientific Revolution would have played out, if at all, if the Tychonic/tweaked Ptolemaic model had persisted as the consensus view past 1740.
    Last edited by wd40; 2018-Mar-25 at 05:49 PM.

  8. #158
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    The world had scarcely been recognized as round and complete in itself when it was expected to relinquish the enormous privilege of being the center of the universe.
    *bashes head against keyboard repeatedly*
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

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  9. #159
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    Quote Originally Posted by parallaxicality View Post
    *bashes head against keyboard repeatedly*
    Ha! Blumenberg did come up with metaphorology, after all.

  10. #160
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    The world had scarcely been recognized as round and complete in itself when it was expected to relinquish the enormous privilege of being the center of the universe.
    I don't agree with essentially anything that Blumenberg claimed in that quote, but this one is the most blatantly inaccurate. It tries to promote the myth that the ancient Greeks placed the Earth at the center of the universe out of some kind of self-congratulation, or "enormous privilege." To understand why that is so wrong, one must understand the Greek view of the four elements. The loftiest element was fire, which travels up toward the exalted heavens and is found in the "heavenly fires" we see in the night sky. The next most lofty was air, which also travels upward but not as far as fire. Then comes water, which is below the air but is pure enough to be used to wash, and sits atop that lowest of the low elements: earth. Earth was the crud, the muck, that sinks to the center. Get it? Some privilege.

    In fact, it is a matter of pure personal preference, and not Copernican doctrine, to decide if you think the Copernican model lowers the rest of the heavens to the status of cruddy Earth, or if it elevates the Earth into a heavenly chariot on a par with those ridden by the gods themselves.
    Last edited by Ken G; 2018-Mar-26 at 08:16 PM.

  11. #161
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    Well yeah that's bad too but I was thinking more about the idea that the Greeks thought the Earth was flat.
    "Occam" is the name of the alien race that will enslave us all eventually. And they've got razors for hands. I don't know if that's true but it seems like the simplest answer."

    Stephen Colbert.

  12. #162
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    Quote Originally Posted by Ken G View Post
    I don't agree with essentially anything that Blumenberg claimed in that quote
    The quote is actually by the famous Wolfgang Johann Goethe in 1810, and brought in Blumenberg's book.

  13. #163
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    Quote Originally Posted by wd40 View Post
    The quote is actually by the famous Wolfgang Johann Goethe in 1810, and brought in Blumenberg's book.
    Famous for lots of things-- but not astronomy, no. I'll give Goethe the benefit of the doubt though, I suspect he was not talking about what the Greeks thought, but rather, how that all got packaged for the common folk of the Renaissance era. Those uneducated people might have thought the Earth was flat (the Greeks did not), and those folks might have thought it was a "privilege" to be at the center (the Greeks did not). And perhaps if we saw the rest of his writings, we might conclude Goethe did not actually think that a "world of innocence" was somehow shattered by removing the Earth from the center of the universe. I mean, did he not know that the main enemy to the Copernican model was the "innocent" inquisition? Perhaps he felt the common folk felt innocent based on what they were being told by the far-from-innocent authorities of their day, innocent by virtue of not being given the facts. The main point Goethe seems to be making is in agreement with what many have argued on this thread: the Copernican picture of the solar system ushered in a revolutionary new era of openmindedness about our place in the cosmos.
    Last edited by Ken G; 2018-Mar-27 at 08:22 AM.

  14. #164
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    For the 16th and 17th centuries, I doubt we would find anything but a continuous spectrum of thought between the ranges of a flat Earth and round one, an open Church (Catholic or Protestant) and an oppressive one regarding heliocentricity, pro-Kepler and anti-Kepler views, pro-Galileans and anti-Galileans, etc. Believing what we tend to want to believe can cause cherry-picking that can lead to false conclusions. Bruno held modern views of astronomy, thus some stumble by arguing that he was killed for these views, ignoring his years of heresy against the key tenets of the faith.

    I can't imagine that many people then would have a problem with a flat Earth. What difference would it really make for them? I also can't imagine that many people then were not convinced of a spherical Earth especially after Aristotle was hammered into Church doctrine thanks mainly to Aquinas (13th century).
    We know time flies, we just can't see its wings.

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