Kepler. Why did he not think of Gravity first?

Discussion in 'Physics & Math' started by Captain Kremmen, Dec 27, 2013.

  1. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    Today is Johannes Kepler's 442nd Birthday, according to google.
    It seems odd to me that the laws of planetary motion were stated before the laws of gravity.

    Johannes Kepler, working with data painstakingly collected by Tycho Brahe without the aid of a telescope, developed three laws which described the motion of the planets across the sky.

    1. The Law of Orbits: All planets move in elliptical orbits, with the sun at one focus.

    2. The Law of Areas: A line that connects a planet to the sun sweeps out equal areas in equal times.

    3. The Law of Periods: The square of the period of any planet is proportional to the cube of the semi-major axis of its orbit.

    http://hyperphysics.phy-astr.gsu.edu/hbase/kepler.html

    Why did Kepler miss the main prize?
     
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  3. kurros Registered Senior Member

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    Well without Newton's framework for describing forces and how they work it would have been shockingly prescient of him to imagine an invisible force which reaches out across space from the sun to the planets. People were not long before him thinking of models with giant invisible rotating spheres with planets stuck on them; he himself had some model involving giant Platonian solids. It was a time when astronomy and astrology were the same thing. He did pretty well considering. Apparently it was shocking to some people that he even considered incorporating ideas of physics into his astronomy, which I guess was considered the domain of God http://en.wikipedia.org/wiki/Johannes_Kepler#Reception_of_his_astronomy. It is easy to forget how far we have come these last 400 years.
     
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  5. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    Kepler died in 1630.
    Newton was born in 1643.

    If Kepler Had not thought of the Laws of Planetary Motion, Newton would have been the first to think of them.
    Without an idea of gravity, they were an amazing advance. Gravity was, of course, implicit in them, but not grasped.
    ("Shoulders of giants")
    Kepler would have kicked himself mightily for not thinking of the concept.
     
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  7. Cyperium I'm always me Valued Senior Member

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    It's very hard to conceive of a unknown concept I guess. Perhaps if a apple had fallen to his head

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    , then he could have related it to a known concept. Some things look easy when you know them but isn't that easily discovered.
     
  8. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    An apple on his head.

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    Yes, I did think of that.
    It was like someone walking over a treasure and not seeing it.
    Not even a buried treasure, He was passing over an enormous heap of visible treasure. If he could see it.
    He would have been embarrassed. He was within millimetres of a greater understanding.

    Newton did have the humility to realise that some of his ideas were improvements rather than new inventions.
    I'll have to have a google, and see if he mentions Kepler.
     
    Last edited: Dec 27, 2013
  9. kurros Registered Senior Member

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    Kepler might have kicked himself, but I don't think it is surprising that he didn't think of it before Newton's laws existed, and the calculus that came along with them. Keplers laws were certainly a great insight to have without Newton's laws to help, but they were empirically driven. Kepler himself was unhappy to abandon the idea of circular orbits, since these were considered more perfect and "Godly", but precise observations forced him to do so, and ellipses were the next best thing I guess. People were really thinking in these practically supernatural terms about astronomy.
     
  10. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    So Newton was the progenitor to Darwin, in a way.
    His real advance was in abandoning preconceived ways of viewing the world.
     
  11. Cyperium I'm always me Valued Senior Member

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    We never know if we have almost stumbled upon something important. You might yourself have contemplated an idea which you ruled out not knowing that in a century it will become the next thing in science

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    , I guess the lesson is that we should always look a bit closer when we think we are unto something, always give it that little bit of extra effort!
     
  12. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    Here's a quote from Newton:

    In the beginning of the year 1665 I found the Method of approximating series & the Rule for reducing any dignity of any Bionomial into such a series. The same year in May I found the method of Tangents of Gregory & Slusius, & in November had the direct method of fluxions & the next year in January had the Theory of Colours & in May following I had entrance into ye inverse method of fluxions. And the same year I began to think of gravity extending to ye orb of the Moon & (having found out how to estimate the force with wch [a] globe revolving within a sphere presses the surface of the sphere) from Keplers rule of the periodic times of the Planets being in sesquialterate proportion of their distances from the center of their Orbs, I deduced that the forces wch keep the Planets in their Orbs must [be] reciprocally as the squares of their distances from the centers about wch they revolve: & thereby compared the force requisite to keep the Moon in her Orb with the force of gravity at the surface of the earth, & found them answer pretty nearly. All this was in the two plague years of 1665-1666. For in those days I was in the prime of my age for invention & minded Mathematicks & Philosophy more then than at any time since.


    http://todayinsci.com/N/Newton_Isaac/NewtonIsaac-Quotations.htm
     
  13. kurros Registered Senior Member

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    Not sure what you mean by the Darwin reference, but yes there is certainly a good reason for Newton's stupendous fame. I think it is not too controversial to say that modern physics began with him.
     
  14. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    What I mean is that both Newton and Darwin made progress by gathering information, and making new theories which best explained that information, rather than accepting received theories, and interpreting information in the best ways those theories would allow.
     
  15. kurros Registered Senior Member

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    Oh, well yes certainly Newton was a powerful influence in the emergence of the modern scientific way of thinking. I like this quote I just found on wikipedia:

    'Thomas Jefferson, the third President of the United States and author of the Declaration of Independence, wrote: "Bacon, Locke and Newton. I consider them as the three greatest men that have ever lived, without any exception, and as having laid the foundation of those superstructures which have been raised in the Physical and Moral sciences"' http://en.wikipedia.org/wiki/Francis_Bacon#Science
     
  16. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    The problem with gravity was that it was force acting at a distance.
    It was impossible then to explain how such a force could exist.
    We still haven't explained it fully, but we accept with Newton that it must exist.
     
  17. wellwisher Banned Banned

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    Kepler was explaining what he saw, and was making a correlation using the scientific method, even before the method was formally declared. I am sure he was trying to come up with ways to explain this, since that is what self sufficient scientists do. But since he could not prove anything, beyond the motion observations, he knew that human nature has a primitive fear of novelty, and it would use any unproven extrapolation as for an excuse to discredit everything. On the other hand, if he stayed simple and used only reproducible data, and this became the new platform for thinking, then and only then, would the next step get half an ear before the defensive panic sets in.

    By the time of Newton, Kepler's ideas was more part of the mainstream, so one could take it to the next step.

    If you introduce anything new in these forums, which challenges the traditions of science, one can see the same reaction Kepler had to face. They will yell, scream, insult and foot drag. To minimize this reaction, at a time they could kill you for hearsay, baby food was needed. Do not give babies steak to chew since they will choke and all the moms will panic. They need it pre-chewed. Gravity would have been like giving a baby a piece of steak, with all the mothers panicking and yelling at Kepler until he is banned or killed and the truth buried. Kepler weighed fame against human nature and opted for something, instead of all or not.

    All of accepted science today had to go through the panic/denial stage. One is required to reduce it to baby food, before those making the decisions can follow and accept. It always puzzled me how babies end up at the top making these decisions. I would assume the adults of science would lead, since they could eat chunks of steak. It is like the system is upside down. It could be due to politics, some can talk the talk, but still cannot eat big people food, just what is on the strained peas script.
     
  18. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    There is no scientific alternative to the theory of gravity.
    And great evidence that the theory is true.
    It is also testable and verifiable in scientific experiment.
    For something to be said to be scientifically true, the latter condition is essential.
    Science does not hold all truth, but it can be depended upon within its limits.
    It is important not to confuse it with faith, belief, emotion etc.
     
  19. brucep Valued Senior Member

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    I'm pretty much sick and tired of 'the cadre of idiot winds' boogering up the threads with this kind of clueless nonsense. This moron is saying that because somebody [scientists] doesn't agree with what 'he thinks should be happening' that they're acting like children [the children I know are so much smarter than this booger eating moron]. This is a sociopathic case of ignorance. Continual irrelevant intellectually dishonest bullshit. Allowing this kind of trolling nonsense in the science threads [any intellectual discourse] is a travesty and not worth being associated with.
     
  20. brucep Valued Senior Member

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    Because thats the case [and really an important one] we should be introducing our students to discussions on the scientific method starting in preschool. By the time the students get to high school they should know how to access the scientific literature as their own personal resource for future studies. IE when they grow up they know that the scientific literature isn't just a bunch of 'hard to learn shit' that's probably a hoax anyways.
     
  21. hansda Valued Senior Member

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    I think, my "Theory of Everything" can explain this as to why Kepler could not discover gravity.
     
  22. Farsight

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    Because he was just a mathematician and an astronomer. Newton was too, but he was also a natural philosopher and a genius. And because things that look straightforward in hindsight aren't always easy to figure out up front.

    You should read up on Newton some more. Check out his 1692 letter to Richard Bentley where he said this:

    "“That gravity should be innate, inherent, and essential to matter, so that one body may act upon another at a distance through a vacuum, without the mediation of anything else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity that I believe no man who has in philosophical matters a competent faculty of thinking can ever fall into it”

    Newton didn't think gravity was some action-at-a-distance force. See this in Opticks queries 20 and 21:

    "Doth not this aethereal medium in passing out of water, glass, crystal, and other compact and dense bodies in empty spaces, grow denser and denser by degrees, and by that means refract the rays of light not in a point, but by bending them gradually in curve lines? ...Is not this medium much rarer within the dense bodies of the Sun, stars, planets and comets, than in the empty celestial space between them? And in passing from them to great distances, doth it not grow denser and denser perpetually, and thereby cause the gravity of those great bodies towards one another, and of their parts towards the bodies; every body endeavouring to go from the denser parts of the medium towards the rarer?"

    Sounds unfamiliar I know, but check out arxiv and look at http://iopscience.iop.org/0256-307X/25/5/014.
     
  23. Captain Kremmen All aboard, me Hearties! Valued Senior Member

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    A "Theory of Everything" must of necessity explain everything.
     

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