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I Understanding of gravity in the Middle Ages

  1. Jan 9, 2018 #1
    In the Divine Comedy Dante describes travellers journeying through the Earth. He and his fellow travellers go down to the centre and continue and immediately realise that they are going "up". This indicates that gravity was understood to be a force or attraction coming from the centre on the Earth rather than, as we now know, a force coming from every part of the mass of the Earth (though in practical terms this difference in understanding only makes a practical difference if you are inside the Earth - outside the Earth the force under the two understandings would behave the same).

    What else did people in the Middle Ages know about gravity? Did they, for example, know that the same force which was responsible for pulling objects on the surface of the Earth down was also responsible for keeping the Moon in orbit?

    Note: At the risk of stating the obvious, Dante did not actually travel inside the Earth: he was writing fiction, albeit fiction which sheds light on contemporary beliefs about the Earth and its gravity.
     
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  3. Jan 9, 2018 #2

    Drakkith

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    No, they had no idea of what kept the Moon in its orbit*. This wouldn't be known until Newton developed his theory of Universal Gravitation in the 1600's. They didn't even have the concept of a "force" as we know it now. Classical mechanics hadn't yet been developed. I remember doing a small presentation on Galileo in school and one of my references talked about science during this time period. I'll try to find that reference, but this was several years ago, so I don't know if I'll be able to.

    *Edit: I should elaborate that they did indeed have ideas about what made the planets and the Moon move, but these weren't scientific ideas, they were religious, and they had nothing at all to do with what kept people on the surface of the Earth.

    For anyone interested, here's a PDF with a quick overview of astronomy in the middle ages: http://www.ifa.hawaii.edu/users/joseph/4.MiddleAges.pdf
     
    Last edited: Jan 9, 2018
  4. Jan 9, 2018 #3

    kuruman

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    I have read that in the Middle Ages people believed that angels pushed the Moon in its orbit, the angelic push presumably being in a tangential direction as per the Aristotelian belief that a force is needed to push an object in its direction of motion. Now we know better. We understand gravity well enough to stipulate that the angels push in the centripetal direction. :smile:
     
  5. Jan 10, 2018 #4

    lekh2003

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    Gravity was something of the future. They didn't even have a clue what a force is or whether an object has inertia. How could they possible have any idea of any of the properties of gravity if they had no knowledge of forces and kinematics. The only thing they knew was that you go down, towards the Earth. Furthermore, they came up with a half-baked theory about why it only applied to objects and humans on Earth (the whole angel business).

    Also, at the time, the modern model of the solar system had not been developed or accepted. They were under the assumption that the sun and moon orbited the Earth. Even if gravity was introduced to them, then they would have so many blocks in their head to accept it since they had no advancements in any other field hinting at it.
     
  6. Jan 10, 2018 #5

    sophiecentaur

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    It's hard to understand how they managed to get on with their lives, being so ignorant about stuff that we find so important and obvious. The approach to Scientific matters was in terms of simple rules which treated the world as if it had human attributes. Hence "Nature abhors a vacuum" was the way gas pressure was appreciated. Even when Newton and his chums started sorting things out in a more objective way, they were limited in how to describe things verbally until they discovered that Maths does the job very well. After that, there was no looking back.
    We were taught by people who (hopefully) had already been taught the modern Science approach so we can find it hard to appreciate why the ancients were so 'dumb'.
    But, then, look at the Climate Change Deniers and Conspiracy Theorists of today. Old attitudes die hard.
     
  7. Jan 10, 2018 #6

    lekh2003

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    They were pretty backward, but this was a long time ago. I guarantee some chap like you or me 500 years in the future will be laughing at our methods of working with QED or other aspects of modern physics.
     
  8. Jan 10, 2018 #7

    russ_watters

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    Your question contains, yet argues against its own answer: it's not important. Not to them. Pretty much all they needed to know is that when the sun rises over there, it's time to plant the crops. They "why" of how the sun got there just didn't matter.
     
  9. Jan 10, 2018 #8

    sophiecentaur

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    I think they will, at least, credit us with learning to do without the idea of an 'agency' at work. That has been one of the very major steps in our Science, imo.
     
  10. Jan 10, 2018 #9

    lekh2003

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    I don't understand, what do you mean by "agency"?
     
  11. Jan 10, 2018 #10

    sophiecentaur

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    You are right. If a society is after stability then rocking the Scientific boat is counter-productive. Things at the moment are moving so fast that we are in great danger of total instability. The possibilities of extinction of the race are so much greater these days.
    I think hunter gatherers had it about right. They had a pretty short working week, by all accounts, and such humans survived for many thousands of years. A short lifespan is not necessarily a sign of an unfulfilled life - as long as they had come to terms with the 'nasty, brutish and short' idea.
     
  12. Jan 10, 2018 #11

    russ_watters

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    Uh, well, ok, but I don't agree with any of that!
     
  13. Jan 10, 2018 #12

    sophiecentaur

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    An agency is something or someone who makes things happen. It's a term that I have heard used by philosophers to describe the human explanation of how and why things happen.
    Our Parents are the first agency we are aware of. Then we may be taught about a divine agency to explain away things. In today's less godly age, we replace that with the government, the football club, etc etc, unless we think more rationally and try to look past that. But this is not a Philosophical Forum and we must not go down that road. :smile:
     
  14. Jan 10, 2018 #13

    lekh2003

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    Ooh, I get it. I also agree with your previous statement then.
     
  15. Jan 10, 2018 #14

    sophiecentaur

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    Good. Such disagreements are healthy.
    I am glad that you can be so optimistic about things. Perhaps I have got too old and crabby.
     
  16. Jan 10, 2018 #15

    kuruman

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    Actually, it's not that hard. Think about how often one uses the well known fact that the Earth is roughly spherical in shape. Apart from NASA people, pilots and navigators of all kinds and other such specialized professions, the common person manages everyday life quite well under the assumption that the Earth is flat. The same applies to the use of the geocentric system. I cannot imagine how I would describe the appropriate time of the day in the heliocentric system without using "sunrise" and "sunset". So I would say that we get on quite well. We use the approximation to ignore scientific facts when it's convenient and safe to do so. Climate Change Deniers find it convenient, but refuse to accept that the approximation is unsafe for us and our descendants.
     
  17. Jan 10, 2018 #16

    sophiecentaur

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    I guess I meant that, were you to return to that time, you would very rapidly run out of patience or 'understanding'. Worse still, you would need to keep your ideas to yourself or you'w be locked up as a loony.
    Ah yes. Amazing how denying climate change is the province of people who find the idea uneconomical.
     
  18. Jan 10, 2018 #17
    That sounds like something Newton might have mused 300 years ago. Should we not say now that the angels push either tangentially, or in a centripetal direction, depending on the frame of reference of the observer?!
     
  19. Jan 10, 2018 #18

    kuruman

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    I would say no if you are talking about traditional reference frames. Depending on that kind of reference frame, the angels generate a centripetal or centrifugal force, but not a tangential force. I would say yes if you are talking about a temporal frame of reference, i.e. Middle Ages vs. Information Age.
     
  20. Jan 10, 2018 #19
    You mean towards the end when he went insane?
    I get what you meant even though it doesn't quite make geometrical sense. I don't know how to say it better but...
    Yeah, something like that.
     
  21. Jan 11, 2018 #20
    @kuruman was making a joke at #3 and I was attempting - not very successfully - to make a joke in response. Difficult to explain the joke - it is a particular type of humour - but my reference to Newton was intended just in connection with centripetal force, not in connection with angels!
     
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