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== History of gravitational theory ==

== History of gravitational theory ==

=== Early history ===

=== Early history ===

Efforts to understand gravity began in ancient times. [[Indian philosophy|Philosophers]] in [[History of science in early cultures#India|ancient India]] explained the phenomenon from the 8th century BC.<ref>Dick Teresi (2002), ''Lost Discoveries: The Ancient Roots of Modern Science - from the Babylonians to the Maya'', Simon & Schuster, New York, ISBN 0-684-83718-8:

Efforts to understand gravity began in ancient times. [[Indian philosophy|Philosophers]] in [[History of science in early cultures#India|ancient India]] explained the phenomenon from the 8th century BC.

<blockquote>"Two hundred years before [[Pythagoras]], philosophers in northern India had understood that gravitation held the solar system together, and that therefore the sun, the most massive object, had to be at its centre."}}</blockquote> According to [[Kanada]], founder of the [[Vaisheshika]] school, "[[Mass|Weight]] causes falling; it is [[Wiktionary:imperceptible|imperceptible]] and known by [[inference]]."[http://arxiv.org/abs/physics/0310001 Indian Physics: Outline of Early History''], p. 22. ''[[arXiv]]''. [[Louisiana State University]].

<blockquote>"Two hundred years before [[Pythagoras]], philosophers in northern India had understood that gravitation held the solar system together, and that therefore the sun, the most massive object, had to be at its centre."}}</blockquote> According to [[Kanada]], founder of the [[Vaisheshika]] school, "[[Mass|Weight]] causes falling; it is [[Wiktionary:imperceptible|imperceptible]] and known by [[inference]]."[http://arxiv.org/abs/physics/0310001 Indian Physics: Outline of Early History''], p. 22. ''[[arXiv]]''. [[Louisiana State University]].

[[Robert Briffault]] (1938). ''The Making of Humanity'', p. 191. In the 1000s, the [[Persian people|Persian]] [[Islamic science|scientist]] [[Ibn al-Haytham]] (Alhacen), in the ''Mizan al-Hikmah'', discussed the theory of attraction between [[mass]]es, and it seems that he was aware of the [[Magnitude (mathematics)|magnitude]] of [[acceleration]] due to gravity. Dr. Nader El-Bizri, "Ibn al-Haytham or Alhazen", in Josef W. Meri (2006), ''Medieval Islamic Civilization: An Encyclopaedia'', Vol. II, p. 343-345, [[Routledge]], New York, London.

[[Robert Briffault]] (1938). ''The Making of Humanity'', p. 191. In the 1000s, the [[Persian people|Persian]] [[Islamic science|scientist]] [[Ibn al-Haytham]] (Alhacen), in the ''Mizan al-Hikmah'', discussed the theory of attraction between [[mass]]es, and it seems that he was aware of the [[Magnitude (mathematics)|magnitude]] of [[acceleration]] due to gravity. Dr. Nader El-Bizri, "Ibn al-Haytham or Alhazen", in Josef W. Meri (2006), ''Medieval Islamic Civilization: An Encyclopaedia'', Vol. II, p. 343-345, [[Routledge]], New York, London.

In 1121, [[Al-Khazini]], in ''The Book of the Balance of Wisdom'', differentiated between [[force]], [[mass]], and [[weight]],<ref>[[Donald Routledge Hill]] (1993), ''Islamic Science and Engineering'', p. 61, [[Edinburgh University Press]]. ([[cf.]] Salah Zaimeche PhD (2005), [http://www.muslimheritage.com/uploads/Merv.pdf Merv], p. 5, Foundation for Science Technology and Civilization.)</ref> and discovered that gravity varies with the distance from the centre of the Earth,<ref name=Abattouy>Professor Mohammed Abattouy (2002). "The Arabic Science of weights: A Report on an Ongoing Research Project", ''The Bulletin of the Royal Institute for Inter-Faith Studies'' '''4''', p. 109-130.

In 1121, [[Al-Khazini]], in ''The Book of the Balance of Wisdom'', differentiated between [[force]], [[mass]], and [[weight]], and discovered that gravity varies with the distance from the centre of the Earth,<ref name=Abattouy>Professor Mohammed Abattouy (2002). "The Arabic Science of weights: A Report on an Ongoing Research Project", ''The Bulletin of the Royal Institute for Inter-Faith Studies'' '''4''', p. 109-130.

though he believed that the weight of heavy bodies increase as they are farther from the centre of the Earth.N. Khanikoff, ed. and trans. (1858-1860), "Analysis and Extracts of ... Book of the Balance of Wisdom, An Arabic Work on the Water-Balance, Written by 'Al-Khâzinî in the Twelfth Century", chap. 5, sect. 3.1, ''Journal of the American Oriental Society'' '''6''', p. 36.  All these early attempts at trying to explain the force of gravity were philosophical in nature.

though he believed that the weight of heavy bodies increase as they are farther from the centre of the Earth.N. Khanikoff, ed. and trans. (1858-1860), "Analysis and Extracts of ... Book of the Balance of Wisdom, An Arabic Work on the Water-Balance, Written by 'Al-Khâzinî in the Twelfth Century", chap. 5, sect. 3.1, ''Journal of the American Oriental Society'' '''6''', p. 36.  All these early attempts at trying to explain the force of gravity were philosophical in nature.