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"Baba wrote over 60 books, almost everyone on a different topic, writing on issues from astronomy, identified stars that European scientists technology could not discover until the late 1800s, calculus before Newton, identified Saturn’s rings, Jupiter’s moons, the orbit of several star systems including the Sirius star system, plotted the orbit of planets accurately to the year 1990, documented an immense force of density not visible to the naked eye (which many scholars essentially interpret as gravity but that term did not exist in his language at that time), documented the structure of the Milky Way galaxy, documented ovens that cooked to over 2000 degrees and made steel. Baba set up a system of calculation for weights for ships that the Songhai had built which were 100 feet long, 13 feet wide and could carry 80 tons. These ships sailed to South America and China and traded in Ivory, gold and silver."

if the "immensive density" part is accurate, wouldn't that mean the idea of universal gravitation predates Newton?

https://www.quora.com/Who-is-was-the-most-brilliant-scientist-of-African-descent https://www.google.com/search?q=ahmed+baba+brilliant&rlz=1C1CHBF_enUS794US794&oq=ahmed+baba+brilliant&aqs=chrome..69i57.2207j0j4&sourceid=chrome&ie=UTF-8

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  • $\begingroup$ The passage you cite is a complete nonsense. $\endgroup$ – Alexandre Eremenko Feb 20 at 0:12
  • $\begingroup$ @alexandre-eremenko I have to agree, and I've been looking for sources for the questioner's statement and for the suggestions made by conifold , and found nothing that supplies a basis for them. $\endgroup$ – terry-s Feb 21 at 8:23
  • $\begingroup$ @terry-s: It is true that at the time of Newton, the idea was widely discussed, and his sentence "It was picked up by Huygens, Hooke, Halley, Wren, etc. Newton's fame is not for suggesting the idea but for convincing everyone that it works, universally" is correct. $\endgroup$ – Alexandre Eremenko Feb 21 at 11:43
  • $\begingroup$ But when Newton was asked to credit Hooke, he famously replied: "Anyone can make conjectures. I do not make conjectures. I prove them." $\endgroup$ – Alexandre Eremenko Feb 21 at 11:45
  • $\begingroup$ @alexandre-eremenko If the sentence you quote is correct, then what would be the sources for it? Huygens never accepted action-at-a-distance, so clearly did not entertain universal gravitation. Hooke, Halley, Wren are on the record in 1684 as making a similar combination as Newton had done in the 1660s, the v^2/r formula coupled with Kepler's 3/2 power ratio, to find that for the circular case there would be a 1/r^2 decline in centrifugal/ centripetal force or conatus, but none of them accounted for planetary elliptical orbits or suggested universal gravitation, so whence the opinion? $\endgroup$ – terry-s Feb 21 at 12:25
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The idea, yes, Aryabhata speculated about something like that as early as c. 500 AD, Brahmagupta called it gurutvākarṣaṇ. So did Kepler, at about the same time as Ahmad Baba al Massufi (late 1500-s), and much less vaguely. Russo even ascribes the idea to Hipparchus (c.150 BC), although this is far fetched.

Even the inverse square law for gravity predates Newton, as he acknowledged in Principia, see Who was first to explain intuitively the inverse square law of gravity? The originator is considered to be Bullialdus, who wrote in 1645:

"It turns with the body of the Sun; now, seeing that it is corporeal, it becomes weaker and attenuated at a greater distance or interval, and the ratio of its decrease in strength is the same as in the case of light, namely, the duplicate proportion, but inversely, of the distances."

It was picked up by Huygens, Hooke, Halley, Wren, etc. Newton's fame is not for suggesting the idea but for convincing everyone that it works, universally - by deriving both Galileo's laws of free fall, and Kepler's laws of planetary motion from it.

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    $\begingroup$ Where exactly do you find in the Principia that Newton acknowledged that the inverse square law for gravity predated him? $\endgroup$ – terry-s Feb 19 at 14:48
  • $\begingroup$ @terry-s Newton project mentions the scholium to the fourth proposition. "The inverse law of gravity holds in all the celestial motions, as was discovered also independently by my countrymen, Wren, Hooke, and Halley", but he removed it from the final draft. He also acknowledged Bullialdus, but I can't recall if it is in Principia or a letter to Halley. $\endgroup$ – Conifold Feb 19 at 19:40
  • $\begingroup$ The passage occurs in all 3 editions of the Principia. It doesn't state that Wren Hooke and Halley did anything before Newton, only that they did something separately/ independently, see both 1729 and 1999 English translations. (The historical record matches that.) 2nd, the passage in the original doesn't mention 'inverse law of gravity', an important misquote, because what was under discussion was 'the case of the 6th corollary' [to prop 4], i.e. a mathematically-modeled combination of the restricted case of uniform circular motion under centripetal accelerative ../.. $\endgroup$ – terry-s Feb 20 at 11:19
  • $\begingroup$ ../.. attraction, plus the three-halves power law linking period and radius. Newton later wrote specifically (e.g. bk 1 sec 11 preamble) that up to then he was doing mathematics aside from physics: thus book 3, not book 1 is the place where he compared the math with the phenomena and concluded a law of gravitational celestial motions. All that Newton allowed as conclusion from bk 1 prop 4 (see scholium) was a decision to explore/explain more fully the implications of (assuming/modeling) an inverse-square attraction. $\endgroup$ – terry-s Feb 20 at 11:20
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'Did the Idea of Universal Gravitation predate Newton?' (The question went on to mention the books of Ahmed Baba.)

I had a look to see whether Baba's work is available in any way online, but found nothing. Could the questioner point to any source, it would help discussion?

Commentators who discuss early origins of gravitational ideas, perhaps as a possible anticipation of Newton, often leave it very unclear just what sort of gravitational ideas they are discussing. Then, when details do emerge, it has always so far turned out that what is being discussed is quite different from Newtonian gravitation.

First, the word 'gravity' means just heaviness, and no-one has ever seriously suggested that Newton discovered that, or that it was unknown before him. Occasionally one reads unconsidered statements that Newton 'discovered gravity', but that is not what he is seriously reputed to have discovered. On the other hand, gravity before Newton was about terrestrial physics -- the properties of bodies at or near the earth's surface. There were older theories about what moved the celestial bodies, but they did not suggest that the same laws of physics applied to celestial bodies as to terrestrial objects. It seems that Newton was the first to suggest, and provide evidence in the form of his 'moon-test', that what moves the celestial bodies is of the same kind as what moves falling terrestrial bodies -- their heaviness, subject to the same laws of motion and inertia as heavy bodies on the earth.

What Newton produced was also very specific. Considered for example in its astronomical application, a Newtonian gravitational force, if I'm not mistaken, is

-- an accelerative force,

-- directed towards a massive body,

-- operating as an attraction on another body,

-- and its measure is inversely proportional to the square of the distance between them.

Besides not accounting for terrestrial and celestial motions in the same way, earlier ideas of celestial motion discussed as possible anticipations of Newton have so far turned out either not to involve accelerative force, or not to involve forces directed centrally, etc. R S Westfall's 1971 book 'Force in Newton's physics' offers detailed discussion of concepts of force before Newton, and shows how some of them were quite vague: the idea was slow to become clarified in the pre-Newtonian world.

For example, Kepler's work is sometimes suggested as an anticipation of Newton, but Kepler's idea of force was not accelerative, he supposed that force maintains velocity, he did not think of it as producing acceleration, and it was not central. Thus, Kepler supposed that the sun's force came from its rotation and somehow impelled the planets along and around their orbital paths, as if their natural state was rest. His ideas about the moon's irregularities of motion were that they are caused by the Sun's illumination of the moon. Kepler's ideas did not include Newton-like ideas either of force or of inertia, see Bruce Stephenson's 'Kepler's Physical Astronomy' for a good discussion.

The quotation from Bullialdus introduced by Conifold expressly states the idea of something that 'turns with the body of the Sun', which appears to show that whatever it is, it is not a central gravitational force: the central forces of Newtonian gravitation do not turn with rotation of the attracting body. (Bullialdus, if he thought that the turning of the Sun's body has anything to do with gravity, may have been expressing a similar idea as the one already mentioned as held by Kepler.)

It is also important to distinguish between the bare idea of an inverse square law and the specifics of Newtonian gravitation. Anything that becomes spread out uniformly through space from a point-source is likely to follow an inverse-square law -- for example, light-intensity, it follows from the geometrical law for the surface area of a sphere, proportional to the square of its radius. Inverse-square laws of something are not peculiar to Newton, but whether that something is anything like Newtonian accelerative gravitation clearly should not be taken for granted and merely assumed.

Newton's fame was, among other things, for producing a newly compiled set of laws of motion, which operate together with what was (then) a new law of accelerative gravitational force inversely proportional to the squares of the distances, and together these have enabled celestial motions to be accounted for with previously-unknown mathematical precision and accuracy.

There have been many excessive claims for the accuracy of this or that ancient historical account of planetary motions and orbits. What is accurate enough in one age or context might be very rough in another. It is very difficult to discuss such suggestions without concrete material such as a particular book or description to go on.

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