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Originally Posted by RascalPuff  ....... we in the third derive from the celestial phænomena the forces of gravity with which bodies tend to the sun and the several planets.
Then from these forces, by other propositions which are also mathematical, we deduce the motions of the planets, the comets, the moon, and the sea.
I wish we could derive the rest of the phænomena of nature by the same kind of reasoning from mechanical principles;
for I am induced by many reasons to suspect that they may all depend upon certain forces by which the particles of bodies, by some causes hitherto unknown, are either mutually impelled towards each other, and cohere in regular figures, or are repelled and recede from each other;
which forces being unknown, philosophers have hitherto attempted the search of nature in vain; but I hope the principles here laid down will afford some light either to this or some truer method of philosophy." - Sir Isaac Newton 1687
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Dear Rascal ..... I have read your other posts regarding Gravity
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Originally Posted by RascalPuff Exerpt (as posted at another location on this forum) follows:
When Einstein's 'curvature of space-time' is a Geodesic Straight Line (illustrated) - Today, 12:37 AM... I wish to cite another accordance of the General Theory; which states that a thrown baseball or a fired bullet does not actually describe a curved or parabolic path to the earth, when projected horizontally above its surface. Instead, they actually move in straight lines which only appear to be curves and parabolas.
The reason for this says Einstein, is that, 'What is 4-Dimensionally straight gives the illusion of being curved or parabolic when projected on the 3 recognized Dimensions Of Space'.
These quasi 3-D parabolas and curves which are not really parabolas and curves, but instead are 4-D straight lines, are called 'geodesics'. |
In your above post .... Einstein's 'curvature of space-time' is a Geodesic Straight Line ... Your drawing is not very clear ... It only seems to refer to the expansion of space as the geodesic .. while time remains linear. But, because I do not know enough I have hesitated to question it before. Also it seems, my emphasis is on 'seems', that you have not allowed for mass increase. Surely this could be used to determine the difference at any point ?
As to the question on the Principia .... my opinion is that Newton refers to the 'forces of gravity' which he describes as acting on 'the particles of bodies'.
He then postulates 'other forces' also acting on 'the particles of bodies'. For example he may be referring to the 'positive & negative' relationship inherent in the Electromagnetic force which 'cohere in regular figures'.
His reasoning underlying the words, I feel, is as follows
'Here we have Gravity, this is a concept which is understandable now that our minds encompass it. It does not explain everything, other forces, unknown, must also exist and must be explainable by similar premises, some of these must act in equal or opposite ways, there is no other way for a force to act. As Galileo has shown by his explanation of mass in freefall all these forces must be atomic in nature'
Please forgive my arrogance in presuming to read Newtons mind. However, tho I may not be correct, my explanation, (as from the Latin
) could be just as correct as yours ??
cool bananas ... greg