Gravity: The Main Points of the Argument
The main points of the argument concerning gravity are these:
1. Newton's law of gravity is quantitative only.
The law accurately predicts the movements of massive bodies (e. g. the orbit of a planet around the sun) as the result of an attractive force that is dependent on the masses of the bodies and the distance between them, but it gives no explanation for that force.
2. The force of gravity is fictitious.
In Newton's theory, the force of gravity is necessary to shift a massive object (such as a planet) from the straight-line course that it would otherwise follow, per his law of inertia. [An object in motion stays in motion with the same speed and in the same direction unless acted upon by an unbalanced force.] Einstein noted that a falling object (a worker falling off a roof) experiences no force.
3. Einstein postulates that mass distorts the geometry of the surrounding space and time.
In the warped geometry surrounding a massive object, the "straight line" of force-free movement is curved, in both space and time. Hence, a planet moves in orbit around the sun free of any force.
4. Einstein's theory of general relativity is more accurate than Newton's law of gravity.
The observed precession of Mercury's orbit around the sun, inconsistent with Newton's theory, is accurately predicted by general relativity.
5. General relativity is quantitative only.
No explanation of the relationship between mass and the curvature of the surrounding spacetime is attempted. With respect to gravity, science has a good understanding of the function of the universe (what happens), but no understanding of the design of the universe (why it happens).
Next: Kepler gets his own article. Someone else distinguishes between function and design.
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