One of foundations of relativity is an object's gravitational field curves the 4-dimensional space-time around it affecting the motion of the observer in their space-time.
I posted on 10/21/2019: Gravitational Physics Had An Initial Crisis.
At the time, I did not realize one of the crucial consequences of that 1957 meeting to discuss relativity.
The attendees actually conceded relativity failed in a simple scenario because relativity dropped the force of gravity replacing it with curvature.
During the meeting, Richard Feynman described a simple thought experiment subsequently called the sticky-bead argument. Details of this discussion in 1957, including its conclusion gravitational waves must exist and should be detectable, are in that post.
Essentially, Feynman's argument is:
a) a moving object with a gravitational field should move a nearby bead on a stick.
b) the bead is called sticky because its motion must overcome friction on the stick, requiring a transfer of energy.
c) Therefore, there must be a force present from the moving object.
d) This motion of an object without an observer was not due to curvature for either body.
e) However the object must exert a force causing a physical motion of another body.
f) The force must be like gravity but since relativity disposed of that force (item d), the energy for this force must be emitted as a gravitational wave.
Feynman was persuasive and the meeting concluded gravitational waves can be detectable because there must be a force which curvature could not explain with just a sticky bead argument.
For that October post, I failed to recognize the crucial detail: this thought experiment involved no observer directing motion using coordinates. Relativity is rooted in the observer.
In the universe, objects move with no observer (ignoring coordinates of space-time) despite the ridiculous adage: “Spacetime tells matter how to move; matter tells spacetime how to curve.”
In 1957, cosmologists had to concede curvature could not explain this motion, a clear admission of a failure in relativity.
The apparent failure was solved by proposing a gravitational wave, the topic of that October post.
Physicists claimed relativity is still fine by proposing a gravitational wave to solve a thought experiment.
The consensus decision of a gravitational wave resulted in the LIGO lunacy.
Wikipedia has this silly statement:
"The predictions of general relativity in relation to classical physics have been confirmed in all observations and experiments to date. "
That is definitely wishful thinking. 1957 should not be forgotten.
I posted on December 10, 2019: Gravitational Slingshot of a Space Probe
That post is relevant here also.
NASA calculates a slingshot trajectory using Newrton's simple force of gravity between 2 bodies, not space-time curvature and not a gravitational field.
A gravitational field is useful for dropping or falling objects (like apples) but cosmology requires the force of gravity.