Excellent observation, Terry.
If you got the notion that we need to take all motions into consideration when considering the behavior of matter, including the fastest motion that Newton and Einstein did not discuss, then you got the essence of the article right there.
But there is something important to declare about the four different motions we are involved in.
* Not all motions are based on gravity.
Here are the four motions, but this time declared as gravity-involved or not.
1. Earth's spin (gravity)
2. Earth's revolution around the Sun (gravity)
3. Earth's circling in the Milky Way (gravity)
4. Earth's speeding with the Milky Way (not-gravity)
The Fourth Motion is actually the first motion ever, because the materialization process itself, 13.8 billion years ago, set that Fourth Motion in place.
So, we have an active throw, an active catapulting, or whatever you want to call the action and 13.8 billion years later it is on-going, more or less at the same speed, and fastest of all motions we are involved in.
It is not based on gravity, so we are not falling toward something in deep space, but rather we had our 'lift off', we got pushed, a deliberate shove, and that means that we will never stop this motion and we will also never return to where the adventure started.
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The problem of talking about the Fourth Motion in language easy to understand is how it is so different from the other motions.
Therefore, I started with the leaf analogy because the essence of the story is not gravity but that Conservation of Momentum.
That 'first shove' we received was not based on gravity.
P.S. I could have called it First Motion, yet by calling it out as Fourth Motion I am appealing to our brains to see that some things are viewed upside down. By starting with ourselves, I appoint ourselves and planet Earth's First Motion as this planet itself spinning.
That way, I follow the scientific discoveries that started out on planet Earth and only later on did we discover more and more. The lesson is then that we can hang on to what we learned in our earlier discoveries too long. We need to let go of them later on with (and just for) the big-picture level.
P.P.S.
Space is just space. It does not move. It does not interact. It does not have any borders. So, when I use the word vacuum, I mean vacuum. I do not use it to describe space. Space is a phenomenon.
The difference in behavior of some matter by itself and lots more matter in a collective; that is the essence of the article. Collective matter (particularly when there is lots of it) influences the behavior(s) of parts.
And that is the essence of what Einstein's Spacetime does not explain. Mercury got pushed and pulled by the Milky Way's collective Momentum (helped by the close proximity of the Sun).
Again, good observation, Terry.
