Nugatory - thank you very much for your answer. As expected, yourself and many others have a much better grasp of this than I do.
There is still a part of this which is still unresolved for me.
Should gravity be treated as a force? If as you say above "a planet really is moving in a straight...
I am going to get laughed out of this forum but at least it will put my mind to rest when this happens. I've been thinking about this for a few years now and what better place for an answer than a physics forum?
Amongst many other things I have read A Brief History of Time seven or eight times...