The explanation of how gravity operates is still a theory, even though the presence of gravity is very clearly observed.
I have never gotten a clear explanation of the cause of gravity although as you say it ''is very clearly observed''.
I asked a neighbor friend to explain what caused gravity and he said it was the spinning of the earth. I said that didn't seem right, that a spinning tire throws mud off. It doesn't hold it on. I have a son who is a bona fide genius in many things and he attempted to explain it but really it amounted to "we don't know for sure".
Gravity is a force of nature and is a good example to give an atheist that doesn't believe in something he cannot see. You can bet your a$$ he believes in gravity.
