Elf Sternberg

Actually, you are confusing the "definition" of gravity with the "explanation" of gravity. The definition is something that we create out of our own defined parameters. We have defined gravity as "the deformation of space-time brought on by mass"...these are the parameters we created for "gravity".

But how gravity actually operates is another story. There is a force that we cannot observe with our physical skills (seeing, hearing, touching, etc) but we guess exists. We can observe with those same physical skills the resulting influence of this force of gravity on physical objects around us, and we get a repetition of those observations the exact same way that can be measured over and over. So we conclude that the force that we guess is there exists, and can be measured by the resulting response to the physical objects.

But we really don't know for sure what this force looks like, is composed of, etc. We guess.