**interaction vs uniaction**

Woody:

My addtional analysis is below:

1. "Gravity" and "space - time curvature" are equivalent descriptions. "Gravity" is the classical description while "space - time curvature" is the modern description. It's masses generate "gravity" and also it's masses generate "space - time curvature".

2. "Gravity" is a bilateral concept. It's mass - mass "interaction". But if people consider that photon is massless, "space - time curvature" will turn to be unilateral concept. It's mass - massless and should be called "uniaction". Logically, they will not be equivalent any more. That will lead to the inconsistency between classic and modern physics.

3."Space" is a bilateral concept. If there is only one planet in cosmos, will the "outside" "space" exist and warp? If people consider that it's the mass of a planet render "space - time" warping from the angle of the planet, then how about from the angle of the "massless" photon? What render "space - time" warping?