We can imagine a sphere floating freely in space. Perhaps it is something like a ping pong ball. We attach a piece of string to a random position on the surface of the sphere. If we vibrate the string, the sphere will be pulled in the direction of the string. If we repeatedly move the vibrating string to various random positions on the surface of the sphere, the force vectors will tend to cancel each other out, and the sphere will not have a tendency to favor any direction over another. However, we can choose some arbitrary fixed point in the 3-space of the sphere’s reference frame, and call this point a target position. Now when we place the vibrating string at some point on the surface of the sphere, we calculate the distance from that chosen point on the surface of the sphere to our target point in space. The smaller the distance, the more vigorously we vibrate the string, and the larger the distance, the less vigorously we vibrate the string. Now the sphere will be pulled in the direction of the target position. That is exactly what happens with the photon energy of an atom. When the photons are closer to the source of gravitation, they are blue-shifted and therefore vibrate with more energy. When they are on the opposite side, further from the source of gravity, they are red-shifted and vibrate with less energy. This has the effect of pulling the atom in the direction of the source of gravity. In fact if the electrons and hadrons of an atom exhibit wave-like properties, then all components of an atom contribute towards the attraction towards the direction of highest gravitational force, due to the red-shift/blue-shift effect.