Light travel time toward and away from a massive object The curvature of space (or space-time) causes light to follow a curved path. We see this, for example, when we look at an "Einstein Cross" in which light from a distant object, e.g., a quasar, follows different paths around an intervening galaxy or cluster of galaxies.  The length of these different paths is different, so the travel time for light is different for these different paths.  (These different travel times are observed by seeing that variations in the light intensity from the different paths arrive at our telescopes at different times.)
In the same way that the curvature of space caused those paths to be of different lengths, leading to different light travel times, will the light travel length and time be different for light traveling into (i.e., toward) a massive object compared to the travel distance and time that the light would have followed if the massive object weren't there?  And will the path length and light travel time be different for light traveling out from the massive object vs. toward it?
 A: Gravitation is caused by diffrence in time frames plus curved space due to the distance between the 2 masses (in this case between the mass and the light). The gravity caused by time is easy to observe but space isn't. It shows up in much larger masses. That's the reason what you are expriencing on Earth is mostly (by mostly I meant it) caused by time. Since photons are massless and travel only trough space but not time they do not exprience the atttaction force caused by the diffrence in time. But they do exprience the curveture in space. So you can calculate the gravitation on a photon by the curveture of the space.
If they exprience this,  (at least in the perspective of a stationary observer) it takes less time to reach point a to b moving while facing the mass and takes more time moving point b to c facing their back to the mass ( point a and c has the very same curveture of space while point b is the lowest possible curveture in the path of the photon).
Used no math for simplicity sake.
