The concept of light traveling in straight lines and the curvature of space due to mass might seem contradictory at first, but they can be reconciled by understanding the effects of gravity on the path of light.
According to Einstein's theory of general relativity, massive objects like stars and planets cause a curvature or warping of the surrounding spacetime. This curvature is what we commonly refer to as gravity. In the presence of mass, the geometry of spacetime is distorted, and objects, including light, follow the curvature of this distorted space.
When we say that light travels in straight lines, we mean that it follows the geodesics, which are the shortest paths in curved spacetime. These geodesics are determined by the local curvature of spacetime caused by nearby masses. So, although the path of light appears curved when viewed from a flat Euclidean space, it is actually following the straightest possible path in the curved spacetime.
To visualize this, imagine a two-dimensional rubber sheet representing spacetime. If you place a heavy object like a bowling ball on the sheet, it will create a depression or curvature in the sheet. Now, if you roll a marble (representing light) across the sheet, it will follow a curved path around the bowling ball. From the perspective of the curved sheet, the path of the marble appears curved, but in reality, the marble is following a straight path on the curved surface.
In the same way, when light passes through the vicinity of a massive object like a star or a galaxy, its path is affected by the curvature of spacetime caused by the mass of that object. Light will follow the straightest path available to it in this curved spacetime, which can result in what we perceive as gravitational lensing or bending of light.
So, while spacetime itself may be curved and warped by mass, light still travels in straight lines, following the curvature of that spacetime. This phenomenon is one of the remarkable predictions of general relativity and has been experimentally confirmed through various observations and measurements.