# Light Travels in straight line even in gravity

As we know light travels in straight line in normal circumstances but when exposed to gravity it bends. But does it actually bends?

• Commented Dec 20, 2020 at 19:15
• Please do not vandalize posts. Once something is posted and the community puts effort into answering it, it's not fair to wipe it out. Thanks! Commented Dec 21, 2020 at 16:35

The notion of a straight line being the shortest path applies only in Euclidean geometries. For a general curved manifold, which we deal with in GR, we instead talk about geodesics. Light does bend, in the sense that it follows curved geodesics, though in these geometries it doesn't make sense to talk about straight lines any more: the notion is replaced by geodesics. By following geodesics, they still traverse the path of least distance. Take a look at here for further details about geodesics in GR. Also see these related question and answers:

Why does light always travel in a straight line?

Why does light travel in straight paths?

In general relativity, light follows the curvature of spacetime, hence when light passes around a massive object, it is bent. This means that the light from an object on the other side will be bent towards an observer's eye, just like an ordinary lens.

It depends on what you mean by "bend."

It travels along a straight line, or geodesic, as defined by general relativity.

However, these straight lines don't have the Euclidean geometry we intuitively expect, so the effect as perceived by us is that, for example, stars near the sun on the celestial sphere appear to have moved.

• The geodesic is in spacetime not space. The spatial trajectory is not a geodesic of the spatial region of a stationary spacetime. Commented Dec 20, 2020 at 19:33