I was reading a book Laws and Symmetry by Bas C. Van Fraassen
I found that there is an argument for arguing that light travel in straight line:
Leibniz's reconstruction of these arguments goes roughly like this. Let it be given that the light travels from point A to point B; demonstrate that its path will be the straight line AB, if these points lie within an entirely homogeneous medium. This is the problem; how does one approach its solution? The problem itself introduces a geometric figure: the pair of points A, B, and the direction from A to B. To define any other direction in space, not along the line AB, one would need to refer to some other point, line, plane or figure, which has not been introduced in the given. Any rule governing the motion of light in this case must therefore either (a) imply that light follows the line AB, or (b) draw upon some feature X of the situation which could single out a direction not along that line. But the assumption that the medium is homogeneous, rules out the presence of such a feature X to be drawn upon. Therefore. . . .
We cannot quite yet conclude that therefore light travels along the straight line. As Leibniz clearly perceived, we need some bridge to get us from the fact that we could not possibly formulate any other rule here to the conclusion that light—a real phenomenon in nature—must follow that rule. The bridge, for Leibniz, is that the world was created by Someone who was in the position of having to solve these problems in the course of creation, and who would not choose without a reason for choice. If there was no such feature X to be preferred, obviously none of the choices of type (b) could then have been made. That God does not act without sufficient reason, implies that any correct science of nature, satisfies the constraint of Sufficient Reason. In the above problem, the conclusion that we cannot formulate any rule for the motion of light under these conditions, except that of rectilinear motion, yields then the corollary that light can follow no other path. The Principle of Sufficient Reason is introduced to fill the gap in the sort of arguments (the above, and also Hero's and Fermat's) here represented, and is in turn grounded in a certain conception of creation.
From my understanding, the basic idea behind is that when there is only two points $A,B$ defined in a homogeneous space (i.e. every point is the same). We can only draw a straight line between $A$ and $B$.
I was not a physics student, but I think of Euclid's postulates that given any two points, except drawing a straight line (Postulate 1), we can also draw a circle by using $AB$ as radius (Postulate 3).
Therefore, a light starting from point $A$ and given another point $B$, the light could in principle travel around $B$ at orbit (a circle).
Is this argument flawed? Can I conclude possible existence of Photon sphere without reference to any theory of gravity?