There is no perfect vacuum, even in deep space. In the space of our Solar System, there is on average 5 atoms in every cubic centimeter. In interstellar space, there is on average 1 atom every cubic centimeter. In intergalactic space, there is on average 1 atom every 100 cubic centimeters. It’s a gradient, but much like the perfectly straight lines and flat planes in the original question, perfect vacuum is a theoretical construct that is impossible to achieve in our reality.
Unless the light is in a vacuum like space
Light bends in space all the time. Our sun has enough gravity to bend light.
I asked my good friend gravitational lensing about light in space, and they said that light can go and get bent
There is no perfect vacuum, even in deep space. In the space of our Solar System, there is on average 5 atoms in every cubic centimeter. In interstellar space, there is on average 1 atom every cubic centimeter. In intergalactic space, there is on average 1 atom every 100 cubic centimeters. It’s a gradient, but much like the perfectly straight lines and flat planes in the original question, perfect vacuum is a theoretical construct that is impossible to achieve in our reality.
Space is not empty