The only lines connecting two points that are truly straight are those that are (1) imagined, that is to say, non-material (Euclidian lines) that can exist only in the brain and, (2) lines physically drawn between two points and regarded only in the isolated frame of reference in which they are rendered.
Any line physically drawn (drawn, meaning accounting for the passage of time during which the line is actually rendered) can never be straight if one considers the ‘nested’ frames of reference in which the rendering of the line plays out.
By nested, I mean the set of frames of reference nested within one another whose ultimate extent (number of frames) is unknowable. Example: the frame of reference (inertial and otherwise) of the solar system is nested within the frame of reference of the galaxy, which in turn is nested within the local group of galaxies, which in turn is nested in a still larger frame of reference (the totality of which are ultimately indeterminate).
Consequently, when viewed cosmologically, what appears to be a straight line drawn between two points on a piece of paper in a particular room somewhere on earth is anything but straight. It’s profile/path is ultimately indeterminate, and it’s length is ultimately unmeasurable. Consequently, that straight line viewed cosmologically will appear as a scribble.
The following somewhat humorous quote seems applicable:
“Every body continues in its state of rest or uniform motion in a straight line, except insofar as it doesn’t.”
Sir Arthur Eddington 1882-1944
British astronomer, physicist and mathematician