rectilinear
1. A hypothetical itinerary parallel to a straight line.

For the purposes of ordinary speech, the word rectilinear is an adjective. It may be used to qualify a noun
such as itinerary, as in 'rectilinear itinerary'. However, for the purposes of science, the word itinerary is a
verb. There is no such physical object as an itinerary. An itinerary is pure motion, a movie of a moving
object. Thus, any qualifier that we use in this context must necessarily be an adverb, a word that qualifies
motion. The incongruous language of ordinary speech cannot be extrapolated to scientific contexts.

For the purposes of Physics, rectilinear motion is surrealistic, an irrational proposal. Each atom occupies
a unique location in every frame of the Universal Movie. This means that no object may occupy a set of
locations aligned rectilinearly with respect to the remaining matter in the Universe. To get around this
objection, the mathematicians concocted the surrealistic 'frame of reference,'  a point of reference to
gauge rectilinear motion. The mathematician anchors a pair of number lines which he calls 'coordinates',
and counts units along them. If the entity travels 5 miles along the x-axis and zero miles along the y-axis, it
is said to travel 'straight,' meaning rectilinearly. For example, a car may be said to travel rectilinearly with
respect to a straight highway. The car may never travel rectilinearly with respect to Jupiter. But what
sense does it make to say that a car travels rectilinearly with respect to the highway? The highway is a
structure and may be perfectly straight. The itinerary of the car is a movie of the car in motion. Each frame
of the movie shows a car at different locations with respect to the highway. Are we going to place the
frames of the movie side by side or above and below each other?
 Fig. 1 A   Straight vs. Rectilinear
 A highway is a physical object and may be qualified as being straight. An itinerary of a car on the highway can at best be said to be rectilinear (i.e., parallel to a straight line). However, what we are really contemplating is a movie of a car moving with respect to the highway. The car is simply at different locations with respect to a small portion of the highway. That's what appears in each frame of the movie. It is irrational to say that the car is traveling rectilinearly. We certify this when the frames of the movie are placed one below the other as shown in Fig. 1 B. Rectilinear with respect to what? Or we can simply compare each frame of this film against the movement of Jupiter. Is the car traveling rectilinearly with respect to the Moon? Rectilinear motion is a surrealistic concoction of Mathematics. Again, Physics is radically different than Math.

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