1. Relativity, as we know, predicts that variations in velocity alter the appearance/characteristics of physical reality. But these effects/distortions are of no consequence to temporal passage: this phenomenon maintains its steady, relentless flow, regardless of the physical circumstances.
What is duration?
Duration may be defined as "a period of elapsed or elapsing time."
If we were to characterize the disparity between points A and B as "a duration of one year," we would be claiming the following:
*** "The time that elapses when an individual relocates from A to B is precisely one year: i.e., this relocation can never be achieved in a time period that is less than one year or greater than one year."
Consider two points on the fourth physical dimension: say the point "Jan. 1, 2010 AD" (point-X) and the point "Jan. 1, 2011 AD" (point-Y). It is, of course, possible for an individual to relocate from X to Y in exactly one year of ELAPSED time. But this period can be reduced.
An observer may accelerate to a velocity much higher than that of the earth, and eventually decelerate. This physical scenario, as we know, permits relocation from 2010 to 2011 in an elapsed period that is less than one year.
By definition: the amount of time that elapses from the beginning to the end of a duration does not vary.(1)
Notice, however:
The endpoints X and Y are not uniquely associated with a particular intervening duration.
We conclude the following: the separation between "Jan. 1, 2010" and "Jan. 1, 2011" is not a duration--it is not an "an elapsing period of time."
2. Suppose there are multiple "paths" connecting two endpoints, X and Y. And suppose that there are multiple durations associated with these paths. ...Then X and Y must be concurrent points existing within a static space.
"Before" and "after" have meaning only within the context of an ELAPSING time. If Y exists/occurs one year after X, then relocation cannot occur from X to Y in an elapsed time of less than one year or greater than one year. This is true BY DEFINITION: temporal passage is steady and relentless and cannot logically elapse any faster or slower than it does. (Note: relativistic "time dilation" effects do not in any way affect the steady, normal flow of [subjective] time).
I've illustrated that relocation from Jan. 1, 2010 to Jan. 1, 2011 is possible in an elapsed period far less than a year. These two points, therefore, cannot be considered to occur one after another (i.e., in temporal succession). They exist, rather, "at once" within a static, four-dimensional physical reality.
1. An elapsed duration (say, one second) is a fixed quantity. The endpoints of a one-second duration (call them points A and B) are precisely one second apart regardless of the frame of reference. (Being an absolute quantity, this period does not get shorter or longer depending on the reference frame.) As we know, however, the spacetime events (S1 and S2) that are associated with these fixed endpoints (A and B) do vary, depending on the reference frame.
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