I joined Physforum (closed now) about 2006 to occupy my mind. Why were these people debating a theory 100 yrs old, with well established experimental evidence, (after more research)? After participation in other forums, and learning the theory SR, my conclusion, those disagreeing with it, don't understand it.
Of course 'time' is primary element of SR. Here is the results of my research.
What is time?
The operational definition of assigning a time to an event as mentioned by A. Einstein in his 1905 paper is essentially what it is, and how it's been done since humans appeared.
It is a correspondence convention, i.e., assigning events of interest to standard clock events, a measure and ordering of activity, with 'time' always increasing/accumulating.
It is an accounting scheme developed out of practical necessity, for human activities like agriculture, business, travel, science, etc. The unit of measure for time initially referred to relative positions of astronomical objects, stars, sun, and moon, which implies earth rotations and earth orbits. The year equates to the periodic motion of the earth relative to the sun, the month, the moon relative to the earth, and the day, the earth rotation relative to the stars. All units of time are by definition, involving spatial motion or distance. The clock further divides the day into smaller units of measure. The reference in the 1905 paper of the watch hand to a position on the watch face involves nothing more than counting hand cycles (hand motion of specific distances representing subdivisions of a day). Current scientific research requires clocks that generate smaller and more precise periods than those of the past. The second is defined as n wave lengths of a specific frequency of light. Note "n wave lengths" is a distance, but labeled as "time".
If we use a light based clock to time the speed of an object along a known distance x, what are we actually doing?
We are comparing the simultaneous motion of an object to the motion of light for a duration (number of ticks). The result is a ratio x/s = vt/ct = v/c or speed. It should be obvious that the ticks serve to correlate the positions of the object with the positions of the light signal, for simultaneous comparisons. If you use Minkowski space-time diagrams the vertical scale is not 'time', but ct, light path distance, i.e. they plot speed. This allows a simple comparison of equivalent entities, without consideration of the nature of those entities.
In summation: A clock provides a beat or rhythm via a periodic process, to coordinate and measure events.
quotes by the author of SR
From 'The Meaning of Relativity', Albert Einstein, 1956:
"The experiences of an individual appear to us arranged in a series of events; in this series the single events which we remember appear to be ordered according to the criteria of "earlier" and "later", which cannot be analyzed further. There exists, therefore, for the individual, an I-time, or subjective time."
"The non-divisibility of the four-dimensional continuum of events does not at all, however, involve the equivalence of the space coordinates with the time coordinate."
"Finally, with Minkowski, we introduce in place of the real time co-ordinate l=ct, the imaginary time co-ordinate..."
Edited by sluggo, 16 June 2019 - 11:58 AM.