So that is what Time is!
Now I get it it!
A Eureka moment!
In an absolutely sterile, environment time does not exist.
Time doesn’t exist of itself, it is created as an effect by processes.
The interval between the start and the end of a process, its Duration is the time created by that process.
Time cannot exist on its own, there has to be something happening, i.e. some kind of process to create time.
Time can only be measured by comparison to other times created by other processes.
That is why we set standards on the Macro scale, e.g. the life of the universe, since the Big Bang, or on the Pico scale, e.g. regular nuclear processes.
Every Event in Spacetime occurs at some unique point in time within the life of the Universe that contains the whole of Spacetime.
If two events occur at the same point in time but at different locations they will be simultaneous wherever they are observed from. That must be an inevitable conclusion from Minkowski’s theory of Spacetime.
Time cannot speed up nor slow down, it is the processes that create time that are measured to run faster or slower, yet the total time they create is still the same.
The measure of Time, the magnitude of the units multiplied by the quantity of the units, what I would call the Absolute Time of a process is constant and unchanging; yet the magnitude of each unit will vary depending on how and from where and by whom it is measured.
Processes create change. Time is created by change. Therefore Time travel back in time cannot be possible; once a time has passed change has occurred and the only way that time might exist to travel back to is for every change to be undone, to be reversed.
So, Time does not exist as a self contained entity, but only as a product of change and is only measured by comparison to other times.
Time cannot vary, yet every observer may measure time differently depending on their perspective and the conditions under which they measure it.
And the irrefutable logic that proves backward time travel impossible is that recreating exactly a former time is in itself a change, in the same way that the return of a pendulum might be considered. Only the count of swings of the pendulum would increase meaning further change rather than change undone.
The very act of time travel being a process would create more time not undo it, so the process of time travel would inevitably take one forward rather than backward in time.