At 14 mins and about 30 seconds into the Royal Institute lecture below, Professor Sean Carroll refers to the t coordinate in Minkowski space-time as ‘floating somewhere in the background of your mind’.
However, as it is a coordinate, surely it must have a location in time and / or space?
I think Professor Carroll is unable to define it any further because he is unable to consider the possibility of Absolute Time. Consequently, he cannot say where it is and so fudges the issue.
I believe that the t coordinate has a very physical reality within my Theory of Universal Absolutivity, and that it lies at rest on the ever-expanding 2D membrane of Absolute Time in which the 4D (Relative) space-time universe resides.
My thinking here is that tau is a variable whereas t is an Absolute Time co-ordinate.
As Professor Carroll expains, Minkowski space-time is embedded within Einstein’s equation for gravity e.g. within the metric tensor:

Therefore, it seems to me to be logical to assume that Absolute Time is implicit within the equations of both Einstein and Minkowski despite the latter’s declaration that:
“Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality”
My interpretation of the our reality is, therefore, 5 Dimensional. There is the Relative dimension of 4D space-time, and a 5th dimensional space of Absolute Time through which the 4D space-time universe travels. This is how we are able to progress nano-second by nano-second into the future.
Einstein was not wrong. How could he be? He had alien intelligence, possessing insights into the macro universe way beyond any other human. But, he was also … only partially correct.
Absolute Time, as has been automatically assumed for centuries, is still the Ultimate Reality!