The Minkowski formula X4=ict indicates that time t does not express the 4th dimension of space-time, i.e., X4 is not t. Therefore, Minkowski space-time is not a 3D+T manifold, it is 4D. The 4D manifold has 4 spatial dimensions and is timeless, in the sense that it does not contain some physical time in which material changes run. In physics we experience the timelessness of 4D space as “Einstein’s Now.” From this perspective, the time that we measure with clocks is just the sequential numerical order of changes, i.e. motions that run in the timeless space of Now. On the other hand, past and future are nothing more than psychological or conceptual realities that derive from the neuronal activity of the brain. Therefore, “time flow” and “arrow of time” have only a mathematical existence.

Now, Time, Space, Space-Time, GPS, Closed Timeline Curve, Arrow of Time