In the theory of #specialRelativity, time (t) and the well-known spatial coordinates (x, y, z) are all treated equally. Just as particles can have physical quantities in space such as position, velocity, momentum, acceleration, etc. Particles can also have a component of these quantities along the time axis. Indeed everything we see is moving all the time, even the stationary bodies. Stationary bodies are stationary in space (with respect to us only), but they move all the time along the time axis.