Question

What is the velocity of the light through spacetime?

Answer 1

Light only has spatial velocity. It has zero temporal velocity.
The less spatial velocity we have, the more temporal velocity we have.
The sum of these two velocities is a universal constant. So far, however, it doesn't have a name

Complete answer:
The speed of light, in a vacuum, is one: one light-year per year, one light-nanosecond per nanosecond.
When traveling through matter, a light goes slower. The velocity of light is a vector that includes the direction the light is going. Speed of light in a vacuum is a defined thing in the universe.
Some physics’ important laws like Einstein’s mass-energy equivalence equation ($E = m{c^2}$) and concepts like space-time are closely related to this constant. It is the most important because nothing can travel at a speed greater than $c$ .
Since it is a physical constant, some of the metric units are defined using this constant like meter(the distance traveled by light in a vacuum in $\dfrac{1}{{299792458}}$ of a second), foot(Distance traveled by light in $E = m{c^2}$ $1.0ns$), etc.
Finally, The speed of the light in a vacuum is $186,282\;$miles per second which refers to$\;299,792\;km$ per second.
By theory, nothing can travel faster than the speed of light it travels $670,616,629{\text{ }}mph$in kilometers

Note: The speed of the light is reduced in any medium compared to its speed in a vacuum.
The speed of the light remains a constant inhomogeneous medium.
The speed of the light decreases when it enters into the denser medium.