My understanding is that Space and Time are manifestations of the same underlying phenomenon -in the same way as time only has meaning when a distance is measured also distance only has meaning when the time taken to measure it is accounted for (unless there are other workable theories that Space and Time are independent phenomena that interact with each other.....)

Now it has occurred to me that in the same way that a "distance" between points in "Space" can be calculated by the square root of the sum of the squares of the distances along the x,y and z axes then (since this last example is only approximate anyway) it should be equally valid and predictive to include the time dimension in the framework .

So my first stab is that the distance in Spacetime from the origin to a point(x,y,z t) could be the square root of the sum of the squares of thoseattributes(is that the right mathematical term?).

Now I can see straight away the the time units and the space units cannot be seconds and metres.Both have to be expressed in a way that is common to both.(unless metres and seconds can both be tied down to a common unit)

Is there a unit that can be applied equally to all 4 Space Time axes?What about the light nano second(or something even smaller) ? or the smallest known frequency connected to the smallest known object of known spacial dimension?

If this unit was applicable to all 4 axes would the distance in SpaceTime as calculated by ,say the square root of the sum of the roots as measured along the 4 axes give a usable or predictive result?

Would it be possible to represent acceleration using this kind of a graph?