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## Main Question or Discussion Point

When reading through this paper(http://www2.warwick.ac.uk/fac/sci/physics/current/teach/module_home/px436/notes/lecture20.pdf), I have trouble understanding some parts of it,

1. Is the r in ρ=Rr a unit vector?

2. it shows x^2 + y^2 + z^2 + w^2 = ρ^2 + w^2 = R^2 but isnt ρ=Rr, thus isnt p^2 itself already R^2?

3. Why is w used for the time component? Is this w the angular frequency?

1. Is the r in ρ=Rr a unit vector?

2. it shows x^2 + y^2 + z^2 + w^2 = ρ^2 + w^2 = R^2 but isnt ρ=Rr, thus isnt p^2 itself already R^2?

3. Why is w used for the time component? Is this w the angular frequency?