So I have the following:
First of all X ist defined in terms of (x,y,z,t). Is is also possible to define it in terms of (t,x,y,z) with t being mu=0.
When I do
this applies only to this one vector and
d_ is still the time differentiation, right?
Then I wanted to construct the divergence
This should give me sth like d1 A1 + ... + d4 A4, but it stays with d_mu A_mu ?!?
Is there also a "function" which does the contraction?
So if I have