Recent content by gentleboy

each time when I tried to submit the revision, the web kept saying it is too short, need to lengthen it to at least 4 characters, i do not know what does that mean.

suppose we have unit vector z=(0,0,0,1), we can use it to form a tensor z^\mu z^\nu , it is easy to check that ∂_\μ( z^\mu z^\nu=0 in Minkowski spacetime, now I want to generalize this equation to general curved spacetime, so that ∇μ ( znew^\mu znew^\nu)=0. But I am not sure how to...