Hi, I'm having some difficulties with my course relativity, more specifically the maths part: To begin with, what is the 'physic' difference between covariance/contravariance four-vector (if they call it like that in English?). I read that they transform the components of the Vectors, but not the Vectors themselves. Does that mean you got the same vector, but only it's components in an other basis, something like that? How do you use them in formula (like: are there different math rules to use, or are only the components different between a covariant vector and its contravariant?) The minkowski metric is same in contra-covariance, but what about other metrics, how do I change them from one to another, with the Minkowski metric or.? Or do we simply have to apply: gμvgvλ = δ(μλ) ? In my course, there is written that a transformation of an element in the Lorentzgroup can be written as: V'μ = [itex]\Lambda[/itex] μvVv What are these elements of the Lorentzgroup? What does [itex]\Lambda[/itex] stand for? Last but not least, what would be the difference between [itex]\Lambda[/itex]μv and [itex]\Lambda[/itex]μv Thanks in advance!