🚀 go-pugleaf

gast@next.ben-fh.tuwien.ac.at (Gast) writes:

>The article was a prety good overview about the subject of four-vectors.  
>Yet, two short remarks:

>Remark 1:
>If you don't set c=1, the coordinates of a point in a Minkowsky-space are  
>(if any doubt, consider the units):

> a
>x = (ct,x,y,z)  (a is an upper index)

>Therefore the transfromation above has to be

>   x -> x' = x cosh phi   + ct sinh phi
>   t -> t' = x/c sinh phi +  t cosh phi 

Right... I should have been more explicit about that.
Through the whole article I'm setting c=1 except where I explicitly
put it in.  But I put it in when I discussed the values of cosh
and sinh phi, which was a little inconsistent.

>Remark 2:
>Because of the metric there are two kinds of coordinates neccessary.
[description of covariant and contravariant vectors]

Right again... *that* I was omitting intentionally for simplicity;
what I call four-vectors are always "upper-index" or contravariant
vectors, in the article, except in the one spot where I define
a lower-index vector.

This becomes far more important in GR.

-- 
Matt McIrvin   mcirvin@husc.harvard.edu   Long live short .sigs