- #1
RiccardoVen
- 118
- 2
Reading Chandrasekhar's The mathematical theory of black holes, I reached the point in which the Newman-Penrose GR formalism is explained. Actually I'm able to grasp and understand the usage of null tetrads in GR, but The null tetrads used in this formalism, are very special, since are made by a couple or real null vectors, and another couple of complex null vector.
I'm struggling a bit in understanding the "geometric" meaning of a complex null vector, in the context of differential geometry. Actually I could take a couple of real vectors and getting their dot product using the metric. If the we take a Lorenz metric, for instance, we can use that metric and check if two 4-vectors are orthogonal having the dot product = 0.
But how a complex vector can be seen as a 4-vector? My problem is I can "see" a 4-vector as a "real vector", but how a complex vector is "embedded" into a 4D spacetime?
I have the feeling, since this refer to Penrose as well, this is something related to the spinorial description of 4D spacetime. But in the original Penrose formulation, the spinors were not there yet.
For example, we may a real null vector n and a real complex vector m, and Penrose requires their product to be 0. How this can expanded, in tensor notation, without using spinors?
How my question makes sense to you.
Thanks
I'm struggling a bit in understanding the "geometric" meaning of a complex null vector, in the context of differential geometry. Actually I could take a couple of real vectors and getting their dot product using the metric. If the we take a Lorenz metric, for instance, we can use that metric and check if two 4-vectors are orthogonal having the dot product = 0.
But how a complex vector can be seen as a 4-vector? My problem is I can "see" a 4-vector as a "real vector", but how a complex vector is "embedded" into a 4D spacetime?
I have the feeling, since this refer to Penrose as well, this is something related to the spinorial description of 4D spacetime. But in the original Penrose formulation, the spinors were not there yet.
For example, we may a real null vector n and a real complex vector m, and Penrose requires their product to be 0. How this can expanded, in tensor notation, without using spinors?
How my question makes sense to you.
Thanks