- #1
Fraser
- 3
- 0
Hi all,
I'm trying to follow through some of my notes of a GR course. The notes are working towards a specific expression and the following line appears:
[tex]R^{\alpha \beta}_{\gamma \delta ; \mu} + R^{\alpha \beta}_{\delta \mu ; \gamma} + R^{\alpha \beta}_{\mu \gamma ; \delta}=0[/tex]
Which by contraction over [tex]\alpha[/tex] and [tex]\gamma[/tex] becomes
[tex]R^{\alpha \beta}_{\alpha\delta ; \mu} + R^{\alpha \beta}_{\delta \mu ; \alpha} + R^{\alpha \beta}_{\mu \alpha; \delta}=0[/tex]
I'm afraid I don't understand this, it seems to relabel [tex]\gamma[/tex] with[tex]\alpha[/tex]. But how can we do this?
I do understand contraction in general, such that for a general tensor
[tex]T^{\alpha}_{\beta}=T^{\rho \alpha }_{\beta \rho} [/tex]
But I don't see how this has been applied here?
Thanks in advance
p.s If this is more of a general maths question then please move to the appropriate forum
I'm trying to follow through some of my notes of a GR course. The notes are working towards a specific expression and the following line appears:
[tex]R^{\alpha \beta}_{\gamma \delta ; \mu} + R^{\alpha \beta}_{\delta \mu ; \gamma} + R^{\alpha \beta}_{\mu \gamma ; \delta}=0[/tex]
Which by contraction over [tex]\alpha[/tex] and [tex]\gamma[/tex] becomes
[tex]R^{\alpha \beta}_{\alpha\delta ; \mu} + R^{\alpha \beta}_{\delta \mu ; \alpha} + R^{\alpha \beta}_{\mu \alpha; \delta}=0[/tex]
I'm afraid I don't understand this, it seems to relabel [tex]\gamma[/tex] with[tex]\alpha[/tex]. But how can we do this?
I do understand contraction in general, such that for a general tensor
[tex]T^{\alpha}_{\beta}=T^{\rho \alpha }_{\beta \rho} [/tex]
But I don't see how this has been applied here?
Thanks in advance
p.s If this is more of a general maths question then please move to the appropriate forum