Confusion on Bianchi Identity proof

In summary, the proof for the equation \nabla_{[a} {R_{bc]d}}^e=0 is as follows: in a coordinate system where \Gamma^a_{bc}=0 at the event, we have \nabla_a {R_{bcd}}^e = \partial_a \partial_b \Gamma^e_{cd} - \partial_a \partial_c \Gamma^e_{bd} + \textrm{ terms in } \Gamma \partial \Gamma \textrm{ and } \Gamma \Gamma \Gamma. Since the first and second terms are symmetric in ab and ac, respectively, and the other terms vanish at the event, the equation holds in this coordinate
  • #1
Dazed&Confused
191
3
This is from a general relativity book but I think this is the appropriate location.

The proof that [tex]
\nabla_{[a} {R_{bc]d}}^e=0[/tex]
is as follows:

Choose coordinates such that [itex] \Gamma^a_{bc}=0[/itex] at an event. We have [tex]
\nabla_a {R_{bcd}}^e = \partial_a \partial_b \Gamma^e_{cd} - \partial_a \partial_c \Gamma^e_{bd} + \textrm{ terms in } \Gamma \partial \Gamma \textrm{ and } \Gamma \Gamma \Gamma.[/tex]

Because the first term on the right-hand side is symmetric in [itex] ab[/itex] and the second in [itex] ac [/itex], and because the other terms vanish at the event, we have [tex]
\nabla_{[a}{R_{bc]d}}^e=0[/tex]
at the event in this coordinate system. However, this is a tensor equation, so it is valid in every coordinate system.

The bit I'm unsure of is how ''the other terms'' vanish at the event, so help would be appreciated.
 
Physics news on Phys.org
  • #2
"The other" terms have the Christoffel symbols as a factor and the Christoffel symbols are all zero because of the choice of coordinates. (You can always find such coordinates for any given event.)
 
  • Like
Likes Dazed&Confused
  • #3
Thanks I think I had a mental block because of the index notation.
 
Last edited:

1. What is the Bianchi Identity?

The Bianchi Identity is a mathematical expression that relates the curvature of a space to its topology. It is used in the study of differential geometry and general relativity.

2. What is the significance of the Bianchi Identity in physics?

In physics, the Bianchi Identity is used to prove that the Einstein field equations, which describe the gravitational field in general relativity, are consistent with the conservation laws of energy and momentum.

3. How is the Bianchi Identity proved?

The Bianchi Identity is proved using differential forms and the exterior calculus. It involves manipulating equations and using properties of differential forms to arrive at the final expression.

4. What are the applications of the Bianchi Identity?

The Bianchi Identity has various applications in physics and mathematics. It is used in general relativity to understand the behavior of gravitational waves and black holes. It is also used in the study of differential geometry and topology.

5. Are there any alternative proofs of the Bianchi Identity?

Yes, there are alternative proofs of the Bianchi Identity using different mathematical techniques such as tensor calculus and Lie derivatives. These proofs may be more intuitive for some individuals and are often used in different contexts.

Similar threads

Replies
7
Views
1K
  • Differential Geometry
Replies
1
Views
1K
Replies
4
Views
954
  • Advanced Physics Homework Help
Replies
4
Views
2K
  • Special and General Relativity
Replies
1
Views
1K
  • Advanced Physics Homework Help
2
Replies
36
Views
3K
  • Special and General Relativity
Replies
13
Views
879
  • Sticky
  • Special and General Relativity
Replies
15
Views
6K
  • Differential Geometry
Replies
7
Views
3K
  • Differential Geometry
Replies
5
Views
2K
Back
Top