# Lorentz or Poincare invariant?

1. Aug 25, 2009

### xiaomaclever

Generally we say GR is local Lorentz invariant. Does it mean the action or field equation?
Why not Poincare invariant? Thanks!!

2. Aug 25, 2009

### javierR

The action (not only in GR but in the standard model) has local Lorentz symmetry, while the field equations, with spacetime tensors for its terms, are covariant (when we write a solution to the field equations, we have to pick a reference frame to write it in, so they must not be *invariant* equations, right?). The Poincare group includes translations, but spacetime does not "look the same" at different points...just from different local Lorentz frames. So no Poincare symmetry. However, a special solution to the field equations does have Poincare invariance: Minkowski.