# Name of general relativity symmetry

1. Nov 13, 2012

### snorkack

People seem to be seriously looking for "Lorentz violating" neutrino oscillations - meaning direct violation of special relativity.

What is a short name for the symmetry that distinguishes general relativity from special (the symmetry between acceleration and gravity)?

2. Nov 13, 2012

### PAllen

I don't see the connection between the first part of post and the second. GR is locally Lorentz invariant. Globally (depending on some definitions or conventions), speed of light or neutrinos can be affected by gravity. This is not normally considered an SR violation because it is a consequence of gravity (see Shapiro time delay).

So far as I know, neutrino oscillations that violate SR also violate GR.

It might help if you have a reference to the searches you are discussing.

[You often hear that GR is diffeomorphism invariant. But so is SR. Further, event Newtonian gravity can be expressed in a way that is diffeomorphism invariatn - see Newton-Cartan theory.]

3. Nov 14, 2012

### Staff: Mentor

GR implies SR, so every violation of SR is a violation of GR.

4. Nov 14, 2012

### snorkack

Indeed. But not vice versa.

What would be the term for phenomena which violate the symmetry between gravity and acceleration?

5. Nov 14, 2012

### PAllen

Ok, now I see: that is the Principle of Equivalence.

It is not an exact principle, without a bunch of qualification (locality of measurement and locality of interaction and not measuring second derivatives of certain quantities).

An example of global interaction is a charged body interacting with its distant field. This distinguishes a charge sitting on a gravitating body (doesn't radiate) from a uniformly accelerating charge (does radiate). [There is some controversy on this, but this is the consensus opinion.] Another, is where gravitational radiation comes into play.

The 'type' of measurement comes into play because curvature does not vanish even at one point; so certain types of devices (theoretical, mostly) could distinguish uniform acceleration from gravity on any scale, however, small. One way around this is to say that acceleration is indistinguishable from 'uniform gravity' which doesn't really exist except as a limit.

In any case, a violation of the principle of equivalence outside of these known limitations would be a major discovery.