
Still no violation of Lorentz symmetry, despite strongest test yet - dnetesn
http://phys.org/news/2016-12-violation-lorentz-symmetry-strongest.html
======
eln1
Lorentz invariance appears naturally in practically all theories with waves -
its violation would be a huge surprise.

To see it, understand STR, the perfect model is sine-Gordon: just many coupled
pendula - we get particles ("kinks") with rest mass, which are
created/annihilated in pairs, the mass grows exactly like in STR and is
released while annihilation ... while moving these particles undergo Lorentz
contraction (speed is limited by speed of massless waves) and oscillating
particles ("breathers") slow down (time dilation) - exactly like in STR.

[https://en.wikipedia.org/wiki/Sine-
Gordon_equation](https://en.wikipedia.org/wiki/Sine-Gordon_equation)

"Universe model with a drill" ;)
[https://www.youtube.com/watch?v=nl5Qq5kUbEE](https://www.youtube.com/watch?v=nl5Qq5kUbEE)

Animation of kink-antikink annihilation:
[https://en.wikipedia.org/wiki/Topological_defect#Images](https://en.wikipedia.org/wiki/Topological_defect#Images)

~~~
hansen
There are lots of non-relativistic models using waves. Nothing special about
them. The most compelling argument for relativity is causality. You can
reconstruct spacetime – up to conformal transformations – just from the
causality relations. I can’t even imagine what physics would be like w/o
causality.

~~~
valarauca1
GR does not imply causality nor does it enforce it. In fact GR works in a non-
causal universe without a problem.

2 very sensitive measurements conducted within the past year seem to suggest
(if GR is true), that we are in a universe that lacks causality. 2/3 LIGO
detections imply one of the merging pair of black holes _should_ be a naked
singularity.

GR allows naked singularities. It models them fine. GR just stops being
_globally deterministic_.

If you look up the history of GR some mathematicians in 50's made some _really
weird_ proposals for non-causal universes that would _appear_ locally causal.
But there isn't a way to test this. So it is more pure mathematics or
philosophy then physics.

~~~
eaq
> 2/3 LIGO detections imply one of the merging pair of black holes should be a
> naked singularity.

Where did you get this impression? All of the LIGO results are consistent with
"standard" GR black holes whose event horizons merge.

~~~
andrewflnr
Possibly referring to this? [http://physics.aps.org/synopsis-
for/10.1103/PhysRevLett.116....](http://physics.aps.org/synopsis-
for/10.1103/PhysRevLett.116.171101)

Background:
[https://en.wikipedia.org/wiki/Gravastar](https://en.wikipedia.org/wiki/Gravastar)

~~~
eaq
Thanks for the links. I find it unfortunate that often in science (and
especially with the LIGO data) much is written about what could possibly be
lurking in the data but isn't actually favored over our current understanding.

This creates more interest, but can obfuscate what the real situation in the
field is. In this case, while Gravastars are certainly something many
scientists actively do and should consider, there is no real evidence from the
LIGO data that favors the hypothesis of "we are in a universe that lacks
causality" over the observation of the merger of two Kerr black holes.

~~~
andrewflnr
I think you're being a bit harsh. Is there any empirical evidence that favors
classic black holes over gravastars, or is our "current understanding" just a
matter of what we thought of first? If the latter, take a chill pill and let
us enjoy the possibilities. :)

~~~
raattgift
> Is there any empirical evidence that favors classic black holes over
> gravastars

Yes.

[http://journals.aps.org/prd/abstract/10.1103/PhysRevD.94.084...](http://journals.aps.org/prd/abstract/10.1103/PhysRevD.94.084016)
(preprint:
[https://arxiv.org/abs/1602.08759](https://arxiv.org/abs/1602.08759))

So you're still left with gravastar models that can co-exist with black holes.

------
jameskilton
Relevant piece of information as to why this is important:

> "Furthermore, so far, it has been impossible to conciliate in one common
> theory these two aspects of physics. To succeed in this quest, almost all
> unification theories predict a breaking of Lorentz symmetry."

~~~
cdetrio
Hmm, does this relate to the article from 6 days ago about the inability to
find proton decay?
[https://news.ycombinator.com/item?id=13201065](https://news.ycombinator.com/item?id=13201065)

------
tzs
Is there a conservation law associated with Lorentz symmetry, the way there
are conservation laws associated with other symmetries in physics
(conservation of energy from symmetry under translation in time, conservation
of angular momentum from symmetry under rotation, conservation of linear
momentum from conservation under translation in space, and so on)?

~~~
moefh
Lorentz symmetry is associated with conservation of center of mass, see [1]

(Note that it's actually talking about Lorentz symmetry _without_ rotations
(called "Lorentz boosts"), because rotations are associated with another
conservation, as you mentioned.)

[1] [http://physics.stackexchange.com/questions/12559/what-
conser...](http://physics.stackexchange.com/questions/12559/what-conservation-
law-corresponds-to-lorentz-boosts)

~~~
raattgift
That's true for the Lagrangian written down in the excellent answer at
stackexchange, but the equivalent Lagrangian of the Standard Model Extension
(SME) (which is what is the topic of the Bourgoin et al. paper) is filled with
additional terms.

For example, a minimal SME photon Lagrangian is developed in section II. A. of
Kostelcky and Mewes @
[https://arxiv.org/abs/0905.0031](https://arxiv.org/abs/0905.0031)

The difference between a minimal SME (mSME) and the full SME is that the
latter admits terms of any mass dimension greater than two, while mSME
requires power-counting renormalizability (in order to be an effective field
theory) so mSME admits only terms of dimension four. As a result mSME can only
have a finite number of Lorentz invariance violation parameters, while SME can
have an infinite number of them.

The bright side is that mSME can represent locally the Lagrangian in the
physics.se answer you link to with a fixing of parameters; the dim side is
that in general one does not want to do this a priori, precisely because the
mSME is a tool to investigate whether the Lorentz SO(3,1; R) group is an exact
feature of nature at every point, rather than postulating that it is (as the
Standard Model does, and indeed as Special Relativity and General Relativity
do).

For example, SME is useful for dealing with things like this:
[https://www.wikiwand.com/en/Bumblebee_models#/Lagrangian](https://www.wikiwand.com/en/Bumblebee_models#/Lagrangian)
where the non-matter term might not reduce (via GL(4, R)) to the groupoid of
local coordinate transforms on the manifold and the local SO(3, 1; R) Lorentz
group on the orthonormal frames (tetrad formalism) which are the symmetries of
General Relativity. The point is to find out under what conditions any such
model does vary from General Relativity. (We already have a good EFT for GR
itself, and the result of the Bourgoin et al. paper is that it remains good.)

~~~
raattgift
Half-jokingly one could say that what's conserved under the transformations of
Lorentz group of the SME is the behaviour of the Standard Model under changes
to the physics of gravity. A bit less jokingly, that corresponds fairly well
to conserving the microscopic description of the centre of mass-energy-
momentum rather than just the centre of mass-energy-momentum (at t=0 for some
total energy) as in phys.se answer in the GP comment.

------
raattgift
preprint: [https://arxiv.org/abs/1607.00294](https://arxiv.org/abs/1607.00294)

