Have any of the new predictions made by LQG been experimentally verified?

Question

A wikipedia template lists under the heading "fully compatible with observation": Einstein-Cartan theory, Gauge theory gravity, Teleparalleism and Euclidean Quantum Gravity.

Does this claim generally mean that:

• the specific, new predictions (disagreeing with classical general relativity) these theories make are confirmed experimentally?
• or just that they reduce to classical general relativity in all the tests done so far/do not contradict any experimental evidence?

Certainly What I find particularly odd is that string theory is not listed under "fully compatible with observation" but rather "disputed" -- which would be at odds with the second, weaker interpretation (since general relativity arises as an effective theory of string theory at the low-energy classical limit).

To add to the confusion, Loop Quantum gravity is listed under "Experimentally constrained", although it contradicts Lorentz symmetry 1. I suppose similar comments apply to "BEC vacuum theory".

Can anyone make any sense out of what these terms mean here?

Answer 1

What I understand by "Fully compatible with observation" is that all its predictions are confirmed by experiments and it has been found to be more accurate than General Relativity.

No, the standard interpretation of this phrase would be that it's not contradicted by any observation.

Re Einstein-Cartan, Trautman 2006 has some relevant remarks at p. 6, with a numerical estimate showing why the theory gives the same results as GR under conditions we have access to.

However, as far as I know, Loop Quantum Gravity violates Lorentz symmetry and has thus been experimentally "excluded"

No. As far as I know, it is still an open question whether LQG's semiclassical limit is GR. People working on it certainly hope that it is. If it is, then it is consistent with Lorentz invariance under currently accessible experimental conditions. There was some hope a while back that it could be tested through searches for dispersion of the vacuum, but it turns out that that was Smolin's incorrect interpretation of the theory.

Trautman, "Einstein-Cartan Theory," http://arxiv.org/abs/gr-qc/0606062

Answer 2

"Fully compatible with observations" is a rather vague statement. Actually, two aspects of adequacy to reality have to be distinguished when a new theory reaches a degree of explicitation. These are

• compatibility with older theories, in domains where the new theory is not supposed to bring more than a new formulation. For instance, special relativity is compatible with newtonian mechanics when velocities are small compared with c. Since older theories taken in reference have been usually thoroughly tested (otherwise you don't take them as reference), this is a good first check for your new theory.

• compatibility with new phenomena. Indeed what makes a new theory interesting is the change of insight that it might bring on reality. And this means that beyond proposing a new description of reality, it shall predict new observable features which older theories don't account for.

As far as LQG is concerned, my understanding is that the first aspect has been addressed in the sense that right from the outset, conpatibility with GR has been used as a guide to develop the theory. For the second aspect, this one of the topics which focuses a good part of the efforts of the LQG community. This means finding new observable features that survive going from the Planck scale to the scales that are accessible to us in experiments or astrophysical observations. It's tricky but not impossible.

So as far as the statement "fully compatible with observations", I would advise to replace it with "compatible with previous observation-tested theories, but still expecting genuine experimental predictions for testing".

Answer 3

None of the links in the first paragraph say that the article in question is "fully compatible with observations".

• Einstein–Cartan theory: not undisputed, in particular it does not fully address the issue of quantum gravity.

• Gauge theory gravity: not undisputed, in particular it clearly states: "The theory has not been widely adopted by the rest of the physics community, who have mostly opted for differential geometry approaches like that of the related gauge gravitation theory.".

• Teleparalleism: a few other theories are presented upon the very page.

• Euclidean quantum gravity: contains a link to Gauge theory.

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Can this template at Wikipedia be true? It seems to suggest that Einstein-Cartan theory, Gauge theory gravity, Teleparalleism and Euclidean Quantum Gravity are fully compatible with observation

The "template" was "true", because it was automatically generated, it has been replaced with a new Navbox (which you refer to as a template). A template is the boilerplate which defines the shape and appearance of the object, a Navbox is the list of links related to the article.

Etymology

Shortening of navigation and box.

Noun

navbox (plural navboxes)

(Wiktionary and WMF jargon) A navigation box; a template placed on a page, outputting a box containing links to other, related articles.

• It is simply links to other pages

• It does not imply endorsement or acceptance of information contained on said pages.

It also suggests that Loop Quantum Gravity and BEC Vacuum Theory among others, are experimentally constrained whereas string theory/M theory are disputed!

You can find someone who would disagree with just about anything. On another stack exchange site someone with an extremely high reputation score proceeded to dispute what they had wrote one comment prior, flipping back and forth between supporting what was written in an answer (that had no editing) and taking issues with it and their prior comments. They resorted to extremes and gross exaggeration to encourage one to accept their point.

Wikipedia is maintained to be neutral and discourages conflict of interest editing. Understand correctly, I neither say that everything on Wikipedia is correct nor that nothing is either not disputed nor agreed upon - the point being made is that "navigation links" do not imply endorsement nor support or disprove content.

Content must be based upon what is known and attempt to present it neutrally, if you have a dispute with a specific page you are free to edit it.

...

"What I understand by "Developmental/Disputed" is that it is still ..."

Wikipedia has a webpage titled: "Alternatives to general relativity" which describes: Self-consistency, Completeness, Classical tests, Agreement with Newtonian mechanics and special relativity, The Einstein equivalence principle (EEP), Parametric post-Newtonian (PPN) formalism, Strong gravity and gravitational waves and Cosmological tests (amongst others) as tests that ought to be met for a theory to gain acceptance.

The "observational test" seems to imply: "It looks good".

So my question is "Is this template really reliable?"

I'm not trying to pick on you. Indeed I mentioned someone else in particular, more than once.

The information presented is only as good as it's interpretation and factualness.