GR Contest: Uncovering the First Evidence of Revision

[David]

You might be interested in the contest that ran at the SLAC Summer Institute this year that asked: "What will be the first evidence to demonstrate that Einstein's theory of General Relativity (GR) must be revised, and when will that be found?"

The http://www.symmetrymagazine.org/cms/?pid=1000189" are in the new symmetry magazine out today.

 

[Garth]

Hi David!

What will be the first evidence to demonstrate that Einstein's theory of General Relativity (GR) must be revised, and when will that be found?

It might be said that the need for GR cosmology to invoke Inflation when the Higgs boson has not been found, DM when the DM particle cannot be found and DE when that cannot be demonstrated in a laboratory (at least to within a factor of 10¹²⁰ or so!) are indications that GR must already be revised. Furthermore the Pioneer anomaly may also be an indication.

However for a controlled experiment I put my money on Gravity Probe B. BTW do you have any feelers over there in Stanford about what they are finding? They are playing their cards very close to the chest!

Garth

 

[David]

I think they're still doing the analysis for GP-B, actually. I don't have any inside information at the moment, sorry.

 

[selfAdjoint]

DM when the DM particle cannot be found

I don't think GR theorists or cosmologists do that; astronomers do, using only Newtonian gravity. As you of course know, the GR people have tried recently to explain this as not DM at all but a nonlinear GR effect.

 

[SpaceTiger]

I don't think GR theorists or cosmologists do that; astronomers do, using only Newtonian gravity. As you of course know, the GR people have tried recently to explain this as not DM at all but a nonlinear GR effect.

I think the majority of "GR people" (particularly cosmologists) would be highly offended to be grouped together with the folks who wrote that paper. Unless GR is wrong in the cosmological limit, there's nothing wrong with using a Newtonian approximation to study dark matter.

 

[selfAdjoint]

I think the majority of "GR people" (particularly cosmologists) would be highly offended to be grouped together with the folks who wrote that paper. Unless GR is wrong in the cosmological limit, there's nothing wrong with using a Newtonian approximation to study dark matter.

Whether it is all right to use Newtonian gravity in these galaxy studies is surely a matter for scientific determination, not edict. I don't see why you think the paper is shocking or would be declasse to GR workers. The scenario where the rotation profiles are the result of nonlinear GR and the observations of matter in the core of the galaxies is something else is surely not outrageous on the face of it?

 

[Garth]

Furthermore, in the case of the galaxy where the mass is in orbit, the non- linear terms are to be expected to be significant, in contrast to the solar system case, where the mass is in the Sun and the planets are treated as test particles, which can be treated in the linear Post-Newtonian approximation.
The fact the the Cooperstock & Tieu paper General Relativity Resolves Galactic Rotation Without Exotic Dark Matter has been criticised by Mikolaj Korzynski in Singular disk of matter in the Cooperstock and Tieu galaxy model because it assumes an infinitely thin disc of matter does not negate the whole concept of the galaxy's rotation curve being explained by the baryonic matter. Their analysis may not be perfect, nevertheless such a distribution of mass makes an approximate model of the real galaxy which does have a disc and bulge distribution of matter.
Garth

 

[SpaceTiger]

Whether it is all right to use Newtonian gravity in these galaxy studies is surely a matter for scientific determination, not edict. I don't see why you think the paper is shocking or would be declasse to GR workers.

Because it's wrong. See this thread for a link to a rebuttal paper:

https://www.physicsforums.com/showthread.php?t=93486"

We also discuss why the idea was implausible based on other observations.

The scenario where the rotation profiles are the result of nonlinear GR and the observations of matter in the core of the galaxies is something else is surely not outrageous on the face of it?

I find it extremely hard to believe that physicists would have missed something as basic as this for so long. I'm not quite sure what you mean by the latter part of the question, however. Are you referring to the possible annihilation signatures from WMAP? I would say that's far from being the strongest evidence for dark matter.

 

[Garth]

I find it extremely hard to believe that physicists would have missed something as basic as this for so long.

That is a good point. GR is a non-linear theory, the Post Newtonian Approximation, used in the solar system tests is a linearised approximation to it. As I have already said, where the mass is in orbit, rather than all at the centre, the non-linear terms could well become significant.

So far this is obvious to any relativist, so is the Cooperstock and Tieu paper the first GR analysis of galactic rotation profiles? I find it very hard to believe that it can be; therefore does anybody know of any previous work, maybe now very 'ancient', which has examined the case and concluded the non-linear effects are in fact not significant? I do not know of any.

Garth