Will we ever have an viable alternative Theory to rival GR?

[beecee]

My interest in asking the above question was raised after reading the following article from "Quanta Mag"

OK as the heading asks, will we ever have a viable alternative to GR? 

https://www.wired.com/story/troubled-times-for-alternatives-to-einsteins-theory-of-gravity/ [05/06/2018]

TROUBLED TIMES FOR ALTERNATIVES TO EINSTEIN’S THEORY OF GRAVITY:

Miguel Zumalacárregui knows what it feels like when theories die. In September 2017, he was at the Institute for Theoretical Physics in Saclay, near Paris, to speak at a meeting about dark energy and modified gravity. The official news had not yet broken about an epochal astronomical measurement—the detection, by gravitational wave detectors as well as many other telescopes, of a collision between two neutron stars—but a controversial tweet had lit a firestorm of rumor in the astronomical community, and excited researchers were discussing the discovery in hushed tones.

Zumalacárregui, a theoretical physicist at the Berkeley Center for Cosmological Physics, had been studying how the discovery of a neutron-star collision would affect so-called “alternative” theories of gravity. These theories attempt to overcome what many researchers consider to be two enormous problems with our understanding of the universe. Observations going back decades have shown that the universe appears to be filled with unseen particles—dark matter—as well as an anti-gravitational force called dark energy. Alternative theories of gravity attempt to eliminate the need for these phantasms by modifying the force of gravity in such a way that it properly describes all known observations—no dark stuff required.

 

much more at link......

I am interested in more than a yes or a no to my question. I've been reading stuff on MOND and other alternative gravity theories such as TeVeS (tensor-vector-scalar) and others.

Here is one such paper......

https://arxiv.org/pdf/1804.03520.pdf

GW170817 event rules out general relativity in favor of vector gravity? (Dated: April 11, 2018)

The observation of gravitational waves by the three LIGO-Virgo interferometers allows for the first time the examination of the polarization of gravitational waves. Here we analyze the binary neutron star event GW170817, whose source location and distance are determined precisely by concurrent electromagnetic observations. Applying a correlation averaging algorithm to the LIGOVirgo strain data, we find ratios of the signals detected by the three interferometers. We conclude that signal ratios are inconsistent with general relativity, but consistent with the recently proposed vector theory of gravity [Phys. Scr. 92, 125001 (2017)]. Moreover, we find that vector gravity yields a distance to the source in agreement with the astronomical observations. If our analysis is correct, Einstein’s general theory of relativity is ruled out in favor of vector gravity and future gravitational wave detections by three or more observatories should confirm this conclusion.

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My complete understanding is obviously limited in that I am not a professional. So I hope that some of the experts on this forum whose knowledge  I have grown to respect will take the time to read the full article and offer comments on that article, my question, and the paper above.

My view? Not for a while yet....The paper seems to make plenty of assumptions that will probably never be able to be tested and as such of course its validity must be questioned. What is this inconsistency it mentions in the Abstract?

 

 

 

Edited June 23, 2018 by beecee

[koti]

We know for a fact that GR is an incomplete theory in the context of a plausible GUT but I would say that there will never be an alternative theory to GR, it hopefuly will be broadened and supplemented with new insight enabling understanding of quantum gravity but there can be no alternative, its there and it works, it just doesn’t explain things beyond it. Having said that, I have to confess I haven’t read the wired and the arxiv articles yet  

[beecee]

28 minutes ago, koti said:

We know for a fact that GR is an incomplete theory in the context of a plausible GUT but I would say that there will never be an alternative theory to GR, it hopefuly will be broadened and supplemented with new insight enabling understanding of quantum gravity but there can be no alternative, its there and it works, it just doesn’t explain things beyond it. Having said that, I have to confess I haven’t read the wired and the arxiv articles yet  

Yep, I agree with that summation. Same actually applies to Newtonian. We cannot say that its wrong as we use it everyday here on earth and as well as space endeavours. GR gives the same results with far more accuracy. Much as using a rule to measure a window frame rather then a set of Vernier calipers. 

I'm interested though in further comment on this  TeVeS (tensor-vector-scalar gravity and the supposed claims it is making re GR inconsistencies.  My view much froth and bubble with not much actual experimental substance and obviously apparently not too much interest with the scientific community in general, which in my book says a lot. 

[MigL]

Any large scale modified gravity  ( TeVeS is a re-worked MOND ) has mostly been put to rest by the recent Gravitational wave detections.

GR is a geometric model, and as such, can only be quantized by quantizing space-time, as LQG attempts.
That doesn't mean that a return to a field model will forever resist quantization, or that an entirely new approach, such as M-theory won't yield the desired results.
The only requirement is that each model reduces to the others ( gives equivalent results ) at the appropriate boundaries.

 

 

 

[Markus Hanke]

There is much tit-for-tat going on with regards to this. Here’s another paper that makes the exact opposite claim, i.e. that observations of this event actually rule out a large number of GR alternatives, including TeVeS:

https://arxiv.org/abs/1710.06168

ArXiv is in fact pretty much awash with papers on both sides of the divide. It is difficult for an amateur such as myself to really arrive at a conclusion, but I tend forwards GR as the model that best fits all our data about how gravity behaves. It is also the simplest possible model, and can be constructed more or less from first principles. TeVeS for example would require an extra vector field, two extra scalar fields, and an arbitrary function; that seems very ad-hoc to me, and does not easily relate back to any of our other physics models.

[Mordred]

I will be honest TeVeS never really gained much strength when it was popular. I agree that the GW waves, place an even greater unlikelyhood of TeVeS being viable. GR is still the most successful model to observation in my opinion.

[beecee]

Thanks for the answers fellas....most align with my thoughts on the matter. In essence, it  shows that scientists are forever trying to improve our knowledge and picture of the universe, and just as obviously, any overwhelmingly successful theory like GR, is not going to be easily surpassed, which is just as it should be. Anything new obviously needs to run the gauntlet before it is accepted along the lines of GR and Newtonian.

And I certainly don't believe there is any forces within mainstream science that will be uneccessarily incalcitrant in any effort to maintain GR as the status quo in the face of any evidence to the contrary. The clambering of young up and coming astronomers, cosmologists and physicists will always attest to that fact, and is borne out with the "hurried release"  of data in the BICEP2 experiment, that was shown to probably be contaminated by mainstream science itself.

 

Edited June 24, 2018 by beecee

[Markus Hanke]

8 hours ago, beecee said:

And I certainly don't believe there is any forces within mainstream science that will be uneccessarily incalcitrant in any effort to maintain GR as the status quo in the face of any evidence to the contrary.

Any genuine physicist would be excited to discover evidence of new physics - that myths of “desperately trying to maintain the status quo” that is often bandied about does not make any sense at all. So yes, there are no such forces, nor will there ever be. There is only a healthy scepticism of extraordinary claims, which is how it should be.

[beecee]

15 hours ago, Markus Hanke said:

Any genuine physicist would be excited to discover evidence of new physics - that myths of “desperately trying to maintain the status quo” that is often bandied about does not make any sense at all. So yes, there are no such forces, nor will there ever be. There is only a healthy scepticism of extraordinary claims, which is how it should be.

Bingo! There is not too many young up and coming physicists who would not give their right arm to be able to formulate a validated theory that extends beyond the accuracy and boundaries of GR, or any other model.

[beecee]

On 6/25/2018 at 4:05 PM, Markus Hanke said:

Any genuine physicist would be excited to discover evidence of new physics - that myths of “desperately trying to maintain the status quo” that is often bandied about does not make any sense at all. So yes, there are no such forces, nor will there ever be. There is only a healthy scepticism of extraordinary claims, which is how it should be.

My apologies if I posted this at an earlier time, when debating the merits or otherwise of alternative hypotheticals to GR. Sometimes, well often actually, we hear criticism of mainstream science being incalcitrant, when it is painfully obvious that this is simply a furphy at best.

  https://arxiv.org/pdf/1704.08373.pdf

Polarization-based Tests of Gravity with the Stochastic Gravitational-Wave Background:

The direct observation of gravitational waves with Advanced LIGO and Advanced Virgo offers novel opportunities to test general relativity in strong-field, highly dynamical regimes. One such opportunity is the measurement of gravitational-wave polarizations. While general relativity predicts only two tensor gravitational-wave polarizations, general metric theories of gravity allow for up to four additional vector and scalar modes. The detection of these alternative polarizations would represent a clear violation of general relativity. The LIGOVirgo detection of the binary black hole merger GW170814 has recently offered the first direct constraints on the polarization of gravitational waves. The current generation of ground-based detectors, however, is limited in its ability to sensitively determine the polarization content of transient gravitational-wave signals. Observation of the stochastic gravitational-wave background, in contrast, offers a means of directly measuring generic gravitational-wave polarizations. The stochastic background, arising from the superposition of many individually unresolvable gravitational-wave signals, may be detectable by Advanced LIGO at design-sensitivity. In this paper, we present a Bayesian method with which to detect and characterize the polarization of the stochastic background. We explore prospects for estimating parameters of the background, and quantify the limits that Advanced LIGO can place on vector and scalar polarizations in the absence of a detection. Finally, we investigate how the introduction of new terrestrial detectors like Advanced Virgo aid in our ability to detect or constrain alternative polarizations in the stochastic background. We find that, although the addition of Advanced Virgo does not notably improve detection prospects, it may dramatically improve our ability to estimate the parameters of backgrounds of mixed polarization.