A question that is not elaborate by anyone as far as I know, because so far all experiments and more than 100m spent to disprove it have failed.
One answer is that it will leave behind it the idea that gravity is not a detached, autonomous sub-system, manifestation but something embeded in the behavior of the bfabric of the world, i.e it is of more fundamental association to universe's workings than other forces, although it might a special class of force even non standard one.
This, i believe thrvsuccesssorvto GR will incorporste these principles. In this way, it will have a greater chance of success since i believe this was Einstein's most valid assumptions that pushed his work forward, not the most celebrated ones.
That's the wrong question, now (it did make sense for a couple of years, basically until 1919, but not anymore) , because it's been understood for many years how GR fits as the description of gravitational phenomena, how it's related to Newtonian gravity and special relativity. There's no problem, anymore, with its mathematical consistency-which would be a way of showing it were wrong-nor with observations, which, however, would show that it's incomplete.
Newton's theory of gravity isn't wrong-it's incomplete. Its completion is GR.
The right question, now, is, whether GR provides a complete description of gravitational phenomena, i.e. whether the metric tensor alone determines the spacetime geometry, or, whether other fields are required, as described by scalar-tensor theories (where additional scalar fields are included) or supergravity (where additional spin-1 and spin-3/2 fields are included). For the moment it appears that such additional fields aren't required.
The presence of such fields would show up as deviations from the equivalence principle, but that wouldn't make GR wrong, only incomplete, since the invariance under diffeomorphisms would, still, be the definition of the more complete theory.
Invariance under diffeomorphisms is a necessary property of any theory of gravity; it's just not sufficient for determining the field content that describes the spacetime geometry.
At the time of Einstein's creation of the theory of gravity, this was a revolutionary idea, and now it's time for new revolutionary ideas. The only strange thing is that no one has offered anything worthy yet.
Mr Nicolis,
Thanks for the answer. I didnt know scalar field theories of gravity have proved wrong or not proven at all.
But my Q was "what if", i.e a thought experiment to cause one to state the real substsnce or diachronic elements of the theory.
You pointed diffeomorphism. My guess is that it is the assumptions t makes about the nature of gravity i.e un embeded to physical reality's background type of phenomenon not a regural force
GR is not just a theory of gravity. It is a modification of our understanding of the nature of space and time. Einstein’s discovery is that spacetime and the gravitational field are the same physical entity. This is an assumption about the nature of gravity that maybe is more important than the theory itself, in my view
The substance of gravity is invariance under general coordinate transformations. There have, by now, been experiments that show that this is the correct description of gravitational phenomena. So an expriment that claims to have found a deviation must explain why the deviation didn't show up in previous experiments.
What invariance under general coordinate transformations=invariance under diffeomorphisms, doesn't single out is, whether the spacetime geometry is defined only by the metric tensor (which is what general relativity says), or, whether additional fields (scalars, vectors, spinors) are required, as well, tha can't be identified as matter fields, because they don't have the properties of matter fields. Such theories are scalar-tensor theories and supergravity. For the moment such fields don't seem to be required. In this regard, general relativity is just one possible theory of gravity among others.
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