The Role of Einstein's Theory of Gravitation in Modern Physics

The general view presented to the world by the physics community is that modern physics as physics after 1900, as opposed to classical physics before 1900,  is based on 

• Einstein's Special Theory of Relativity SR and General Theory of Relativity SR replacing Newton's Theory of Mechanics NM, together with
• Quantum Mechanics QM for atomic physics as an extension of Maxwell's Theory of Electromagnetism ME and Newton's Mechanics NM to atomic scales.

The completely new aspect of modernity are Einstein contributions to physics offering a completely new insight into basic aspects of space and time with SR presented in 1905 followed by GR in 1916 after an 11 year long hard struggle. 

But the reception by the physics community of Einstein's revelations were met with skeptics or refutation or ignorance, in particular by the Nobel committee for the Physics Prize 1921, which awarded Einstein for explaining the law of photoelectricity but with the explicit mention that his relativity theory was not included in the motivation. This situation changed only after Einstein's death in 1955, but then slowly accelerated to its position today as the fundamental theory of gravitation replacing Newton's Theory of Gravitation NG included in NM, which had served humanity so incredibly well for 300 years. The history is captured in the book Building the General Relativity and Gravitation Community during the Cold War by Roberto Lalli.

Here is a typical reaction to GR (Charles Lane Poor):

• The Relativity Theory, as announced by Einstein, shatters our fundamental ideas in regard to space and time, destroys the basis upon which has been built the entire edifice of modern science, and substitutes a nebulous conception of varying standards and shifting unrealities. 
• And this radical, this destroying theory has been accepted as lightly and as easily as one accepts a correction to the estimated height of a mountain in Asia, or to the source of a river in equatorial Africa.

This is where we stand today: Physics is based on GR for gravitation and QM for atom physics, but the big trouble is that GR and QM are viewed to be incompatible, which is a catastrophe from scientific point of view.

But NG is compatible with QM, and so it is natural to ask if it is really necessary to give up Newton for Einstein? 

A modern physicist will tell you that in fact GR reduces to NG in the case of (i) weak  and (ii) static gravitation, and then admit that this covers almost everything. In fact, what is not included in (i)+(ii) is something extremely speculative, such as collision of black holes, for which the physics is unknown and so the functionality of GR. 

In other words, NG works as well today as ever before, as the most successful mathematical theory all times, and the claim that NG has to be replaced by GR appears to have little factual basis. In fact, GR is so computationally demanding that simulation of even a simple system like the Solar system is unthinkable, while with NG this is captured in a couple of lines of code and executed on a laptop in seconds. 

If NG still works fine, what was the motivation to promote GR after Einstein's death but reject it before?

Was it the result of a stalemate of modern physics in 1960s after the immense success of the atomic bomb at the end WW2? When constructive new ideas are missing, a return to some old ideas may come to rescue.

In any case GR was lifted up from obscurity to top position, but then GR as theory had to be inspected with new eyes and this was far from easy, since GR is so mathematically demanding that it can be grasped by only a few, if any. 

Today this is handled as follows: GR is fundamental and very difficult to understand and apply, but since NG works so fine it is not necessary to dig into the theory of GR in any detail. It is sufficient to know that GR has replaced NG, while NG is used in practice. GR can then be presented as a fundamental step forward as concerns fundamental aspects of space and time as an expression of the power of modern physics. 

The only trouble is that GR is incompatible with QM, and so either GR or QM must be wrong.