These are quite specious arguments. Gravity (Einstein or Newton -- take your pick) is a foundational theory of physics. The same is true of Maxwell's equations and all subsequent QED theories.
Several folk have already addressed this post of yours, PS, including DD himself.
However, there's one aspect (at least!) that hasn't been commented on yet.
Here's the question that MM agreed to answer, again (I have added some bold):
"Can you, MM, empirically demonstrate that gravity and EM fields exist in nature, in a controlled experiment,
regardless of what opinions I, DRD, might have on these subjects?"
That qualification - "
regardless of what opinions I, DRD, might have on these subjects" - is critical.
The question, as asked, is loaded with many aspects fundamental to the whole enterprise of science, such as consistency of (key) terms, definition of (key) terms, and logic.
My response - calling what MM says is 'gravity' 'inflation', rejecting his entire 'EM fields' experiment because he did not use that exact term - may seem flippant, but it goes to the heart of what I think is the gulf between MM and most (all?) other participants in this discussion.
Namely, a lack of common agreement on the meanings of key words used in this discussion. There are a great many examples of this, but perhaps RC's recent post (that I responded to) will serve to illustrate what I mean.
You see, MM certainly does not use key words in the same way as (almost) everyone else - look at the wasted bandwidth on his misunderstanding of GR, for example. That alone all but guarrantees disagreement and frustration.
But more fundamentally, MM's own use of key words is inconsistent; at one time, for example, "EU theory" means "the essential content of Birkeland's works", at another it means "the application of MHD and GR", at yet another it is essentially meaningless, and it also has been used to mean "all of astronomy, astrophysics, space science, and much of geophysics too".
Many people have twigged to this inconsistency as it relates to "empirical" or "controlled experiment"; however, I think few have yet realised that it is consistent feature of almost all the key words he uses.
In short, to the extent that science requires both clear definition of key terms and consistency in their use, what MM writes is ascientific. As a consequence, no meaningful discussion is possible.
Asking MM to demonstrate the existence these phenomena as some sort of test that is supposed to equate to the (quite hypothetical) existence of DE and inflation is so much sophistry.
The only thing I'd like to add to what has already been posted is that "DE", in the form of lambda, is part of GR ... so, by definition, it
is gravity.
MM's complaint is that DE and inflation cannot be demonstrated in a lab. He is correct, but his complaint has no merit since there exist a multitude of astronomical phenomena that cannot be duplicated in a lab, which nevertheless have a strong scientific basis.
Including, as has been pointed out, many of the things MM has been quite passionate (shall we say) about ... for example, he is co-author of a published paper whose key content concerns neutron stars; curiously, he has not addressed the question of how one can go from 'observations' of neutrons in a controlled experiment in a lab here on Earth to accepting the existence, "
in nature" of neutron stars.
Myself, I suspect that one reason why (he has not done so) is because the concrete steps in such a demonstration could be easily repeated ... to demonstrate the existence, "
in nature" of CDM (non-baryonic DM), to take one example.
The current prevailing theory of gravity could possible be modified or amplified some day to some small degree; but it is not going to be overturned. However, it is still possible that DE will be overturned by a new approach coming from new observations.
[...]
Do you realise just how dramatically different 'gravity' is, in GR, from Newtonian 'gravity'? I mean, how different can geometry be from a force?
Surely the point is that whatever replaces GR, or however it is extended, it must do at least as good a job of accounting for all the experimental and observations results that GR accounts for.
Oh, and "DE" has at least two consistent meanings ... one is purely empirical (
pace MM), a shorthand for 'the net of relevant SNe Ia, BAO, and CMB observations'; the other is 'lambda, the cosmological constant, in the EFE'. In either meaning, your statement is at best confusing.
LOL! 
bold added)
