Saying "flat spacetime" you declare existence of rigid rulers and exact clocks.

Also you can't embed black hole into flat spacetime. Topology is involved.

Thank you for your interest in my question.

Can you please suggest a reference? The idea of embedding a black hole into flat spacetime is intriguing.

Spacetime and curvature of spacetime are only a mathematical model in order to searching to explain the physical behaviour of the universe in particular theories. It is manifest by this time that mathematical model of postmodern physics and others derived from it are obsolete and other physico-mathematical models are possible in contemporary physics. Length contraction and time dilation are relativistic effects that happen with respect to different moving reference frames in a theory that is based on a particular mathematical model, but it doesn't mean they are real physical effects. Other solutions are possible in different physico-mathematical models.

These are differents things, Einstein's curvature space time is need in general relativity ( when gravity and accelaration are considered ) 

flat space time in which lenght and time are different from a repere to the other, relate to relativity within galilean repository ,it stays  true in generale relativiy but you need to add the effects of space time curvature.

Basicaly, they are not equivalent,  you cannot substitute one by the other, flat space time is a specific case of the curved one that applies in relativity when no gravitationnal fields and accelerations are considered. 

I hope it will help you and that i did not made too many english mistakes.

"...equivalent to a flat space time.." As far as I know no such theory of gravitation exists except Newtonian gravitation which we know falls short.

Yes I've heard the same thing many times. The conventionality of geometry is mathematical theory and as far as I know is still an unproven claim. And it doesn't alter what I said above. GR of course reduces to SR in the small, that is in an infinitesimal neighborhood. If indeed black holes involve true singularities, that would not be true but I think there's a lot of controversy about that.

The change in the rate of time has been physically measured.  In order for the speed of light to remain constant locally in such a frame, one would likely require that distance also changes with the change in the passage of time.  This effects the plank constant of time/space warping it or bending it in regions of gravity.  Nonlocally the speed of light should slow down in gravity but local measurements make it appear the speed of light is constant.  A parallel to relativity is the polarizable vacuum concept by Puthoff I think his name is.  

Robert B. Scott>  "... truely equivalent ..."

It can't be equivalent, because curved space-time in general has non-vanishing curvature, while flat spacetime has not. But Rindler space is a very nice explicit model which implements Einsteins elevator analogy. It is a description of a portion of flat spacetime in curvilinear (accelerated) coordinates. I think the description can also be derived from a limiting case of the Schwarzschild geometry.

https://en.wikipedia.org/wiki/Rindler_coordinates

There exists an Lorentz ether interpretation of the Einstein equations of GR.  It is using harmonic coordinates.  See http://ilja-schmelzer.de/ether for details. For all the nearby observations there is no difference.  

But it would exclude non-trivial topologiesas well as causal loops like the Gödel rotating universe and so on.  It would also prefer among the FLRW universes that with the spatial curvature being zero, because only this would be homogeneous in the ether interpretation.  As far, this is no problem, the universe we see is globally flat, no wormholes or causal loops have been observed yet.  

Black holes are a very interesting example for the Lorentz ether interpretation.  The result is that a collapsing star which becomes a black hole can be described in the ether interpretation too, with no differences how the result looks like from the outside.  But what is the complete solution for the ether interpretation (that means, for all values of undistorted, absolute time,  is only the part of the full GR solution outside the horizon.  So, the black hole becomes a frozen star, the dilation of the clocks on the surfaces increases so much that their clock showings always remain below a finite number - the time when the observer would reach the horizon in the GR solution. 

Very unfortunately, not only Einstein’s theory of relativity is just a faked story or pseudoscience, but also the so-called Standard Model should result in pseudoscience if we cannot rightly treat it. May you see:

https://www.researchgate.net/publication/317014509_Anti-ethics_and_pseudoscience_On_Albert_Einstein%27s_theory_of_relativity

I am spreading this article. If anyone should help to this spreading, I should thank him/her very much.

Data Anti-ethics and pseudoscience: On Albert Einstein's theory o...

Yin Zhu, it is nonsense that "all of the results in the theory of relativity are ascribed to Einstein".  Look at the names of key objects of relativity:  Lorentz transformations, Poincare resp. Lorentz group, Minkowski spacetime, Einstein-Hilbert Lagrangian.  This already tells you that many results are ascribed to Lorentz, Poincare, Minkowski and Hilbert.  

Then, it is no risk to criticize Einstein.  In his discussion with Bohr, most modern physicists are on the side of Bohr, not Einstein.  And, of course, Einstein has made a lot of original contributions to relativity.  The papers are public domain, so everybody can see this. 

And, of course, even if you would be right that some results are wrongly attributed to Einstein, this would not make the results themselves wrong or "pseudoscience".