## Is Einstein's theory of GR shaky

To be fair, there has never been (or at least their hadn't when i last looked for such a things a few years back) a strong field test of GR. Only first-order, weak-field corrections.
 Please predict black holes in the weak-field limit of GR.

 Quote by Dickfore Please predict black holes in the weak-field limit of GR.
Please give evidence for GR's black holes (with singularities?) that cannot be called "shaky".
Does that book say anything about black holes?

PS I looked it up at Amazon, and I see that he does write about them (but I can't access those pages)

Anyway, I see, a bit to my surprise, that it is a textbook complete with exercises and answers.
Near the end of the introduction he writes "What science should teach us is to doubt - to consider that many of the beliefs [..] may simply be wrong." - very true!
And he ends that section with: "if this book can contribute to teaching that lesson, it will have done its job".
That explains the sentence with which this thread started.

 Quote by harrylin Please give evidence for GR's black holes (with singularities?) that cannot be called "shaky".
Ok, so first of all, let us define what was meant by 'ParticleGrl':
 To be fair, there has never been (or at least their hadn't when i last looked for such a things a few years back) a strong field test of GR. Only first-order, weak-field corrections.
Look at the gravitational field of a point mass in Newtonian gravitation:
$$\mathbf{g}(\mathbf{x}) = -G \frac{m}{x^2} \, \hat{\mathbf{x}}$$
As $x \rightarrow 0$, $g \rightarrow \infty$, i.e. it is unbounded. At some point, what was called "weak" must fail to hold, because, how can infinity be weak (unless you compare it to another infinity)?

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 Quote by ParticleGrl To be fair, there has never been (or at least their hadn't when i last looked for such a things a few years back) a strong field test of GR. Only first-order, weak-field corrections.
To be doubly fair, we still don't have a strong field test theory for GR. So even if we had everyday access to black holes we don't have a theoretical framework to test it against. All we have is the PPN.

 Quote by Dickfore Ok, so first of all, let us define what was meant by 'ParticleGrl': [..]
Sorry, I remained at what was meant by robertjford80 and March.

 Quote by harrylin Sorry, I remained at what was meant by robertjford80 and March.
My comment followed 'ParticleGrl' attempt at pedantry of what predictions of the theory of GR had been tested so far. I thought it was obvious.

 Quote by Dickfore My comment followed 'ParticleGrl' attempt at pedantry of what predictions of the theory of GR had been tested so far. I thought it was obvious.
It wasn't clear, and I wonder if you missed the point... some textbooks write such "pedantry", emphasizing that GR could be found to be an approximation of a better theory - just as Newton's mechanics is an approximation of GR.

 Quote by harrylin some textbooks write such "pedantry", emphasizing that GR could be found to be an approximation of a better theory
ORLY? What books would that be? Care to give references? Also, until such a "better theory" is proposed, it is pointless to discuss it. Do you know of any proposals of such theories?

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 Quote by ParticleGrl To be fair, there has never been (or at least their hadn't when i last looked for such a things a few years back) a strong field test of GR. Only first-order, weak-field corrections.
Binary pulsar systems qualify as "strong field" in at least some respects (certainly they require corrections beyond first order), and so far all observations of those have matched GR predictions. See the living reviews site here:

http://relativity.livingreviews.org/...ge=node23.html

 Quote by Dickfore ORLY? What books would that be? Care to give references? Also, until such a "better theory" is proposed, it is pointless to discuss it. Do you know of any proposals of such theories?
Just a guess here: the point here might be Quantum Mechanics and General Relativity are incompatible, and so one might think both are approximations(?)

 Quote by ParticleGrl To be fair, there has never been (or at least their hadn't when i last looked for such a things a few years back) a strong field test of GR. Only first-order, weak-field corrections.
The tests aren't limited to "first-order", if by that you mean first order in m/r (in geometrical units). Of the three classical tests (or four, counting Shapiro), the redshift was basically a zeroth order test, since it must be satisfied by any metrical theory with the equivalence principle, and the light deflection and Shapiro are first order tests in m/r, but the perihelion advance is second-order in m/r. That's why it is by far the strongest test of general relativity.

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 Quote by ParticleGrl To be fair, there has never been (or at least their hadn't when i last looked for such a things a few years back) a strong field test of GR. Only first-order, weak-field corrections.
In a few years, we should be able to "image" (using microwaves) the black hole at the centre of our galaxy and stuff falling into the black hole,

https://www.cfa.harvard.edu/~loeb/sciam2.pdf.

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