* A*nyone writing that Einstein was fundamentally wrong has not understood General Relativity. There are really two different things which are General Relativity. There are the principles that define General Relativity in particular the Einstein Equivalence Principle. Then there are mathematical realizations of those principles like the Einstein Hilbert Action, from which we derive predictions from the big bang, to light bending due to the Sun, to Black Holes, and gravitational waves. So if you see a headline saying Einstein was wrong the answer is no. His theories were incomplete descriptions of nature. We seek to extend this with modified theories, and test those with experiments. Any such theories would include general relavity within their structure. This is similar to the way Einstein's theory reduces to Newtons laws at smaller masses and lower speeds.

This mathematical realization has been remarkably successful and passed every test thrown at it. However, we still test it to look for alternatives and extensions to it. For example, we look for various ways to extend our mathematical formulation of General Relativity by adding new fields, or new interactions between gravity and those fields.

The most robust approach holds that instead of gravity being described by the Ricci curvature R it is instead a function, f, of the Ricci curvature R. f(R) in the traditional mathematical formulation of general relativity f(R)=R. This formulation has gotten us all the modern astrophysics you have ever heard of.

There are many other models of f(R). I developed a few of my own which I either gave talks about or published however those models were extraordinarily complex and, in a way, mostly academic. These days the most interesting f(R) is due to Alexi Starobinsky f(R)=R+bR^2 . This model is the simplest function of R possible other than adding a constant such as the cosmological constant. This model gives cosmic inflation and preserves all the predictions of the traditional formulation. However, how does one test for this?

This is where gravitational wave observations may be instructive. Extreme mass ratio in spirals. This is where a black hole interacts with an object which is much less massive. This could be a super massive black hole and a neutron star or a black hole and an ordinary planet. The LISA probe to be launched by the European Space Agency with a little cooperation with NASA is going to investigate this and many other things.

In simple terms think of these devices as being like tuning forks. Strike a tuning fork on one side of the room. An identical tuning fork will resonate with the sound of the one you struck. The frequency of the tuning fork depends on the size of the tuning fork. LIGO is not sensitive to EMRI interactions as it does not have the scale to be sensitive to them. These low frequency interactions just are not visible to LIGO but they will be to LISA which will be much larger.

None of this even considers issues of how to incorporate gravity into quantum mechanics or perhaps vice versa.

**Einstein can be built upon, and physicists will do just that. Einstein and Hilbert were not perfect. However, if anyone says, “Einstein was wrong”, at this point, they are a quack. **

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