Of the known four forces, it is the one which does not work in a renormalizable quantum field theory.
It is expected to be modified in the ultraviolet, but Dvali, Gabadadze, and Porrati have proposed that it might behave unexpectedly in the infrared as well. The associated symmetry principle for this force is general covariance, or diffeomorphism symmetry. Of the known four forces, it is the one which does not work in a renormalizable quantum field theory. The most accurate theory we have of it is general relativity, although Newton provided a good approximation long ago. FTP, what is this attractive force between any two masses?
It is expected to be modified in the ultraviolet, but Dvali, Gabadadze, and Porrati have proposed that it might behave unexpectedly in the infrared as well.
{gravity}