The first famous nuclear physicist who began to think of an alternative explanation for gravity, was none other than Andrei Sakharov.
He suggested that gravity might not be a fundamental interaction at all, but rather a secondary or RESIDUAL effect associated with other, non- gravitational fields. Gravity might be an effect brought about by changes in the zero-point energy of the vacuum, due to the presence of matter.
If correct, you could then consider gravity as a variation on the Casimir theme, in which the pressures of background zero- point energy were again responsible. Although Sakharov did not develop the concept much further, he did outline certain criteria such a theory would have to meet - for example, predicting the value of the gravitational constant G in terms of the parameters given by zero-point energy theory.
Another one was Timothy Boyer (New York University), he began asking what would happen if we took classical physics as it was and introduced a background of random, classical fluctuating zero-point fields. Could such an all-classical model reproduce quantum theory in its entirety, and might this possibility have been overlooked by the founders of quantum theory who were not aware of the existence of such a fluctuating background field?
Boyer began by tackling the problems that led to quantum theory being introduced in the first place, such as the blackbody radiation curve and the photoelectric effect. His upstart, neoclassical approach reproduced the known quantum results one by one. This approach is called STOCHASTIC ELECTRODYNAMICS (SED), in contrast to QUANTUM ELECTRODYNAMICS (QED). Indeed, Peter Milonni at the Los Alamos National Laboratory in the US noted in a review of the Boyer work that if physicists in 1900 had thought of taking this route, they would probably have been more comfortable with this classical approach than with Max Planck's hypothesis of the quantum. One can only speculate as to the direction that physics would have taken them.
In order to understand what zero-point energy really is, we must go back to the aether theory.