Final answer:
The first experiment to address the detection loophole in gravitational waves was proposed by Rainer Weiss in 1972, aiming for accuracy in measurement more precise than the diameter of a proton.
Step-by-step explanation:
The first experiment that addressed the detection loophole in observing gravitational waves was suggested by Rainer Weiss of MIT in 1972. Weiss proposed a method to measure the minuscule changes in distance with extraordinary precision to detect gravitational waves, a phenomenon predicted by Einstein's theory of general relativity. This detection required measuring the distance to a mirror with an accuracy better than one ten-thousandth the diameter of a proton. The ability to perform such precise measurements is a testament to the clear thinking and analytical prowess akin to that of Einstein, who through thought experiments came to conclusions that would later be confirmed through empirical evidence. The Michelson-Morley experiment and the exploratory work on neutrinos by Raymond Davis are examples of prior significant experiments that sought to understand elusive physical phenomena.