Experiment
Experiments can tell us if a theory is false, or if something does not work. They cannot tell us if a theory is true. When Einstein said that gravity could affect light, it took a few years before astronomers could test it. General relativity predicts that the path of light is bent in a gravitational field; light passing a massive body is deflected towards that body. This effect has been confirmed by observing the light of stars or distant quasars being deflected as it passes the Sun.<ref>Shapiro S.S. et al 2004. Measurement of the solar gravitational deflection of radio waves using geodetic very-long-baseline interferometry data, 1979–1999. Phys. Rev. Lett'. 92 (12): 121101. </ref>