Dark matter is an invisible phenomenon that acts on visible matter through gravity. It accounts for 6 times more mass in the universe than normal matter. Fritz Zwicky discovered evidence of "invisible matter" in galaxies in 1933 while Vera Rubin provided further evidence in the 1970s, though they were initially disregarded. String theory may help explain dark matter through postulated supersymmetric particles. Dark energy is a hypothetical form that permeates space, causing accelerated expansion of the universe, and may account for most of its mass. It produces an opposite effect to gravity. String theory also provides several potential explanations for dark matter through concepts like supersymmetric particles, branes, and extra dimensions.