In 1932, the dutch scientist Jean Hoort studied the stars moving away from the milky way. Soon enough, as expected, gravitational pull attracted them backwards. By studying the positions and speed of these repatriated stars, Hoort was able to calculate the mass of our galaxy. To his surprise, he discovered that visible matter represented only 50% of the mass necessary to produce such a gravitational pull. Where had the other half of the universe gone? Phantom-matter was born, omnipresent but invisible.
from Jean-Luc Godard, Histoire(s) du Cinéma, "4b - Les signes parmi nous", 1998