article_snippet: It has been described as 'the most important unsolved problems in modern physics.'
article_snippet: When physicists study the dynamics of galaxies and the movement of stars, physicists are confronted with a mystery.
article_snippet: If physicists only take visible matter into account, physicists equations simply don't add up; the elements that can be observed are not sufficient to explain the rotation of objects and the existing gravitational forces.
article_snippet: From this physicists deduced that there must be an invisible kind of matter that does not interact with light but does, as a whole, interact by means of the gravitational force.