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Key Concepts in Physics: Dark Matter

Swiss astronomer, Fritz Zwicky is the "Father of Dark Matter," coining the term itself. Dark matter was postulated by Zwicky in 1933 to partially account for evidence of missing mass in the universe. He realized that a nearby giant cluster of galaxies was behaving in a way that implied its mass was much greater than the weight of all the stars in all the galaxies within it. He inferred that some unknown dark matter accounted for 400 times as much material as luminous matter. What a surprise!  Its existence meant that most of the universe was not in the form of stars and gas but something else. So what is this dark stuff?
Dark matter is a hypothetical form of matter that is undetectable by its emitted electromagnetic radiation. Although we cannot see dark matter directly, we can detect its mass through its gravitational pull on other astronomical objects and also light rays. For example, if the moon did not reflect light, if it were dark, we could still detect its presence because its gravity would affect the orbit of the Earth. There is currently much ongoing research by scientists attempting to discover exactly what this dark matter is, how much there is, and what effect it may have on the future of the Universe as a whole.
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