Dark matter, by definition, is a matter of unknown composition that doesn't reflect enough electromagnetic radiation to be observed first hand. Scientists believe that such concept exists due to dark matter's gravitational effects on other visible objects. This is mostly true for the universe.

However, the concept of dark matter has been under fire recently with some researchers and scientists saying that it doesn't exist at all. Add now Canadian astronomers John Moffat and Joel Brownstein to that growing list of scientists who believe that dark matter is nothing but an unproven concept.

According to the two, the universe is not being held together by dark matter. Instead this can be explained by the Modified Gravity theory or MOG. Moffat explained:

MOG gravity is stronger if you go out from the center of the galaxy than it is in Newtonian gravity. The stronger gravity mimics what dark matter does. With dark matter, you take Einstein and Newtonian gravity and you shovel in more dark matter. If there's more matter, you get more gravity. Whereas for me, I say dark matter doesn't exist. It's the gravity that's changed.