Physicists and astronomers have long tried to identify exactly what our universe is made of. In the late 19th century scientists believed an ‘aether’ permeated the cosmos and was the medium through which light passed. Eventually this idea was disproved by subsequent discoveries such as general relativity and the structure of subatomic particles. Now scientists are met with a new problem, the universe is a lot heavier than it looks.

Gravity is the force that holds the large scale structures of the universe together. It causes all matter to attract to all other matter, proportionally to their collective mass and inversely to their distance apart squared. Scientists can estimate the mass of stellar bodies based on their size and composition. As scientists have been observing galaxies, though, they have been seeing indicators that they have hidden mass we cannot see. Objects are in orbit around the center of galaxies faster than the size of those galaxies should allow.

As opposed to just deciding that our laws of gravity, which had worked perfectly up until this point, were just flawed, scientists came to the conclusion that there must be some hidden mass that doesn’t interact in ways we can see: dark matter. This theory goes that dark matter permeates galaxies and interacts with particles of regular matter via gravity, but not significantly through the other major forces. It gives the galaxies their missing mass, but does not affect anything else.

One strong candidate for what dark matter could be is so called W.I.M.P.s, or Weakly Interacting Massive Particles. These particles would have a gravitational influence on matter and would interact a little bit with the weak nuclear force, but not the strong nuclear or electromagnetic forces.

The most astonishing thing about the theory of dark matter is how much of it there must be in the universe. According to NASA [the National Aeronautics and Space Administration], the universe may have 5.4 times as much dark matter as regular baryonic matter in it.

While this theory has yet to be proven, scientists are working on it. Massive detectors built deep underground are trying to get W.I.M.Ps to move a few atoms around, so that scientists can see their direct effect. Until this theory can be proven, though, 84% of the universe’s mass is still missing.

What I find so fascinating and uplifting about this subject is that while some people may be discouraged if they find out all the precise model’s they have spent decades perfecting are wrong, physicists have taken it in stride. They saw this discovery as an opportunity to better understand the mysteries of our universe, to uncover some secret order that the cosmos is built upon. Theories like dark matter are what drive scientific discussion and scientific innovation, and they are what inspire me to pursue a career in science.

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