Tuesday, April 22, 2014

Dark Matter

The matter that we see is everything that is made up of atoms and molecules. However, the universe we live in is made up of more than just visible matter. In fact, visible matter only accounts for less than 5% of the mass-energy of the Universe. Matter is very easy to understand. There are five states that it can switch in and out of (being Bose-Einstein condensates, solids, liquids, gases, and plasmas), and it must take up space to be matter. On the other hand, there is the other 95% of the Universe that we still have yet to understand fully: 27% dubbed dark matter and 68% called dark energy.

Dark matter was first hypothesized to exist in the 1930s as a means to explain the uncharacteristically large velocities of galaxies in a distant cluster. Fritz Zwicky of the California Institute of Technology discovered that the galaxies should fly apart because the gravitational attraction created by visible matter isn’t enough to hold the galaxies together on its own. He thus theorized that there must be some sort of dark matter to hold them together. Scientists didn’t necessarily buy into his findings for some time. The next breakthrough for dark matter came in 1970. Vera Rubin noticed that the stars at the edges of Andromeda didn’t move more slowly than those nearer the center, as one should expect according to Newton’s laws. Like Zwicky, she pointed to something invisible that had to be causing this effect. Then in 1973, two Princeton physicists tried to put together a simulation of the Milky Way using what they already knew about the Universe. In their simulation, which did not include dark matter, the arrangement of mass particles came out all wrong. When they added a uniform source of mass, the simulation suddenly worked, thus providing further evidence of dark matter. The rest is history as scientists have been continually searching to detect dark matter.

The interesting part about dark matter is that we are more confident about what it is not, than what it is. To start, it is not found in the form of stars and planets that we see. Second, it is not made in the form of dark clouds produced by normal matter. Scientists have been able to confirm this because through sending radiation into these clouds, we should be able to detect the dark matter, and we have not as of yet. Dark matter is also different from antimatter, since if it were comprised of antimatter, it would decay away and disappear over the age of the Universe. The most common prediction for what dark matter is is that it is a WIMP (Weakly Interacting Massive Particle). WIMPs interact through a weak nuclear force in combination with gravity. WIMPs would prove as a viable explanation to solving the problem with identifying dark matter because they rarely interact with visible matter and cannot be detected through electromagnetic observations.

The future of dark matter research is very exciting. The hope is that dark matter can be discovered in the coming years, which would unlock a lot about the history of our Universe, and help explain how it all interacts.
Tyler Wellener