Day 13: Dark Matter and Dark Energy

           Dark Matter and Dark Energy are quite similar, and could possibly be the same thing. It's hard to define them, since astrophysicists really don't know what they are yet. In a nutshell, Dark Energy is a mysterious and directly undetectable (in other words, cannot be seen by looking at it) force that is accelerating the expansion of the Universe. Dark Matter is a mysterious and directly undetectable type of matter that is influencing things in the Universe in weird ways. In fact, Dark Matter is thought to take up 23% of the Universe, Dark Energy takes up 72%, and regular matter takes up only 4.6%, and the .4% belongs to some complicated topic.

          One may ask, so how do scientists know that these things exist anyway? Well, one way of detecting Dark Energy is by referencing the Doppler effect. The Doppler effect is basically the change of frequency of a wave relative to the observer. On the electromagnetic spectrum, the color we that we see depends on the wavelength of the light. The Universe is already expanding, but we can detect the extra acceleration of the expansion by looking at distant stars and galaxies. If the stars and galaxies are flying further away from us, then the wavelength would increase, shifting toward the red part of the spectrum, and we would see "redder" light. This is called a red shift. Because many stars and galaxies are further red shifting, we know that there must be an unknown force occurring, which is Dark Energy.

          Dark Matter, on the other hand, is detected in many ways, one of them being through gravitational phenomenon. Because it does not give out light, or other electromagnetic radiation as a matter of fact, it cannot be seen directly. One way scientists have detected its presence is by looking at the rotation of galaxies. Strange enough, the outer parts of galaxies rotate as fast as the inner part of the galaxy. According to NASA, "This only makes sense if there is a spherical distribution of matter in each galaxy, which is not what we see. Therefore we infer that there is a certain amount of Dark Matter in each galaxy."

          One theory states that Dark Matter may be WIMPS (Weakly Interacting Massive Particles.) It would make perfect sense because WIMPS don't interact with electromagnetism (one of the four fundamental interactions), so they cannot be seen directly. Also, WIMPS don't interact with the strong nuclear force, so they don't interact with atomic nuclei, so once again, we can't notice WIMPS directly. Another theory states that Dark Matter could be gravity from another dimension. It would also make sense because we cannot directly detect other dimensions. In the Brane-World theory, the ends of strings (referring to the string theory) are attached to out brane, and can only move within the brane. However, the theory states that gravitons, (the hypothetical particle that carries out gravitation) are closed stings, like a donut, so are therefore not attached and can "seep" through other branes (in this case dimensions.)

          It seems that for a while, whatever Dark Matter truly is will remain a mystery for years to come.