Dark Matter and Energy

Dark Matter

     Many people today have heard of mysterious forces in the Universe, such as dark matter and dark energy. While these things a certainly still mysterious to the scientific community, their role in the Universe is not as magical and complicated as it may seem to the public eye. The actual physics and math behind them is quite complicated and not something to be understood without a lot of background knowledge, but the basic concepts and theories proposed about these substances are relatively simple.

     Let's start off with the common word in the two names. While space is dark and both dark matter and dark energy are dark, the way it is used is a bit more absolute than the way that we usually think of "dark." Dark, in the everyday usage, means a lack of light. Photons and radiation being at a low level so that our eyes cannot percieve what is happening around us very well. The dark in physics is similar to this definition, but there are key differnces. Dark in physics implies not only a lack of light, but, in the case of dark matter, the object does not interact with the photons or any electromagnetic forces. It does not absorb nor emit enough light for us to detect it at all. In fact, the only way that scientists have come to observe it is through gravitational patterns on galactic scales and, of course, the Cosmic Microwave Background.

     After observing the motions of galactic clusters and the rotation of spiral galaxies, physicists realized that the amount of observable matter in the galaxies was not enough to account for the motions they observed. Therefore, there must be some other factor playing a role in the movement of the galaxies. This is where dark matter comes in. The dark matter gives the galaxies the extra mass that they need to explain exactly how they appear to be moving and interacting. The CMB contributes to this evidence through a series of needed explanations similar to the gravity problem and involves dark matter, dark energy, and the cosmological constant and will be looked at once each of these have been looked at.

Dark Energy

     Dark energy is another thing in the Universe that little is known about, but, from what we have observed, is required to exist to explain our model of the Universe. Dark Energy also requires the cosmological constant and some other relevant information to justify its existence, so we will look at that on the next page. For now, let's just take a look at what dark energy is and what it does. Dark energy is another substance that we know almost nothing about. The makeup of it is unkown and even its existence is contested. It does, however, explain some phenomena in the Universe quite nicely. We have known for quite some time that the Universe is expanding, but how and why is still a mystery that dark energy helps explain. Dark energy is essentially seen as the "stuff" that makes up the vacuum of space. It has a uniform, extremely small density and permeates the entire Universe. It is also what is causing the Universe to expand at an accelerated rate. Because dark energy is between all the galaxies and all the galaxies are expanding away from each other, it is thought that dark energy has a "negative pressure" that forces it to expand away from itself, essentially pushing everything in the Universe away from each other with a force that contests gravity.