2. History of Dark Matter
2. History of Dark Matter
How did we discover dark matter? Who discovered dark matter? What exactly is the history behind all of this dark stuff? Why is important that we make discoveries about it?
We, members of the human race, are quite obsessed with explaining our existence, from justifying our nationality to justifying the universe and our place in it. So, while it is certainly frustrating to attempt to map the universe because of its size, it is even more frustrating to try to explain away matter in the universe that cannot be observed directly, matter that seems invisible because it does not emit light, but we know exists. Such matter is called dark matter, and for the majority of the 20th Century its discovery and research have dominated the field of cosmology.
Why exactly is researching dark matter so important? It is so important because there are three different theories about the structure or shape of the universe: it can be ‘open’ and look a Pringle potato chip; it can be ‘closed’ and look like a tennis ball’; or it can be ‘flat’ and look like a sheet of paper. Discovering the shape of the universe is paramount to explaining lots of characteristics about the universe today, its past, its evolution and its fate. Thus, learning about dark matter helps determine the shape of the universe, because the shape of the universe depends on the kind of stuff in it. Moreover, because dark matter comprises such a large amount of the universe, understanding its nature and behavior are integral.
Fritz Zwicky was the pioneer in this field. In 1933, at the California Institute of Technology, the Swiss astrophysicist Zwicky was the first to theorize dark matter after he observed that there was 400 times the mass in the Coma cluster of galaxies than there ‘should’ have been or that he had expected there to be. According to Zwicky, there must have been something that couldn’t be seen that accounted for the rest of this mass. Furthermore, he came to the conclusion by looking at groups of galaxies tens of millions of light-years away from one another. Zwicky observed that their relative speeds were much too great for them to be held together by the gravitational attraction of the visible matter alone, and that therefore, there must have been something else holding them together. He called this something else ‘invisible matter’ or ‘dark matter’. And then other discoveries sprang forth.
Fritz Zwicky
In 1950, a woman named Vera Rubin made another startling discovery. Newton’s laws predicted that bodies orbiting around a center move more slowly the farther they are from that center. (This has to do with the strength of gravitational attraction being stronger when it is farther away. An example of this is the longer orbits of Pluto compared with Mars: one is much closer to the sun than the other.) Instead, Rubin’s conclusions contradicted Newtonian laws. She built on the theories of Zwicky to discover that galaxies showed an ‘extra motion’: by examining galactic light signatures, she found that bodies orbiting around the outskirts of galaxies traveled at approximately the same speed as the bodies orbiting near the center of a galaxy, therefore some other matter had to exist in the outskirts, some matter that we couldn’t see, that was acting upon the visible bodies. Can you guess the punch line? It was dark matter.
Vera Rubin
Over the last half of the 20th Century many other important contributions to theories of dark matter have been made by the like of Mordehai Milgrom and Yakov Zel’dovich. However, the most important thing to remember in learning about the history of dark matter theories is that there is always room for improvement, always a new way to think about things, always a new way to open our minds to crucial questions about the universe. It is explicable, as is dark matter. Anyone could pioneer the next dark matter breakthrough, even you. But before you become a world-famous cosmologist, go on and learn some more about what kind of stuff makes up dark matter, is it MACHOs or WIMPS?
Posted by bsalmon on March 27, 2005 at 6:55 PM