Mar 18 2009
The Gravitational Shadow of Dark Matter
A number of years ago I heard a recording of a physics lecture by Richard Feynman, one of the “fathers” of quantum theory. It was an excellent talk and I came away from it with the clearer realization that knowledge of the universe depends upon our observations of it. Whether those observations are few, first hand and informal (less scientific) or many and strictly methodological with instruments involved (more scientific).
In a sense, to observe something you must interact with it. Preferably you can do it a number of times in a way that is verifiable/replicable. This notion, by the way, makes me strongly doubt any supposedly supernatural entity/phenomenon. How is a natural entity to observe via natural processes something supposedly beyond and undetectable by natural processes?
Quantum physics has revealed a philosophical conundrum at the atomic scale. To know something of tiny particles, you must interact with them. And the interaction changes the very thing you are attempting to gain knowledge of. Precisely measuring one attribute makes another less precisely knowable. Quantum uncertainty.
A more recent conundrum in the field of physics is that of “dark matter.” And we have just zoomed from the realm of the very small to the other extreme. Dark matter is called dark because it cannot be observed. So we are blind to it. We look and see only darkness.
Fortunately, scientists can be a clever lot. And they have recently found new evidence of the elusive matter. But not by directly observing. By finding indirect signs of it.
As the ScienceDaily post puts it -
First proposed about 80 years ago, dark matter is thought to be the “glue” that holds galaxies together.
But if you can’t see it, how can you detect it? The problem is not completely unlike detecting your own existence by seeing your own shadow. Technically, you don’t really see yourself or even your shadow. You see a void in the sunlight. Rather than direct evidence of something, you detect an effect of the existence of that something. In terms of dark matter, the effect is gravitational.
Because dark matter cannot be seen astronomers detected its presence through indirect evidence. The most common method is by measuring the velocities of individual stars or groups of stars as they move randomly in the galaxy or as they rotate around the galaxy. The Perseus Cluster is too far away for telescopes to resolve individual stars and measure their motions. So Conselice and his team derived a new technique for uncovering dark matter in these dwarf galaxies by determining the minimum mass the dwarfs must have to protect them from being disrupted by the strong tidal pull of gravity from larger galaxies.
Very cool.
