One of the courses I teach, Astronomy, is such a delight. I get to see, again and again, the awe in my students as I show them images and videos of various objects in the universe. Just showing a close up of the Sun’s surface can elicit such gasps from them. And a few of these students have not been outside a metropolitan area with all its light pollution. They have no idea how majestic the night sky is with the Milky Way visible.
Every year, however, I find that, whenever the topics of dark matter and dark energy come up, there is a momentary pause when invariably at least one student will ask whether or not these really exist. For the uninitiated, neither dark matter nor dark energy is known to actually exist. Both are theorized based on observations of the universe made within the framework of our already-developed gravitational model of reality. We see unexpected motion in galaxies that contradicts what our model predicts based on the amount of matter and energy that we can detect. In fact, we see a coherence in galaxies that should not be possible. The amount of matter is too small to keep these galaxies together, and the speed of the stars are evenly matched in the outer parts as well as the inner parts of galaxies. We observe gravitational lensing, which means there must be some large amount of matter bending space-time that can only be explained if both dark matter and dark energy exist. Furthemore, the universe’s expansion is accelerating, so there must be some energy accounting for this phenomenon. A lot of effort has gone into the detection of dark matter and dark energy, but so far scientists have not been able to detect either. And both must exist in far greater amounts than what we do detect. Dark matter is thought to be six times more abundant than normal matter and 68% of the energy in the universe is theorized to be dark.
The notion of dark matter and energy can be challenging to some high school students. Invariably I’ll have one or two who don’t get that something unobservable can be theorized about. And I do have to admit to them neither may exist. It could be that the current model of the universe is flawed on a basic level, and it may yet turn out that it will need revision. Indeed, there is a minority of scientists who don’t believe in dark matter and dark energy.
In the final analysis, the universe is a large space with so much left to be discovered. It is not just awe-inspiring for young students. It is awesome for any who attempted to study it’s mysteries, dark or otherwise.