What is dark matter? No one really knows for sure. All we know is that ordinary matter, the stuff we know and love, the stuff we're made of, makes up about 4.9% of the known universe. Everything else? That's dark matter, a substance that doesn't radiate or absorb any as we know it. Saying that ordinary matter accounts for only 4.9% of the universe is like saying that we can only see the top layer of the soup in our bowl. We know something else is there. We just need a spoon to get to the bottom.
Dark matter is not just some sort of "out there" phenomenon, in some distant galaxy. Scientists are also finding fleeting evidence of dark matter in the closest star, the sun. Analysis of the energy emitted from the sun suggests that variations in the energy from the sun can only be explained with dark matter.
This development is very similar to the discovery of infrared light in 1800, with further work over the next century to show that our eyes can only see a tiny sliver of the electromagnetic spectrum. The rainbow we're so familiar with excludes most of the electromagnetic spectrum. That spectrum looks like this:
See that rainbow box? Now look at the lines going from the box to smaller box for the visible electromagnetic spectrum. That's the sliver I was talking about. To put it simply, there is a lot more going on than meets the eye.
For many years I've known that our eyes capture what amounts to a peephole on the universe in terms of spectrum. As I sit here, I recognize that all sorts of other radiation, in the form mostly of infrared light, is illuminating the room. But for some reason, we have adapted to the familiar spectrum of light. When I enter a room without lights turned on, I know that there is infrared light in the room, even if I can't see it.
During the day, I know that there is ultraviolet light falling from the sun onto me and all around me. I can't see it, but the bees can see it. Other animals have adapted more to night vision and can see in the near infrared. Even those animals still only see a small fraction of the light in the environment.
Yet, I am still surprised at the extent to which dark matter and energy rule the universe. That means that we haven't got a clue about about what is going on in the universe. We only know enough to get into trouble. We can only sense enough to stay alive.
Maybe that is all we need, but I'm glad to see scientists reaching out to see what is really there, in front of me. All the time.