Dark Matter Day 2022

October 31st is not only Halloween but also Dark Matter Day. Space South Central interviewed Professor David Bacon, Associate Director of the Institute of Cosmology and Gravitation at the University of Portsmouth. Dark Matter can seem like a daunting subject but in reality is just the unknown. David breaks down the subject of dark matter and whether it is something that should scare us?

In short, what exactly is Dark Matter?

“In all sorts of situations in the Universe, we find that there’s more gravity than we might expect. The visible matter in the Universe provides a certain amount of gravity, but we see several times more. Why is this? We think it’s due to there really being a lot more matter out there, of a new type - matter that doesn’t glow or cast a shadow, but which provides more gravity. We call this dark matter.”

If we can’t see Dark Matter, how do we know it exists?

“If we see leaves swirling around, we suppose that there’s a gust of wind even though we can’t see it. It’s similar with dark matter; we can see its effects. For instance, we see the images of distant galaxies looking very distorted; this is because the light from those galaxies has been bent by a lot of gravity, more than we can account for by visible material. So we think dark matter is providing more gravity.”

Are we closer to observing dark matter, even though it seems un-observable?

“There are two ways we could ‘see’ it. 1) We could make a map of the patches of gravity in the Universe due to dark matter, from our measurements of distorted galaxy images. We’ve already done this with the international Dark Energy Survey, for a large region of the Universe, and can ‘see’ a web of dark matter with galaxies shining like dew drops on the web. 2) We could detect individual particles of dark matter in our particle physics experiments, like the Large Hadron Collider. No such particle has yet been discovered, but let’s see what happens if we build more powerful colliders.”

If we could hypothetically obtain and observe Dark Matter, could it be useful to us and how?

“I think it’s hard for us to tell until we understand it better. At the very least, it will be important for humanity to properly understand how it fits with the other physics we know, putting us on the right track for a deep understanding of the cosmos.”

Dark Matter Day is on the 31st of October (Halloween). Is Dark Matter something that should scare us?

“Only if it’s actually made of invisible spiders. And I don’t think it is.”