Question: What is dark matter and why would it exist? Is it hard working with things that you can't and won't be able to see in front of you?

Edward Banks answered on 16 Mar 2020:

This is a really good question and I’ll try to break down dark matter properly here- please follow up if anything doesn’t make sense!
So we still don’t know exactly what dark matter is!
There is a lot of evidence that suggests that something like dark matter should exist. A big one is looking at the rotation curves of galaxies. These are pretty straightforward to make; you take a galaxy and plot how fast a star is moving around the centre compared to how far out it is from said centre.
Now we think we know how gravity works: you throw a ball and it comes back down, and you can predict exactly how fast it will come down based on how hard your threw it. The amount of gravity something generates is based on how much mass it has; the more mass the more gravity. So a person doesn’t have very much, and a planet has a lot! But the centre of a galaxy will have a huge amount.
Gravity also dictates how fast things will orbit; bigger mass objects will cause planets or stars to orbit around them faster. So back to the rotation curves: we know how fast stars should be going, because we know how much mass there is (roughly) in the galaxy centre. But the stars are actually going way faster than we predict!
This means one of two things: 1) our understanding of gravity is pretty badly wrong or 2) There is a whole load of mass there that we cannot see. Normally scientists choose option 2 and call this “Dark Matter”- dark because we literally cannot see it.

There’s other clues like the large-scale structure of galaxy clusters, structures in the cosmic microwave background and something called gravitational lensing (but all of those are big questions on their own!) that make people think option 2 is more likely. The best idea we have right now for what DM is are particles called WIMPs; Weakly Interacting Massive Particles. But these haven’t been confirmed to exist- that’s what we’re working on.

For the second part of your Q, it is challenging working with things you can’t experience directly, but in some ways it feels like you are interacting with another plane of existence! This fantastic world which is governed purely by equations and mathematics, the kind that feel a little abstract in day to day life. So that aspect of the work is great fun!