Question: what is dark mater

Kate Salmon answered on 9 Mar 2014:

This is a tricky question! I’m not sure exactly what dark matter is and I’m not sure a lot of astronomers know either. Dark matter is one of those things that people are still trying to understand and because it is hypothetical (that means we can’t actually see it or measure it), then it is very hard to prove that it is there at all! Perhaps during your lifetime, astronomers will be closer to understanding it and I will be able to answer this question in 20 years time…