Question: what is dark matter?

Jen Gupta answered on 20 Jun 2011:

Great question – no one really knows! We can see evidence that there is extra stuff in the universe that has mass (and therefore affects things with its gravity) but doesn’t emit or reflect light or any type of electromagnetic radiation that we can detect. We see this evidence for example when looking at how fast stars in galaxies move around the centre (eg http://cosmology.berkeley.edu/Education/Essays/galrotcurve.html) – this is something that I actually got to use a small radio telescope at Jodrell Bank to confirm when I was in my third year of university! We just don’t know what it is!

It is possible that dark matter could be things like brown dwarfs which are things bigger than planets but too small for fusion to happen so they aren’t quite stars. A lot of scientists think that dark matter might be something called Weakly Interacting Massive Particles or WIMPs. One of my lecturers in university once said that it could just be a load of rocks floating in space! I have no idea though – do you have any ideas?