Some cosmologists are searching outer space for dark matter. Others are looking for it in mines deep inside the Earth.
But Anne Green's looking for it in her office at the University of Nottingham, hoping her computer programs will help unlock the secret.
I filmed this quick interview when I popped in to Anne's office unannounced. It is all a bit raw and impromptu.
In this rough edit, I've cast the pictures in black and white to emphasise the rawness. Just bit of an experiment really, but I quite like it.