Science from scratch: how do you look for dark matter?

How do we examine matter that doesn't interact with light or almost anything else in the known universe? Christopher Clarke explains how. Matter is something that we can see or touch, owing to the way it interacts with light and other matter. So how do we examine matter that doesn't interact with light or almost anything else in the known universe? How do we even know that this 'dark' matter exists? In 1932 Dutch astronomer Jan Oort was the first to propose the existence of dark matter to explain the movement of certain stars in our galaxy. At the time it was assumed that this movement was dependent on gravity exerted by the surrounding matter; but there just didn't seem to be enough matter at that location to explain it. Oort deduced that there had to be some strange missing matter, which he named 'dark matter'. Since then, various studies of galaxies and the universe as a whole have been able to tell us that around 85 per cent of the matter in the universe is dark matter. For example, an experiment on the International Space Station - the Alpha Magnetic Spectrometer - has been looking for the tiny antimatter particles that are thought to emerge when particles of dark matter collide.