Have scientists found dark matter?
3 April 2013 Last updated at 09:14 BST
Have scientists finally found dark matter?
It is important because it accounts for a quarter of all the mass and energy in the Universe.
Today will hear the first results from the Alpha Magnetic Spectrometer, which was bolted on to the International Space Station and which has been scanning the heavens for evidence that it exists.
Dark matter is not easy to find because it is invisible and does not interact with either light or the atoms that stars, planets and even people are made from.
The Today programme's science correspondent Tom Feilden reports.
First broadcast on BBC Radio 4's Today programme on Tuesday 2 April 2013.