This week Science Weekly stares into the universe's heart of darkness. We're talking dark matter – the mysterious, invisible, undetectable stuff that makes up some 20% of the universe. Its presence can only be inferred, because without it galaxies would fall apart and the universe would look very different.
What exactly is it?
To help us answer this question, Alok Jha spoke to Carlos Frenk, director of the world-renowned Institute for Computational Cosmology at Durham University, where he builds model universes inside supercomputers.
Alok asked him what scientists are doing to find dark matter and what happens if, after every avenue has been explored, it still remains missing.
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