Looking for evidence of dark matter
6 February 2013 Last updated at 01:53 GMT
Beneath a mountain, an experiment is about to begin that could prove the existence of some of the strangest particles known to science.
Physicists are hoping to find the first evidence of dark matter - a hidden substance that is thought to pervade the Earth and the Universe.
BBC World Service science reporter Rebecca Morelle has been to Italy to take a look inside the Darkside50 experiment at the Gran Sasso National Laboratory before it is switched on.