This thought experiment is called to be Berkeley's:
If a tree falls in a forest and no one is around to hear it, does it make a sound?
(http://en.wikipedia.org/wiki/If_a_tree_falls_in_a_forest)
Philosopher George Berkeley, in his work, A Treatise Concerning the Principles of Human Knowledge (1710), proposes,
But, say you, surely there is nothing easier than for me to imagine trees, for instance, in a park [...] and nobody by to perceive them. [...] The objects of sense exist only when they are perceived; the trees therefore are in the garden [...] no longer than while there is somebody by to perceive them."
― A Treatise Concerning the Principles of Human Knowledge, 1734. section 45.
From this quote, it looks like he says that matter doesn't exist when it isn't perceived. Or, in Latin:
Ecce est percipi ― To be is to be perceived
However, then Berkeley wonders (paraphrased): how is it possible that when I go to work, and come back to my home in the evening, my house still exists? There must have been some moment nobody perceived it... That's the point that God enters Berkeley's philosophy: because God always perceives everything, matter can still exist even though there is no human being to perceive it.
Do keep in mind that this is just one opinion, and other philosophers may or may not think different.
