I was reading this ( http://news.bbc.co.uk/2/hi/science/nature/5272226.stm ) but find I don't quite understand exactly what dark energy and dark matter are. In layman's terms what is dark energy and dark matter? Is dark matter just rocks, dust, carbon and etc that doesn't reflect light? Is it left over junk from the big bang? As far as dark energy, I have no clue as to what it is.