Physicists have managed to make light travel backwards at negative speeds which appear faster than the usual speed of light as defined by Einstein. The experiments are being carried out by physicist Costas Soukoulis and his research group at the US Department of Energy's Ames Laboratory at Iowa State University. Soukoulis explained that making light travel backwards at speeds apparently in excess of 186,000 miles per second is "like rewriting electromagnetism". However, Soukoulis acknowledged that scientists involved in efforts to manipulate the direction and speed of light cannot do so with naturally occurring materials. The endeavour requires exotic, artificially created materials known as 'metamaterials' which can be manipulated to respond to electromagnetic waves in ways that natural materials cannot.