Chinese scientists have created the world’s lightest substance -- a material so insubstantial it can perch on the petals of a delicate flower without crushing them. A cubic centimeter of the record-setting stuff, carbon aerogel, has a mass of only 0.16 milligram, according to a new study by scientists at Zhejiang University. That’s 12 percent lighter than an equal volume of the previous record-holder, a substance known as aerographite.