Stephen William Hawking is an English theoretical physicist and cosmologist, whose scientific books and public appearances have made him an academic celebrity. He is an Honorary Fellow of the Royal Society of Arts, a lifetime member of the Pontifical Academy of Sciences, and in 2009 was awarded the Presidential Medal of Freedom, the highest civilian award in the United States. Hawking’s key scientific works to date have included providing, with Roger Penrose, theorems regarding gravitational singularities in the framework of general relativity, and the theoretical prediction that black holes should emit radiation, which is today known as Hawking radiation (or sometimes as Bekenstein–Hawking radiation). Hawking has a neuro-muscular dystrophy that is related to amyotrophic lateral sclerosis, a condition that has progressed over the years and has left him almost completely paralysed. He became the first quadriplegic to float free in a weightless state. This was the first time in 40 years that he moved freely beyond the confines of his wheelchair.