Stephen Hawking smiles during a 2002 symposium in honor of his 60th birthday at the University of Cambridge. Hawking has died at 76.

Stephen Hawking smiles during a 2002 symposium in honor of his 60th birthday at the University of Cambridge. Hawking has died at 76.

Stephen Hawking smiles during a 2002 symposium in honor of his 60th birthday at the University of Cambridge. Hawking has died at 76.

Stephen Hawking smiles during a 2002 symposium in honor of his 60th birthday at the University of Cambridge. Hawking has died at 76.