judgment to negotiate successfully, but i'm an optimist. if we can avoid disaster for the next two centuries, our species should be safe as we spread into space. >> let's go live to london and bring in cnn's samuel burke. what will his legacy be, samuel? >> reporter: good morning. the fact that he merged einstein's theory of relativity with quantum theory to suggest that space and time begin with the big bang and end with black holes. even if you don't understand the science, it was clear to everyone that he defied the odds. he was diagnosed with als in 1963, given just a few years to live. he forged on from his wheelchair, using a voice synthesizer to bring science to the masses through media. tv shows, entertainment. ways to connect people to