If Stephen Hawk­ing could talk with Albert Ein­stein, what would he say?

“I would ask him why he did­n’t believe in black holes,” says Hawk­ing in this video from Time mag­a­zine. “The field equa­tions of his Gen­er­al The­o­ry of Rel­a­tiv­i­ty implied that a large star or cloud of gas would col­lapse in on itself and form a black hole. Ein­stein was aware of this but some­how man­aged to con­vince him­self that some­thing like an explo­sion would always occur to throw off mass and pre­vent the for­ma­tion of a black hole. What if there was no explo­sion?”

The famous cos­mol­o­gist, the­o­ret­i­cal physi­cist and author of the best­seller A Brief His­to­ry of Time made the remark in late 2010, when he agreed to take part in the Time’s “10 Ques­tions” series. The mag­a­zine invit­ed read­ers from around the world to sub­mit ques­tions for Hawk­ing, but because of the sci­en­tist’s disability–he is ful­ly par­a­lyzed due to motor neu­rone dis­ease and has to painstak­ing­ly com­pose his answers using a sin­gle cheek mus­cle to oper­ate his word processor–the inter­view was pared down to sev­en ques­tions.

One read­er asks if Hawk­ing thinks civ­i­liza­tion will sur­vive long enough to extend itself into deep space. “I think we have a good chance of sur­viv­ing long enough to col­o­nize the Solar Sys­tem,” says Hawk­ing. “How­ev­er, there is nowhere else in the solar sys­tem any­thing like as suit­able as the Earth, so it is not clear if we would sur­vive if the Earth was made unfit for habi­ta­tion. To ensure our long-term sur­vival we need to reach for the stars. That will take much longer. Let’s hope we can last until then.”

Relat­ed con­tent:

A Brief His­to­ry of Time: Errol Mor­ris’s Film of Stephen Hawk­ing

Stephen Hawk­ing’s Uni­verse: A Visu­al­iza­tion in Stars and Sound

Stephen Hawk­ing: Aban­don Earth or Face Extinc­tion