In a book excerpt published by The Guardian, Hawking contends that humans need to venture deep into space for the sake of adventure and the survival of our species. He also thinks that "the new space age" we're experiencing now could get us there. "We are entering a new space age, one in which we will help to change the world for good," Hawking said in the How To Make A Spaceship book excerpt. "I believe that life on Earth is at an ever-increasing risk of being wiped out by a disaster, such as a sudden nuclear war, a genetically engineered virus, or other dangers. I think the human race has no future if it doesn’t go to space." Hawking isn't the only one with this opinion. SpaceX founder Elon Musk and NASA administrator Charles Bolden have both championed the idea that humans need to become a multi-planet species for the good of our survival. "The probable life span of human civilisation is much greater if we’re a multi-planet species as opposed to a single-planet species," Musk said in 2015. "If we’re a single planet species, then eventually there will be some extinction event." Musk and other billionaires like Jeff Bezos and Richard Branson envision the world where private citizens can fly to space as well as professional astronauts. Bezos, Musk and Branson want to reduce the cost of flying to space, making it viable for everyday people to experience the glory of looking down on Earth from above. While none of the billionaire entrepreneurs have accomplished that goal yet — all three are in various stages of testing for crewed vehicles that will be way too expensive for regular people to fly on at first — Hawking thinks that private spaceflight is the way of the future. "I believe in the possibility of commercial space travel — for exploration and for the preservation of humanity," Hawking stated. "I believe that we need a new generation of explorers to venture out into our solar system and beyond. These first private astronauts will be pioneers, and I hope to be among them." Hawking does have a ticket to fly to suborbital space aboard the Branson-backed Virgin Galactic SpaceShipTwo when it does start flying customers. (Hawking is the only customer that didn't have to pay for a SpaceShipTwo ticket, which usually cost about $250,000.) Virgin Galactic has started test flights of its space plane, but it's unclear when tourists will fly onboard the vehicle. A fatal accident during a test flight in 2014 destroyed Virgin Galactic's first SpaceShipTwo, greatly setting back the company's progress on the spaceflight system. The new SpaceShipTwo was named Unity by Hawking, who said, "I would be very proud to fly on this spaceship," when the craft was unveiled in February 2016.