(CNN) -- Theology is unnecessary. So says Stephen Hawking, the world-famous physicist who controversially argues in a new book that God did not create the universe.

"God may exist, but science can explain the universe without the need for a creator," Hawking told CNN's "Larry King Live" in an interview that aired Friday.

Hawking, 68, says in his book "The Grand Design" that, given the existence of gravity, the universe can and will create itself from nothing. "Spontaneous creation," he writes, is the reason why the universe and humanity exist.

"Gravity and quantum theory cause universes to be created spontaneously out of nothing," Hawking told Larry King.

King asked Hawking why he thinks people have reacted so strongly to his book.

"Science is increasingly answering questions that used to be the province of religion," Hawking replied. "The scientific account is complete. Theology is unnecessary."

Hawking said his book is an attempt to give a "broad picture of how the universe operates and our place in it. It is a basic human desire and it also puts our worries in perspective."

The idea behind it is "M-theory," which, he says, allows there to be many universes that were created out of nothing, none of which required the intervention of God.

That's because if there are many universes, one will have laws of physics like ours -- and in such a universe, something not only can, but must, arise from nothing, Hawking says. Therefore, he concludes, there's no need for God to have played a part.

That's the point of his book, Hawking told King -- "that science can explain the universe, and that we don't need God to explain why there is something rather than nothing, or why the laws of nature are what they are."

Hawking said that if he could travel through time -- which he said is theoretically possible -- he would go to the future to "find if M-theory is indeed a theory of everything."

Hawking has ALS, or amyotrophic lateral sclerosis, which has confined him to a wheelchair and leaves him unable to speak without the help of a computerized voice synthesizer. The disease is also known as Lou Gehrig's Disease in the United States and motor neuron disease, or MND, in Britain.

He told King he's doing "pretty well" with the disease, 45 years after he was first diagnosed. The disease has a life expectancy of two to five years, according to the ALS Association.