Super Christian Kirk Cameron says Stephen Hawking is WRONG about the non-existence of Heaven -- insisting Hawking is just as ignorant as ... (wait for it) ... John Lennon.

Kirk -- who is HUGELY active in his evangelist church -- tells TMZ Hawking has no scientific evidence to back his claim that Heaven is merely a, "Fairy story for people afraid of the dark."

Cameron tells us, "Professor Hawking is heralded as 'the genius of Britain,' yet he believes in the scientific impossibility that nothing created everything and that life sprang from non-life."

He adds, "Why should anyone believe Mr. Hawking's writings if he cannot provide evidence for his unscientific belief that out of nothing, everything came?"

So how does John Lennon fit in to all this? Cameron explains:

"[Hawking] says he knows there is no Heaven. John Lennon wasn't sure. He said to pretend there's no Heaven. That's easy if you try. Then he said he hoped that someday we would join him."

"Such wishful thinking reveals John and Stephen's religious beliefs, not good science."

So there you have it ... Stephen Hawking and a Beatle connected through Mike Seaver.