Does the man dream that he is a butterfly or is the butterfly dreaming that he is a man: Can we really tell our dreams from reality?

This question, asked by a netizen on China's most popular microblog site Weibo on Thursday, was directed at the official account of world-renowned British theoretical physicist Stephen Hawking.

Hawking replied, "We don't or perhaps can't."

The question was discussed by influential ancient Chinese philosopher Zhuangzi, who was known for his philosophy of skepticism. It was Zhuangzi who had dreamed of being a butterfly, or perhaps it was the butterfly who dreamed he was Zhuangzi. Either way, it has been the starting point for discussions on reality, self, illusions and more for over 2,000 years.

In his fourth posting on the microblog, Hawking, who has 3.6 million followers on Weibo - more than the population of Wales - selected the question from comments left on his previous updates.

"Zhuangzi dreamed of being a butterfly - perhaps because he was a man who loved freedom," he said.

Hawking said, in his case, he might dream of the universe and wonder if the universe dreamed of him, "but we humans just don't and perhaps can't know if we are living in our dreams or reality, at least not until we start to understand more about consciousness and the universe."

The era in which Zhuangzi lived is considered by many Chinese thinkers to be a time "when a hundred schools of thought contended."

Chinese philosophers argue that Dao (the Way), from which Daoism gets its name, is the most indefinable of them all.

The Way of the universe is change: Night into day, joy into sorrow, life into death. Nothing is fixed, nothing definable. Moreover, everything is connected. No one knows where the Way leads.

Over 40,000 web users had commented on or forwarded the post within 24 hours of it being published. One follower said Hawking's answer was "a historic conversation."

Since Hawking opened his Sina Weibo account on April 12, his four posts have been forwarded 572,000 times, received 620,000 comments and been liked by over two million users.

In a previous post, Hawking introduced his Chinese followers to his latest project - Alpha Centauri, an astonishing space mission to our nearest star system.

Hawking said that the project, a collaboration with Russian venture capitalist Yuri Milner and Facebook CEO Mark Zuckerberg, would revolutionize space travel as it would use tiny nano-spacecraft able to travel fast enough to relay information to humans within a life time. It means humans would learn more about the galaxy, and ultimately themselves.