George Smoot, the 2006 Nobel Prize winner in Physics and a professor with the Institute for Advanced Study, HKUST, said the greatest impression that Hawking left on him was his strong spirit.

"He didn't give up because of disease. Instead, he worked even harder and became even stronger. He had a brilliant mind and offered the world many great insights that inspired the world's scientists. He made life possible."

Saying that they got to know each other since the mid-'70s, Smoot said he had lots of memorable encounters with the British scientist in conferences around the globe.

Recalling a private lunch with Hawking and his daughter in Brooklyn, he said: "At that time, he and his daughter was working on a book together."

"Scientifically, we help each other, and in some ways, we compete each other," Smoot joked.

Smoot sees Hawking's death as a loss for the world's science of physics, hoping that budding physicists of today's generation will follow Hawking's step. "There're some young talents in physics already emerging."