This is because his theories about the Black Hole and the Big Bang -- though accepted in theoretical physics -- were never verified.
According to Timothy Ferris, author of 'The Science of Liberty' in National Geographic magazine, "The problem was that there was no way to verify the idea. Black holes are too long-lived to be observed today in their death throes".
The Nobel Foundation excludes posthumous nominees.
The US space agency tweeted: "Remembering Stephen Hawking, a renowned physicist and ambassador of science. His theories unlocked a universe of possibilities that we & the world are exploring. May you keep flying like superman in microgravity, as you said to astronauts on @Space_Station in 2014," NASA said.
(This story has not been edited by Business Standard staff and is auto-generated from a syndicated feed.)