Humans must find a new planet to colonise within the next 100 years or risk becoming extinct, says Stephen Hawking. This isnt the first time Prof.Hawking has given a doomsday prediction. In recent years, hes warned about how super artificial intelligence (AI) would end humankind and how contacting extraterrestrial life would go bonkers for humanity. Why does Prof.Hawking warn us? Explains R.Sathyanathan who presents science news in simple Tamil.