Physicist Stephen Hawking has been urgently admitted to hospital in Britain.
Professor Hawking, 67, who is almost completely paralysed by a motor neurone disease, was taken to a hospital in Cambridge.
He is best known to the general public as the author of A Brief History of Time.
It was followed another book, The Universe In A Nutshell, as well as documentaries and cameo appearances in television shows such as The Simpsons and Star Trek: The Next Generation.
Cambridge University says Professor Hawking has been unwell for a couple of weeks and is now very ill.
He has been Lucasian professor of mathematics at Cambridge, a position once held by Isaac Newton, since 1979.