Physicist Stephen Hawking remained hospitalized today, a day after he was admitted with undisclosed symptoms.

Hawking, 67, has suffered from the neuro-degenerative disorder amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig's disease, for more than 45 years and is mostly paralyzed. The University of Cambridge, where he's a mathematics prof, reported that he was "very ill" when brought to nearby Addenbrooke Hospital. No details were released on the nature of his aliment, but he canceled an April 6 appearance at Arizona State University because of a chest infection.

“Professor Hawking is being kept in for observation at Addenbrooke's hospital this morning,” says a statement posted on his Web site today. “He is comfortable and his family is looking forward to him making a full recovery.”

Hawking is known around the world for simplifying physics for non-scientists. His long life with ALS, which typically kills within three to five years, is highly unusual. Brian Dickie, director of research at the Motor Neurone Disease Association, told the British Guardian that Hawking "is at the extreme end of the scale when it comes to survival.”

Image of Stephen Hawking, 1999/NASA via Wikimedia Commons