LONDON — Cambridge University says celebrated physicist Stephen Hawking has been forced to cancel several public engagements because of ill health.

The university said Tuesday that the affected public appearances include the BBC's annual Reith Lectures, which Hawking was scheduled to record on Thursday at the Royal Institution in London.

The university did not provide any details about the condition of the 73-year-old professor, who is thought to be one of the longest-living survivors of motor neurone disease.

Hawking was expected to discuss black holes and answer questions from BBC radio listeners for his lecture. The BBC said his lecture is postponed until the new year and once he is better.