The University of Cambridge says renowned physicist Stephen Hawking isn't well enough to attend a conference held to celebrate his 70th birthday.

Hawking's remarkable career is being honored Sunday as part of a daylong conference on cosmology being hosted at the university.

But the celebrity scientist, who suffers from Lou Gehrig's disease, was released from hospital on Friday. And university Vice Chancellor Leszek Borysiewicz says Hawking's "recovery has not been fast enough for him to be able to be here."

Borysiewicz added that he believed Hawking would be well enough to meet some of the attendees over the next week and that he hoped Hawking would be able to follow the proceedings via videolink.