Stephen Hawking, the most famous theoretical physicist in the world, turned 70 on Sunday.

Born on Jan. 8, 1942, Hawking was diagnosed with motor neurone disease (Lou Gehrig's disease), at the age of 21. Doctors predicted at the time that he would die within two years.

Hawking is a medical miracle as the first person to live for such a long time after being diagnosed with Lou Gehrig's disease.

As part of Hawking's birthday celebration, leading physicists from around the world gathered at the University of Cambridge this week to raise a toast to the most renowned of their number, The Guardian reported.

There were discussions on the theoretical frontiers of black holes, cosmology, and fundamental physics as part of a symposium entitled "The State of the Universe."

On Sunday, Hawking himself is expected to deliver a public lecture on "A Brief History of Mine" at Cambridge's Center for Theoretical Cosmology.

Hawking is currently director of research at the department of applied mathematics and theoretical physics at Cambridge.

Check out the images of some of the moments in the life of the genius, Stephen Hawking.