One of the greatest scientific minds of our time has died. Stephen Hawking was 76-years-old .
A UW-Milwaukee professor once worked side-by-side with Hawking on some of his greatest physics projects.
"That's me over on the side here," said Leonard Parker.
Parker spent part of his Wednesday looking through old photos.
"Stephen is in the center here," Parker said.
Reminiscing on memories of his friendship and work with Hawking.
"Well, it was shocking," he said. "People have been expecting something like that."
Over several decades, Parker and Hawking met overseas to dig deep into the unknowns of science.
"He could sit there and do his calculations largely in his head."
Hawking discovered particles that enter black holes in the universe eventually evaporate and disappear.
"Hawking actually found beautiful ways to extend the work to black holes and he beat me to it, let's put it that way," Parker said.
Hawking was diagnosed with A.L.S., commonly known as Lou Gehrig's Disease when he was 21. It left him using a wheel-chair and a speech synthesizer to communicate.
"He was a very friendly person actually, a lot of the time he spent quietly thinking," Parker said.
Parker remains astonished how the physicist overcame such a debilitating illness for so many years.
"No one else in Hawking's situation would have been able to do what he did," he said.