pushing us to look beyond our planet,

Stephen Hawking left this earth in the early hours this morning

Doctor's Told him he wouldn't live long. Yet, he went on to explain time itself.

He explored the wonders of the universe from a wheelchair.

His children offering this quote from their dad this morning.

IT WOULDN'T BE MUCH OF A UNIVERSE IF IT WASN'T HOME TO THE PEOPLE YOU LOVE.

>> I STUDY THE MARRIAGE OF SPACE AND TIME.

>> Reporter: LONG BEFORE THE OSCAR-WINNING PORTRAYAL OF HIM,

, WITH HIS UNIQUE COMPUTER VOICE.

>> MY NAME IS STEPHEN HAWKING.

>> ITS AMERICAN.

>> IS THAT A PROBLEM?

Reporter: AND PLAYING HIMSELF ON "THE BIG BANG THEORY."

>> ITS AN HONOR AND A PRIVILEGE TO MEET YOU, SIR.

>> I KNOW.

>> Reporter: BRITISH PHYSICIST STEPHEN HAWKING EXPLODED ON THE WORLD STAGE

WITH THEORIES OF HIS OWN.

"A BRIEF HISTORY OF TIME," a 1988 runaway best selling book

TURNING COMPLEX MATTER INTO RELATIVE SIMPLICITY TO FOR THE MASSES

HE UNITED THE TWO GREAT THEORIES OF THE UNIVERSE, RELATIVELY AND QUANTUM THEORY.

BORN IN 1942 IN OXFORD, ENGLAND,

HE WASN'T A WHIZ KID AND DIDN'T GET SERIOUS ABOUT HIS STUDIES AND PHYSICS

HE IMMERSED HIMSELF WITH COSMOLOGY AND ASTRONOMY.

AND DURING THAT TIME, HE WAS DIAGNOSED WITH ALS, Lou Gehrig's DISEASE

, CONFINING HIS BODY TO A WHEELCHAIR. HIS VOICE EVENTUALLY TO A MACHINE.

>> MY ILLNESS MEANS I CANNOT USE PENCIL AND PAPER

I HAVE TO DO THINGS IN MY HEAD.

>> Reporter: HIS MIND, BY THEN, BOUNDLESS.

HIS QUEST TO EXPLORE AND EXPERIENCE, INSATIABLE,

INCLUDING THIS 2007 WEIGHTLESS FLIGHT.

HAWKING CONCLUDED, OUR UNIVERSE BEGAN ABOUT 15 BILLION YEARS AGO

BEGAN ABOUT 15 BILLION YEARS AGO WITH A BIG BANG, TIME STARTED

WITH A BIG BANG, TIME STARTED SIMULTANEOUSLY.

ULTIMATELY, THE UNIVERSE WILL COLLAPSE, HE ARGUED,

UNTIL TIME MARCHES ON UNTIL THE END.

>> THERES NOTHING LIKE THE THRILLYOU DISCOVER SOMETHING THAT NO ONE KNEW BEFORE.

>> Reporter: GIVEN JUST TWO YEARS TO LIVE AFTER FALLING ILL AT 21,

STEPHEN HAWKING PACKED AN INCREDIBLE LIFETIME OF

ACHIEVEMENTS IN THE DECADES THAT FOLLOWED. BEATING THE ODDS.

HEARTFELT TRIBUTES COMING THICK

AND FAST THIS MORNING.

"THE BIG BANG THEORY" CAST,

SAID, IN LOVING MEMORY OF STEPHEN HAWKING.

IT WAS AN HONOR TO HAVE HIM ON "THE BIG BACK THEORY."

THANK YOU FOR INSPIRING US.

HIS DAUGHTER, LUCY, POSTING TO FACEBOOK.

THE BEST AND THE BRAVEST,

GOOD-BYE TO MY BELOVED FATHER WHO CHANGED THE WORLD.

IN A WORLD WHERE PEOPLE CAN SEEM SMALL-MINDED,

STEPHEN HAWKING GAVE US A DIFFERENT WAY OF

GAVE US A DIFFERENT WAY OF THINKING.

MY GOAL IS SIMPLE, HE SAID.

ITS A COMPLETE UNDERSTANDING OF THE UNIVERSE.

AND TO DESCRIBE HIS LIFE, HE SAID. MY EXPECTATIONS WERE REDUCED TO ZERO WHEN I WAS 21.

EVERYTHING SINCE THEN HAS BEEN A BONUS.