Stephen Hawking has died at the age of 76, according to his family. Here is a look back on his life as one of the world's foremost theoretical physicists. USA TODAY
Stephen Hawking, the British theoretical physicist who died Wednesday at 76, was one of the most famous scientists of the modern age.
He showed resilience in the face of a type of motor neuron disease that left him almost completely paralyzed.
For the non-specialist, Hawking's contributions to his subject can be hard to grasp. Here are some of his achievements, explained:
Hawking probed the origins of the universe by bringing together several different fields of study including cosmology (evolution and structure of the universe), gravity (the force that attracts separate objects), quantum theory (matter and energy), thermodynamics (heat and energy) and information theory (how data are stored and sequenced).
According to Albert Einstein's theory of relativity (a theory for space and time), the Big Bang — the idea that all matter in the universe began about 14 billion years ago with a massive explosion — started with a "singularity" (a tiny, single, concentrated point when all the laws of physics broke down).
Hawking's Ph.D. thesis at Cambridge University sought to prove that this tiny, single point was physically possible. Up until this point, it was not clear if a "singularity" was something real.
Hawking advanced our understanding of black holes, those places in space where gravity is so intense that no light can escape.
His first big idea was that black holes may not in fact really be black at all. He concluded that they emit heat particles or radiation, a theory that many physicists disagreed with because it contradicted some basic laws of quantum mechanics.
Today, this theory is known as "Hawking radiation."
However, Hawking struggled to fully explain how these particles could possibly escape and later in his life he revised this theory. He came to believe that any information that a black hole emits may actually be stored at its "event horizon" — the theoretical boundary space around a black hole that can't be observed from the outside.
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