The Theory of Everything: The Origin and Fate of the Universe is an unauthorized 2002 book of some collected works by Stephen Hawking. It was assembled from seven lectures on audiotape by Hawking originally released in 1994 under the title, Stephen W. Hawking's Life Works: The Cambridge Lectures. The book's title is in reference to the theory of everything, a physicists' jargon term for a theory in physics which unifies the four fundamental forces of nature: gravity, the strong force, the weak force, and the electromagnetic force.
Several years ago Stephen Hawking said that there was a fifty-fifty chance that an actual unification of the four fundamental forces – a Theory of Everything – would be achieved. Recently, however, he has become more pessimistic on this score.

From the book

On April 29, 1980, I gave my inaugural lecture as the Lucasian Professor
of mathematics at Cambridge. My title was, Is the End in Sight for
Theoretical Physics? I described the progress we had already made in the
last hundred years in understanding the universe and asked what the
chances were that we would find a complete unified theory of everything
by the end of the century. Well, the end of the century is almost here.
Although we have come a long way, particularly in the last three years, it
doesn’t look as if we are going to quite make it.
In my 1980 lecture I described how we had broken down the problem of finding a theory of
everything into a number of more manageable parts. First of all we had divided the
description of the universe around us into two parts. One part is a set of local laws that tell us
how each region of the universe evolves in time, if we know its initial state, and how it is
affected by other regions. The other part is a set of what are called boundary conditions.
These specify what happens at the edge of space and time. They determine how the universe
begins and, maybe, how it ends. Many people, including probably a majority of physicists,
feel that the task of theoretical physics should be confined to the first part, that of formulating
local laws that describe how the universe evolves in time. They would regard the question of
how the initial state is determined as being beyond the scope of physics and belonging to the
realms of metaphysics or religion. But I’m an unashamed rationalist. In my opinion the
boundary conditions of the universe that determine its initial state are as legitimate a matter
for scientific inquiry as are the laws that govern how it evolves.
In the early 1960s the forces that were known to physics were classified into four categories
that seemed to be separate and independent of each other. The first of the four categories was
the gravitational force, which is carried by a particle called the graviton. Gravity is by far the
weakest of the four forces. However, it makes up for its low strength by having two important
properties. The first is that it is universal. That is, it affects every particle in the universe in
the same way. All bodies are attracted to each other. None are unaffected or repelled by
gravity. The second important property of the gravitational force is that it can operate over
long distances. Together, these two properties mean that the gravitational forces between the
particles in a large body all add up and can dominate over all other forces.

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