A Brief History of Time: From the Big Bang to Black Holes is a book on theoretical cosmology by the physicist Stephen Hawking.

In A Brief History of Time, Hawking writes in non-technical terms about the structure, origin, development and eventual fate of the universe, which is the object of study of astronomy and modern physics.

Mitton was doubtful about all the equations in the draft manuscript, which he felt would put off the buyers in airport bookshops that Hawking wished to reach.

In A Brief History of Time, Stephen Hawking explains a range of subjects in cosmology, including the Big Bang, black holes and light cones, to the non-specialist reader.

He first describes the Aristotelian idea that the naturally preferred state of a body is to be at rest, and which can only be moved by force, implying that heavier objects will fall faster.

He mentions Danish scientist Ole Rømer's discovery that light travels at a very high but finite speed through his observations of Jupiter and one of its moons Io as well as British scientist James Clerk Maxwell's equations on electromagnetism which showed that light travels in waves moving at a fixed speed.

Einstein and Henri Poincaré later argued that there is no need for aether to explain the motion of light, assuming that there is no absolute time.

In 1924, Edwin Hubble discovered a method to measure the distance using the brightness of Cepheid variable stars as viewed from Earth.

Moreover, many astronomers also tried to avoid the implications of general relativity and stuck with their static universe, with one especially notable exception, the Russian physicist Alexander Friedmann.

His assumptions were later proved when two physicists at Bell Labs, Arno Penzias and Robert Wilson, found unexpected microwave radiation not only from the one particular part of the sky but from everywhere and by nearly the same amount.

Even if we calculate, the current expansion rate is more than the critical density of the universe including the dark matter and all the stellar masses.

The first model included the beginning of the universe as a Big Bang from a space of infinite density and zero volume known as 'singularity', a point where the general theory of relativity (Friedmann's solutions are based in it) also breaks down.

Roger Penrose used light cones and general relativity to prove that a collapsing star could result in a region of zero size and infinite density and curvature called a black hole.

Hawking then describes the eventual development of quantum mechanics by Heisenberg, Austrian physicist Erwin Schroedinger and English physicist Paul Dirac in the 1920s, a theory which introduced an irreducible element of unpredictability into science, and despite German scientist Albert Einstein's strong objections, it has been proven to be very successful in describing the universe except for gravity and large-scale structures.

While Danish scientist Niels Bohr's theory only partially solved the problem of collapsing electrons, quantum mechanics completely resolved it.

In this chapter, Hawking discusses black holes, regions of spacetime where extremely strong gravity prevents everything, including light, from escaping from within them.

Hawking describes how most black holes are formed during the collapse of massive stars (at least 25 times heavier than the sun) approaching end of life.

Hawking then describes how astronomers discover a black hole not directly, but indirectly, by observing with special telescopes the powerful X-rays emitted when it consumes a star.

According to Hawking, black holes must very slowly shrink over time and eventually "evaporate" because of this radiation, rather than continue existing forever as scientists had previously believed.

At the start of the Big Bang, the universe had an extremely high temperature, which prevented the formation of complex structures like stars, or even very simple ones like atoms.

These "wormholes" would appear identical to black holes from the outside, but matter which entered would be relocated to a different location in spacetime, potentially in a distant region of space, or even backwards in time.

However, later research demonstrated that such a wormhole, even if possible for it to form in the first place, would not allow any material to pass through before turning back into a regular black hole.

Hawking also describes his own "chronology protection conjecture", which provides a more formal explanation for why faster-than-light and backwards time travel are almost certainly impossible.

Quantum field theory (QFT) and general relativity (GR) describe the physics of the universe with astounding accuracy within their own domains of applicability.

Hawking believes that such refinement has a limit and that by studying the very early stages of the universe in a laboratory setting, a complete theory of Quantum Gravity will be found in the 21st century allowing physicists to solve many of the currently unsolved problems in physics.

In this final chapter, Hawking summarises the efforts made by humans through their history to understand the universe and their place in it: starting from the belief in anthropomorphic spirits controlling nature, followed by the recognition of regular patterns in nature, and finally with the scientific advancement in recent centuries, the inner workings of the universe have become far better understood.

He recalls the suggestion of the nineteenth-century French mathematician Laplace that the universe's structure and evolution could eventually be precisely explained by a set of laws whose origin is left in God's domain.

However, Hawking states that the uncertainty principle introduced by the quantum theory in the twentieth century has set limits to the predictive accuracy of future laws to be discovered.

However, for Hawking, most scientists today who work on these theories approach them with mathematical calculation and empirical observation, rather than asking such philosophical questions.

Hawking nonetheless expresses hope that one day everybody would talk about these theories in order to understand the true origin and nature of the universe, and accomplish "the ultimate triumph of human reasoning".