A Brief History of Time

by Stephen Hawking

As we shall see, the concept of time has no meaning before the beginning of the universe.

But in 1929, Edwin Hubble made the landmark observation that wherever you look, distant galaxies are moving rapidly away from us. In other words, the universe is expanding.

A theory is a good theory if it satisfies two requirements. It must accurately describe a large class of observations on the basis of a model that contains only a few arbitrary elements, and it must make definite predictions about the results of future observations.

The eventual goal of science is to provide a single theory that describes the whole universe.

Today scientists describe the universe in terms of two basic partial theories – the general theory of relativity and quantum mechanics.

Yet if there really is a complete unified theory, it would also presumably determine our actions. And so the theory itself would determine the outcome of our search for it!

The fundamental postulate of the theory of relativity, as it was called, was that the laws of science should be the same for all freely moving observers, no matter what their speed.

As an object approaches the speed of light, its mass rises ever more quickly, so it takes more and more energy to speed it up further. It can in fact never reach the speed of light, because by then its mass would have become infinite, and by the equivalence of mass and energy, it would have taken an infinite amount of energy to get it there. For this reason, any normal object is forever confined by relativity to move at speeds slower than the speed of light. Only light, or other waves that have no intrinsic mass, can move at the speed of light.

Another prediction of general relativity is that time should appear to run slower near a massive body like the earth.

Newton, and others, should have realized that a static universe would soon start to contract under the influence of gravity.

In general, quantum mechanics does not predict a single definite result for an observation. Instead, it predicts a number of different possible outcomes and tells us how likely each of these is.

Dante said of the entrance to Hell: ‘All hope abandon, ye who enter here.’

There was a young lady of Wight Who travelled much faster than light. She departed one day, In a relative way, And arrived on the previous night.

‘The sole remaining task for philosophy is the analysis of language.’