A Brief History of Time

by Stephen Hawking

only in the few universes that are like ours would intelligent beings develop and ask the question, “Why is

the universe the way we see it?” The answer is then simple: if it had been different, we would not be here!

This work on inflationary models showed that the present state of the universe could have arisen from quite a large number of different initial configurations. This is important, because it shows that the initial state of the part of the universe that we inhabit did not have to be chosen with great care. So we may, if we wish, use the weak anthropic principle to explain why the universe looks the way it does now.

But if the universe is really completely self-contained, having no boundary or edge, it would have neither beginning nor end: it would simply be. What place, then, for a creator?

This says that in any closed system disorder, or entropy, always increases with time. In other words, it is a form of Murphy’s law: things always tend to go wrong!

The increase of disorder or entropy with time is one example of what is called an arrow of time, something that distinguishes the past from the future, giving a direction to time.

There are at least three different arrows of time. First, there is the thermodynamic arrow of time, the direction of time in which disorder or entropy increases. Then, there is the psychological arrow of time. This is the direction in which we feel time passes, the direction in which we remember the past but not the future. Finally, there is the cosmological arrow of time. This is the direction of time in which the universe is expanding rather than contracting.

it is more probable that the system will be in a disordered state than in an ordered one because there are more disordered states.

One can show that this increase in disorder is always greater than the increase in the order of the memory itself. Thus the heat expelled by the computer’s cooling fan means that when a computer records an item in memory, the total amount of disorder in the universe still goes up.

The direction of time in

which a computer remembers the past is the same as that in which...

Conditions in the contracting phase would not be suitable for the existence of intelligent beings who could ask the question: why is disorder increasing in the same direction of time as that in which the universe is expanding?

Einstein refused to believe in the reality of quantum mechanics, despite the important role he had played in its development.

Why did one time dimension and three space dimensions flatten out, while the other dimensions remain tightly curled up? One possible answer is the anthropic principle. Two space dimensions do not seem to be enough to allow for the development of complicated beings like us.

In Newton’s time it was possible for an educated person to have a grasp of the whole of human knowledge, at least in outline. But since then, the pace of the development of science has made this impossible.

In effect, God was confined to the areas that nineteenth-century science did not understand.

we have redefined the task of science to be the discovery of laws that will enable us to predict events up to the limits set by the uncertainty principle.

Up to now, most scientists have been too occupied with the development of new theories that describe what the universe is to ask the question why.

When a book was published entitled 100 Authors Against Einstein, he retorted, “If I were wrong, then one would have been enough!”