A Brief History of Time

In our daily life we do not understand almost anything in the world. Shortly think the mechanism that generates the light of the sun and enables life; in the gravity, that glues us to an Earth that otherwise would launch us in rotation to the space; or the atoms that we are made and whose stability we depend crucially. Except for the children (who do not know enough to do not only important questions), few of us spend much time considering the nature is the way it is, from which emerged the cosmos, or whether he ever existed, if the time sometime go back, making the effects before the causes, or whether there are maximum limits to human knowledge. There are even children - knew some of them - who want to know in what looks like a black hole; which is the smallest portion of matter; why we remember the past and not the future; how to explain, if there was a primordial chaos, that there is order now, at least apparently; and why there is an universe.

In our society it is not unusual for parents and teachers respond to most of these questions with a shoulder to give, or appealing to religious concepts vaguely remembered.  Some do not comply with such attitudes, because they viscerally expose the limitations of human understanding.

Much of the philosophy and science was driven by these questions. A growing number of adults begin to dare asking this genre questions and occasionally gets surprising answers. Equidistant of atoms and stars, expand our exploratory horizon to reach the knowledge of both the smaller as bigger phenomena.

Carl Sagan
Cornell University
Ithaca, Nova York

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To talk about the nature of the universe and discuss issues such as whether it has a beginning or an end, we must have a clear view of what is a scientific theory. In a more simplistic view, the theory is only a model of the universe, or a restricted part of its whole; a set of rules that relate model's quantities for comments that we can do. It exists only in our thinking and has no other reality (whatever it means). One theory is considered good if it meets two requirements: to accurately describe a large class of observations, based on a model that contains only predictions defined as the results of future observations. For example, the Aristotle's theory that everything arose from the four elements, earth, wind, water and fire, it was easy enough to qualify, but did not set any forecast. On the other hand, Newton's theory of gravity is based on an even simpler model, where the bodies are attracted with a proportional force called mass quantity, and inversely proportional to the square of the distance between them. Predicted, however, the movements of the Sun, Moon and planets, with a high degree of accuracy.

The eventual goal of science is to promote a single theory that describes the entire universe. However, the approach that most scientists currently follows is separating the problem into two parts. First there are the laws that explain the changes of the universe over the time. (If we know how the universe is behaving at any given moment, these physical laws will told us how it will be at any moment later.) Second is the issue of initial state of the universe. Some people believe that science should focus only on the first part: they take the initial situation issue as a subject for metaphysical or for religion. They would say that God, being omnipotent, could have started the universe as wanted. Maybe so, but in this case he could have done themselves to develop on a completely arbitrary way. Even more: it seems that he chose to do it evolve in a manner quite regularly, according to certain laws. It is therefore also reasonable to suppose that there are also laws governing the initial state. (*)

The uncertainty principle

The success of scientific theories, particularly Newton's gravity, led a French scientist, the Laplace's Marquis, at the beginning of the nineteenth century, to argue that the universe was completely deterministic. Laplace suggested that there should be a set of scientific laws that they would predict everything that happened in the universe, just as much for who knew the complete state of the universe at a given time. For example, if we knew the Sun's and planet's positions and speeds in an x time, then we could use Newton's Laws to calculate the Solar System's state at any other time. The determinism seems quite obvious here, but Laplace goes beyond, assuming that there are similar laws governing everything else, including human behavior.

The scientific determinism doctrine was strongly rejected by who believed that it infringed the divine freedom interference in the world; meanwhile remained the standard's science assumption until the early years of this century. One of the first indications that this belief should be abandoned appeared when the calculations of British scientists Lord Rayleigh and Sir James Jeans suggested that a heated object, or a body like a star, must radiate energy in an infinite reason. In accordance to the laws in what was believed at that time, a heated body must deliver electromagnetic waves (such as radio waves, visible light or X-ray) also in all frequencies. It should, for example, emit the same amount of energy in waves with frequencies between one and two trillion waves per second, as in waves with frequencies between two and three trillion waves per second. But since the number of waves per second is unlimited, the total energy radiated is infinite.

To avoid such an outcome obviously ridiculous, the German scientist Max Planck suggested, in 1900, that light, X-rays and other waves could not be emitted to an arbitrary reason, but only in certain amounts that called quanta. Each quantum would have a certain energy quota, the greater the higher the frequency of the waves; so at a high enough rate, the emission of a single quantum require more energy than available. Therefore, radiation at high frequencies would be reduced, then the rate of energy loss of a body would be finite.


It has proved very difficult to find a theory that describes the entire universe. So the problem is divided into several parts and many partial theories are invented. Each one of them describes and predicts a limited number of observation categories, relegating the effect of other quantities, or those represented by simple sets of numbers. It may be that this approach is completely wrong. If everything in the universe, in a fundamental manner, depends on everything else, it may be impossible to reach a whole solution through the full investigation of the isolated problem parts. Still, this was certainly the way in which it has made progress in the past. The classic example is again Newton's gravity theory, which states that the gravitational force between two bodies depends only on a number associated to each body, its mass, but is, moreover, regardless of the materials which they are made. Therefore, is not need to have a structure and composition theories of the sun and the planets to calculate their orbits.

However, if in fact we discover a complete theory, it will, over time, be understood, roughly, by all and not just by a few scientists. So should all, philosophers, scientists and even lay people, be able to be part of discussions on the question of why we and the universe exist. If we find the answer to this we will have the final triumph of human reason, because then we reached the knowledge of the mind of God.

Translated from: Uma Breve História do Tempo - Stephen W. Hawking, Editora Rocco.
Original title: A Brief History of the Time: From the Big Bang to Black Holes, 1988.

The universe is a big equation where we are the result. We just have some unknowns that equation.



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