en
Stephen Hawking

A Briefer History of Time

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    Lina Pratiwije citiraoпрошле године
    Instead we use the light-year, which is the distance light travels in a year. In one second, a beam of light will travel 186,000 miles, so a light-year is a very long distance.
    exAspArkje citiraoпре 5 година
    in the nineteenth and twentieth centuries, science became too technical and mathematical for the philosophers, or anyone else except a few specialists. Philosophers reduced the scope of their inquiries so much that Wittgenstein, the most famous philosopher of the twentieth century, said, "The sole remaining task for philosophy is the analysis of language." What a comedown from the great tradition of philosophy from Aristotle to Kant!
    exAspArkje citiraoпре 5 година
    So even if we do find a complete set of basic laws, there will still be in the years ahead the intellectually challenging task of developing better approximation methods so that we can make useful predictions of the probable outcomes in complicated and realistic situations.
    exAspArkje citiraoпре 5 година
    On the other hand, seventy years ago, if Eddington is to be believed, only two people understood the general theory of relativity. Nowadays tens of thousands of university graduates do, and many millions of people are at least familiar with the idea. If a complete unified theory is discovered, it will be only a matter of time before it becomes digested and simplified in the same way and taught in schools, at least in outline.
    exAspArkje citiraoпре 5 година
    Further, the rate of progress is so rapid that what you learn at school or university is always a bit out of date. Only a few people can keep up with the rapidly advancing frontier of knowledge, and they have to devote their whole time to it and specialize in a small area. The rest of the population has little idea of the advances that are being made or the excitement they are generating.
    exAspArkje citiraoпре 5 година
    In Newton’s time, it was possible for an educated person to have a grasp of the whole of human knowledge, at least in broad strokes. But since then, the pace of the development of science has made this impossible. Because theories are always being changed to account for new observations, they are never properly digested or simplified so that ordinary people can understand them. You have to be a specialist, and even then you can only hope to have a proper grasp of a small proportion of the scientific theories.
    exAspArkje citiraoпре 5 година
    What this seems to indicate is that there is a sort of democracy (in the sense of having equal voices) among supergravity, string, and p-brane theories: they seem to fit together, but none can be said to be more fundamental than the others. Instead they all appear to be different approximations to some more fundamental theory, each valid in different situations.
    exAspArkje citiraoпре 5 година
    String theories, however, have a bigger problem: they seem to be consistent only if space-time has either ten or twenty-six dimensions, instead of the usual four!
    exAspArkje citiraoпре 5 година
    Some go much further and propose a strong version of the principle. According to this theory, there are either many different universes or many different regions of a single universe, each with its own initial configuration and, perhaps, with its own set of laws of science. In most of these universes the conditions would not be right for the development of complicated organisms; 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!
    exAspArkje citiraoпре 5 година
    Presumably, in the very early universe all the dimensions would have been very curved. Why did one time dimension and three space dimensions flatten out, while the other dimensions remain tightly curled up?
    exAspArkje citiraoпре 5 година
    Why don’t we notice all these extra dimensions if they are really there? Why do we see only three space dimensions and one time dimension?
    exAspArkje citiraoпре 5 година
    The main difficulty in finding a theory that unifies gravity with the other forces is that the theory of gravity—general relativity—is the only one that is not a quantum theory: it does not take into account the uncertainty principle.
    exAspArkje citiraoпре 5 година
    the discovery that the speed of light appeared the same to every observer, no matter how he was moving, led to the theory of relativity—and the abandoning of the idea that there was a unique absolute time.
    exAspArkje citiraoпре 5 година
    Newton’s laws of motion put an end to the idea of absolute position in space. We have now seen how the theory of relativity gets rid of absolute time.
    exAspArkje citiraoпре 5 година
    If, say, the sun suddenly disappeared, Maxwell’s theory tells us that the earth wouldn’t get dark for about another eight minutes (since that is how long it takes light to reach us from the sun) but, according to Newtonian gravity, the earth would immediately cease to feel the sun’s attraction and fly out of orbit. The gravitational effect of the disappearance of the sun would thus have reached us with infinite speed, instead of at or below the speed of light, as the special theory of relativity required.
    exAspArkje citiraoпре 5 година
    Einstein’s 1905 theory of relativity is called special relativity. That is because, though it was very successful in explaining that the speed of light was the same to all observers and in explaining what happens when things move at speeds close to the speed of light, it was inconsistent with the Newtonian theory of gravity.
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