| 作者 |
 西方思想家百人之第九十三：阿尔伯特•爱因斯坦 Albert Einstein ( 1879-1955) |
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提个建议行么， -- 笑笑 - (38 Byte) 2009-11-23 周一, 22:45 (513 reads) |
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作者：网客JT 在 海归茶馆 发贴, 来自【海归网】 http://www.haiguinet.com
这里： （耽误了我20分钟灌水时间敲进去的。 偶尔为之没有问题。每篇都附原文似乎没有足够需求。）
German-born physicist of Swiss parentage, Einstein became a naturalised American in 1935, after leaving Hitler’s Germany to avoid persecution as a Jew. After an unpromising start to his academic career, at one time declaring, ‘I have given up the ambition even to get to a university’, he accepted a job in the Bern patent office, where he conceived the theories of general and special relativity which were to found modern physics. Einstein was also politically active, both in the cause of world peace and Zionism. In 1952 he was offered presidency of Israel but declined, claiming he was too naive in politics. On the relation between his scientific and political interests he once said, ‘Equations are more important to me, because politics is for the present, but an equation is something for eternity’.
The philosophical import of Einstein’s work is enormous. His theory of relativity assigns an unprecedented importance to the role of the observer in his description of the physical world, threatening the received notions of space and time, as found in Newton, Locke, Kant and others. The central aspect of Einstein’s works is that the speed of light is constant. It gives rise to the two most famous ideas of relativity physics: the equivalence of mass and energy expressed in the equation E=mc^2 (where E is energy, m is mass and c is the speed of light), and the law of nothing can travel faster than the speed of light.
These have at least two philosophically important consequences. First, it follows from relativity that one cannot speak of an event occurring at precisely the same time for different observers. Each observer’s time frame is relative to himself. Imagine an observatory on Jupiter looking at an observatory on Earth. In each an astronomer looks through his eyeglass at the other at, we might suppose, exactly the same time. Since light takes 35 minutes to travel from Jupiter to Earth, the event on Jupiter in which the astronomer looks through his telescope must have taken place 35 minutes before the astronomer on Earth observes the event. Equally, the same applies to the astronomer on Jupiter: as he observes the astronomer on Earth he is observing an event that took place 35 minutes prior to his own time frame. It is tempting to think there is some absolute position in which the two events could be observed as simultaneous, but this is exactly the possibility ruled out by relativity theory. Space and time are not independent dimensions, but form a four-dimensional unity, space-time, in which every event can only be recorded relative to a local time-frame.
The second philosophically interesting consequence of relativity is that although the speed of light is constant, its frequency (the number of waves of light per second) varies closer to massive objects like planets. This means time appears to run slower near a massive body than farther away. In 1962 physicists confirmed this prediction by using two very accurate clocks, one at the base and one at the top of a water tower. The clock at the base was found to run slower than the other. This gives rise to the famous ‘twins paradox’. Suppose one twin goes for a lengthy journey into space while the other stays on Earth. When he returns he would appear to be much younger than his twin. The paradox arises from the assumption of an absolute time frame. The relativity thesis means that each body carries around its own personal time scale which does not, in general, agree with the time scale of other entities. Relative to each other, fifty years near a massive gravitational body is a shorter duration than fifty years far away from a massive body. Thus while fifty years might have passed on Earth the space traveling twin might find he has only been away in space for thirty five years. The exact difference depends on the gravitation influences on the two twins throughout their lives.
The philosophical consequences of Einstein’s relativity theory, like the empirical consequences, are yet to be fully known. Issues about time-travel, the passage or ‘flow’ of time, the asymmetry between past and future and between cause and effect, are all issues that require an understanding of Einstein’s momentous work.
作者：网客JT 在 海归茶馆 发贴, 来自【海归网】 http://www.haiguinet.com
上一次由网客JT于2009-11-24 周二, 13:39修改，总共修改了2次
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