How to Build a Time Machine

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Time travel has been a popular science-fiction theme since H. G. Wells wrote his celebrated novel in 1895. But can it really be done? Is it possible to build a machine that would transport a human being into the past or future?


For decades time travel lay beyond the fringe of respectable science. In recent years, however, the topic has become something of a cottage industry among theoretical physicists. The motivation has been partly recreational—time travel is fun to think about. But this research has a serious side, too. Understanding the relation between cause and effect is a key part of attempts to construct a unified theory of physics. If unrestricted time travel were possible, even in principle, the nature of such a unified theory could be drastically affected.



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