The Physics of Time Travel: Part I
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Before we start talking about the physics of time travel, let me say a few more words on time itself, in a way slightly less metaphysical that was the discussion in the previous chapter (which is why I’m writing this here, in a chapter with an increased emphasis on the analytical). When we speak of journeying to either the future or the past, we are implicitly making a distinction in the direction of the time traveler’s trip. But does time actually have a direction? Is there an arrow that points the way? The answer seems obvious: of course time has a direction. After all, everybody ‘knows’ it flows from past to future. There is a curious language problem here, however, because we also like to say the present recedes into the past, which implies a ‘flow’ in the opposite direction, from future to past. Well, despite this snarled syntax, can we at least distinguish past from future, whichever way time flows?