Einstein came to this conclusion using a series of thought experiments (Fig. 5.2).3 In one of these, he imagined himself sitting on a train traveling away from a clock tower approaching the speed of light. Since light coming from the clock carried information about the change in position of the hands of the clock—that is, about the passage of time—he realized that if he traveled near the speed of light, information about the movement of the clock hands would take longer and longer to catch up to him as he moved away from the clock at higher and higher speeds and got closer and closer to
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