Unformatted text preview: c takes her 4/0.6 years, or 80 months. BUT he doesn’t see her turn around until 4 years later, because of the time light takes to get back to earth from alphacentauri! In other words, he will actually see her aging at half his rate for 80 + 48 = 128 months, during which time he will see 64 flashes. When he sees his sister turn around, she is already more than half way back! Remember, in his frame the whole trip takes 160 months (8 light years at 0.6 c ) so he will only see her aging at twice his rate during the last 160  128 = 32 months, during which period he will see all 64 flashes she sent out on her return trip. Therefore, by counting the flashes of light she transmitted once a month, he will conclude she has aged 128 months on the trip, which by his clock and calendar took 160 months. So when she steps off the spacecraft 32 months younger than her twin brother, neither of them will be surprised!...
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 Fall '10
 DavidJudd
 Physics, Light

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