## Conceptual Physics (12th Edition)

Published by Addison-Wesley

# Chapter 35 - Think and Explain: 62

#### Answer

Yes, it is possible because there is no absolute standard of time.

#### Work Step by Step

Imagine a star is 20,000 light-years from us, so we agree that light takes 20,000 years to get to us. From our viewpoint, an astronaut traveling close to c would take just over 20,000 years to travel there. However, from the traveling astronaut's frame of refer­ence, the distance is contracted. If she travels sufficiently close to the speed of light, say, such that the $\gamma$ factor is 20,000, the distance to her will appear to be much shorter: short enough to cover in 1 year of her time. Earthlings would see her clock as moving at a snail's pace: 20,000 times slower than our clocks. She could make a round trip in well under a 70-year lifespan. However, the Earth she returns to will have aged at least 40,000 years!

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