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DAH

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After reading this thread it got me thinking about the twin paradox, so I looked through some old notes from a module I studied on this subject. According to one of my textbooks, if the traveling twin travels to Alpha Centauri (which is 4.2 light years from Earth) at a speed of 0.9 c, then the Earthbound twin would record a time of 4.7 years to complete the journey. However, for the traveling twin in his reference frame that time would be reduced to 2 years due to time dilation.

The textbook also mentions the relativity of simultaneity, but further reading it also states that in this case the traveling twin who is essentially traveling to another star system, experiences length contraction, where the space in front of the ship contracts and therefore the distance to Alpha Centauri decreases for the traveling twin. For the Earthbound twin however, he doesn't experience length contraction therefore he sees the ship travel the full 4.2 light years.

Is this correct or is my textbook wrong?