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During the journey from Earth to Homestead II, Jim tries to send a message back to Earth. The computer informs him that it will take 19 years for the message to reach Earth.

Since we know that the ship is travelling at 50% of lightspeed and since we know that it's been 30 years since the ship set off, shouldn't the message should reach Earth in 15 years rather than 19?

marked as duplicate by Gallifreyan, Jason Baker, Dave Johnson, Möoz, bleh Jan 11 '17 at 22:04

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

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    Most likely something about them traveling and sending the message at the same time, they were moving farther as the message was going towards earth. – Riker Jan 11 '17 at 20:50
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    @Cascabel - That was my instinct. We see them slingshotting a star to pick up speed and in the original script at one point they plough through a small nebula. I'm guessing the ship was traveling faster for the first few years of the journey and is gradually slowing down as they collide with interstellar dust. – Valorum Jan 11 '17 at 21:09
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    Well, the ship has engines. Perhaps they were at max burn for the first few years, got up to .8 of lightspeed and have been gradually slowing down due to interstellar friction. – Valorum Jan 11 '17 at 21:34
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    The fact that you can only justify marking this question as a duplicate if you reference a particular answer, is a huge screaming clue that the questions are not, in fact, duplicates. (Also "the second answer" is totally devoid of meaning in a Stack Exchange context.) – Martha Jan 11 '17 at 21:52
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    @Martha - I've amended my answer (on the dupe) in order to more specifically address the point raised above. – Valorum Jan 11 '17 at 22:09

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