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A very basic question -- traveling to a destination several thousand light years away

  1. Jan 20, 2015 #1
    Where has my thinking gone wrong in the following?

    A man begins traveling to a destination several thousand light years away, accelerating to a velocity of near-light speed. Time dilations and space contractions would result in the trip lasting only a few years from his perspective. From the perspective of people at the destination point, the trip would last longer than the time it would take for light to traverse several thousand light years. Hence, many generations of people at the destination would come and go over the course of the trip, which would only be few years for the traveler.

    Where is the flaw here? Any help would be greatly appreciated.
  2. jcsd
  3. Jan 20, 2015 #2


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    The people at the destination won't know that the man is coming their way until just a few years before he arrives. Many generations will pass from the time he leaves until they see him leave. At that time they will see him come towards him very quickly and they will see time on his spaceship progress very rapidly. After they see him leave and after he arrives, they can calculate when he left according to their rest frame and they will establish that he left several thousand years earlier.
  4. Jan 20, 2015 #3


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    No flaw - that's what I'd expect.

    What's bothering you about it?
  5. Jan 20, 2015 #4
    Thank you, Ibix. Embarrassingly, a lack confidence prompted my post. I wanted to confirm that my account of what would happen under the specified conditions is consistent with relativity theory. I appreciate your response.
  6. Jan 20, 2015 #5


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    Concur with Ibix. The scenario accurately describes a relativistic rocket trip.
  7. Jan 20, 2015 #6


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    You might want to look up "relativity of simultaneity", which is the third element of the description of a relativistic trip. Not only do observers in relative motion disagree on distances and elapsed times between events, they disagree on what is "now". So according to observers on the origin and destination planets, calendars on the two planets show the same dates. According to the traveller, however, the calendars do not agree.

    The disagreements over distance, elapsed time and what is "now" are always add up to a coherent picture of the trip from any perspective.
  8. Jan 20, 2015 #7
    I will. Thanks again.
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