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A question

  1. Aug 2, 2005 #1
    There are 2 people, who are twins. One was born on earth, and the other was born in space. Because earth orbits the sun, so the twin born on earth is like traveling on earth. So, would the twin born on earth age slower than the twin who stayed at space?
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  3. Aug 3, 2005 #2


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    What is space born twin motion relative to earth? (How did they get born in different locations from the same mother???)
  4. Aug 3, 2005 #3


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    Excellent question. :rolleyes:

    aznpride2pac: see this and following posts.
  5. Aug 3, 2005 #4
    how could they be twins if one was born in space and the other on earth?
    o well, carry on.... :)
  6. Aug 3, 2005 #5


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    Are they "Irish twins"? :wink: If so, they may not agree on simultaneity. :smile:
  7. Aug 3, 2005 #6
    I assume you mean that there is some point in space that the earth passes by each year in its orbit - and one twin remains fixed at that location and the other rides along with the earth. To answer the question, you will need to know how one twin acquired motion wrt to the other - did they both get plunked out on earth and then one got snagged on a sky hook as the earth traveded along in its orbit - or did they arrive in space and one then hitched a ride as the earth passed by. When you decide this, you can say that the twin that acquires motion after they were at rest in the same frame - will age slower.
  8. Aug 3, 2005 #7


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    There is not enough information to give a direct answer for the problem as stated.

    For instance, if we assume the second twin is hovering with a rocket or light sail, stationary with respect to the sun, way out in the Oort cloud, the space twin will age [correction- faster, dang it] than the Earth twin because of the difference in gravitational potential. While I have not performed an exact calculation for this case, I expect that the gravitational time dilation will outweigh the velocity-induced time dilation, much as it does for GPS satellites. In this case, the space-twin would be out of the gravity well of both the Earth and the Sun.

    http://www-astronomy.mps.ohio-state.edu/~pogge/Ast162/Unit5/gps.html [Broken]

    Last edited by a moderator: May 2, 2017
  9. Aug 4, 2005 #8


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    That´s nonsense. Neglecting gravity, the twin staying in an inertial frame will age faster, no matter how he got there.
    So the twin on earth will age slower.
  10. Aug 4, 2005 #9
    you know what i cant make up my mind....nvmd im pretty sure i agree that that is not nonesense though

    yes... now i am sure without gravity on earth... you would be right, but earth is moving relativley slow compared tot he speed of light, and we would not see a great amount of velovity induced time diation... now suppose you stop mars from moving, and put one twin on there... and your speculation would be correct... otherwise, i agree with the big guy up there (the one with like 2000 posts, forgot his name by now)
    Last edited: Aug 4, 2005
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