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Relativity and Space Travel

  1. Sep 11, 2006 #1
    This question might not belong in this category, and it may seem a bit of an out there question also...
    Based on the principals of relativity, if aliens are real (that i hope so), wouldn’t they come back to their planet far into the future after visiting our own planet?? I ask this because they must have to travel at a very high velocity and doing so over a great distance will bring you into the future of that planet.
    Does physics support the possibility of aliens visiting earth, or does it disagree with this theory?
  2. jcsd
  3. Sep 11, 2006 #2


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    They could leave tomorrow and still arrive before you post this message... :eek:
  4. Sep 11, 2006 #3


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    Staff: Mentor

    Physics makes it very difficult for aliens to get here, though not impossible. They could have much longer lifespans than us, not care about their age upon return, etc, but it does constrain the practicality of spaceflight to other solar systems.
  5. Sep 11, 2006 #4

    Ivan Seeking

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    In the sense that some people believe that ET might be visiting - coming and going at will - ET would have to know much that we don't. Based on what we do know from Relativity, it seems unlikely that any species would undertake an interstellar flight. The energy requirement is highly problematic if not impossible to ever achieve.

    Physics is not complete so we can't really be sure what is and is not possible.
  6. Sep 14, 2008 #5


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    Depending on how close to the speed of light that they are traveling, "they" (i.e. the travelers) would have aged much more slowly than those on their home planet (or ours).

    But that's not the real issue. As you approach the speed of light, things start getting much, much more massive (traveling the speed of light would cause you to have infinite mass). This requires more and more (exponential) amounts of energy (to travel the speed of light would require an infinite amount of energy). So, (hopefully) there're some important things about astrophysics that we don't know yet.

    Wormholes provide a interesting possibility, but that is just a hypothesis right now.
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