Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Do we not even exist in some FoR?

  1. Dec 16, 2011 #1
    What I mean is are there things traveling so fast in outer space that we don't exist in their FoR?

    Or we haven't even been born yet in their FoR?
  2. jcsd
  3. Dec 16, 2011 #2
    Beats me! And what about rocket man, orbiting a huge black hole, we get 50,000 years older while he ages a day? Assuming he can escape the vicinity of the black hole and return to "normal" time, this suggests that the future is pre-determined.

    This kinda stuff hurts my head...
  4. Dec 18, 2011 #3
    What do you mean by "yet"?

    We do exist in all frames of reference.

    If there's an event (like us being born) in one frame, it occurs in all frames of reference.

    It's just that its coordinates (position, and time) with respect to some other event vary from frame to frame. So if our birth and some other event are separated by a spacelike interval - there are frames in which we are born before, during, and after the occurence of this other event.

    A question whether there is a frame in which we haven't been born yet - I think is irrelevant. It sounds like "is there a frame in which now (at this instant of time) we don't exist yet" - but there's no such thing as universal time.
  5. Dec 18, 2011 #4


    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor
    2018 Award

    This is a very strange and vague question, and at this point, I do not see it as being a physics question, much less a Relativity-related question. I'll give it a bit more time, but if this has very little physics content, then this topic will be closed.

  6. Dec 18, 2011 #5


    User Avatar
    Science Advisor


    Since that thread discussed physics and philosophy, let me recommend the OP in that thread for the formulation of the problem, and DaleSpam's post #9 (I'm not sure it's correct, but I do so because he's usually accurate, and I'm too lazy to think).
    Last edited: Dec 18, 2011
  7. Dec 18, 2011 #6


    User Avatar
    Gold Member

    No. Nothing locally is moving with respect to us at faster than the speed of light. Any object, moving at any speed in our vicinity will perceive us as moving arbitrarily slow, approaching zero.
  8. Dec 18, 2011 #7
    If you take the Earth as an event, is there some way that in someones FOR the Earth is an event which has yet to happen?
  9. Dec 18, 2011 #8
    I just thought that certain events happen at certain times depending on what FOR you refer to?

    So is there a frame of reference where the Earth or even our Solar system hasn't been formed yet?
  10. Dec 18, 2011 #9


    User Avatar
    Gold Member

    As viewed from a point 6 billion light years away, yes, the solar system is still a condensing ball of dust and gas.
  11. Dec 18, 2011 #10
    I was under the impression that the relativity of simultaneity had more to do with an object moving than distance.

    Wouldn't the point that is 6 billion light years away still agree on the time of the Earth happening if he is moving in uniform motion to the Earth?

    I'm not really sure what I meant to say with my original post.

    I just have this idea in my head that depending on the FOR you are in things happen at different times than other FOR. I just wonder if something is traveling so fast out there that the formation of our planet has not happened in their FOR.
  12. Dec 19, 2011 #11


    User Avatar
    Science Advisor

    The earth is not an event. You being born on the earth is an event.

    The quick answer to your question is "yes".

    See the link in post #5, especially DaleSpam's https://www.physicsforums.com/showpost.php?p=1765715&postcount=9 explanation as to why this is not a true paradox, only an apparent paradox like the twin paradox.
  13. Dec 19, 2011 #12
    My birth may have not happened in some FOR correct?

    That means anything from that moment on hasn't happened either (in that FOR), correct?
  14. Dec 19, 2011 #13


    User Avatar
    Science Advisor

  15. Dec 19, 2011 #14


    User Avatar
    Science Advisor
    Gold Member

    Please go back and reread Loro's response to you in post #3. He said every event occurs in every frame. Even in your rest frame, if you set the time coordinate to a value prior to your birth, then you have not yet been born. The same thing is true in every other frame. If you set the time coordinate before the event of your birth, then you have not yet been born.

    I think what may be confusing you is that you are thinking that because there is a reality to "now" in your FoR, then there must be a corresponding "now" in all other FoR's and in some of those you have not yet been born. But as far as the FoR is concerned, all times and all locations are on an equal footing--they don't correspond to any particular observer's experience as they encompass all observers in all states of motion from one end of the horizon to the other and in all directions from eternity past to eternity future.

    And don't be confused by the term "event". It isn't restricted to an actual "happening" at a particular place and time. It is simply any arbitrary collection of the four coordinates making up a particular location at a particular time, even if nothing exists at that location, or if time never occurred at that location, either in the past or in the future (for example 100 billion years ago or 100 billion years in the future). But we can still use the Lorentz Transform to see what the coordinates for an event a trillion light years away and occuring a trillion years in the future would be in a frame that was moving at .999999c away from the first frame.
  16. Dec 19, 2011 #15
    I was my understanding that there are galaxies on the "other side" of the universe moving away from us faster than light. Therefor, our light cones will never intersect.
  17. Dec 20, 2011 #16
    I suppose the simple answer to the OP is that the term "exists" is global, and is not relative to any frame or observer. Hence a simple double negative answer (we don't not exist to anyone).

    But there are several interesting elementary issues.

    As has been said, one point in space-time may be either within or outside another point's light cone. If inside, a signal from the the first point can reach the second point. This condition can be true either one way, the other way or neither way, but not both ways.

    But even if an object is not visible from another object, it can have been influenced by it in the past. And even if an object cannot be seen by another object, it may potentially affect it in the future. This is a good reason why it is unreasonable to restrict the concept existence to what can be observed.

    Relevant to the original question is that the concepts of being "potentially visible" and "potential influence" do not depend on speed at all, only location in space-time.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook