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RELATIVE Space/Time and Lightspeed question

  1. May 2, 2012 #1
    Hey everyone,
    First off I am not a physics major or a math guru. Physics has always been some thing that I have been interested in though. Physical science and the way things work has always interested me. I mention this, because I do not want to come off sounding like an idiot. I know most people that probably come to these forums probably have a better education and a far greater understanding of these concepts than I do.
    The concept of light speed, space time, and relativity has made sense, but something has always alluded me. From what I understand the speed limit of light can not be changed (in a pure vacuum state that is), and it is space and time that change, not the speed of light itself. That brings me to my question:
    Say we have two space ships (that is the easiest way I can describe this so just go with me on this one) and both head in opposite directions from one another slowly accelerating. At some point, Ship A is heading one way and reaches over 1/2 the speed of light from it's starting point. Likewise, Ship B hits over 1/2 the speed of light from it's starting point heading in the complete opposite direction. At that point, the differential between the two would exceed light speed. I'm pretty sure that there are objects in our own universe that currently are doing this. What happens in relation to eachother?
    To ask more specific questions, would Ship A and Ship B still see eachother? What would time be like in relationship to eachother, would one ship appear to be going backwards in time in relation to the other? If there were a doorway, lets say a 'wormhole', were connected between the two, what would be the difference from walking from ship A to ship B? Would that constitue time travel (even though I would guess that would be a yes, I am just not sure in what direction)?
    In case I am missing some law or theory, would it be any different when the ships reached 99.9% the speed of light in opposite directions, in theory meaning they are nearly doubling the speed of light in velocity from one another?
    This has been something that has boggled me since I started becoming interested in physics. If someone could answer it, it would be very much appreciated! If possible, please explain in the most basic of terms (equations and "so-and-so's theory of what-not says," will probably be more than I am aquainted with, but you don't have to describe it like you are talking to a kindergartener either). Thank you so much for your time and input. Any help is greatly appreciated!
  2. jcsd
  3. May 2, 2012 #2


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    Welcome to PF!

    Hey Riptide! Welcome to PF! :smile:
    Each regards the other as moving at 4c/5, see http://en.wikipedia.org/wiki/Velocity-addition_formula#Special_theory_of_relativity :wink:
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