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Why does warping space time still violate causality?

  1. Aug 19, 2015 #1
    I am having a tough time getting my head around this. I get that traveling faster then c in itself has an effect on the the flow of time from the reference of external observation and the person doing it (isn't actual FTL velocity causing backwards time?). But in a "warp bubble" for lack of a better term, time should flow the "same" as being relatively stationary-ish with respect to the reference you entered the bubble from (and this warp bubble would have no external frame of reference itself since it is actual time space warping, right?). If warping space time is like folding two pieces of paper together to effectively shorten the distance between two points, then how is causality somehow violated? You are just taking a shortcut.

    Think of it this way...if I could snap my fingers and transport myself to a point of space 10ly away, then I am in my own frame of reference not moving, but am just changing my coordinates. This seems to be the same as bending space time to bridge the gap between point A and B. Other than the impossibility of my snapping my fingers doing more than making a snapping sound, none of that seems to violate anything. But then if I snap my fingers and travel back to the initial coordinates, this somehow violates causality?

    Now, I get that when two objects in space are moving at various % c relative to each other, that there could be causality problems with instantaneous travel (or transmission of information) where the effect could be viewed from the frame of reference of the destination prior to the cause. But when you are effectively shrinking the distance, and then not actually traveling instantaneously how does this still cause that? I mean...instantaneous anything does not actually exist. t can never = absolute 0 when some action is performed.

    The only thing I can think of is that time itself is actually different at different points of space within the universe. Is this true? If the Big Bang is t=0, are all points in the universe the same t=x, or is the x variable due to the warping of space time due to the gravity of masses? Is "now" different everywhere you go? I've seen the diagrams of relative movement of bodies and how what appears to be "now" is different from the frame of reference locally compared to what you are observing (A, B, C happen in progression, simultaneously, and in reverse, as well as the train thought experiment-Relativity of Simultaneity), but is actual time different from one point in space to another? Is the universe only 3 billion years old near a black hole, and 30 billion years old near a "void"?

    And if so, does it even matter when warping between two points? I mean, lets say that from the Earth's frame of reference the universe is 13.82 billion years old. I want to travel to another star system where, from their frame of reference the universe appears to be 13.92 billion years...so time flows a tad faster. If I travel back to earth 5 minutes later, am I going to end up back in time?

    I know this "question" is actually seeded with about a dozen individual questions, but what I really would like an explanation of is why something like a warp drive or Alcubierre drive violates causality. How do I kill my grandfather by simply taking a shortcut which does take a finite and not instantaneous amount of time? How does changing my coordinates in a short amount of time allow for time travel without actually moving FTL within my frame of reference?
  2. jcsd
  3. Aug 19, 2015 #2
    As far as I know, the Alcubierre drive doesn't violates causality, and generally is considered as very clever piece of mathematics.
    The problem is that to physically realise it you would need to have exotic forms of matter that are not known to exist, and an enormous but stable source of energy.
    The concept is similar to the idea of trying to engineer a 'wormhole'.
  4. Aug 19, 2015 #3


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