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Does the 4th dimension mean our universe is definite?

  1. Jul 8, 2010 #1
    I've recently been learning about relativity and quantum physics. I understand it quite well now but i have a thought experiment that doesn't make sense.

    If i travel into the future through a high speed train and see the world blown up by some epic disaster, doesn't this mean that this was destine to happen?

    Since we can travel back and fourth in the 4th dimension(easily forward, but not so much backwards) does this mean that every thing in the universe is definite and fate is real?

    Quantum mechanics obviously doesn't allow for this but from my understanding(which could easily be wrong) this is only due to the 5th dimension, not the fourth.
  2. jcsd
  3. Jul 8, 2010 #2
    We cannot discuss things like 'destiny' or 'fate' in science; they lie in the realms of religion and/or philosophy. We can discuss causality however. There are debates in the philosophy of science as to whether or not random microscopic events actually affect the macroscopic causality that is a part of our everyday world. If you search for articles on say, physics news.org you can find several titles that point out that the macroscopic world can in fact be influenced by microscopic events (ex. macroscopic resonance in circuits due to quantum tunneling of electrons). My 'philosophical' opinion is that the macroscopic world behaves largely independently of microscopic events, and can therefore be referred to as 'causal'. This being the case, the future of a planet is largely laid out by causal events. If you want to refer to this large-scale causality as 'fate' or 'destiny' beware that you are beginning to cross the line into discussions outside the realm of 'science'; this is something you'll have to wrestle with yourself.
  4. Jul 8, 2010 #3


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    The question of whether a classical theory is deterministic or not doesn't depend on the structure of spacetime (the question of whether the speed that's the same in all inertial frames is finite or inifinite). It only depends on whether the equations of motion have a unique solution or not.

    I don't know what this would be a reference to.
  5. Jul 8, 2010 #4
    I'm concerned about your use of traveling "back and fourth" in time. Theoretically, a photon can move 'backwards' in time because it travels 'at' the speed of light, thus you could say that 'time does not apply' to it (I don't even want to discuss tachyons here because there's too much hand-waving in my opinion on that topic). In this regard, 'information' in the form of light could theoretically travel 'backwards' in time, where by 'backwards' I really mean it will at least appear to travel a finite distance 'instantaneously' if you were traveling with the photon (see Feynman diagrams), but you cannot. As you've pointed out yourself, we can only travel into the future, but not backwards, but you kind of contradicted yourself in the same sentence. I'm hardly a critic because I'm prone to making the same kind of sentential mistakes; I'm simply saying 'be mindful' about what you say when discussing time travel; there are way harder critics than me, I know, I've met them! ;)
    Last edited: Jul 8, 2010
  6. Jul 8, 2010 #5
    What makes you think we can travel backwards?

    Perhaps you have an awkward definition of dimension. A dimension is nothing more than how many coordinates are needed to specify a location. If you say you were at coordinates x, y, and z by some predefined coordinate system, does this mean if I go to coordinates x, y, z, that I'll find you? No, because it is missing the time coordinate, when you were there. Just because time is a coordinate doesn't mean you can travel that coordinate in either direction. We have only learned that we can change how fast we travel that coordinate in one direction, relative to someone else, not stop or go the other direction.
  7. Jul 12, 2010 #6
    The time-dimension is not necessarily the fourth dimension. Anyways, nothing is definite. Suppose you are traveling through your time-line and you see that your father gets shot. You can see everything after that with him not being there. Now suppose you jump into time right before it happens and shoot the man who would have shot your father. Now the times have changed. You will come back into your dimension that allows you to view all of time and it will be completely different, all the next events will still have your father in them and you will have no recollection of a the previous time-line, it no longer exists and therefore in the past never existed either. I hope my example made sense.
  8. Jul 12, 2010 #7
    A little twist on that scenario. Suppose a person travelled back in time and shot themself at that previouis time.

  9. Jul 12, 2010 #8
    See. In classic understanding people would think that a paradox just happened. He is now dead so he never could have gone back in time in the first place to kill himself because when he shoots himself he also kills him-self.
    According to my theory after he kills himself he's dead. He will no longer exist in the future and no one will have recognition of him ever existing past that point. They will just recall that one day a man who looked just like him shot him, he died and the other man teleported out of there (aka ceased to exist).
  10. Jul 12, 2010 #9
    By shooting himself I mean't committing suicide. Its all nonsense anyway.

  11. Jul 12, 2010 #10
    Why do you think it would be the ONLY possible outcome..... if that is what you are implying....

    Fredrik said it well:
    What leads you to THIS conclusion? You might want to reconsider, maybe study both a little more.....those subjects are NOT intuitively obvious and represent some of the most original and non intuitive science ever experimentally verified.
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