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Time as a dimension

  1. Apr 28, 2009 #1
    Hi there,
    I have a question.

    To me, measuring spacial dimensions is quite a bit different than measuring the time dimension. I was thinking the other day and it seemed very obvious to me what the main difference was.

    Time never goes the other way. A dimension defines two equal and opposite vectors.
    So really the thing I'm poking at is that all this while we've been contributing 8 vectors made from 4 dimensions in spacetime, when we know that one of those vectors is not a possible route of travel for any object - time cannot "run" backwards. Causality states that what happens before causes what happens after. Time cannot logically run backwards. It's impossible.

    So really we don't have 8 vectors making up 4 dimensions we have 7 vectors making up 3 and 1/2 dimensions.

    We have 6 spacial vectors (up, down; left, right; forward, backward) and one time vector (forward in time) because the other time vector (backwards in time) goes against Darwinist nature.

    Could this have effected any of Einsteins calculations?
    Is this lack of the "opposite" vector of time's movement documented?
    What are the ramifications on time as a dimension if it is really a uni-mension???
  2. jcsd
  3. Apr 28, 2009 #2
    no, we have 4 dimensions. 3 of them 'spacelike', 1 of them 'timelike' and all of them are together in a 4d spacetime with metric of either (-, +, +, +) or (+, -, -, -).

    There is also nothing particularly special about the direction of time we have in almost every physical theory, with them functioning just as well forwards as backwards. The only case where this isn't really true is during the R (measurement) process of quantum mechanics.
  4. May 1, 2009 #3
    what confused me abou this is how can up down left right be said to be dimensions, whats the different between them if there is no edges?, could you also say that a north north easterly direction is a spatial dimension. where do the dimensions up and right meet?
  5. May 1, 2009 #4


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    Yes you could.
    In fact, this becomes obvious if once you realize that left and right on the Moon are completely different directions than left and right on Earth (and in fact, change as the bodies move).

    You can define the dimensions any way you like, as long as they are all perpendicular to each other.
  6. May 1, 2009 #5


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    You lost me on that one, Dave. Isn't left/right always relative to the observer?
  7. May 1, 2009 #6
    No...Euclidean 3-space is defined by just three orthogonal vectors, because coordinates can be measured as positive or negative. You're right that time is different from the spatial dimensions (in many ways). However to measure coordinates in a 4 dimensional space you still need only 4 numbers and yes time can be negative because it depends on your reference frame.
  8. May 1, 2009 #7


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    Yes. Which means they're not objective. Which means when I'm pointing left on the Moon, it might very well be NNE on Earth, as the poster asks. The orientation is arbitrary. The three spatial dimensions can be defined at an infinite number of orientations (N or NNE or NE or ENE, etc.) The only requirement is that there are three, and that the three are perpendicular to each other.
  9. May 1, 2009 #8


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    Right, then. Thanks, Dave. My mistake was in not properly correlating your answer with the original post. (Beer has that effect upon me sometimes.)
  10. May 2, 2009 #9
    doesn't einstein explain time like time is over there just like my bike is outside.
  11. May 2, 2009 #10
    There is a fantastic video on youtube called Measuring the 11th Dimension or words to that effect (youtube is blocked here in china so I cant check..im an expat) but it defines time as our 4th dimension and states that our inability to measure it as any other dimension is due to the fact that we are just not capable of it. Its like a an object living in a 2D world, how is that object going to measure the 3rd dimension? it cant, because it is all around but it can't move in it. We are in that way "trapped" in time.

    This might be controversial to other conventional physics views, but I thought the video portrayed it nicely. I recommend it!
  12. May 2, 2009 #11


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    It's more of a case of terminology. Just as many phycists don't like the term centrifugal force when used to describe the reaction force from centripetal force, some of us don't like using the term dimension for time. If you want to consider tuples or generic sets of numbers, you could include position (x, y, x), time, weight, density, speed, acceleration, color, ... and invent special vector math to deal with this, but I wouldn't call these dimensions.
  13. May 3, 2009 #12
    Except of course that entropy gives a temporal direction, and it shows up in almost every physical theory.
  14. May 5, 2009 #13
    So is there then an example demonstrated by Einstein's physics where time for another body would appear to go at all in the negative to an observer.

    (is there a scenario where one can witness events happening "backwards")??????
  15. May 5, 2009 #14
    You can measure time in a 3D and a 2D world. In fact, a flatland would be three dimensional since it includes time as a dimension.

    You just cannot measure a higher spacial dimension.

    Also I bolded the circular reasoning (it's unscientific).
    Last edited: May 5, 2009
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