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Nature of Time (please help settle a bet)

  1. Feb 10, 2004 #1
    Hey Everyone,

    Please help settle a bet between a co-worker and myself. Neither of us are trained physics (I have a philosophy degree and he has a computer science degree), but we are both "amateurs" interested in physics.

    OK, here's the issue: My friend argues that time, explained as the "fourth dimension" of space-time is a cold hard fact that has been proven by many experiments and observations. I, on the other hand, claim that this view of time is still just a "theory"; that although this theory seems to satisfactorily explain many of the experimental results and physical observations thus far, that the absolute Truth of the nature of time has not yet been "proven" since there are exceptions to the theory (as in quantum physics, for example) and we are all still "learning" about physics and physical truths every day. This is not to say that we should not "follow" the theory and continue to use it since it HAS proven very stable in various equations and physical applications, but we should also be aware that new experiments and understandings may show that this theory is incorrect or incomplete.

    We've tried to find books at our local library to prove our respective points, but frankly it has been very difficult to find references to this specific issue (fact or theory) without reading 12 different textbooks. Both of us feel we've read these views before or learned them somewhere, but neither of us can remember where. If anyone out there could suggest a few books on the subject, point us in the right direction, and of course, settle our bet, it would be greatly appreciated.

    Thanks!
     
  2. jcsd
  3. Feb 10, 2004 #2

    chroot

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    One of the basic tenets of the scientific method is that no theory is ever proven. You can collect a pile of experimental evidence in support of a theory, but that doesn't mean the theory has been "proven." There might be one more experiment, not yet done, that would disprove the theory.

    You can't prove scientific theories, only disprove them.

    As far as time being the fourth dimension, that's just a representation in a model -- the special and general theories of relativity, to be specific. Spacetime is just a mathematical formalism -- a tool, if you will. You don't (and can't) prove mathematical formalism any more than you can prove a hammer.

    What is correct is that, so far, all of the predictions made using relativity (with its spacetime formalism) have all been corroborated experimentally.

    - Warren
     
  4. Feb 11, 2004 #3
    n- dimension area suppose an equal properties of each dimension .
    In 3-d area it is evidently. What about 4-d in that context?
     
  5. Feb 11, 2004 #4
    Why the heck are you guys arguing about this at work?
     
  6. Feb 11, 2004 #5
    What you do mean?
     
  7. Feb 11, 2004 #6

    selfAdjoint

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    I, on the other hand, claim that this view of time is still just a "theory"; that although this theory seems to satisfactorily explain many of the experimental results and physical observations thus far, that the absolute Truth of the nature of time has not yet been "proven" since there are exceptions to the theory (as in quantum physics, for example) and we are all still "learning" about physics and physical truths every day.

    Quantum mechanics does not deny the basic unification of time and space as found in the Lorentz transformations. This essentialy says that when two observers A and B are moving at a contant speed relative to each other, A will experience the B's space as a function of A's space and A's time and the speed, and B's time as another function of A's space, A's time, and the speed. And B will experience A's space and time with the inverse functions of B's space and time, and the speed with the sign changed.

    So that in special relativity you cannot treat time on a separate footing from the way you treat space. This is well established, though not of course proven in the mathematical sense, by experiments probably now going up to the millions (every time they run a circular pattern atom smasher, and it works, is such an experiment). So although your general position about always learning is correct, we do not expect to see this falsified any more than we expect to learn that the Earth is truly flat.
     
  8. Feb 11, 2004 #7
    Unification of space and time is fundamentally different than the idea that time is a physical dimension. I believe Scott is asking if time is truly a dimension in the same traditional sense that the other three dimensions exist. It seems to me that if time is in fact a dimension with the same properties as the three others, our position within that dimension has thusfar been static or at a (relatively) constant vector. Therefore, I would tend to think that argues that our representation of time as a dimension is more a metaphor. However, I'm in the same position as Scott, just an physics hobbyist at this point. Can someone with a more knowledgable background elaborate on the description of time as a dimension?
     
  9. Feb 11, 2004 #8

    LURCH

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    No expert I, but I can offer this much;

    Your conclusion regarding the uniformity of time is well-reasoned. If all movement through time is constant or static, that would seem to indicate that time is something other than a dimension (in the conventional sense). In fact, the very idea of time as a dimension only became common after Eintein's proposal of SR, which showed that progress through tine is not uniform. This theory also showed that progress through time is effected by progress through space, just as progress through one dimension of space effects progress through other spacial dimensions.

    For example, let us envision a trip "up north". If we get on a road that goes strait north and drive 60mph, we will proceed 1 mile north for each minute we travel. But if we try the same thing on a road that goes northeast, we will only get 1/2 mile north each minute, and 1/2 mile east, add these two together, and we get 1 mile per minute total volocity.

    In the same way, travel through any spacial dimension effects travel through time, slowing time so that the total volocity of any object still adds up to lightspeed. So when we travel strait north, we travel c-60mph forward in the direction of time. And when we go northeast, we go 30mph east, 30mph north, and c-60mph "future-ward". And when we sit stationary, we travel forward through time at c. Since time is effected in this way, inasmuch as movement through any one spacial dimension effects progress through time in exactly the same way it effects progress through any other dimension, time can be treated like a dimension, same as the others.
     
  10. Feb 11, 2004 #9
    Saying about dimensions, we should not forget:
    n+1 dimension must be at 90 degree to previous n dimensions.
     
  11. Feb 12, 2004 #10

    Rog

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    A book I would suggest, which is quite enlightning in regard to time thoery and conjecture is "About Time" by Paul Davies. I think its about 4 years old now but I beleive most of the theories considered are still current.
     
  12. Feb 12, 2004 #11
    Interesting point, I wonder if anyone has ever attempted to prove that time is perpendicular to normal space? I suppose that could be done using relativity equations to determine the effect of your velocity in space versus your velocity in time. Unfortunately, I don't know those equations. Anyone?
     
  13. Feb 12, 2004 #12

    chroot

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    It is meaningless to talk about the angle between the time and space dimensions. They are fundamentally different, yet related (e.g. through the Lorentz transforms).

    - Warren
     
  14. Feb 12, 2004 #13
    Thanks!

    Thanks to all of you for your responses! [Rog: I will definitely look for the book you suggested. Thanks!]
     
  15. Feb 12, 2004 #14
    Time is just as real as space. Spacetime embodies both, and would not exist without time; neither would space alone in physics as we know it. Time and space are interchangable through the constant c, the speed of light. Time may seem unreal because c (seen as a correlation factor) is so far removed from everyday velocities relative to the speed of familiar matter. Using c, h (Planck's constant) and G (Newton's gravitational constant), among the most fundamental physical parameters, one can construct T*~5x10-45 seconds, the Planck time of unified physical theories.
     
  16. Feb 12, 2004 #15
    Why no? 2-d, being added to 1-d, causes the line to be square.
    3-d, being added to 2-d, causes the square to be cube.
    4-d, being added to 3-d, causes the cube TO ROTATE.
    It is obvious.
     
  17. Feb 13, 2004 #16
    So what you're saying is that time is certainly not a physical dimension but is only a dimension in the most basic sense that it is used to describe our position in spacetime?

    http://dogfeathers.com/java/hyprcube.html
    Here is a link showing a stereoscopic 4-d 'hypercube' projected into 3-d space. Note that it is rotating by default, but need not be rotating to be 4-dimensional. However, this is merely another physical dimension added into the 3 that we perceive, time is apparently entirely different.
     
    Last edited: Feb 13, 2004
  18. Feb 13, 2004 #17

    russ_watters

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    Time is not a space dimension, its a time dimension. Like warren said - its different. Its still a "physical dimension" though in that it is physically real.
     
  19. Feb 13, 2004 #18

    chroot

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    Basically, an angle exists within a space. Time does not exist within a space. Thus, there can be no angles with respect to time.

    It is meaningless to ask "what is the angle between the time dimension and the positive x-axis?"

    - Warren
     
  20. Feb 13, 2004 #19
    Then by that definition, couldn't a wide range of other properties also be considered dimensions? For example, the charge or spin angle of a particle? IE, given a certain location in 3-d space, at a certain time, all particles have a certain spin angle. Therefore it could be argued that spin is a dimension?

    I guess what I'm really asking is, what distinguishes time as a dimension?
     
  21. Feb 13, 2004 #20

    chroot

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    1. The least number of independent coordinates required to specify uniquely the points in a manifold.

    2. The range of such a coordinate.

    - Warren
     
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