<p><BR/>Replying to:<BR/><DIV CLASS='Discussion_PostQuote'>You know magazines, all generalizations and oversimplification. I'm not sure how they came up with that but I assumed it was statistical, based on computer models.I already filled my quota of annoying conjecture but I have one more. We often refer to time as a dimension. I have also heard it argued that it's a product, like entropy. As a dimension, it has a unique restriction of travel, forward only, more like a vector. A vector can just as easily be 2 dimensional. Since one restriction has already been established, why not more? No, I'm not referring to science fiction multiple time lines or a picture of Schrodinger's lost cat on a telephone pole. Even a time plane, as opposed to line, would imply more than one common source and is disqualified. It could allow for curves in time.Is it possible that time has more than one dimension? <br />Posted by SHU</DIV></p><p>Vectors are in fact points and really don't have a dimension. What has a dimension is a <u>vector space,</u> which is an algebraic structure whose elements are vectors with the additional notions of vector addition and subtraction and scalar multiplication. That additinal structure is what is responsible for the notion of dimension (see a text on linear algebra for the details).</p><p>Once you have a notion for the dimensin of a vector space, that notion provides the notion of dimension for Euclidean spaces, which are just vector spaces with additional structure that allows the measurement of distance (also angles), which in turn provides a topology, and multi-variable calculus. That in turn permits the development of the theory of topological and differentiable manifolds which is the theory required for general relativity (Riemannian geometry).</p><p>There would be a problem with a multi-dimensional notion of time, the inability to provide, even locally, the ordering necessary to what we experience as the "flow" of time. There have been some speculations to the contrary -- I seem to recall Hawking contemplating complex time, but I don't think it ever went anywhere. You can already think about curves related to time and that is pretty much what happens in general relativity with curved space-time, and in fact time gets a bit mixed up with space over large expanses.</p><p>The bottom line is that time is not all that well understood, and in particular the reason that time seems to flow in one direction is not explainable from more fundamental principles. It is a topic of research. Einstein was of the opinion that time is basically statistical in nature, but no one has ever provided a rigorous and useful formulation of that notion as a predictive theory. <br /></p> <div class="Discussion_UserSignature"> </div>