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Subject: Large Extra Dimension -- a Time Dimension
Date: 2000/04/14 |

There are an increasing number of papers discussing the modelling of the universe as a "3-brane" on a large extra dimension. In every case, the extra dimension is supposed to be a spatial dimension. I wish to point out that the whole thing is more sensibly done by modelling the large extra dimension as a second time dimension, not a fourth spatial dimension. The time dimension is apropos in that gravity and time map into eachother under GR, so the second time dimension can serve as the source of gravity, warped by massive bodies to where we have the naive impression that the gravity comes from the mass itself, rather than mass being the conduit. A new paper "hep-th/0004056" models distortions in the large extra (spatial) dimension consequential to universal expansion, and suggests that this is the source of "dark energy". In other words, universal expansion is begetting a gravitational scalar. This evokes my old posting that gravity is the result of universal expansion, or more precisely, the linear drift of a universal parameter which mimics spatial expansion. This idea unifies with GR simply by modelling the large extra dimension as a time dimension, instead of a physical dimension. So the 5-manifold consists of three spatial dimensions and two time dimensions, the second one of which bears a migrating universal parameter which at once yieds gravity and makes the universe seem to be physically expanding. Eric Flesch

Subject: Re: Large Extra Dimension -- a Time Dimension
Date: 2000/04/14 |

eric@flesch.org (Eric Flesch) wrote, in part: >I wish to point out that the whole thing is more sensibly done by >modelling the large extra dimension as a second time dimension, not a >fourth spatial dimension. While this doesn't directly relate to your theory (in relation to which, I'll note that any extra dimension is normally called a spatial dimension simply because time is what we all move along at a fixed rate), I remember coming up with an amusing little 'theory' that, although it didn't really include a second time dimension, came close. In order to allow the tachyon to exist while preventing it from defying causality, I worked things out this way: - a photon, having no real or imaginary mass, must move through both space and time at the speed of light - a matter particle, having no imaginary mass, but some real mass, must move through time at the speed of light, but must move through space more slowly - a tachyon, having no real mass, but some imaginary mass, must move through space at the speed of light, but must move through time more slowly (instead of having to move through space faster than the speed of light, which is sort of equivalent, since velocity is units of space moved through per unit of time) But to make 'moving through time more slowly' meaningful, I changed time to "time", a spatial dimension, while *real* time was causal time. So I called this the 'tin can theory of the Universe'. The lid on the top of the can was the matter Universe. The rim of the top of the can is the photons from the Big Bang. (So there can be no cosmic background radiation, hence the theory fails to match up with observation.) The can itself, its pipe-like wall, is the tachyon universe. The bottom of the can is an antimatter universe. (Note another rim of backwards-moving photons.) So the theory at least accounts for the lack of antimatter in our universe. Inside the can is a four-dimensional realm of particles having *both* real and imaginary mass; this dangerous expanse of complex-mass particles is where someone would end up who built what he _thought_ was a time machine! (Cute idea for a science-fiction story...) The direction from the bottom to the top of the can is the spatial time axis; two axes on the lid of the can represent space, and the can grows with the passage of time at the speed of light in all directions. But a particle can move in space and in spatial time both at the speed of light, or slightly below: in this 4-D realm, if velocities were calculated in the ordinary way, photons would move at sqrt(2) times the speed of light. This is as close as I can get to imagining another time dimension; an anisotropic spatial dimension that from our perspective as matter beings instead of tachyon beings is associated with time. John Savard (jsavard<at>ecn<dot>ab<dot>ca) http://www.ecn.ab.ca/~jsavard/crypto.htm

Subject: Re: Large Extra Dimension -- a Time Dimension
Date: 2000/04/14 |

In article <38f78797.8331391@news.iconz.co.nz>, eric@flesch.org (Eric Flesch) wrote: >There are an increasing number of papers discussing the modelling of >the universe as a "3-brane" on a large extra dimension. In every >case, the extra dimension is supposed to be a spatial dimension. > >I wish to point out that the whole thing is more sensibly done by >modelling the large extra dimension as a second time dimension, not a >fourth spatial dimension. The time dimension is apropos in that >gravity and time map into eachother under GR, so the second time >dimension can serve as the source of gravity, warped by massive bodies >to where we have the naive impression that the gravity comes from the >mass itself, rather than mass being the conduit. > >A new paper "hep-th/0004056" models distortions in the large extra >(spatial) dimension consequential to universal expansion, and suggests >that this is the source of "dark energy". In other words, universal >expansion is begetting a gravitational scalar. This evokes my old >posting that gravity is the result of universal expansion, or more >precisely, the linear drift of a universal parameter which mimics >spatial expansion. > >This idea unifies with GR simply by modelling the large extra >dimension as a time dimension, instead of a physical dimension. So >the 5-manifold consists of three spatial dimensions and two time >dimensions, the second one of which bears a migrating universal >parameter which at once yieds gravity and makes the universe seem to >be physically expanding. I came up with my own little theory a few years ago along these lines. I wrote Maxwell's equations in 3+2 spacetime and then assumed all the fields were independent of this second time dimension. We can then divide the Maxwell antisymmetric tensor into the classical electric field, the classic magnetic field, a three vector, and a scalar.

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Subject: Re: Large Extra Dimension -- a Time Dimension
Date: 2000/04/15 |

Just saw this in Physics News Updates. It addresses the matter of an "expanding universe" bequeathing a gravitational scalar. Just extrapolate this into a second time dimension and you have an elegant simplification which removes the need for an expanding universe. The so-called "accelerating" expansion is then simply mapped into a linearly-migrating cosmological parameter operating out of that second time dimension. Eric __________ article follows _______________- DARK ENERGY AND THE MICROWAVE BACKGROUND. The theory of general relativity introduced the notion that spacetime could be warped or curved by the presence of matter. Locally, stars or any object with mass will curve space, but the expansion of the universe itself may introduce a curvature of its own. This is how cosmologists summarize things: a static universe with no matter (if such a thing were possible) would have no curvature. If, however, the empty universe were expanding it would have negative overall curvature. Increase the mass density from zero and the curvature would be less negative. Add still more mass and you might reach a net zero curvature. The ratio of matter to the critical matter needed for zero curvature is called omega; the popular version of the big bang model, featuring a very rapid expansion in an early "inflation" phase, predicts that omega should equal 1 exactly. A new paper in Physical Review Letters by Scott Dodelson of Fermilab and Lloyd Knox of the University of Chicago (773-834-3287) provides the theoretical underpinning for the higher-precision mappings of the cosmic microwave background (CMB) reported over the past nine months. The paper was prepared just as the first of the observational results appeared last summer: a Princeton-Pennsylvania collaboration taking data from Cerro Toco in Chile. Their findings (preprint astro-ph/9906421) can be plotted as the size of the observed fluctuations in the CMB as a function of the angular size of the fluctuation region (actually astrophysicists usually transform the data so that it can be plotted against the size of angular moment, or "l"). These data and those of the "Boomerang" (preprint 9911444 and 9911445; also see Update 460) and "Viper" (preprint 9910503) groups sit right on top of a theoretical curve drawn by Dodelson and Knox corresponding to the case where omega equals 1 and the net curvature of the universe is zero. With the contribution of matter (luminous and dark) to the density of the universe expected to be about one-third the critical value (of omega=1), this presents a stronger-than-ever argument in favor of the existence of yet another form of energy, often called "dark energy," to provide the missing two-thirds of the energy needed to make omega=1. This dark energy would also provide the "negative pressure" or repulsiveness needed to make the expansion of the universe greater than in the past, a development suggested independently by studies of distant supernovas. (Dodelson and Knox, Physical Review Letters, 17 April; Select Article.)