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A Wrinkle In Space-Time, How Shockwaves Could Crinkle Space
Math shows how shockwaves could crinkle space

Mathematicians at UC Davis have come up with a new way to crinkle up the fabric of space-time -- at least in theory.
Two-dimensional analogy of spacetime distortion. Matter changes the geometry of spacetime, this (curved) geometry being interpreted as gravity. The grid lines do not represent the curvature of space but instead represent the coordinate system imposed on the curved spacetime, which would be rectilinear in a flat spacetime.
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Blobrana


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Title: Self-completeness and spontaneous dimensional reduction
Authors: Jonas Mureika, Piero Nicolini

It has recently been shown via an equivalence of gravitational radius and Compton wavelength in four dimensions that the trans-Planckian regime of gravity may by semi-classical, and that this point is defined by a minimum horizon radius commensurate with the Planck mass. We generalize this formalism to an arbitrary number of dimensions d, and show that gravity in d > 3 dimensions remains self-complete, while in lower dimensions it is not. Most interesting is the case for a (1+1)-dimensional dilaton gravity model resulting from dimensional reduction of Einstein gravity, which we show to be self-incomplete with no lower bound on possible black hole masses. Potential phenomenological implications of this result are considered.

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Blobrana


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Title: On topological restrictions of the spacetime in cosmology
Authors: T. Asselmeyer-Maluga, J. Krol

In this paper we discuss the restrictions of the spacetime for the standard model of cosmology by using results of the differential topology of 3- and 4-manifolds. The smoothness of the cosmic evolution is the strongest restriction. The Poincare model (dodecaeder model), the Picard horn and the 3-torus are ruled out by the restrictions but a sum of two Poincare spheres is allowed.

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Blobrana


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No evidence for "knots" in space

Theories of the primordial Universe predict the existence of knots in the fabric of space - known as cosmic textures - which could be identified by looking at light from the cosmic microwave background (CMB), the relic radiation left over from the Big Bang.
Using data from NASA's Wilkinson Microwave Anisotropy Probe (WMAP) satellite, researchers from UCL, Imperial College London and the Perimeter Institute have performed the first search for textures on the full sky, finding no evidence for such knots in space.
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Blobrana


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Space 'textures' nearly ruled out in WMap study

The very fabric of space is not as "knotted" as many theories predict it should be, say researchers.
Just after the Big Bang, the Universe began to coalesce into the structure we see today, which in some theories would result in knots or "textures".
The warm glow left over from that is now spread across all of space, and is used to test theories of those moments.
But a close study of this glow reported in Physical Review Letters has found no evidence of these textures.
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Blobrana


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Title: Special theory of relativity in a three-dimensional Euclidean space
Authors: Amrit Sorli and Davide Fiscaletti

In the 20th century, physicists have understood space and time as being coupled into a space-time manifold, a fundamental arena in which everything takes place. Space-time was considered to have three spatial dimensions and one temporal dimension. Out of the experimental facts, one can conclude that time t we measure with clocks is only a numerical order of duration of motion, i.e. material change in a three-dimensional space. This view allows description of electromagnetic phenomena in a three-dimensional Euclidean space.

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Title: Constraining the topology of the Universe using the polarised CMB maps
Authors: P. Bielewicz, A.J. Banday, K.M. Gorski

We study the possibility for constraining the topology of the Universe by means of the matched circles statistic applied to polarised cosmic microwave background (CMB) anisotropy maps. The advantages of using the CMB polarisation maps in studies of the topology over simply analysing the temperature data as has been done to-date are clearly demonstrated. We test our algorithm to search for pairs of matched circles on simulated CMB maps for a universe with the topology of 3-torus. It is found that the noise levels of both Planck and next generation CMB experiments data are no longer prohibitive and should be low enough to enable the use of the polarisation maps for such studies. For such experiments the minimum radius of the back-to-back matched circles which can be detected are determined. We also showed that the polarisation generated after reionisation does not have an impact on detectability of the matched circles.

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Blobrana


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The Fabric of Space-Time



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Blobrana


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Geometry of the Universe
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Title: Measuring the Geometry of the Universe from Weak Gravitational Lensing behind Galaxy Groups in the HST COSMOS survey
Authors: James E. Taylor, Richard J. Massey, Alexie Leauthaud, Matthew R. George, Jason Rhodes, Thomas D. Kitching, Peter Capak, Richard Ellis, Alexis Finoguenov, Olivier Ilbert, Eric Jullo, Jean-Paul Kneib, Anton M. Koekemoer, Nick Scoville, Masayuki Tanaka

Gravitational lensing can provide pure geometric tests of the structure of space-time, for instance by determining empirically the angular diameter distance-redshift relation. This geometric test has been demonstrated several times using massive clusters which produce a large lensing signal. In this case, matter at a single redshift dominates the lensing signal, so the analysis is straightforward. It is less clear how weaker signals from multiple sources at different redshifts can be stacked to demonstrate the geometric dependence. We introduce a simple measure of relative shear which for flat cosmologies separates the effect of lens and source positions into multiplicative terms, allowing signals from many different source-lens pairs to be combined. Applying this technique to a sample of groups and low-mass clusters in the COSMOS survey, we detect a clear variation of shear with distance behind the lens. This represents the first detection of the geometric effect using weak lensing by multiple, low-mass systems. The variation of distance with redshift is measured with sufficient precision to constrain the equation of state of the universe under the assumption of flatness, equivalent to a detection of a dark energy component Omega_X at greater than 99% confidence for an equation-of-state parameter -2.5 < w < -0.1. For the case w = -1, we find a value for the cosmological constant density parameter Omega_Lambda = 0.85+0.044-0.19 (68% C.L.), and detect cosmic acceleration (q_0 < 0) at the 98% C.L.. We consider the systematic uncertainties associated with this technique and discuss the prospects for applying it in forthcoming weak-lensing surveys.

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Prof Brian Cox on the difference between space and time



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