scholarly journals Infinity of geodesics in a homogeneous and isotropic expanding space-time

2016 ◽  
Vol 13 (04) ◽  
pp. 1650048 ◽  
Author(s):  
Fayçal Ben Adda ◽  
Hélène Porchon
Keyword(s):  
Space Time ◽  
Geometric Optics ◽  
Discrete Simulation ◽  
Cosmic Inflation ◽  
Inflation Model ◽  
Isotropic Space ◽  
Variable Topology

In this paper, we construct a discrete simulation of an expanding homogeneous and isotropic space-time that expands via expansion of its basic elements to figure out properties and characteristics of such a space-time and derive conclusions. We prove that in such an expanding space-time, the geodesics are curved and more precisely, they fluctuate on the boundaries of the expanding basic elements. The non-existence of privileged expansion direction leads to the existence of an infinity of fluctuating geodesics between any two locations in this space-time, that provides a prediction of polarization in geometric optics, and a prediction of an earlier acceleration of the expansion as for the cosmic inflation model. This simulation is a case study and an example of space-time with variable topology using the principle of variation of topology via a transformation that creates holes.

Socioeconomic variations and disparity in space–time accessibility in suburban China: A case study of Guangzhou

Urban Studies ◽  
2020 ◽  
pp. 004209802091641
Author(s):  
Zifeng Chen ◽  
Anthony Gar-On Yeh
Keyword(s):  
Structural Equation ◽  
Time Perspective ◽  
Space Time ◽  
Time Constraints ◽  
Service Access ◽  
Service Accessibility ◽  
Home Based ◽  
Household Heads ◽  
And Gender

The concept of conventional place-based accessibility, despite being well researched, tends to ignore people’s space–time constraints arising from mandatory activities (e.g. work and household duties), which confine people’s potential movement and delimit the accessible opportunities. As people with different socioeconomic statuses may have different space–time constraints even while living in similar locations, using the place-based measures could lead to an underestimation of accessibility inequality. This study applies a space–time measure to unravel the disparities in service accessibility in suburban China. Since the late 1970s, suburbanisation in Chinese cities has fostered income inequality and has elevated other dimensions (e.g. institutional status and gender) of disparity within each income class. Within this context, we conduct a case study of suburban neighbourhoods in Guangzhou, based on the activity diary data derived from a home-based questionnaire survey. Findings indicate that the use of a space–time measure effectively captures the disparities in service accessibility among residents in suburban Guangzhou. On the basis of structural equation modelling, we further identify that certain socioeconomic groups (e.g. high-income residents, public sector workers, local hukou holders, male household heads and welfare housing residents) tend to experience fewer space–time constraints from rigid activities, such as work, commuting and household duties, and are thus more advantaged in accessing service facilities. These findings imply that urban planning should address the space–time perspective to promote equal service access for the highly heterogeneous social groups in suburban China and to incorporate time-sensitive policies (e.g. flexitime policies).

A GENERALIZED METRIC OF GRAVITATION

1992 ◽  
Vol 07 (13) ◽  
pp. 3133-3139 ◽  
Author(s):  
ALI EL-TAHIR
Keyword(s):  
Scalar Curvature ◽  
Weak Field ◽  
Space Time ◽  
Isotropic Space ◽  
Generalized Metric

Useful expressions relating the metric components grr and gtt of the static isotropic space–time, and the scalar curvature R, with the general Lagrangian are obtained. A generalized metric of gravity is introduced, which is essentially nonsingular, and reducible to cosmological and hence Schwarzschild geometries by imposing a weak-field constraint.

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