An Origami Approximation to the Cosmic Web
Abstract
The powerful Lagrangian view of structure formation was essentially introduced to cosmology by Zel'dovich. In the current cosmological paradigm, a darkmattersheet 3D manifold, inhabiting 6D positionvelocity phase space, was flat (with vanishing velocity) at the big bang. Afterward, gravity stretched and bunched the sheet together in different places, forming a cosmic web when projected to the position coordinates.
Here, I explain some properties of an origami approximation, in which the sheet does not stretch or contract (an assumption that is false in general), but is allowed to fold. Even without stretching, the sheet can form an idealized cosmic web, with convex polyhedral voids separated by straight walls and filaments, joined by convex polyhedral nodes. The nodes form in `polygonal' or `polyhedral' collapse, somewhat like spherical/ellipsoidal collapse, except incorporating simultaneous filament and wall formation. The origami approximation allows phasespace geometries of nodes, filaments, and walls to be more easily understood, and may aid in understanding spin correlations between nearby galaxies. This contribution explores kinematic origamiapproximation models giving velocity fields for the first time.
 Publication:

The Zeldovich Universe: Genesis and Growth of the Cosmic Web
 Pub Date:
 October 2016
 DOI:
 10.1017/S1743921316009686
 arXiv:
 arXiv:1412.6114
 Bibcode:
 2016IAUS..308...97N
 Keywords:

 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 6 pages, 5 figures. Proceedings of IAU Symposium 308 "The Zeldovich Universe: Genesis and Growth of the Cosmic Web", 2328 June 2014, Tallinn, Estonia. Interactive tetrahedralcollapse model at http://skysrv.pha.jhu.edu/~neyrinck/TetCollapse