The distribution of galaxies shows how matter was distributed in the early universe. As a result, it contains data on several cosmological variables, including the density of matter. The ideal method for data analysis is still under discussion. Although this approach is considered inadequate, most studies focus on calculating the correlation functions of galaxy distributions and comparing them to physical models.

While many alternatives have been proposed, there needs to be more consensus on which ones have practical utility, and few are natural from a theoretical standpoint.

A new study shows that tools from disordered heterogeneous media theory are well suited to characterize the distribution of galaxies and provide more information about the structure and evolution of the Universe.

Based on a series of simulations, scientists have begun to explore the heterogeneous structure of the Universe by analyzing the distribution of galaxies as a collection of points rather than a continuous distribution, similar to the individual particles of matter that make up a material. This method has made it possible to quantify the relative disorder of the universe and to use mathematics developed for materials science to better understand the fundamental structure of the universe.

Oliver Philcox, a co-author of the study, said: “What we found was that the distribution of galaxies in the universe is quite different from the physical properties of conventional materials, with its unique signature.”

Scientists analyzed the public simulation data generated by Princeton University and the Flatiron Institute. Each of the 1,000 simulations consists of a billion “dark matter” particles, and the clusters they create through gravitational evolution act as stand-ins for galaxies.

One of the paper’s key findings is the correlations between pairs of galaxies that are topologically connected using the pair-connectedness function. The research team showed that on a larger scale (on the order of several hundred megaparsecs), the Universe is approaching hyperuniformity. In contrast, at smaller scales (up to 10 megaparsecs), it becomes nearly antihyperuniform and highly inhomogeneous. Based on this and the variety of other descriptors that emerge in the theory of heterogeneous media.

Salvatore Torquato, frequent member and visitor of the Institute for Advanced Study and Lewis Bernard Professor of Natural Sciences based in Princeton University’s chemistry and physics departments, said: “The perceived shift between order and disorder depends largely on scale. Georges Seurat’s pointillist technique in the painting A Sunday on La Grande Jatte produces a similar visual effect; the work appears disordered up close and very ordered from afar. In terms of the universe, the degree of order and disorder is more subtle, like a Rorschach inkblot test that can be interpreted in infinite ways.

The scientists created a consistent and unbiased framework for evaluating order thanks to statistical methods including nearest neighbor distributions, clustering diagnostics, Poisson distributions, percolation thresholds and the pair-connectedness function. These conclusions therefore apply to several other dynamical physical systems, even if they are formulated in a cosmic framework.

Scientists noted, “This interdisciplinary work, which combines the techniques of cosmology and condensed matter physics, has future implications for both fields. In addition to the distribution of galaxies, these tools allow the investigation of many other features of the Universe, including cosmic voids and the ionized hydrogen bubbles that formed during the reionization phase of the universe.”

Magazine reference:

  1. Oliver HE Philcox and Salvatore Torquato. Disordered heterogeneous universe: distribution and clustering of galaxies over length scales. Physical Review X. DOI: 10.1103/PhysRevX.13.011038