M7 Inflation and Formation of Structures

Topic

The central element of this model is the primordial perturbation field and its subsequent growth.

Cosmic inflation is a fleeting period of accelerated exponential expansion in the early universe; this expansion simultaneously explains the universe's flatness and homogeneity, as well as the quantum origin of the seeds that would later give rise to all observed structure. A minimum number of cycles of this exponential expansion ensures that the entire currently observable universe fits within the horizon generated by inflation itself.

The primordial power spectrum resulting from inflation is nearly flat but slightly tilted toward large scales: larger-scale perturbations have an amplitude only slightly greater than that of smaller perturbations.

The growth factor describes how these same density perturbations—already present in the cosmic microwave background—are amplified by gravity to form the structures observed today; during the matter-dominated era, this growth proceeds in direct proportion to the universe's scale factor.

The correlation function and the power spectrum are the two-point statistics used in large-scale galaxy surveys to measure how this matter is clustered throughout the universe today.

However, the overall amplitude of these density fluctuations reveals a persistent tension between the value inferred from the cosmic microwave background and the value measured directly via weak gravitational lensing—an unresolved discrepancy between two methods that are otherwise consistent with each other. Thus, from the primordial perturbation field with which this document begins to the unresolved tension with which it concludes—spanning cosmic inflation, the primordial power spectrum, and the growth factor—structure formation transforms those same perturbations, born of a fleeting quantum origin, into the entire galactic structure observed today, even though two independent methods have yet to reach full agreement on their exact amplitude.

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