Gravity causes homogeneity of the universe

Date:
September 24, 2020
Source:
University of Vienna
Summary:
Gravity can accelerate the homogenization of space-time as the
universe evolves.



FULL STORY ==========================================================================
The temporal evolution of the universe, from the Big Bang to the present,
is described by Einstein's field equations of general relativity. However, there are still a number of open questions about cosmological dynamics,
whose origins lie in supposed discrepancies between theory and
observation. One of these open questions is: Why is the universe in its
present state so homogeneous on large scales?

==========================================================================
From the Big Bang to the present It is assumed that the universe was in
an extreme state shortly after the Big Bang, characterized in particular
by strong fluctuations in the curvature of spacetime. During the long
process of expansion, the universe then evolved towards its present state, which is homogeneous and isotropic on large scales - - in simple terms:
the cosmos looks the same everywhere. This is inferred, among other
things, from the measurement of the so-called background radiation,
which appears highly uniform in every direction of observation. This homogeneity is surprising in that even two regions of the universe that
were causally decoupled from each other -- i.e., they could not exchange information -- still exhibit identical values of background radiation.

Alternative theories To resolve this supposed contradiction, the so-called inflation theory was developed, which postulates a phase of extremely
rapid expansion immediately after the Big Bang, which in turn can explain
the homogeneity in the background radiation.

However, how this phase can be explained in the context of Einstein's
theory requires a number of modifications of the theory, which seem
artificial and cannot be verified directly.

New findings: Homogenization by gravitation Up to now it was not clear
whether the homogenization of the universe can be explained completely
by Einstein's equations. The reason for this is the complexity of the
equations and the associated difficulty to analyze their solutions --
models for the universe -- and to predict their behavior.

In the concrete problem, the time evolution of the originally strong
deviations from the homogeneous state as cosmological gravitational
waves has to be analyzed mathematically. It has to be shown that they
decay in the course of the expansion thus allowing the universe to get
its homogeneous structure.

Such analyses are based on modern mathematical methods in the field
of geometric analysis. Until now, these methods could only achieve
such results for small deviations from the homogeneous space-time
geometry. David Fajman from the University of Vienna has now succeeded
for the first time to transfer these methods to the case of arbitrarily
large deviations.


========================================================================== Story Source: Materials provided by University_of_Vienna. Note: Content
may be edited for style and length.


========================================================================== Journal Reference:
1. David Fajman. Future Attractors in 2 1 Dimensional L
Gravity. Physical
Review Letters, 2020; 125 (12) DOI: 10.1103/PhysRevLett.125.121102 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200924114121.htm

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