Cosmological constraints on dark energy

TL;DR

This paper reviews the multiple observational methods confirming dark energy's role in accelerating the universe, emphasizing the consistency of the simplest constant model despite diverse evidence and the lack of a comprehensive theoretical explanation.

Contribution

It summarizes various observational techniques confirming dark energy and highlights the robustness of the simple constant model over alternative theories.

Findings

Multiple independent measurements confirm dark energy's existence.

The simplest constant dark energy model remains consistent with all observations.

Current theories lack a comprehensive explanation for dark energy.

Abstract

It has been only ~15 years since the discovery of dark energy (although some may argue there were strong indications even earlier). In the short time since measurements of type Ia supernovae indicated an accelerating universe, many other techniques have now confirmed the acceleration is real. The variety of ways in which dark energy has been confirmed is one of the reasons we are so confident in the statement that most of the energy in the universe is in a form we can not see except through its gravitational influence. This review aims to summarise briefly the many varied ways we now have measured dark energy. The fact that these different techniques all indicate that the simplest model remains the best -- that dark energy contributes a constant background acceleration -- is remarkable, since each of these different types of measurements represented opportunities for this simplest model to fail. Although we currently lack a compelling theoretical explanation for this acceleration, any explanation will have to explain the wide variety of complementary observations that we review here. This is an informal presentation, following the lines of the talk I presented at the General Relativity and Gravitation (GR20) conference in Warsaw in July 2013.