Lectures on Dark Energy and Cosmic Acceleration

TL;DR

This paper reviews the observational evidence for cosmic acceleration, discusses potential explanations like dark energy or modified gravity, and outlines future observational strategies to understand this phenomenon.

Contribution

It provides a comprehensive overview of dark energy theories, observational evidence, and future probes to address the mystery of cosmic acceleration.

Findings

Accelerating universe confirmed by multiple observations

Dark energy constitutes about 76% of the universe's energy content

Future observational probes are crucial for understanding cosmic acceleration

Abstract

The discovery ten years ago that the expansion of the Universe is accelerating put in place the present cosmological model, in which the Universe is composed of 4% baryons, 20% dark matter, and 76% dark energy. Yet the underlying cause of cosmic acceleration remains a mystery: it could arise from the repulsive gravity of dark energy -- for example, the quantum energy of the vacuum -- or it may signal that General Relativity breaks down on cosmological scales and must be replaced. In these lectures, I present the observational evidence for cosmic acceleration and what it has revealed about dark energy, discuss a few of the theoretical ideas that have been proposed to explain acceleration, and describe the key observational probes that we hope will shed light on this enigma in the coming years.