Accelerating Universe: Observational Status and Theoretical Implications

TL;DR

The paper synthesizes Type Ia supernova distance measurements to reconstruct the recent expansion history via $H(z)$ and $d_L(z)$, highlighting the evidence for late-time acceleration and its interpretation through dark energy with equation of state $w$. It contrasts the cosmological constant ($w=-1$) with dynamical dark energy models, deriving $w(z)$ from $H(z)$ and discussing the theoretical viability of quintessence, phantom, and scalar-tensor theories. A key focus is the phantom regime ($w<-1$) and its dramatic Big Rip fate, including implications for bound systems, while evaluating how current data favor or disfavor various models. The paper also surveys current and planned observational programs aimed at tightening constraints on $w(z)$ and distinguishing between LCDM and alternative dark energy scenarios, underscoring the ongoing interplay between observations and theory in understanding cosmic acceleration.

Abstract

This is a pedagogical review of the recent observational data obtained from type Ia supernova surveys that support the accelerating expansion of the universe. The methods for the analysis of the data are reviewed and some of the theoretical implications obtained from their analysis are discussed.

Figures (17)

• Figure 1: The luminosity distance obtaned from the apparent and absolute luminosities
• Figure 2: The Hubble diagram. In an accelerating universe luminous objects at a given redshift appear to be dimmer.
• Figure 3: Typical SnIa light-curve.
• Figure 4: Search strategy to discover of supernovae in a scheduled, systematic procedure perlmuter97
• Figure 5: Supernova 1998ba, an example of a supernova discovery using the search strategy described in the text involving subtraction of images.