Observational evidence of dark energy

Abstract

The existence of dark energy is supported by a number of observations. This includes (i) the age of the Universe compared to oldest stars, (ii) supernovae observations, (iii) Cosmic Microwave Background (CMB), (iv) baryon acoustic oscillations (BAO), and (v) large-scale structure (LSS). Even before 1998 it was known that in a CDM Universe the cosmic age can be smaller than the age of the oldest stars. Dark energy can account for this discrepancy because its presence can make the cosmic age longer. The first strong evidence for the acceleration of the Universe today came however by measuring the luminosity distance of the type Ia supernovae (SN Ia). The CMB observations are also consistent with the presence of dark energy, although the constraint coming from the CMB alone is not so strong. The measurements of BAO have provided another independent test for the existence of dark energy. The power spectrum of matter distributions also favors a Universe with dark energy rather than the CDM Universe. In the following we shall discuss this observational evidence for dark energy. The statistical method used to constrain cosmological parameters will be discussed in Chapter 13. More details on present and future observational aspects to detect dark energy will be presented in Chapter 14. The age of the Universe As we alreadymentioned, the inverse of the Hubble constant H 0 is a rough measure of the age t 0 of the Universe.