Cosmology in Scalar-Tensor Gravity pp 197-228 | Cite as

# The Present Universe

Chapter

## Abstract

In 1998 it was discovered that, contrary to the popular belief at that time, the expansion of the universe at the present cosmological epoch is
where

*accelerated*, i.e.,*d*^{2}*a/dt*^{2}> 0. This conclusion is based on observations of distant type Ia supernovae [738, 703], which have a characteristic light curve and constitute reasonable standard candles for cosmological studies [149, 438] . The systematic search for type Ia supernovae followed two decades of progress in the study of such objects and improved understanding of their light curves. The observations revealed that these supernovae are fainter than expected, an effect attributed to the structure of the universe. Then, at fixed redshift, the supernovae must be more distant than one expects in a decelerating universe, according to the expression (valid for moderate redshifts*z*)$$
{H_0}{D_L} = z + \frac{1}{2}(1 - {q_0}){z^2} + \ldots ,
$$

(8.1)

*q*≡ —äa/ (à)^{2}is the deceleration parameter and*DL*is the luminosity distance. For an accelerating universe (*q*< 0),*DL*is larger than for a decelerating one with*q*> 0. If the universe expanded more slowly in the past than today, it is actually older than previously thought and the apparent faintness of the supernovae is explained. Cosmic acceleration also helps reconcile the age of the universe with that of globular clusters, a problem that resurfaces now and again in cosmology.## Keywords

Dark Matter Dark Energy Scalar Field Present Universe Nonminimal Coupling
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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© Springer Science+Business Media Dordrecht 2004