good improvement in the cosmological parameter estimation in the future and have the enormous potential to be one of the most competitive cosmological probes in constraining dark energy.'
author:
- Yan Liu
- 'Jing-Fei Zhang'
- 'Xin Zhang[^1]'
title: 'Real-time cosmology with SKA'
---

Introduction {#sec:intro}
============

The accelerated expansion of the universe has been discovered and confirmed by cosmological observations for about twenty years, which is undoubtedly one of the greatest scientific discoveries in the modern cosmology. However, the science behind the cosmic acceleration, i.e., the nature of dark energy, still remains mysterious for us. To measure the physical property of dark energy, one should precisely measure the expansion history of the universe. Currently, the mainstream way is to measure the cosmic distances (luminosity distance or angular diameter distance) and the corresponding redshifts, and to establish a distance-redshift relation, by which constraints on the parameters of dark energy (and other cosmological parameters) can be made. However, a more straightforward way is to directly measure the expansion rate of the universe at different redshifts, although this measurement is more difficult in the observational cosmology.

With the fast advancement in technology over the past several decades, the possibility of measuring the 