Gravitational Lensing and the Extragalactic Distance Scale

TL;DR

This paper discusses how gravitational lensing can be used to measure the Hubble constant directly, emphasizing recent advances in time delay measurements and the challenges in modeling to achieve less than 10% error.

Contribution

It critically assesses the potential and challenges of using gravitational lens time delays to accurately determine the Hubble constant.

Findings

Recent accurate time delay measurements enable this method.

Modeling uncertainties impact the precision of Hubble constant estimates.

Prospects for sub-10% error measurements are promising but require careful analysis.

Abstract

The potential of gravitational lenses for providing direct, physical measurements of the Hubble constant, free from systematic errors associated with the traditional distance ladder, has long been recognized. However, it is only recently that there has been a convincing measurement of a time delay sufficiently accurate to carry out this program. By itself, an accurate time delay measurement does not produce an equivalently definite Hubble constant and the errors associated with models of the primary lens, propagation through the potential fluctuations produced by the large-scale structure and the global geometry of the universe must also be taken into account. The prospects for measuring several more time delays and the feasibility of making the corresponding estimates of the Hubble constant with total error smaller than ten percent are critically assessed.