The use of time-delay gravitational lenses to examine the cosmological expansion introduces a new standard rulerwith which to test theoretical models. The samplesuitable for this kind of work now includes 12 lens systems, whichhave thus far been used solely for optimizing the parameters of ΛCDM. In this work, we broaden the base of supportfor this new, important cosmic probe by using these observations to carry out a one-on-one comparison betweenΛCDM and theR_h= ct universe. To facilitate a direct comparison between these two competing models,we showin Figure 1 the 12 observed time-delay distance R_obs comparedwith those predicted by these two theoretical models. 
( By with WEI Jun-Jie ) Figure 1. 2D region with the 1σ and 2σ contours for the parameters H0 and η in the Rh = ct universe, using a sample of 1000 time-delay lenses, simulated with Rh = ct as the background cosmology. The assumed value for H0 in the simulation was H0 = 70 km s−1 Mpc−1.(A color version of this figure is available in the online journal.)
The currently available sample indicates a likelihood of ~70%–80% that the R_h= ctuniverseis the correct cosmology versus ~20%–30% for the standard model. Thispossibly interesting result reinforces theneed to greatly expand the sample of time-delay lenses, e.g., with the successful implementation of the Dark EnergySurvey, the VST ATLAS survey, and the Large Synoptic Survey Telescope. In anticipation of a greatly expandedcatalog of time-delay lenses identified with these surveys, we have produced synthetic samples to estimate howlarge they would have to be in order to rule out either model at a ∼99.7% confidence level. We find that if the realcosmology is ΛCDM, a sample of ∼150 time-delay lenses would be sufficient to rule out R_h= ctat this levelof accuracy, while ∼1000 time-delay lenses would be required to rule out ΛCDM if the real universe is insteadR_h= ct. This difference in required sample size reflects the greater number of free parameters available to fit thedata with ΛCDM. The work by Jun-Jie Wei, Xue-Feng Wu, and FulvioMelia has been published in the Astrophysical Journal. Please see ApJ, 788, 190for more details(http://iopscience.iop.org/0004-637X/788/2/190/).
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