> The preprint is 1909.06712

Two additional preprints are at

1907.04869 and

1910.06306

These report direct measurements of gravitational lens distances rather than a recalibration of the standard distance ladder.

The lead author Shajib of 06306 spoke here today and showed an updated version of Fig 12 of the 04869 preprint. The upshot is that the discrepancy between the local and the CMB measurements of H_0 is between 4 and 5.7 sigma, depending on how conservative one wants to be about assumptions. The impression I got is that either there’s a systematic error somewhere or there’s new physics. The local H_0 is based on two independent methods — distance ladder and lensing — so big systematic errors in local H_0 seem unlikely. The CMB H_0 is based on Planck with WMAP having given an H_0 value more consistent with the local one. “New physics” could be something as simple as time-varying dark energy, but for now it’s too soon to say much.

One other note from the talk: ** it takes an expert modeler about 8 months to a year to model a single lens system**. Shajib and others are trying to automate the modeling, but until that’s done, measuring a large sample of lenses will be labor-intensive. Even then, it will be cpu-intensive.

needed to give the desired precision of local H_0.

> The preprint is 1909.06712

Two additional preprints are at

https://arxiv.org/abs/1907.04869 and

https://arxiv.org/abs/1910.06306

These report direct measurements of gravitational lens distances rather than a recalibration of the standard distance ladder.

The lead author Shajib of 06306 spoke here today and showed an updated version of Fig 12 of the 04869 preprint. The upshot is that the discrepancy between the local and the CMB measurements of H_0 is between 4 and 5.7 sigma, depending on how conservative one wants to be about assumptions. The impression I got is that either there’s a systematic error somewhere or there’s new physics. The local H_0 is based on two independent methods — distance ladder and lensing — so big systematic errors in local H_0 seem unlikely. The CMB H_0 is based on Planck with WMAP having given an H_0 value more consistent with the local one. “New physics” could be something as simple as time-varying dark energy, but for now it’s too soon to say much.

One other note from the talk: ** it takes an expert modeler about 8 months to a year to model a single lens system**. Shajib and others are trying to automate the modeling, but until that’s done, measuring a large sample of lenses will be labor-intensive. Even then, it will be cpu-intensive.

needed to give the desired precision of local H_0.

Perhaps not surprising, as, compared to the CMB, such measurements are “local”.

]]>