COSMO In the literature: open

Does the tension persist in measurements independent of ladders and rulers?

In plain words

Some methods measure the expansion rate in one step, using gravitational waves from colliding neutron stars or time delays between multiple images of a lensed quasar. They avoid both the distance ladder and the early-universe ruler.

Precise statement

Measure $h$ to 1 percent from at least one method independent of both the distance ladder and $r_d$: gravitational-wave standard sirens, strong-lens time delays with independent mass-profile constraints, water-maser distances, or $r_d$-free galaxy clustering. An answer is $h$ with uncertainty below 0.007 and a statement of which side it matches.

What would settle it

About 200 standard sirens with electromagnetic counterparts, or tens of time-delay lenses with spatially resolved stellar kinematics.

Status in the literature

Unverified note

A single quadruply lensed quasar (TDCOSMO XXV, 2026) gives $h = 0.732 (+0.048, -0.047)$; no ladder-free method reaches 1 percent.