By my calculations, the expansion of the universe should cause LIGO’s interferometers to alternate between constructive interference and destructive interference every couple days. Is this a practical way to measure the Hubble constant directly? If not, what prevents this method from being feasible?
The Hubble constant ≈ 70 (km/s)/MPc ≈ 2E-18 (m/s)/m.
(5E-7 m)/(1E6 m)/(2E-18 m/s/m) ≈ 2E5 s ≈ 2 days for the laser travel distance to increase by half a wavelength.