He that sitteth in the heavens shall laugh... Psalm 2:4
"Calculations based on observations of the early universe — namely, the
cosmic microwave background (CMB) that is a sort of afterglow of the Big
Bang — produce one answer for the Hubble constant.
Observations of the “late universe” instead compare the distances of astronomical objects, often standard candles
with known distances, to the speed those objects are moving away from
us. The two 
techniques provide different answers, a discrepancy that has
become known as the Hubble-constant tension.
Two independent groups using data from the Hubble Telescope have just
published new studies measuring the Hubble constant in different ways,
....The results give further credence to the
late-universe consensus of an expansion rate around ~73 km/s/Mpc.
But it also serves to deepen the tension, as studies published in the
last decade calculating the rate from the properties of the CMB give an
answer around ~67 km/s/Mpc. This may seem like no big deal, but the difference is big enough that some astrophysicists are calling it a “crisis for cosmology.”
“Cosmic microwave background radiation doesn't give a direct measurement
of the Hubble constant today,” Blakeslee says. “It needs to be combined
with a cosmological model, which can then predict the expansion history
of the universe.” And it’s possible that something vital has been “lost
in translation.”
Hsin-Yu Chen (MIT), a member of the LIGO collaboration, and the
author of a few studies pioneering the use of gravitational waves to
measure the current expansion rate, says that everyone disagrees about
the nature of the disagreement between early and late universe
measurements.
“Perhaps the discrepancy is from systematic errors,” she says. “Or
maybe the standard cosmological model needs to be fixed. Maybe it is
wrong. Everyone has their own opinion.” Sky&Telescope
