Physical mechanisms have been proposed to increase the value we get from the cosmic microwave background (CMB), such as unexpected effects of dark matter and dark energy or maybe physics beyond the standard model. This is exciting on paper, but other measurements of the CMB show that it behaves as predicted, so maybe there’s no physics hiding there.
“The history of cosmology has abundant examples both of discrepancies that ushered in new discoveries, and others that turned out to be unknown systematic errors," wrote Freedman. "Based on the current data, I believe that the jury is still out.”
What we need is more data. The first method uses the light of stars and supernovae that have a specific luminosity. This property allows us to use them as standard candles, like distant sign posts placed across the universe. The Gaia mission and the James Webb Space Telescope will see these objects further than ever before, and they should refine the value of the Hubble Constant we get from galaxies. To improve on the other value, we will have to wait for future CMB experiments, like the South Pole Telescope and the Atacama Cosmology Telescope, to come online.
Hopefully, that will provide some clarity to this fascinating debate.