The Expanding Universe Might Not Depend On How You Measure It, But When
“It’s definitely the case that different methods of measuring the expanding Universe give different values, but this is the first time that the same method has yielded two different results depending on whether you look at the full data set or the late-time measurements alone. The expansion rate of the Universe has been one of the most contentious issues in all of modern science — the Hubble space telescope was even named for its main science goal of measuring that rate, also known as the Hubble constant — and this new result provides a major clue.
Could factoring the effect of cosmic voids in all measurements account for the full discrepancy? Could we be seeing evidence that something, even if it’s not dark energy, is evolving in the Universe in an unexpected fashion? Or, quite possibly, could this be a suggestion that it’s the cosmic microwave background data that’s somehow mistaken, after all? One thing is clear: more and better data, which should be on the way with Euclid, LSST, and WFIRST, will help us decide.”
If you measure the current-day expansion rate of the Universe by looking back and measuring the distances and redshifts to various objects, you get a particular value of around 74 km/s/Mpc. On the other hand, if you look at the earliest light from the Universe, like from the cosmic microwave background, you get a different, inconsistent value of 67 km/s/Mpc. Now, using data from the large-scale structure of the Universe, a new team has discovered something remarkable: if they use all of their data, and factor in the effects of cosmic voids, they get an in-between value of 69 km/s/Mpc. On the other hand, if they restrict themselves to relatively nearby measurements, they get a much higher value: closer to 72.3 km/s/Mpc.