Category: cosmic distance ladder

If Cosmology Is In Crisis, Then These Are The …

If Cosmology Is In Crisis, Then These Are The 19 Most Important Galaxies In The Universe

“In science, different methods of measuring the same properties should yield the same results. But when it comes to the expanding Universe, two sets of groups get consistently different outcomes. Signals from the early Universe yield expansion rates of 67 km/s/Mpc, while late-time signals yield systematically larger values. However, every individual measurement is subject to errors and uncertainties inherent to the method used.”

The strength of any method used in a scientific practice is only as good as the weakest assumption or measurement that’s made. In the case of measuring the expanding Universe, astronomers using an early-time signal get results that are systematically 9% smaller than astronomers using a late-time signal. Of all the late-time signals, the one method with the smallest uncertainties relies on the cosmic distance ladder: tying parallax measurements to Cepheids in the Milky Way, then tying Cepheids to galaxies with Type Ia supernovae, then measuring supernovae everywhere in the Universe. However, there are only 19 galaxies where Type Ia supernovae have been observed that are close enough to have observed Cepheids within them. A tiny statistical fluctuation in the properties of these galaxies could be enough to resolve most or even all of this discrepancy.

It may not be the most likely outcome, but it’s something to keep an eye on. If cosmology is in crisis, then these may be the 19 most important galaxies of all.