The uncertainties in measuring cosmic expansion
Ninety years after Edwin Hubble discovered the systematic motions of galaxies and George Lemaitre explained them as cosmic expansion from a point using Einstein’s equations of relativity, observational cosmology today is facing a challenge. Values deduced from the two primary methodologies—the properties of galaxies and the cosmic microwave background radiation (CMBR)—disagree with each other at roughly the ten percent level, yet each one is precise at the level of a few percent. Uncorrected observational errors are possible, but estimates suggest they are too small to account for the differences. As a result, no consistent and precise value of the expansion—Hubble’s constant—has been found. The problem is not so much the value itself—the age of the universe will not change by much either way—rather, it is that something unexplained is clearly going on connected with the fact that the CMBR data arise from a vastly different epoch of cosmic time than do the galaxy data. Perhaps new physics is needed.
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2021-01-04
