Home SCIENCE 10 insights about the expanding Universe from a Nobel Laureate | by Ethan Siegel | Starts With A Bang! | Sep, 2024

10 insights about the expanding Universe from a Nobel Laureate | by Ethan Siegel | Starts With A Bang! | Sep, 2024

by NORTH CAROLINA DIGITAL NEWS


If you measure the expansion rate of the Universe using an early relic method, like the light from the CMB (top right), you get a value of around 67 km/s/Mpc. If you measure it by constructing a distance ladder (below left), such as with Cepheids and type Ia supernovae, you get a value more like 73 km/s/Mpc. This discrepancy is at the root of the Hubble tension. (Credit: Annelisa Leinbach / NASA, Adobe Stock)

In the expanding Universe, different ways of measuring its rate give incompatible answers. Nobel Laureate Adam Riess explains what it means.

One of the most surprising discoveries in all of astronomical history occurred nearly a full century ago: when we discovered that the distant galaxies in our Universe aren’t stationary, but are mutually receding from one another. This realization first came about in 1927, and has since been interpreted to mean that the Universe is expanding, with the space between galaxies, galaxy groups, and galaxy clusters “stretching” to greater and greater distances as time continues onwards. For most of the 20th century, the main quest of cosmology was to measure two parameters: how fast the Universe was expanding right now, and how that expansion rate changed and evolved over time.

In the late 1990s and early 2000s, both of those questions were finally answered with sufficiently good data. Our Universe was expanding at a rate of around 72 km/s/Mpc, with an uncertainty of only around 10%, and the recession speed of a distant galaxy wasn’t decreasing as we expected, but was actually increasing as time goes on. The latter discovery was a tremendous surprise, and compelled us to add a new species…



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